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The design of the Transmission Line (TL) as a part of the Electron Cyclotron Heating (ECH) system for Divertor Tokamak Test facility (DTT) is approaching the conceptual design maturity. With an ECH system of 16 MW installed for the first phase and with a total of 32 gyrotrons (170 GHz, ≥ 1 MW, 100 s) the TL design is undertaking the challenge of an evacuated Multi-Beam TL (MBTL) concept to deliver the large number of beam lines from the gyrotron hall to the torus hall buildings. The system is organized in 4 clusters, each of them including 8 beamlines. The routing consists of single-beam TL section used to connect the gyrotron output to a beam-combiner mirror unit for each cluster, a common MBTL running in a suspended corridor reaching the Tokamak building and a beam-splitter mirror unit to connect to the ex-vessel optics and launchers sections located in the equatorial and upper ports of one sector, for a total of 4 DTT sectors. The TL mirrors will be actively water cooled to cope with the heat load in long pulses due to the high power incident radiation, with the possibility to include advanced concepts for the cooling design compatible with additive manufacturing technology. The characteristics of the system and its components are presented, showing both the progress of the adopted solutions and the current design. Since the main challenge of this TL is to maintain the overall losses below 15%, in this paper we present the expected ohmic and spillover losses, including beam coupling simulations evaluating losses given by high order Transverse Electro-Magnetic modes (i.e. aberrations). We describe how the effects have been estimated with electromagnetic simulations and how losses could be mitigated, since TL efficiency could significantly drop due to the presence of non-idealities, like the deformations of mirrors surface ascribed to the microwaves heat loads and possible misalignments and aberrations effects occurring along the line. [ABSTRACT FROM AUTHOR]

• Proposals of different CAD designs of a parabolic mirror (and its cooling channel) of the Multi-Beam Transmission Line of DTT ECH system. • Thermal and structural analyses to choose the best design configuration. • Optimisation of mirror performance on the best configuration found, in terms of thickness and hydraulic parameters. • Complete transient thermo-structural analysis on the optimized configuration. The Italian tokamak DTT (Divertor Tokamak Test) is a facility for research on nuclear fusion with the aim of investigating alternative power exhaust solutions to be exploited in the future DEMO fusion power plant. DTT foresees three additional heating systems to provide the plasma with sufficient power: Electron Cyclotron Heating (ECH) is the main one, with up to 32 MW installed. It consists of 4 clusters, each one composed of eight radio-frequency sources (gyrotrons) with their single-beam transmission lines, one quasi-optical Multi-Beam Transmission Line (MBTL) and eight independent launchers. The power produced by the source is transmitted quasi-optically through multiple reflections on metallic mirrors, the basic component of the transmission line, and then injected into the plasma. In the MBTL the reflection of the eight microwave beams on the mirror surface leads to heating of its whole structure due to the absorbed fraction of the beam power (0.21–0.27 %) ascribed to the ohmic heating at the mirror surface. During the radio-frequency power pulse (100 s), the mirror temperature increases, generating deformations that could result in a loss of beam transmission efficiency. For this reason, these mirrors need to be carefully designed from thermal and structural points of view, to guarantee the required optical performances. In the present paper, a preliminary study concerning the design of the MBTL parabolic mirror, and its cooling is presented, resorting to a coupled thermal and structural finite element simulation. The preliminary analyses address a main objective: minimize the surface mirror temperatures and consequently the deformation associated with thermal expansion, to reduce the impact on beam transmission efficiency drop. Different design choices, namely materials, body thickness and cooling solutions, in terms of cooling channel shape and water flow, are discussed. [ABSTRACT FROM AUTHOR]

• Based on the heat transfer theory and Thermal-Electric module, a simple method for quickly predicting the maximum temperature of water-cooled busbar with connector is proposed, which is convenient for engineering application. • Compared with V-T method and experimental results, the simple method in this paper has the advantages of global temperature distribution analysis and better temperature prediction accuracy, and can be used for the design of the same type of transmission lines. • The relationship among cooling water flow rate, contact resistance and maximum temperature of CRAFT busbar under rated working condition is determined, which can provide reliable guidance for actual operation of busbar. Due to the shortcomings of time-consuming and complicated operation of traditional fluid software simulation, a simple temperature prediction method that can quickly determine the reasonable working parameters of water-cooled busbar with connector is needed in the design of fusion power supplies. In this paper, considering the influence of contact resistance, the connector maximum temperature under same working conditions is studied by two kind of methods (combination method of heat transfer theory and Thermal-Electric module in ANSYS, Contact Voltage-Temperature (V-T) method), respectively. The comparison between simulation and experimental results shows that this method has the advantage of analyzing the global temperature distribution and predicting the maximum value more accurately than the latter. Based on this method, the relationship among contact resistance, water flow rate, and maximum temperature of the busbar connector used in Comprehensive Research Facility for Fusion Technology (CRAFT) is determined. This method can be applied to the rapid temperature analysis of fusion power busbar connector, which greatly reduces the design cycle. [ABSTRACT FROM AUTHOR]

• Description of enhancements brought to the ITER EU EC Test Facility installed at SPC (CH) to host two new experiments. • EGYC is a grant contracted with F4E in order to complete the development, of the ITER EU gyrotron manufactured by THALES (F). • FALCON is an experiment involving the ITER RU gyrotron installed on the TF to test the ITER EC components in a real environment. A Test Facility (TF) has been designed and installed at SPC to allow for the commissioning of the EU gyrotrons developed in view of their integration to the ITER EC system. The first phase of operation of this TF was dedicated to the development of the EU 2 MW coaxial cavity gyrotron [ 1 , 2 ]. The EU gyrotron development for ITER has been reoriented since then and is presently advancing a 170 GHz/1MW/CW gyrotron developed within the EGYC consortium and manufactured by THALES. At the same time, the TF has been enhanced to host the FALCON project [ 3 ], consisting in the integration of a second 170 GHz/1MW/CW gyrotron delivered by GYCOM. This new experiment is aiming to test the main RF components of the EC Transmission Line (TL) and of the Upper Launcher system to be installed on ITER. This paper describes the technical modifications brought to the existing TF to comply with the requirements of both 1 MW gyrotrons operation. Effort has been put in switching of the auxiliaries from one tower to the other within a short time (<1 week) while maintaining operator safety and equipment protection. A detailed description of the additional implementation and of the strategy followed to share the main auxiliaries (like the HVPS, the cooling system, the control system, etc.) will be presented. Moreover, most of the new equipment, such as the control hardware, have been designed to fulfil ITER site standards. Finally, the preliminary operation results with this reconfigured TF will be presented. [ABSTRACT FROM AUTHOR]

• Thermal Induced Electromotive Force measurements on mineral insulated cables. • Optimization of test procedure. • Thermal simulation of mineral insulated cables. The ITER Diagnostics components are located all over on the inner and outer shell of the ITER vacuum vessel, in the ports, on the Divertor Cassettes and in the Cryostat as well. Sensors require electrical transmission lines to transmit both the diagnostic and the control signals across the vacuum boundaries. To transmit the signals, Mineral Insulated (MI) cables are used. During the last 2 years in the frames of an F4E contract, the Tokamak Services for Diagnostics (TSD) group has performed several experiments on MI cables, in close collaboration with F4E and IO team members. This paper outlines one of these experiments to measure the thermal gradient induced voltage in the cable cores. This is needed to evaluate the electrical noise levels due to the thermal gradients in order to know if the noise has significant effect on the signal quality of some sensitive diagnostics. The subjects of the tests are a couple of Twisted Twin Mineral Insulated Cables (MICs) as this type of cables are used by the magnetics in the ITER machine. [ABSTRACT FROM AUTHOR]

The Plasma Position Reflectometry (PPR) diagnostic system is planned to provide information related to the edge electron density profile and plasma position at four defined locations distributed both poloidally and toroidally in the ITER vacuum vessel. It consists of five fully independent reflectometers grouped in three different paths, depending on the port through which are routed (Equatorial Port 10, Upper Port 01 and Upper Port 14), with different lengths and waveguide number and distribution. The sections of the ex-vessel transmission lines (TL) in the Gallery, between the two secondary confinement barriers, are considered "captive components". They are installed as close as possible to the ceiling and are trapped by other systems installed below so they will not be accessible for repair. This paper summarizes the design, the analysis strategy and main results of global analyses for each PPR route in the Gallery in order to analyze global deformations, reactions on supports and identify the critical parts of the whole PPR system. Based on the results obtained in the global model, detailed models will be built in future studies for critical components to assess their structural integrity. [ABSTRACT FROM AUTHOR]

• The design of the EC window unit, already optimized by FEM analysis, was advanced by ASME III-NC and the manufacturing aspects. • The design of the EC window unit was adapted to the ITER project decision to reduce the inner diameter of the waveguides from 63.5 to 50 mm. • The design of the EC window unit is sufficiently mature to start the prototyping and testing activity in view of the ITER final design review. The torus window unit is a very particular component of the ITER EC H&CD upper launcher aiming to provide the primary vacuum and confinement boundary between the vacuum vessel and the transmission lines (TLs). The high power 170 GHz millimeter-wave beams generated by the gyrotrons travel along the TLs and pass through the window units, before being quasi-optically guided into the plasma via the upper launchers. The design of the window unit shall thus meet stringent requirements to guarantee the safety function, the millimeter-wave beam transmission and the structural integrity during normal operation and off-normal events. The unit consists of an ultra-low loss CVD diamond disk brazed to two copper cuffs; this structure is then integrated into a metallic housing by welding. The compliance with the requirements shall be assured by applying the ASME Section III – Subsection NC code and a dedicated experimental qualification program. This paper reports the way in which the design of the unit, already optimized by FEM analyses against the ITER loading conditions, was further improved by the application of the ASME III-NC code, leading to a more feasible and simpler manufacturing and assembling sequence. In addition, the impact of the ITER project decision to change the inner diameter of the waveguide from 63.5 to 50 mm, to improve the beams' mode purity, was assessed and it is also discussed. Different materials for the metallic housing and in particular for the millimeter-wave inserts of the unit were compared using appropriate engineering criteria to mitigate the significant increase of the millimeter-wave thermal loads on the waveguides when the diameter is decreased. [ABSTRACT FROM AUTHOR]

The future EC systems will consist of several gyrotron sources providing MW-level millimeter wave power at a frequency around or above 170 GHz. The development of matched loads is necessary to test the new sources, the components for the transmission lines and the launchers, and must ensure high qualification for compatibility with the nuclear environment. The development at IFP-CNR and LTC of several compact high-power prototypes during the last decade led to a refinement of the overall design, resulting in the present low-reflectivity vacuum-compatible loads. The activity on loads is supported by F4E in view of the development of the EU gyrotron for ITER and required high-power tests at QST (Naka, Japan). Qualification is now supported by new tests at SPC (Lausanne, Switzerland) using the FALCON test-bed designed to test components and the EU gyrotron prototype for the EC system of ITER. These high-power tests, performed on the first CW prototype load (provided with 16 + 16 cooling channels in parallel) and shown in this paper, highlighted the need to improve the mechanical, vacuum and hydraulic design to reach the final goal of 1000s at ∼1 MW. [ABSTRACT FROM AUTHOR]

The Electron Cyclotron diamond window which is located inside the port cell serves, together with an isolation valve, as primary vacuum boundary between the ITER vacuum vessel, the transmission lines and the port cell atmosphere and it functions as confinement barrier. The window consists of an ultra-low loss Chemical Vapor Deposition (CVD) diamond disk brazed into a metallic housing and it has to guarantee the compliance with very stringent nuclear safety requirements and an adequate transmission capability for high power mm-waves (1.31 MW at 170 GHz). The design of the window unit is approaching its final phase including design validation analyses, the development of a dedicated qualification program and prototyping activities. In preparation of the testing of complete window prototypes, pressure tests were performed on a mock-up formed by a diamond disk (D = 80 mm, d = 1.11 mm) brazed to two copper cuffs. The scope of the experiments was to show both the capability of the joining between the disk and the cuffs to keep the required vacuum tightness as well as the integrity of the disk when exposed to pressure loads. Based on the requirements defined for the pressure scenarios during normal operation and off-normal events, a test program was developed accounting for cyclic tests at low pressure differentials and overpressure tests up to 2 bar pressure difference over the disk to simulate severe accidental conditions. This paper gives an outline of the ongoing development of the overall qualification program of the ITER torus window and reports specifically on the experimental set-up and the successful outcome of the pressure tests of the brazed diamond disk mock-up. The test program for the complete window prototype needs discussion and approval by F4E and ITER and will directly determine the final qualification program for the series diamond windows. [ABSTRACT FROM AUTHOR]

• A new cooling concept for the ITER EC MB mirror was proposed to better dissipate the deposited power during the mm-wave normal operation. • The off-centered beam configuration obtained in the FALCON facility was used in these analyses. • The maximum temperature for the MB mirror appears on the reflecting surface at the beam center, reaching a value of 174.6ºC. • The comparison between the categorized stresses and the allowable design limits show that the MB mirror design can withstand the expected loads. The ITER Upper Launcher for the Electron Cyclotron system has as primary goal to deliver mm-wave power at 170 GHz at the appropriate rational surfaces to stabilize magneto-hydrodynamic instabilities. Each Upper Launcher is connected to the gyrotrons through eight Transmission Lines. Diamond Window Units located at the port cell ceiling more than a dozen meters from the torus defines a barrier for the ITER primary vacuum at these Transmission Lines, defining the Ex-vessel Waveguide system. The Ex-vessel Waveguide system consists of straight corrugated waveguide components of 50 mm inner diameter with Miter Bends that are used to create a Z-shaped layout in each port cell. Recent tests at the FALCON facility have shown that the ohmic losses deposited on the Miter Bend mirror reflecting surface during the beam transmission do not follow the pure HE 11 theoretical distribution given by a perfectly-centered Bessel heat flux profile. For this reason, the Miter Bend mirror cooling design has been modified to a three-channel spiral-shaped configuration, which is able to better cope with possible beam offsets. This paper reports the status of the Miter Bend mirror as well as the fluid-dynamic and thermo-mechanical analyses carried out to validate this design. [ABSTRACT FROM AUTHOR]

The main function of the Collective Thomson Scattering (CTS) diagnostic system for ITER is to diagnose the alpha particles resulting from Deuterium-Tritium fusion reactions. It consists of a microwave scattering diagnostic with a probing frequency of 60 GHz and emitted power of 1.2 MW from the gyrotron, with one launcher and nine receiver transmission lines. The CTS will be installed in the equatorial port EP#12, which is one of the ports that have to be operational for the ITER First Plasma. The transmission lines outside the Port Plug (Ex-PP) are routed through the Interspace, Port Cell, Gallery, Assembly Building and Diagnostic Building, reaching more than 100 m in length. The preliminary design of the ex-PP components is currently being undertaken in the framework of an Implementing Agreement between ITER Organization, the Instituto Superior Técnico (IST) and CIEMAT. Within this collaboration, CIEMAT is responsible for the structural analyses and calculations required to ensure the structural integrity and performance of the preliminary design of the Ex-PP transmission line components, which will be summarized in this paper. In this work, the required analysis and calculations will be presented together with the redesign performed for the transmission lines in order to guarantee that their components will withstand the loads defined in the Ex-PP CTS Load Specifications. The evaluation of the structural integrity of the CTS Ex-PP components will be carried out in accordance with the 2007 RCC-MR Code for mechanical components in nuclear installations. [ABSTRACT FROM AUTHOR]

This paper presents the method toward quantifying the global uncertainty on the blackbody temperature measurement from the infrared (IR) diagnostics of WEST. To address this goal, the main functional elements of the IR diagnostics are identified. Then the temperature calibration and calculation principles are presented and analysed to extract the main potential uncertainty contributors, such as the optical transmission coefficients and their stray lights, or the accuracy of temperature references used for calibration. These contributors are individually estimated, or experimentally measured when a supposed effect on the overall uncertainty is identified, like environmental conditions or parasitic radiations. In particular, effects of environmental temperature on the transmission lines and camera is thoroughly studied. All contributions are then aggregated in the uncertainty propagation calculation and results in an overall temperature uncertainty versus the temperature estimation. The uncertainty is in the range of 5–10% for blackbody temperatures above 200 °C, and progressively worsens when temperature decreases. [ABSTRACT FROM AUTHOR]

SPIDER operation, started in 2018, pointed out performance-limiting issues caused by the technology employed in RF generators, based on tetrode free-running oscillators. One of these limits, namely the onset of frequency instabilities, prevented operation at the full rated power of 200 kW. In addition, tetrodes require high voltage to operate, which translates to risk of flashovers and the necessity to perform conditioning procedures, limiting the overall reliability. These disadvantages, combined with the positive experience gained in the meanwhile on smaller facilities with solid state amplifiers, led to the proposal of a complete re-design of the radiofrequency power supplies. This paper describes the modeling activities used to define specifications and design criteria of the solid-state amplifiers for SPIDER and MITICA, which can be directly transposed to the ITER HNB units when their functionality is proven. We detail the topology of the generators, consisting of class D amplifier modules combined to achieve the required 200 kW, which design is mainly driven by the necessity to deliver nominal power to the ion source, mitigate the risk of obsolescence, and improve the reliability through modularity. Due to the non-standard application, we gave particular focus to the integration of generators in the RF systems of SPIDER and MITICA. Numerical analyses were performed to verify the impact of harmonic distortion on transmission line and RF load components, to address the effect of mutual coupling between RF circuits on the generator output modulation, and to assess the magnitude of common mode currents in the electric system. These studies, as well as the experience gained from SPIDER operation, helped to define dedicated circuit design provisions and control strategies, which are currently being implemented in the detailed design and construction phase of the new RF amplifiers. [ABSTRACT FROM AUTHOR]

The in-vessel components of the ITER Diagnostics are located all over the inner shell of the Vacuum Vessel, in the Ports and on the Divertor Cassettes as well. The electrical transmission lines which transmit the signals from the sensors across the vacuum boundaries are Mineral Insulated Cables. These cables will be arranged into looms, which will be fixed to the vacuum vessel with different kinds of attachments. The ITER tokamak is at a stage where manufacturing and testing of each component are becoming more and more important. For this reason, to allow IO to assess feasibility, gain experience and obtain feedback with respect to the suitability of the current designs regarding handling and installation of in-vessel signal cables and loom components, GEMS Engineering has carried out a series of installation trials on full-scale mockups of in-vessel and divertor looms, upper and lower port marshalling area looms. Beside of installation trials, the scope of the work also covered the manufacturing and testing of cable clamps and clips for in-vessel and divertor looms and marshalling areas. This paper outlines the results of the manufacturing of prototypes and assembly trials of the above-mentioned components. [ABSTRACT FROM AUTHOR]

The paper gives an overview of the coupling physics of an ICRF antenna array to the plasma and of the original conceptual solutions proposed by the LPP/ERM-KMS group for the compact ITER antenna array and its matching to the RF power sources. The main contributions are (i) the use of an array of short straps grouped in triplets, (ii) the triplet feed by a four port junction and the use of a service stub to enlarge its frequency response, (iii) the multistep prematching to decrease the VSWR and minimise the voltage in the feeding transmission lines, (iv) the use of a decoupler network to neutralize the mutual coupling effects between different RF power sources and to simultaneously control the current distribution of the antenna array, (v) the various options to connect the decouplers and 3 dB hybrids for different array phasing cases in order to maintain the correct functioning of the decouplers together with load resiliency to fast variations of the plasma density in the edge (caused by e.g. pellet injection or Edge Localized Modes), (vi) the solution of the grounding problem of the ITER antenna plug-in, (vii) the test on mock-ups in front of a dielectric dummy load of the performance of the different solutions and particularly of the automatic matching and decoupling control of the complete ITER antenna array. [ABSTRACT FROM AUTHOR]

Abstarct India is developing a very high power test bed (∼MW level) based on concept of Travelling Wave Resonator (TWR) for testing of passive transmission line components [3] . Data acquisition and control system is required for safe and reliable operation of TWR. It includes online monitoring of input power and circulating ring power. Acquired RF signal provides information about forward and reflected RF power. For MW power level testing, system is protected against arc and thermal effect during CW operation. National Instrument make hardware and software have been used to acquire signals from RF detector, Arc detectors, IR camera and thermocouples etc. LabVIEW™ based software has been developed for calculation of RF parameters. Graphical user interface is developed for better visualization. Initial testing of the TWR setup with 10 dB coupler provides a power gain of 13.58 dB (22X). For future 3 MW TWR test bed the required power gain is ∼20 dB (100X) since the available source is ∼40 kW. This paper describes the detail design and integrated test results for data acquisition and control system for TWR test bed. [ABSTRACT FROM AUTHOR]

Abstract: The 100keV Ion Source Test facility – Source for the Production of Ions of Deuterium Extracted from RF plasma (SPIDER) – is aimed to test the full scale prototype of the Ion Source for the ITER 1MeV Neutral Beam Injector (NBI). The SPIDER facility requires the construction of a High Voltage Deck (HVD) and of a High Voltage Transmission Line (TL) respectively to host the Ion Source Power Supplies system polarized at 100kV and to carry the power and signal conductors to the beam accelerator. In already existing NBI systems with beam energy above 100keV, the TL is realized with the SF6 Gas Insulated Line technology. In the SPIDER TL case, the presence of a large inner conductor (half meter diameter), would make the pressurized TL a complex and costly component; therefore a free air insulated solution has been proposed. The paper focuses on the design of this TL, which has to host inside the complex high potential (100kV) inner electrode a number of power and measuring conductors and has to minimize the Electro Magnetic Interferences (EMI) produced by the frequent grids breakdowns. Finite Element (FE) analyses have been performed to verify the configuration from the electrostatic point of view, to evaluate EMI screening effectiveness and to assess the impact of the relatively high thermal dissipation of power conductors located inside the high potential electrode. Moreover, an experimental test campaign has been carried out on a TL mockup to validate the TL electrostatic configuration under DC voltage. Finally, the paper reports on the status of procurement activities for the Transmission Line. [Copyright &y& Elsevier]

Abstract: This paper deals with the electro magnetic interferences (EMI) induced on diagnostics and control circuits of fusion experiments, due to fast common mode voltages (V cm) transients. The V cm can excite the circulation of noise currents through parasitic capacitances, which couple different parts of the circuit designed to be isolated one to another. Equivalent electric circuits of the phenomena observed in RFX have been derived, which explain the induced noises and have been utilized to identify suitable correction measures; the paper describes these analyses and the experience gained in coping with the reduction of these types of EMI interferences. [Copyright &y& Elsevier]

The commissioning of the 28 GHz power transmission line of the TJ-II stellarator, designed for the excitation of electron Bernstein waves (EBW) through the O-X-B mode conversion process, is presented in this paper. Based upon a comprehensive set of thermal measurements, its purpose is to go into details about the several problems that arouse during the whole process, namely higher order modes excitation because of the wider beam size and alignment mismatches at the waveguide mouth. All these drawbacks may have prevented the correct O-X mode conversion, thus providing a reasonable explanation for the unsuccessful EBW heating experiments. [ABSTRACT FROM AUTHOR]

The ITER Passive Magnetic Shield (PMS) main function is to protect the Neutral Beam Injector (NBI) from the external magnetic field coming from the tokamak, and to shield the NB cell from the radiation coming from all activated components. The shielding from the external magnetic field is performed in association with the Active Compensation Cooled Correction Coils (ACCC). The Bushing and Transmission Line (TL) PMS also provides structural support for HV bushing, allowing its maintenance and providing air sealing function between NBI cell and High Voltage deck room. The paper summarizes the structural analyses performed in order to evaluate the mechanical behaviour of the HNB PMS under operation combined with seismic event. The RCC-MR Code is used to validate the design, assuming creep is negligible, since the structure is expected to be at room temperature. P-type damage is assessed. [ABSTRACT FROM AUTHOR]

The ITER Electron Cyclotron (EC) plant is a complex system, essential for plasma operation. The system is being designed to supply up to 20 MW of power at 170 GHz; it consists of 24 RF sources (or Gyrotrons) connected by switchable transmission lines to four upper and one equatorial launcher. The complexity of the EC plant requires a Plant Controller, which provides the functional and operational interface with CODAC and the Plasma Control System and coordinates the various Subsystem Control Units, i.e. the local controllers of power supplies, Gyrotrons, transmission lines and launchers. A conceptual design of the Electron Cyclotron Control System (ECCS) was developed, starting from the collection of the user requirements, which have then been organized as a set of operational scenarios exploiting the EC system. The design consists in a thorough functional analysis, including also protection functions, and in the development of a conceptual I&C architecture. The main aim of the work was to identify the physics requirements and to translate them into control system requirements, in order to define the interfaces within the components of the ECCS. The definition of these interfaces is urgent because some of the subsystems are already in an advanced design phase. The present paper describes both the methodology used and the resulting design. [ABSTRACT FROM AUTHOR]

The neutral beam system for ITER consists of two heating and current drive neutral ion beam injectors (HNB) and a diagnostic neutral beam (DNB) injector. The proposed physical plant layout allows a possible third HNB injector to be installed later. The HNB Passive Magnetic Shield (PMS) works in conjunction with the active compensation/correction coils to limit the magnetic field inside the Beam Line Vessel (BLV), Beam Source Vessel (BSV), High Voltage Bushing (HVB) and Transmission Line (TL) elbow to acceptable levels that do not interfere with the operation of the HNB components. This paper describes the current design of the PMS, having had only minor modifications since the preliminary design review (PDR) held in IO in April 2013, and the assembly strategy for the vessel PMS. [ABSTRACT FROM AUTHOR]

Abstract: This paper deals with a first analysis of the Remote Handling (RH) maintenance procedure for the replacement of Removable Vacuum Transmission Lines (RVTL) of the ICRH antenna Port Plug (PP). In the framework of the grant F4E-2009-GRT-026, CEA IRFM studied the maintenance in parallel with the design of the antenna provided by CCFE. The RVTL are 8 components of the ICRH antenna which form the interface between the matching system and the four port junction integrating the straps. A folded stub is attached to the principal line to ensure water cooling of the interspace. At the front and the rear of the RVTL are installed double RF windows that provide the first tritium barrier. In case of failure of the first window, all the RVTL have to be replaced. Due to the contamination and activation, the replacement must take place in the hot cell. The complete maintenance sequence is studied. It starts when the PP is in place in the Tokamak equatorial port, it continues with: the preparation in the port cell, transfer to the HC, cleaning, RVTL replacement, returns to the port cell. It finishes with reconnection to the port. The ITER requirements [1] and the hot cell constraints [2] are used to extract specifications for the RH tooling (for handling, cutting, welding, etc.). Each step is studied and suitable tools identified. For specific steps, mechanical concepts for dedicated tools are proposed. Furthermore, the critical steps identified are simulated to check the feasibility. [Copyright &y& Elsevier]

• For Negative Neutral Beam Injectors (NNBI) utilizing RF negative ion source, grid breakdown is a routine phenomenon during system conditioning and operation phases. During grid breakdown event, there are chances that electrostatic energy stored in the high voltage transmission line is dumped in the grids, which may possibly damage them. • NNBI system with long high voltage transmission line, major contribution for the stored energy emanates from the inter-conductor capacitance of transmission line. The inter-conductor capacitance and thus stored energy of high voltage transmission line could be reduced by proper designing of it. • It is equally difficult and challenging to estimate the inter-conductor capacitance of the transmission line with non-generic cross sections that forms initial step for designing high voltage transmission line. Estimation of inter-conductor capacitance for non-generic cross section (vertical configuration) of transmission line is done. • Stored energy for 1m long prototype of 1:1 scale is estimated experimentally and verified with energy estimated from inter-conductor capacitance. • The stored energy for 120m long high voltage transmission line during grid breakdown is estimated. TWIN source is a two driver based negative ion source currently operational at IPR. The two driver RF negative ion source test bed to extract and accelerate H- ion beams up to 50 keV. For Negative Neutral Beam Injectors (NNBI) utilizing RF negative ion source, grid breakdown is a routine phenomenon during system conditioning and operation phases. During the grid breakdown event, there are chances that electrostatic energy stored in the transmission line is dumped in the grids, which may possibly damage them. In case of NNBI system with long high voltage transmission line, contribution for the stored energy emanates from their inter-conductor capacitance. The inter-conductor capacitance and thus stored energy could be reduced by proper designing of the HVDC Transmission line. However, it is equally difficult and challenging to estimate the inter-conductor capacitance of the transmission line with non-generic cross sections. This paper discusses estimation of inter-conductor capacitance, an experimental set up to realize a grid breakdown and thus estimate the stored energy of a HVDC transmission line prototype (1m length). The HVDC transmission line prototype (1m length) has vertical placement of conductors. Inter-conductor capacitance is estimated for vertical topology. The stored energy values from estimated inter-conductor capacitance value is compared with experimental results for HVDC transmission line prototype (1m length). Also, modeling of HVDC transmission line is done to simulate a grid breakdown and thus compute the stored energy for entire transmission line length (120m). [ABSTRACT FROM AUTHOR]

Abstract: The Electron Cyclotron (EC) system for the ITER tokamak is designed to inject ≥20MW RF power into the plasma for Heating and Current Drive (H&CD) applications. The EC system consists of up to 26 gyrotrons (between 1 and 2MW each), the associated power supplies, 24 transmission lines and 5 launchers. The EC system has a diverse range of applications including central heating and current drive, current profile tailoring and control of plasma magneto-hydrodynamic (MHD) instabilities such as the sawtooth and neoclassical tearing modes (NTMs). This diverse range of applications requires the launchers to be capable of depositing the EC power across nearly the entire plasma cross section. This is achieved by two types of antennas: an equatorial port launcher (capable of injecting up to 20MW from the plasma axis to mid-radius) and four upper port launchers providing access from inside of mid radius to near the plasma edge. The equatorial launcher design is optimized for central heating, current drive and profile tailoring, while the upper launcher should provide a very focused and peaked current density profile to control the plasma instabilities. The overall EC system has been modified during the past 3 years taking into account the issues identified in the ITER design review from 2007 and 2008 as well as integrating new technologies. This paper will review the principal objectives of the EC system, modifications made during the past 2 years and how the design is compliant with the principal objectives. [Copyright &y& Elsevier]

Abstract: Oversized waveguides allow to transmit high electromagnetic power, but require components able to filter the unwanted modal content unavoidably excited along their path. In this paper mode filters based on corrugations partially filled with absorbing materials are described; they have been studied aiming at optimizing their performance and overcoming their intrinsic limitations. More precisely the dependence of the filtering performance on various geometrical parameters is derived using analytical and numerical approaches. The problems related with the power handling capability of mode filters are shortly considered too. Finally the role of degenerate modes in deteriorating the filtering performance is explained and a solution to this problem is presented. [Copyright &y& Elsevier]

Abstract: In the framework of the EFDA task HCD-08-03-01, the ITER lower hybrid current drive (LHCD) system design has been reviewed. The system aims to generate 24MW of RF power at 5GHz, of which 20MW would be coupled to the plasmas. The present state of the art does not allow envisaging a unitary output of the klystrons exceeding 500kW, so the project is based on 48klystron units, leaving some margin when the transmission lines losses are taken into account. A high voltage power supply (HVPS), required to operate the klystrons, is proposed. A single HVPS would be used to feed and operate four klystrons in parallel configuration. Based on the above considerations, it is proposed to design and develop twelve HVPS, based on pulse step modulator (PSM) technology, each rated for 90kV/90A. This paper describes in details, the typical electrical requirements and the conceptual design of the proposed HVPS for the ITER LHCD system. [Copyright &y& Elsevier]

Abstract: The use of rectangular oversized waveguides in the Main Transmission Lines of the Lower Hybrid Current Drive (LHCD) system of ITER, requires to investigate the problem of bends. The principal specifications that characterize the oversized bend design concern the minimization of the reflection of the fundamental mode and the maximization of its transmission, limiting at the same time its coupling to spurious modes that could propagate at the operational frequency. In this paper, the performances of bends with different geometries are compared. They are simulated using the commercial finite element software Ansoft HFSS. An innovative modified mitre-bend solution with trapezoidal-elements is proposed and analyzed. [Copyright &y& Elsevier]

Abstract: A limitation of the mean power rating of a coaxial transmission line arises from the coupling elements, which connect adjacent sections of the inner conductor by means of contact springs that are subjected to thermal degradation. This paper is focused on the design applied in a commercially available transmission-line coupling element. The main scope is to demonstrate the possibility to extend the working range of its spring contacts up to 200°C. Presently this component is extensively used in several transmission lines of fusion experiments working with short pulses and operating with a maximum temperature of 150°C at the inner conductor. Test components are successively exposed to a well controlled temperature of 200°C over certain time periods and are characterized afterwards with regard to the resilient forces of the contact lamellae with an accurate experimental setup. The weakening of the spring force in dependence of the cumulative annealing time is studied and the remaining spring force is compared to the minimum required force to ensure proper electrical contact, which is also determined experimentally within this work. [Copyright &y& Elsevier]

• The accumulation model of the surface charge for the solid-gas composite insulation structure is established. • Three material models of the post insulator are proposed and compared. • The effect of the bulk conductivity on the accumulation of the surface charge is analyzed. • The effect of the superficial conductivity on the accumulation of the surface charge is analyzed. For the negative-ion based neutral beam injectors (NNBI) system, the High voltage transmission line (HVTL) is a vital link between the radio frequency ion source system and the power supply system. Under the action of DC voltage, the surface of the internal post insulator of the HVTL will accumulate lots of charge, which can easily cause the post insulator to flashover. Therefore, the study of the accumulation characteristics of the surface charge for the post insulator under DC voltage is very significative to enhance the performance of the insulation and the reliability of the operation for the DC HVTL of the NNBI system. In this paper, taking the main post insulator of the HVTL as the research object, the accumulation model of the surface charge for the solid-gas composite insulation structure is established. Through finite element analysis, the effects of the bulk and superficial conductivity on the surface tangential electric field intensity and the surface charge density under three different material models are obtained. According to the calculation results, some suggestions and strategies for restraining the accumulation of surface charge are given, which provides a theoretical basis for the selection of material properties of the solid post insulator in the HVTL of the NNBI system. [ABSTRACT FROM AUTHOR]

• Indigenously development of mock-up ICRH components. • Capable to automatically match any arbitrary load (VSWR from 1.5 to 4). • Matching technique with developed algorithm based on VSWR. • Faster speed response. This paper presents the development of a mock-up Ion Cyclotron Resonance Heating (ICRH) system along with a new algorithmic approach for fast automatic impedance matching. The mock-up is developed for low power (few watts) and frequency (182.5 MHz) i.e. five times the ICRH frequency of SST-1. The size of the mock-up is considerably reduced to be fit on the test bench using it. The main objective of the work is to develop different matching approaches in order to get the optimum speed of matching. Reducing the size of the mock-up allows frequent implementation and testing of new algorithms which is generally difficult to implement in the real system of tokamak because of its size and complexity. The system consists of indigenously developed components such as 3 dB hybrid coupler, 20 dB directional coupler, tapped transmission line, rigid coaxial stub tuners, line stretcher, service stub, RF antenna, movable water tank based load. The developed system is capable of automatically match any arbitrary load in the range, (35–260) Ω , resistive + (-j25 to +j220) Ω , reactive or VSWR in the range 1.5–4.0 within 200 ms. The matching system also consists of power detectors which automatically sense the forward and reflected power using coupler and the feedback controlled moving coaxial stubs, line stretchers respond as per developed algorithms. The matching algorithm incorporates the various matching steps based on VSWR which have been interpreted for the controller program to control the devices used in the matching network. The developed system is tested using an RF antenna facing the movable saltwater tank that emulates the plasma-like loading behavior. The developed setup is also useful for various high power RF applications like RF heating, sputtering, plasma generation, RADAR, etc. in the RF frequency range. [ABSTRACT FROM AUTHOR]

Abstract: Maintaining plasma current under steady state conditions is one of the most important pre-requisites for a tokamak-based reactor. Lower hybrid current drive (LHCD) system aims to drive tokamak plasma current by means of RF power. The LHCD system on SST-1 tokamak is based on two 500kW, CW klystrons operating at 3.7GHz. A waveguide transmission line transmits power from source to the antenna. A phased array waveguide antenna is used to couple power to the plasma. The antenna side of the transmission line is placed inside the tokamak vacuum vessel. The design and fabrication of this In-Vessel system has to satisfy the demands of high power RF as well as ultra high vacuum (UHV) compatibility. This paper describes some of the critical UHV compatible In-Vessel RF devices, their design, fabrication, and test results. [Copyright &y& Elsevier]

Abstract: At the TEXTOR tokamak a 140GHz, 800kW, 10s gyrotron is employed for studies on ECW heating and ECCD. A key program is the suppression of tearing modes, which is aided by the unique facility at TEXTOR to program magnetic structures during a discharge (DED). A scheme is under development which aims to detect the perturbations on the electron cyclotron emission caused by these instabilities via the same line of sight as is used by the ECRH beam, and to use this information for feedback control of the instability. A brief overview of TEXTOR and relevant island parameters is given as well as a description of the upgraded ECRH system. This is followed by a description of the design of the transmission line coupler and receiver for island detection which constitutes the main topic of the paper. The final section sketches the feedback controller that processes the receiver signals, and controls the moveable launcher and the gyrotron power. [Copyright &y& Elsevier]

Abstract: In the last years there has been a growing interest on black box approaches to disruption prediction. The drawback of these approaches is that the system could deteriorate its performance once it does not get updated. This could be the case of a disruption predictor for JET, where new plasma configurations might present features completely different from those observed in the experiments used during the training phase. This ‘novelty’ can be incorrectly classified by the system. A novelty detection method, which determines the novelty of the input of the prediction system, can be used to assess the system reliability. This paper presents a support vector machines disruption predictor for JET, wherein multiple plasma diagnostic signals are combined to provide a composite impending disruption warning indicator. In a support vector machine the analysis of the decision function value gives useful information about the novelty of an input and, on the reliability of the predictor output, during on-line applications. Results show the suitability of support vector machines both for prediction and novelty detection tasks at JET. [Copyright &y& Elsevier]

Abstract: The lower hybrid current drive (LHCD) system for superconducting steady state tokamak-1 (SST-1) machine is in advanced stage of integration and commissioning. The system is designed to launch 1MW of RF power at a frequency of 3.7GHz to sustain 220kA of plasma current non-inductively for 1000s. The system employs a conventional grill antenna (having 2×32 waveguides), vacuum and air transmission lines and high power source system. A new design for vacuum transmission line, which enables better vacuum and RF compatibility has been successfully executed and tested. The transition from the narrow waveguide to WR284 waveguide system is achieved through a simple design, having stacks of copper plates with the waveguides milled in them, referred as transforming module and is successfully tested for mechanical, vacuum and RF performance. Many of the critical components have been successfully fabricated and tested as per the designs. The components and sub-systems are made ready and the integration is in progress. All the components are actively cooled and are compatible with 1000s operation.The performance tests and current status of various sub assemblies and partially integrated LHCD system is discussed in detail in this paper. [Copyright &y& Elsevier]

Abstract: JET''s new Microwave Access system requires a configurable interface to share the transmission lines between the various reflectometric instruments. A confocal quasi-optical system made of modular blocks was designed and built for operation in the 60–160GHz range, allowing full configuration and polarization flexibility. This paper deals with the design and test of the instrument. [Copyright &y& Elsevier]

A new ITER-like (International Thermonuclear Experimental Reactor) ICRH antenna is being developed to deliver over 7 MW at high power density (8 MW/m2) to the JET plasmas. The paper discusses the RF, mechanical and hydraulic design aspects of the option for Internal Vacuum Transmission Lines based upon in-vessel motor actuators. [Copyright &y& Elsevier]

The Divertor Tokamak Test facility (DTT) is the new tokamak whose construction is starting in Frascati (Italy), with the main aim of testing different divertor magnetic configurations and technologies in view of DEMO. In the present design, the DTT heating mix includes one Negative Neutral Beam Injector (NBI), with a power injected in the plasma of 10 MW and a beam energy of 500 keV. The NBI conceptual design is under development and includes solutions already adopted for ITER (RF-driven ion source, gas neutralizer, electrostatic Residual Ion Dump), but with some simplifications to reduce costs and complexity deemed feasible for DTT. In particular, the beam source is air-insulated and fed by the gas-insulated Transmission Line through gas-air bushings. This paper presents the status of the conceptual design of the main power supplies of the DTT NBI. The main ratings are collected from physics requirements and NBI design. On this basis, the reference technical solutions are selected, considering the experience gained at the ITER Neutral Beam Test Facility in Padova (Italy), the specific design of the DTT NBI and the layout constraints of the DTT Site. For the Acceleration Grid Power Supply, besides the ITER-like design, an innovative approach based on the Modular Multilevel Converter technology, never adopted in this application, is considered; pros and cons of the two solutions are evaluated. [ABSTRACT FROM AUTHOR]

Spectroscopic measurements have been recently proposed in DEMO for divertor detachment control. In its current design, the DEMO Divertor Survey Visible High-Resolution Spectrometer is foreseen to perform spectroscopy measurements by integrating three optical subsystems into an equatorial port (EP). Behind the first wall, light travels through a set of metallic mirrors and ducts before it reaches the closure plate of the EP. This paper presents a nuclear analysis performed with the Monte Carlo simulation program MCNP6 for two alternative configurations of the system. The results show that the configuration with 5 mirrors per transmission line is very effective to reduce the neutron streaming through the port. However, it will not be possible, with the current design, to introduce standard electronics along the spectroscopy ducts, as the dose rate limits for non-critical electronic components are exceeded in both configurations. In the plasma-facing mirrors, the heat loads are below 2 mW/cm3, which shows that the strategy of recessing the first mirrors and placing them behind small-diameter openings is effective to decrease the loads in the mirrors. FISPACT simulations for different materials show that material transmutation in the mirrors will be negligible throughout the DEMO reactor lifetime. [ABSTRACT FROM AUTHOR]

The pre-conceptual layout for an electron cyclotron system (ECS) in DEMO is described. The present DEMO ECS considers only equatorial ports for both plasma heating and neoclassical tearing mode (NTM) control. This differs from ITER, where four launchers in upper oblique ports are dedicated to NTM control and one equatorial EC port for heating and current drive (H&CD) purposes as basic configuration. Rather than upper oblique ports, DEMO has upper vertical ports to allow the vertical removal of the large breeding blanket segments. While ITER is using front steering antennas for NTM control, in DEMO the antennas are recessed behind the breeding blanket and called mid-steering antennas, referred to the radially recessed position to the breeding blanket. In the DEMO pre-conceptual design phase two variants are studied to integrate the ECS in equatorial ports. The first option integrates waveguide bundles at four vertical levels inside EC port plugs with antennas with fixed and movable mid-steering mirrors that are powered by gyrotrons, operating at minimum two different multiples of the fundamental resonance frequency of the microwave output window. Alternatively, the second option integrates fixed antenna launchers connected to frequency step-tunable gyrotrons. The first variant is described in this paper, introducing the design and functional requirements, presenting the equatorial port allocation, the port plug design including its maintenance concept, the basic port cell layout, the transmission line system with diamond windows from the tokamak up to the RF building and the gyrotron sources. The ECS design studies are supported by neutronic and tokamak integration studies, quasi-optical and plasma physics studies, which will be summarized. Physics and technological gaps will be discussed and an outlook to future work will be given. [ABSTRACT FROM AUTHOR]

LIPAc is the Linear IFMIF Prototype Accelerator developed within the framework of the IFMIF project under the Broader Approach (BA) agreement signed between EURATOM and the Japanese Government in 2007. The IFMIF accelerator aims to provide an accelerator-based D-Li neutron source to produce high intensity neutron fluxes with appropriate energy spectrum in order to characterize materials envisioned for future fusion reactors. Because the IFMIF accelerator has to reach unprecedented performances, the feasibility is being tested through the design, manufacturing, installation, commissioning and testing activities of a 1:1-scale prototype accelerator, namely LIPAc, from the injector to the first cryomodule together with the High Energy Beam Transport line and the High Power Beam Dump. After outstanding results obtained in 2019, the LIPAc project has entered 2020 in the preparation of the third commissioning stage, i.e., validation in continuous-wave mode of the complete accelerator up to 5 MeV with its final beam dump. The validation until the nominal energy of 9 MeV will be made after the completion of cryomodule assembly. After a brief overview of the goals already achieved in the framework of the IFMIF/EVEDA program, this paper will present a synthesis of the results that have been obtained so far with the LIPAc accelerator as well as the future developments planned beyond 2020. [ABSTRACT FROM AUTHOR]

• The -400 kV transmission line is the link between the ion source and the power supply system. • The design elements of -400 kV transmission line are reported. • A 2-D simplified electrostatic analysis model of transmission line is established. • The effect of the layout of transmission line on the distribution of electric field is reported. • The optimal layout of -400 kV transmission line is determined. Based on the development of Experimental Advanced Superconducting Tokamak (EAST), Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP) has launched the project of China Fusion Engineering Test Reactor (CFETR). In order to explore and master fusion DEMO level key technologies, build key prototype systems for CFETR, a Comprehensive Research Facility for Fusion Technology(CRAFT)is being established. Negative-ion based Neutral Beam Injectors (NNBI), as one of the important parts of CRAFT, can provide neutral beam with 200∼400 keV beam energy and 2 MW beam power. Stable high voltage transmission is needed for the establishment and safe operation of NNBI. As one of the key components of high voltage transmission, transmission line (TL) plays an extremely important role. In this paper, four indexes, including the maximum electric field intensity (E m a x), the inner surface electric field intensity (E s u r) of the electromagnetism interference screening (EMIS), the equivalent distributed capacitance (C e q) and the electric field non-uniformity coefficient (f), are used to evaluate the electric field performance of TL. And the relationship between these indexes and the position of acceleration grid (AG) conductor, the position of extraction grid (EG) conductor and the radius of EMIS is obtained by finite element (FE) analysis. Under the requirements of E s u r and f , in order to reduce the maximum electric field intensity in the TL and equivalent distributed capacitance of the TL, the layout position of the TL is determined, which lays some theoretical foundations for the engineering design of the TL. [ABSTRACT FROM AUTHOR]

• A new design concept of both upper and lower MBMBs, compliance with ITER EC UL requirements, is described in this paper. • The fluid-dynamic analyses show that the highest temperature values occur in the MB mirror centers, reaching up to 203°C. • The thermo-mechanical analyses demonstrate that the stress peak takes place at the MB mirrors, reaching up to 324 MPa. • The categorized stresses obtained in the MBMBs are lower than the allowable limits defined in the ASME code. The ITER Electron Cyclotron Heating (ECH) system will be used to counteract magneto-hydrodynamic plasma instabilities by aiming up to 20 MW of mm-wave power at 170 GHz. The primary vacuum boundary at the Electron Cyclotron Upper Launcher (EC UL) extends into the port cell region through eight beamlines, defining the so-called First Confinement System (FCS). Each beamline, designed for the transmission of 1.31 MW, is delimited by the closure plate at the port plug back-end and by a diamond window in the port cell. The FCS essentially consists of a Z-shaped set of straight corrugated waveguides (WG) connected by Mitre Bends (MB) with a nominal inner diameter of 50 mm. Due to the space restrictions, the eight MBs at the last FCS section are grouped into two monoblocks. Each Monoblock Mitre Bend (MBMB) consists of a body with corrugated feedthroughs defining a specific angle for each beamline and four mirrors attached by bolted connection to reflect the mm-wave power. The thermal expansion arising from the ohmic losses, the cooling pressure, the bolt pre-tension and the imposed displacements coming from the connection with the transmission lines are the primary design loads for the MBMBs. The fluid-dynamic analyses performed for both upper and lower MBMBs show that highest temperature takes place in the MB mirrors, reaching a maximum value of 203 °C at the beam center. The thermo-mechanical analyses demonstrate that the peak stress also occurs at this location with a maximum value of 324 MPa. These stresses are categorized and compared with the allowable limits defined in the ASME code, what probes that the current design of both upper and lower MBMBs are able to withstand the loads taking place during the mm-wave normal operation. [ABSTRACT FROM AUTHOR]

• The polarization strategy for ECRH systems with two elliptical grating polarizers was studied. • The polarization purity of the polarization strategy was analyzed. • The elliptical polarizer was tested at the low power experiment. The grating polarizer is a critical component in the millimeter-wave transmission line in an electron cyclotron resonance heating (ECRH) system, the main function of which is to change the polarization characteristics of the millimeter-wave. This paper presents an optimal polarization strategy for the millimeter-wave transmission line in an ECRH system. With two identical sinusoidal-groove elliptical grating polarizers, an arbitrary polarization can be realized. A special elliptical grating polarizer has thus been designed and its performance has been tested on a low power test bed. The results of the low power experiments agree well with the theoretical calculation values. The purity of the polarization achieved via the polarization strategy developed in this work has also been calculated and is found to be no less than 99.98 %. The analysis indicates that almost all the polarization states can be obtained by this polarization strategy. [ABSTRACT FROM AUTHOR]

• This paper evaluated the capability of electron cyclotron emission (ECE) diagnostic in the Chinese Fusion Engineering Testing Reactor (CFETR), by simulated ECE spectra using the code SPECE. • The results indicate that measurement of X-mode and O-mode ECE spectra combined are capable of providing the information of local electron temperature with fairly good spatial resolution and adequate radial range. • Followed with the simulation results, the conceptual design of the front-end, transmission line, instrumentation, and the calibration strategy are discussed briefly. To evaluate the capability of electron cyclotron emission (ECE) diagnostic in the Chinese Fusion Engineering Testing Reactor (CFETR), ECE spectra have been simulated using the code SPECE. The results indicate that measurements of the 2nd harmonic X-mode and the 1st harmonic O-mode ECE spectra combined are capable of providing the information of local electron temperature with fairly good spatial resolution and adequate radial range covering from the plasma core to the edge. Followed with the simulation results, the conceptual design of the front-end, transmission line, instrumentation, and the calibration strategy are discussed briefly. Base on the state-of-the-art techniques, no foreseen technical obstacles exist. However, it is worthy to study the relativistic down-shift effect in the high temperature plasmas in order to obtain the position of the emission layer with required precision in a timely manner. [ABSTRACT FROM AUTHOR]

• The S F 6 gas insulation standard was determined. • The dimension of the NNBI transmission line was preliminarily determined. • The wall thicknesses of central conductors are determined and checked. • The wall thickness of the grounding shell is determined. In order to satisfy the requirements of China Fusion Engineering Test Reactor (CFETR) for neutral beam injector system, a Negative-ion Based Neutral Beam Injector system (NNBI) test platform will be established by Institute of Plasma Physics Chinese Academy of Sciences (ASIPP). The high voltage Transmission Line (TL) plays an important role in the NNBI system, connecting the ion source and the power supply system. The TL will be insulated by gas insulation technology, that is, Gas Insulated Transmission Line (GITL). This paper mainly focuses on the insulation dimension design of TL2, which is the longest and main section of the TL. Firstly, the method of determining the design criteria of TL2 gas insulation is given, the gap required by gas insulation is analyzed and the condition of electric field strength to prevent the movement of conductive particles is put forward; secondly, the basic design principles of TL2 insulation design are put forward and the design method of wall thickness of TL2 central conductor and grounding shell is given. Finally, according to the above insulation requirements and design methods, some basic structural parameters of TL2 of the NNBI test platform are determined, including the outer radius and wall thickness of the central conductor and the inner radius and wall thickness of the grounding shell. The outer radius and the wall thickness of the intermediate voltage (rated as −200 kV) conductor are selected as 50 mm and 5 mm, the outer radius and the wall thickness of the high voltage (rated as −400 kV) conductor are selected as 250 mm and 5 mm, while the inner radius and the wall thickness of the grounding shell with tolerated gas pressure from 0.45 MPa to 0.6 MPa, are selected as 525 mm and 10 mm, which lays a foundation for the subsequent detailed design of TL. [ABSTRACT FROM AUTHOR]

• The JET ILA S-Matrix Arc Detection (SMAD) protection system has been improved and fully re-commissioned. • The SMAD error remains small in the operating frequency range (29–51 MHz) and under all different plasma conditions tested. • The time delay to issue a trip is typically 6 – 8 μs. • The delay between the trip and the removal of the power on the lines is measured to be about 25 μs. • The system is reliable, robust and within the JET specifications. Arc detection is an essential protection system for high power RF systems. It is commonly realised by monitoring the Voltage Standing Wave Ratio (VSWR) in the transmission lines. The JET ILA is a load-tolerant ICRF antenna with a low impedance section, for which the standard VSWR protection is ineffective. The Scattering-Matrix Arc Detection (SMAD) was proposed and implemented on JET to protect the low-impedance section around the T-junction against arcing. It is based on a consistency check of the RF signals around this section using a table of coefficients obtained from RF modelling. The paper reviews the SMAD principle, its commissioning on JET and the latest improvements to the system. It shows an example of operation and the time response of the system is analysed. The latest improvements have increased the robustness and reliability of SMAD, making it a choice of arc detection system for critical sections on existing and future RF systems. [ABSTRACT FROM AUTHOR]