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An off-the-shelf Phase-Locked Loop (PLL) system is used to stabilize the free-running oscillation frequencies of the 140 GHz, 1 MW CW gyrotrons of the companies Thales, France, and CPI, USA, that both operate at the ECRH system of the Wendelstein 7-X (W7-X) stellarator at IPP Greifswald, Germany. Both tubes are equipped with diode-type Magnetron Injection Guns (MIGs). Considering each of both type of gyrotrons as a Voltage Controlled Oscillator (VCO), each individual gyrotron is controlled by the variation of the body voltage. The results of the experiments demonstrate the capability of the developed and implemented inexpensive off-the-shelf PLL system. It is possible to stabilize the oscillation frequency within a full -20 dB bandwidth of < 100 kHz. Applications such as Collective Thomson Scattering (CTS) systems to accurately diagnose the ions in fusion plasmas could benefit from this development in future.

The Collective Thomson Scattering (CTS) diagnostic measures the scattering spectrum of incident radiation off collective fluctuations in plasmas. In Wendelstein 7-X (W7-X) the diagnostic uses a 140 GHz heating gyrotron as a source of the probing radiation. At this frequency, the CTS spectra are heavily affected by the electron cyclotron emission, and the microwave beam propagation is restricted at typical W7-X plasma parameters. The diagnostic was successfully commissioned in the last experimental campaign and demonstrated ion temperature measurements. However, the signal-to-noise ratio was too low for measuring other quantities such as the fast-ion velocity distribution function or the fuel ion ratio. Currently, the W7-X CTS diagnostic is undergoing an upgrade to a frequency of 175 GHz. This will increase the sensitivity of the diagnostic, since the noise due to electron cyclotron emission will be reduced, and it will relax the constraints on microwave beam propagation in W7-X. Here we present the salient features of the upgraded CTS system and discuss its prospects for both thermal-ion and fast-ion measurements.

Electron cyclotron resonance heating (ECRH) is the main heating mechanism in the Wendelstein 7-X stellarator (W7-X). W7-X is equipped with five absolutely calibrated sniffer probes that are installed in each of the five modules of the device. The sniffer probes monitor energy flux of unabsorbed ECRH radiation in the device and interlocks are fed with the sniffer probe signals. The stray radiation level in the device changes significantly during the start-up phase: Plasma is a strong microwave absorber and during its formation the stray radiation level in sniffer probes reduces by more than 95%. In this paper, we discuss the influence of neutral gas pressure and gyrotron power on plasma breakdown processes.

Here we report the first measurements of the power levels of stray radiation in the vacuum vessel of Wendelstein 7-X using absolutely calibrated sniffer probes. The absolute calibration is achieved by using calibrated sources of stray radiation and the implicit measurement of the quality factor of the Wendelstein 7-X empty vacuum vessel. Normalized absolute calibration coefficients agree with the cross-calibration coefficients that are obtained by the direct measurements, indicating that the measured absolute calibration coefficients and stray radiation levels in the vessel are valid. Close to the launcher, the stray radiation in the empty vessel reaches power levels up to 340 kW/m(2) per MW injected beam power. Furthest away from the launcher, i.e., half a toroidal turn, still 90 kW/m(2) per MW injected beam power is measured.

During the last years, electron cyclotron heating (ECH) was proven to be one of the most attractive heating schemes for stellarators because it provides net-current-free plasma startup and heating. Both the stellarator Wendelstein 7-X (W7-X), which is under construction at the Max-Planck-Institut fu umlr Plasmaphysik, Greifswald, Germany, and the International Thermonuclear Experimental Reactor (ITER) tokamak, which will be built in Cadarache, France, will be equipped with a strong ECH and current-drive system. Both systems are comparable in frequency and have continuous-wave capability (140 GHz, 10 MW for W7-X and 170 GHz, 24 MW for ITER). The commissioning of the ECH plant for W7-X is well underway; the status of the project and the first integrated full-power test results from two modules are reported and may provide valuable input for the ITER plant. The ten gyrotrons at W7-X will be arranged in two subgroups symmetrically to a central beam duct in the ECH hall. The RF wave of each subgroup will be combined and transmitted by a purely optical multibeam-waveguide (MBWG) transmission line from the gyrotrons to the torus. The combination of five 1 MW gyrotron beams to one beam line with a power of 5 MW reduces the complexity of the system considerably. The single- and MBWG mirrors and the polarizers have been manufactured. Cold tests of a full-size uncooled prototype line delivered an efficiency exceeding 90%. The microwave power will be launched to the plasma through ten chemical-vapor-deposited-diamond barrier windows and in-vessel quasi-optical plug-in launchers, allowing each 1-MW RF beam to be steered independently. The polarization, as well as the poloidal and toroidal launch angles, will be adjusted individually to provide optimum conditions for different heating and current-drive scenarios.

This paper reports the results of the high-power test of a remote steering launcher mock-up at 140 GHz, which were performed at the ECRH installation for the future stellarator W7-X at IPP Greifswald. The mock-up test system consists of a 6.62 m long corrugated square waveguide with a steerable optic at the entrance and various diagnostics at the exit of the waveguide. A straight and a dog-leg version of the launcher were investigated. The high-power tests of the straight setup have been performed with powers up to P0 = 700 kW (typically 500 kW) and pulse lengths of up to 10 seconds. For both polarizations (parallel and perpendicular to the steering plane), no arcing was observed in spite of the fact, that the experiments were performed under ambient atmospheric conditions. After the integration of 2 mitre bends in the setup, arcing limited the usable parameter range. The ohmic loss PΩ of the waveguide was measured via the temperature increase of the waveguide wall, and was used to calibrate the calculated angular dependence of the total ohmic losses of the waveguide. Short-pulse radiation pattern measurements with thermographic recording show high beam quality and confirm the steering range of −12° < < 12°.

Electron Cyclotron Resonance Heating (ECRH) is the main heating method for the Wendelstein 7-X Stellarator (W7-X), which is under construction at IPP-Greifswald. A 10 MW ECRH plant with CW-capability at 140 GHz is under construction to meet the scientific objectives. The microwave power is generated by 10 gyrotrons with 1 MW each two gyrotrons are operational at IPP in Greifswald. The tubes are equipped with a single-stage depressed collector for energy recovery and operate with an output power modulation between 0.3 and 1 MW with a sinusoidal frequency of up to 10 kHz which is achieved by modulating the depression voltage and is an interesting feature for NTM control at ITER. The general features of the ECRH-plant such as frequency power, cw-capability, flexibility and the experimental experience are of high relevance for the ITER system. Each gyrotron is fed by two high-voltage sources. A high-power supply for driving the electron beam and a precision low-power supply for beam acceleration. The high-power facility consists of modular solid state HV-supplies (−65 kV 50/100 A) providing fast power control and high flexibility. The low-power high-voltage source for beam acceleration is realized by a feed back controlled high-voltage servo-amplifier driving the depression voltage. A protection system with a thyratron crowbar for fast power removal in case of gyrotron failure by arcing is installed. Both the high power and low-power high-voltage sources have the capability to supply a 2 MW ITER gyrotron without any modification. Analogue electronic devices control the fast functions of the high-voltage system for each gyrotron and a hierarchy of industrial standard PLCs and computers supervise the whole ECRH-plant.

Summary form only given, as follows. Electron cyclotron resonance heating (ECRH) has proven during the last few years to be one of the most attractive heating schemes for stellarators, as it provides net current free plasma start tip and heating. Extensive measurements on stellarators at IPP Garching provide a solid physical and technological basis for ECRH systems. Therefore, ECRH will be the main heating method for the Wendelstein 7-X stellarator (W7-X) now under construction at Greifswald / Germany. A 10 MW ECRH system with continuous wave (CW) possibilities operating at 140 GHz will be built to meet the scientific goals of the stellarator at Greifswald with inherent steady-state capability at reactor relevant plasma parameters. A prototype gyrotron with an output power of 1 MW was developed in collaboration between European research laboratories, and European industries. The gyrotron is equipped with a single stage depressed collector for increasing the efficiency, an optimized quasi-optical mode converter and a CVD-diamond window. The prototype gyrotron has been successfully tested with an output power of 0.89 MW at a pulse duration of three minutes and all output power of 0.54 MW for about 15 minutes. The specified value of Gaussian beam output power exceeding 0.9 MW has been obtained for about 1 minute. Further results will be given.

The construction of the 140 GHz, 1 MW CW gyrotrons for the 10 MW ECRH system of the stellarator W7-X at IPP Greifswald is ongoing. While acceptance testing of the gyrotrons is progressing, reliable output parameters and stable production have been achieved. This report summarizes the actual status and some topical results. Focus is put on the final construction and latest parameters measured at factory-acceptance tests and site-acceptance tests. Parallel to the design optimization a new spectral measurement method has been developed, which allows time-dependent broadband spectral measurements with µs resolution for ms range pulses. Results of measurements done with W7-X gyrotrons are shown.

ECH & CD is widely used in fusion plasmas. Gyrotrons are applied as power sources as they offer continuous wave operation at MW power level. This contribution reports on the status and plans of major projects of KIT towards high power gyrotrons, i.e. results from series production of the W7-X gyrotron, the development of the EU pre-prototype coaxial-cavity gyrotron, the 2 MW, 170 GHz CW coaxial cavity gyrotron for ITER and a frequency step-tunable gyrotron.

Electron Cyclotron Resonance Heating (ECRH) is a key component in the heating arsenal for the next step fusion devices like W7-X and ITER. These devices are equipped with superconducting coils and are designed to operate steady state. ECRH must thus operate in CW-mode with a large flexibility to comply with various physics demands such as plasma start-up, heating and current drive, as well as configuration- and MHD - control. The request for many different sophisticated applications results in a growing complexity, which is in conflict with the request for high availability, reliability, and maintainability. 'Advanced' ECRH-systems must, therefore, comply with both the complex physics demands and operational robustness and reliability. The W7-X ECRH system is the first CW- facility of an ITER relevant size and is used as a test bed for advanced components. Proposals for future developments are presented together with improvements of gyrotrons, transmission components and launchers.

A 10 MW, 140 GHz ECRH system with a pulse duration of 30 minutes is currently under construction for the stellarator W7-X at Greifswald. The RF power will be provided by 10 gyrotrons. A European collaboration has been established to develop and build 9 (out of 10) tubes each with an output power of 1 MW for continuous wave (CW) operation. This contribution reports on recent progress with the series gyrotrons.

High power gyrotrons for plasma heating utilize a single stage depressed collector potential in order to reduce the collector load and to recover a large fraction of the remaining energy of the spent electron beam. This operation mode requires two high voltage power supplies which usually possess different characteristics. In the case of RF modulation, both power supplies must nevertheless operate synchronously and with a certain timing. In addition, the power must be shut down instantaneously when the collector load exceeds a certain limit, e.g. due to a dropout of the RF output. This paper discusses the realization of the above functionality in a single FPGA and describes the implementation at the W7-X stellarator.

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The HELIAS‐type Stellarator Wendelstein 7‐X, which is currently under construction in Greifswald, Germany, will be equipped with a 140 GHz, 10 MW, CW ECRH system. It will be the main plasma heating system for W7‐X. The key features and capabilities of the ECRH plant will be discussed together with the envisaged start‐up and heating scenarios. We also report on the ECRH stray radiation test facility MISTRAL and on the extension of the gyrotron frequency range.

Amplitude modulation of the 50 Hz AC sweeping current of transversal sweeping systems reduces the maximum averaged power density on the collector wall as compared to an unmodulated system. This makes transversal sweeping a very attractive alternative to conventional longitudinal sweeping systems for high power CW Gyrotrons.

Electron Cyclotron Resonance Heating (ECRH) is the main heating method for the Wendelstein 7-X Stellarator (W7-X), which is under construction at IPP- Greifswald. A 10 MW ECRH plant with CW-capability at 140 GHz is under construction to meet the scientific objectives. The microwave power is generated by 10 gyrotrons with 1 MW each. Three gyrotrons are already operational at IPP in Greifswald. The W7-X gyrotrons are designed for single frequency operation at 140 GHz. The operation regime of the W7-X stellarator experiments is restricted to magnetic fields matched to the ECRH-frequency and it would be interesting to extend the operation regime to a second resonant magnetic field. Therefore gyrotron operation at a second frequency was investigated. The standard vertical collector sweep systems of gyrotrons inherently display a pronounced peaking of the collector heat loading. An improved collector sweep system was successfully tested on the TED gyrotrons, which creates an almost homogenous heat loading. This system is of particular interest for next generation gyrotrons with an output power up to 2 MW.

Electron-cyclotron-resonance heating (ECRH) is an important heating system for the stellarator W7-X. For this system a total power of 10 MW at 140 GHz is needed in 30 min operation. In a collaboration with European research laboratories and European tube industry (Thales Electron Devices (TED) in France), cylindrical cavity gyrotrons designed for an output power of 1 MW, CW at 140 GHz have been developed. They are equipped with a single-stage depressed collector for increasing the efficiency and reducing the power loading at the collector wall, an advanced quasi-optical (q.o.) mode converter system with minimized stray radiation, and a single-disk diamond window made by chemical vapor deposition (CVD diamond). Details of the design can be found in Ref. (Dammertz et al, 2002). The first series gyrotron (SN1) has been tested successfully in long pulse operation with full power (30 min, 920 kW, efficiency close to 45 %) and meets the specifications (Dammertz et al., 2006). In this contribution we discuss experimental results of the second and third series gyrotron (SN2, SN3).

Electron Cyclotron Resonance Heating (ECRH) is the main heating method for the Wendelstein 7-X stellarator (W7-X) which is presently under construction at IPP Greifswald. The mission of W7-X is to demonstrate the inherent steady state capability of stellarators at reactor relevant plasma parameters. A modular 10 MW ECRH-plant at 140 GHz with 1 MW CW-capability power for each module is also under construction to support the scientific objectives. The commissioning of the ECRH-plant is well under way; three gyrotrons are operational. The strict modular design allows to operate each gyrotron separately and independent from all others. The ECRH-plant consists of many devices such as gyrotrons and high voltage power supplies, superconductive magnets, collector sweep coils, gyrotron cooling systems with many water circuits and last but not least the quasi-optical transmission line for microwaves with remote controlled mirrors and further water cooled circuits. All these devices are essential for a CW operation. A steady state ECRH has specific requirements on the stellarator machine itself, on the microwave sources, transmission elements and in particular on the central control system. The quasi steady state operation (up to 30 min) asks for real time microwave power adjustment during the different segments of one stellarator discharge. Therefore, the ECRH-plant must operate with a maximum reliability and availability. A capable central control system is an important condition to achieve this goal. The central control system for the 10 MW ECRH-plant at W7-X comprises three main parts. In detail these are the voltage and current regulation of each gyrotron, the interlock system to prevent the gyrotrons from damages and the remote control system based on a hierarchy set of PLCs and computers. The architecture of this central control system is presented.

The 10 MW, 140 GHz, CW ECRH‐plant for W7‐X is in an advanced state of commissioning and the installation was used to investigate advanced applications for extended heating‐ and current drive scenarios. The operation of the TED gyrotrons was recently extended to a 2nd frequency of 103.6 GHz at reduced output power and first results are presented. An improved collector sweep system for the W7‐X gyrotrons with enhanced power capability and smooth power distribution was developed, results are reported.

Experiments were performed with the 1 MW, CW 140 GHz prototype gyrotron for the stellarator W7-X. The maximum output power of 970 kW at an efficiency of 44% was achieved for a pulse length of 11.7 s. For 180 s, an output power of 890 kW could be obtained. At reduced output power of 540 kW, a pulse length of 939 s was achieved. The second prototype has been improved in order to achieve the specified values. Experiments can be performed.

The development of high power gyrotrons (118 GHz, 140 GHz) in continuous wave operation (CW) has been in progress for several years in a joint collaboration between different European research institutes and industrial partners. In this frame, two 140 GHz prototype gyrotrons for CW operation had been constructed and tested at the Forschungszentrum Karlsruhe. According to the results of the prototypes, seven 140 GHz CW gyrotrons were ordered. The first tube was operated at the Forschungszentrum Karlsruhe. A power of 950 kW at efficiency of 43 % (with energy recovery) could be obtained for pulse lengths of 180 s (limited by the available high-voltage power supply). A 30 minute pulse was performed with an output power of 540 kW. During this pulse almost no decrease in performance was found, especially the tube pressure only increased in the range of 10/sup -9/ mbar.

Electron Cyclotron Resonance Heating (ECRH) is the main heating system for the W7‐X stellarator and the only one for CW‐operation in the first stage. The mission of W7‐X, which is presently under construction at IPP‐Greifswald, is to demonstrate the inherent steady state capability of stellarators at reactor relevant plasma parameters. W7‐X is therefore equipped with a superconducting coil system operating at 3 T and a divertor for 10 MW steady state heat removal. A 10 MW ECRH plant with CW‐capability at 140 GHz is under construction to meet the scientific objectives. The commissioning of the ECRH plant is well under way, the status of the project and first full power, cw test results are reported.

Electron Cyclotron Resonance Heating (ECRH) is the main heating method for the Wendelstein 7‐X Stellarator (W7‐X), which is the next step device in the stellarator line of IPP and is presently under construction in the Greifswald branch of IPP. The experiment aims at demonstrating the inherent steady state capability of stellarators at reactor relevant plasma parameters. W7‐X (major radius 5.5 m, minor radius 0.55 m) is equipped with a superconducting coil system operating at 3 T for steady state operation and a divertor for 10 MW steady state heat removal. A 10 MW ECRH plant with CW‐capability at 140 GHz is under construction to meet the scientific objectives. The microwave power is generated by 10 gyrotrons with 1 MW each. A European R&D program aiming at the development of a prototype gyrotron for W7‐X has been successfully terminated by fall of 2002. A prototype gyrotron with the same specifications was developed for W7‐X at CPI (USA). Test results and limitations are reported. The distinct microwave beams from each gyrotron are combined and transmitted to the W7‐X Stellarator ports by an open quasi‐optical transmission system with high transmission efficiency, which runs at normal pressure and consists of water cooled imaging mirrors. Cold tests of a full size, uncooled prototype line and the related RF‐diagnostics are presented. The microwave power is launched to the plasma through 10 synthetic diamond barrier windows and in‐vessel quasi‐optical plug‐in launchers, which allow an independent steering of each beam. The commissioning of the ECRH plant is well under way and the status is presented.

Malignant hyperthermia (MH) in humans is usually triggered by volatile anaesthetics and depolarizing muscle relaxants. However, other factors or drugs (e.g. cresol) are thought to induce MH. We report a case of fulminant MH associated with a ketoacidotic diabetic coma. After therapy for diabetic coma with insulin (containing the preservative cresol) and electrolyte solutions was started, the patient complained of increasing myalgia, developed a high fever and respiratory and metabolic acidosis and lost consciousness. MH was treated immediately with dantrolene; the patient recovered within 14 days. Five months later the patient was diagnosed as MH-susceptible by the in vitro caffeine and halothane contracture test. This case supports the assessment that MH and diabetes are associated diseases and that cresol could possibly trigger MH. Furthermore, therapy with dantrolene has been demonstrated to be beneficial in the treatment of MH associated with diabetic coma.

A new laryngoscope was constructed in order to improve visualization of the larynx and to adjust the instrument to individual situation. The Kleinsasser laryngoscope was divided into two parts. The width between these two halfs can be changed by screws. Because the laryngoscope is open laterally there is more space for the operator and shorter instruments can be used.

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The first series tube of the gyrotrons for the 10-MW electron cyclotron resonance heating system of the stellarator W7-X was tested at Forschungszentrum Karlsruhe (FZK) and yielded a total output power of 0.98 MW, with an efficiency of 31% (without a single-stage depressed collector) in short-pulse operation and of 0.92 MW in pulses of 180 s (efficiency of almost 45% at a depression voltage of 29 kV). The Gaussian mode output power was 0.91 MW. The pulselength at full power (1 MW) is limited at FZK by the available power supply. At a reduced electron beam current, it is possible to operate at longer pulselengths. At an output power of 0.57 MW (electron beam current of 29 A), the pulselength was increased to 1893 s. There was no physical reason for a limitation of this pulse: The pressure increase during the pulse was less than a factor of two and ended up at a very low value in the 10-9 mbar range. The tube was delivered to Max-Planck-Institut fuumlr Plasmaphysik Greifswald for tests at full power and up to 30-min pulselength. The Gaussian mode RF output power, measured in a calorimetric load after a 25-m-long quasi-optical transmission line (seven mirrors), was 0.87 MW at a total output power of 0.92 MW in 30-min pulses. Again, no indications for a limitation in pulselength were found. The second series tube was tested in short-pulse operation and showed a strange behavior concerning a mode hopping which has not yet been understood. The third series gyrotron delivers up to now 0.65 MW at a pulse duration of 180 s. Preliminary operation of the prototype tube as a two-frequency gyrotron delivered 0.41 MW in 10-s pulses at 103.8 GHz (TE21,6 mode)

A new laryngoscope was constructed in order to improve visualization of the larynx and to adjust the instrument to individual situation. The Kleinsasser laryngoscope was divided into two parts. The width between these two halfs can be changed by screws.