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In ITER, an Electron Cyclotron Emission (ECE) diagnostic is planned to measure the electron temperature by measuring the cyclotron radiation in the frequency range of 70-1000 GHz. The cyclotron radiation is usually of low power and needs to be transported with low attenuation over a long distance of ~ 43 m, through a suitable transmission system. Pertaining to long distance, the transmission system will consist of straight waveguide sections, miter bends and waveguide joints. Low power, low loss transmission in a broadband frequency range over long distance makes the design of the transmission system challenging. To arrive at a suitable transmission system, attenuation measurements of three types of transmission lines (TLs) have been performed i.e. circular smooth walled, corrugated and dielectric coated waveguide. A polarizing Michelson interferometer based on Martin-Puplett design has been used to measure the spectrum from waveguide set ups and liquid nitrogen has been used as the black body radiation source. The measured spectrum shows atmospheric water vapour absorption lines in all types of TLs. The preliminary measurement shows that the attenuation of smooth walled waveguide is found to be comparable to corrugated waveguide up to ~ 600GHz and better than corrugated waveguide above 600 GHz for the chosen set of experimental conditions. Further, to avoid water absorption lines, a smooth walled TL is evacuated up to rough vacuum (~10-2mbar) and it was observed that the attenuation is decreased and overall transmission is improved.

To drive plasma current non-inductively, a lower hybrid current drive (LHCD) system has been designed, fabricated and successfully installed on ADITYA tokamak. The system is designed to launch 120 kW of RF power, at a frequency of 3.7 GHz. The system mainly consists of a high power CW klystron source, a long waveguide transmission line of about 100 m length, a UHV compatible modular waveguide line of about 2.65 m, and a conventional grill type antenna. Independent phase shifters, one each in the eight lines, are used to adjust the antenna phasing and also provides the flexibility to launch a composite spectrum. The antenna is designed to launch lower hybrid waves (LHW) with parallel refractive index ( N || ), in the range, 1 N || The complete system development includes design, fabrication and testing of number of waveguide components, modular waveguide lines and their integration. Different cost effective fabrication techniques are adopted to achieve good RF performance. Special attention is paid on the flanged joint seals in the long transmission line to minimize the RF losses. The entire LHCD system is calibrated, especially, in terms of phase, insertion loss and return loss measurements. After the successful integration of the system on ADITYA tokamak, some initial experiments have been carried out to assess the system commissioning and its performance. The experiments were done with a plasma (hydrogen) density of 2–5 × 10 12 cm −3 at a toroidal magnetic field of 0.8 T with 10–25 kA of plasma current. Initial results indicate that, good coupling is achieved in the presence of proper edge density. Measurements obtained from second harmonic electron cyclotron emission (ECE) and hard X-ray diagnostics suggest generation of suprathermal electrons in the presence of LH pulse. Plasma current pulse elongation with LH power is observed but needs further investigation to derive conclusions. This paper presents the design, fabrication, testing and integration of the waveguide lines, waveguide components and UHV compatible modular transmission lines of the LHCD system on ADITYA tokamak and discusses some of the initial results.

In tokamaks, the temperature measurement using different techniques like Electron Cyclotron Emis- sion (ECE), Thomson scattering etc. shows differences because of various phenomena. The physical reasons for this are not entirely understood. Thus to have comprehensive understanding of these difference, the contribu- tion from each phenomenon needs to be individually understood. The phenomenon affecting radial temperature profile measurement includes harmonics overlap, relativistic down shifting, presence of non-thermals etc. For ITER like plasma, radial temperature profiles can be obtained from the first harmonics ordinary (O) mode or second harmonic extra-ordinary(X) mode of ECE spectrum. It is possible that, higher harmonics produced from the non-thermals can be relativistically downshifted to second harmonics and results a deviation in the measured temperature profile. We performed a parametric study on the e ffect of non-thermal electrons on measured ECE temperature for ITER scenario-2. All the numerical calculations reported in this paper are performed using NOTEC computer code which is capable of handling non-thermal populations. After proper validation of nu- merical methods using normal electron population (without non-thermals) a parametric study with non-thermals is performed. In the parametric study radial locations of non-thermals, energy of non-thermals and fraction of non-thermals are considered. This study is initially performed for normal view and later extended in to oblique views. The range of deviation of temperature over the examined parametric regime as well as the possible phys- ical reasons will be presented. The effect of parallel component of non-thermal energy is also examined. Finally results of one set of study for oblique view (where the detector is not exactly normal to the magnetic field) with non-thermal electrons are also presented. In ITER apart from an Electron Cyclotron Emission (ECE) detector placed normal to magnetic field an oblique view detector is planned to grab information about non-thermal electrons. Usefulness of such an additional detector for a better radial resolution is examined. The differences in the ECE spectrum from a tokamak plasma between a direct LOS (normal to toroidal magnetic field) and a slightly oblique LOS have been modelled. A typical ITER tokamak scenario has been chosen in this study. The intensities of radiation, as observable from the low-field side, covering the first harmonic O-mode spectral frequencies 105-230 GHz have been compared. The physical reasons for the code-predicted results, regarding the differences between the direct and oblique spectra, are elucidated. Finally, signatures of the presence of non-thermals from a comparison of normal view and oblique view are also examined.

Spectroscopy of Electron Cyclotron Emission (ECE) has been established as adequate diagnostic technique for fusion research machines. Among various instruments for ECE diagnostics, only Fourier-transform spectrometers with Martin-Puplett interferometers can measure electron cyclotron radiation in a broadband frequency range from 70 to 1000 GHz. Before these measurements, a complete system including a frontend radiation collector, a transmission line, an interferometer and a radiation detector should be absolutely calibrated. A hot/cold calibration source and data-averaging technique are used to calibrate the total ECE diagnostic system. It takes long time to calibrate the ECE system because of the low power level of the calibration source and high values of the noise equivalent power (NEP) of the detection system. A new technique, Hilbert-transform spectral analysis, is proposed for the ITER plasma ECE spectral measurements. An operation principle, characteristics and advantages of the corresponding Hilbert-transform spectrum analyser (HTSA) based on a high-Tc Josephson detector are discussed. Due to lower NEP-values of the Josephson detector, this spectrum analyser might demonstrate shorter calibration times than that for the Martin-Puplett interferometer.

The ITER Electron Cyclotron Emission (ECE) diagnostic system will provide information about plasma electron temperature and its fluctuations and other important plasma parameters which are required for plasma control and physics studies. The temperature profile measurement in the first harmonic ECE frequency range from 122-230 GHz (for BT = 5.3 T) is obtained by using an O-mode heterodyne radiometer. It is difficult to cover this wide frequency band by one radiometer, due to technological challenges in achieving wide bandwidth for the mixers. So, the present radiometer design has been optimized by considering four receivers, each of bandwidth ~ 30 GHz which can provide reliable temperature measurements. The splitting of frequency band into four receiver bands is efficiently achieved by considering a combination of quasi-optical and waveguide diplexers, optimizing power loss and cross-talk between the channels. The target spatial resolution of a/30, where "a" is the minor radius of the plasma cross section, is achieved by choosing Radiometer IF filter bandwidth of 1-2 GHz. Further, the radiometer is designed to achieve noise temperature < 10 eV. In this paper, the preliminary design and performance of O-mode Radiometer has been discussed.

This paper presents the design of an eight-channel W band radiometer as an electron cyclotron resonance (ECE) diagnostic to measure the electron temperature for phase I (Bt0 = 1.5 T) operation of SST-1. A double-sideband (DSB) mixer cum power divider method is used to cover the full range of ECE frequencies. The noise figure, sensitivity and expected output signal of the radiometer are estimated and a calibration technique is discussed. A time resolution of 5 μs and a spatial resolution of 0.6 cm for 2fce = 70 GHz are achieved by this radiometer.

Broad band millimeter wave transmission lines are used in fusion plasma diagnostics such as electron cyclotron emission (ECE), electron cyclotron absorption, reflectometry and interferometry systems. In particular, the ECE diagnostic for ITER will require efficient transmission over an ultra wide band, 100 to 1000 GHz. A circular corrugated waveguide transmission line is a prospective candidate to transmit such wide band with low attenuation. To evaluate this system, experiments of transmission line attenuation were performed and compared with theoretical loss calculations. A millimeter wave Michelson interferometer and a liquid nitrogen black body source are used to perform all the experiments. Atmospheric water vapor lines and continuum absorption within this band are reported. Ohmic attenuation in corrugated waveguide is very low; however, there is Bragg scattering and higher order mode conversion that can cause significant attenuation in this transmission line. The attenuation due to miter bends, gaps, joints, and curvature are estimated. The measured attenuation of 15 m length with seven miter bends and eighteen joints is 1 dB at low frequency (300 GHz) and 10 dB at high frequency (900 GHz), respectively.

The Electron Cyclotron Emission (ECE) diagnostic system in ITER provides essential information for plasma control and for evaluating the plasma performance. It measures the electron temperature profile (edge/core), electron temperature fluctuations and radiated power in the electron cyclotron frequency range from the plasma. Virginia Diodes Inc. (VDI) has designed and developed a state-of-the-art prototype receiver to detect emission in the 200-300 GHz frequency range. The prototype receiver developed by VDI has been tested at DIII-D tokamak to check its performance by measuring higher frequency ECE harmonics in high temperature plasmas. Bench testing verifies the receiver’s band coverage and noise temperatures. Good sensitivity has been obtained meeting the ITER requirement. Also, the receiver performance is assessed for ITER by comparing the data from the receiver and the existing Michelson interferometer for the same DIII-D plasma shot. The measurement results show that the receiver provides accurate temperature information for the plasma emission throughout the frequency band.

Considerable progress has been made on the design of the ITER electron cyclotron emission (ECE) diagnostic over the past two years. Radial and oblique views are still included in the design in order to measure distortions in the electron momentum distribution, but the oblique view has been redirected to reduce stray millimeter radiation from the electron cyclotron heating system. A major challenge has been designing the 1000 K calibration sources and remotely activated mirrors located in the ECE diagnostic shield module (DSM) in the equatorial port plug #09. These critical systems are being modeled and prototypes are being developed. Providing adequate neutron shielding in the DSM while allowing sufficient space for optical components is also a significant challenge. Four 45-meter long low-loss transmission lines transport the 70–1000 GHz ECE from the DSM to the ECE instrumentation room. Prototype transmission lines are being tested, as are the polarization splitter modules that separate O-mode and X-mode polarized ECE. A highly integrated prototype 200–300 GHz radiometer is being tested on the DIII-D tokamak in the USA. Design activities also include integration of ECE signals into the ITER plasma control system and determining the hardware and software architecture needed to control and calibrate the ECE instruments.

The Electron Cyclotron Emission diagnostic on ITER requires electron temperature profile with 10 μsec time and 6 - 7 cm spatial resolution. The diagnostic is also useful to study many plasma physics phenomenon like temperature fluctuation, non-thermal electrons population and the power loss due to ECE. The conceptual design being considered for ITER ECE consist of a radiometer of frequency range 122 to 220 GHz for O-mode radiation measurement and two Fourier transform spectrometers of frequency range 70 to 1000 GHz as measuring instruments for O-mode and X-mode radiation measurement. There are two lines of sight for the collection of cyclotron radiation. One is radial view and other is oblique view at 10 degree (1). The radiation collected by both view will be transmitted through the polarization splitter boxes and four transmission lines to the diagnostic area. In this paper we will summarize the conceptual design details and changes proposed at the Conceptual Design Review. The required calibration time for the ECE measuring instrument will be discussed in the paper.

A Gaussian optics lens antenna system has been designed, fabricated and tested for the plasma diagnostic systems on the Aditya Tokamak. The performance of the designed antenna system is compared with our own designed conventional conical horn antenna in Ka-band spectrum. A gain improvement of 11 dB has been achieved in GOLA system, having gain about 33 dB and half power beam width 1.6deg, compared to conical horn, which has gain about 22-dB and half power beam width 12deg respectively.The performance of indigenously designed and fabricated antenna system has also been simulated using CST Microwave Studio and ZEMAX optical designing software. The simulated findings of gain and 3 dB bandwidth of both antenna systems are well matched with experimental findings.

ITER ECE diagnostic [1] needs not only to meet measurement requirements, but also to withstand various loads, such as electromagnetic, mechanical, neutronic and thermal, and to be protected from stray ECH radiation at 170 GHz and other millimeter wave emission, like Collective Thomson scattering which is planned to operate at 60 GHz. Same or similar loads will be applied to other millimetre-wave diagnostics [2], located both in-vessel and in-port plugs. These loads must be taken into account throughout the design phases of the ECE and other microwave diagnostics to ensure their structural integrity and maintainability. The integration of microwave diagnostics with other ITER systems is another challenging activity which is currently ongoing through port integration and in-vessel integration work. Port Integration has to address the maintenance and the safety aspects of diagnostics, too. Engineering solutions which are being developed to support and to operate ITER ECE diagnostic, whilst complying with safety and maintenance requirements, are discussed in this paper.

In this study, the baseline design for the ITER electron cyclotron emission (ECE) diagnostic has entered the detailed preliminary design phase. Two plasma views are planned, a radial view and an oblique view that is sensitive to distortions in the electron momentum distribution near the average thermal momentum. Both views provide high spatial resolution electron temperature profiles when the momentum distribution remains Maxwellian. The ECE diagnostic system consists of the front-end optics, including two 1000 K calibration sources, in equatorial port plug EP9, the 70-1000 GHz transmission system from the front-end to the diagnostics hall, and the ECE instrumentation in the diagnostics hall. The baseline ECE instrumentation will include two Michelson interferometers that can simultaneously measure ordinary and extraordinary mode ECE from 70 to 1000 GHz, and two heterodyne radiometer systems, covering 122-230 GHz and 244-355 GHz. Significant design challenges include 1) developing highly-reliable 1000 K calibration sources and the associated shutters/mirrors, 2) providing compliant couplings between the front-end optics and the polarization splitter box that accommodate displacements of the vacuum vessel during plasma operations and bake out, 3) protecting components from damage due to stray ECH radiation and other intense millimeter wave emission and 4) providing the low-loss broadbandmore » transmission system.« less

The ITER ECE diagnostic has recently been through a conceptual design review for the entire system including front end optics, transmission line, and back-end instruments. The basic design of two viewing lines, each with a single ellipsoidal mirror focussing into the plasma near the midplane of the typical operating scenarios is agreed upon. The location and design of the hot calibration source and the design of the shutter that directs its radiation to the transmission line are issues that need further investigation. In light of recent measurements and discussion, the design of the broadband transmission line is being revisited and new options contemplated. For the instruments, current systems for millimeter wave radiometers and broad-band spectrometers will be adequate for ITER, but the option for employing new state-of-the-art techniques will be left open.

For the absolute measurement of temperature using Radiometer system, Radiometer must be calibrated with known incident power. Calibration setup is indigenously developed to calibrate the various (E, Ka AND F-Band) ECE Radiometer systems available at IPR. "Hot and Cold technique" is used with blackbody sources, one at room temperature and another at Liquid Nitrogen temperature. New calibration technique using DSP, as well as the conventional technique using Lock-in amplifier, are implemented to remove the noise of system. The blackbody sources are chopped with high accuracy DC motor to generate the temperature difference. Calibration coefficients for individual channels are determined. Inherent noise and losses are calculated by analytical way as well as experimental measurements. Theoretical and experimental measurement has shown necessitate for High temperature black body target. Prototype is generated for High temperature blackbody calibration source. Various materials are analyzed for thermal and dielectric properties.