Electron Cyclotron Emission and Electron Cyclotron Resonance Heating (EC-16)

The following sections are included:

• PREFACE

• CONTENTS

The presentations focusing on the physics and applications of heating and current drive in the electron cyclotron range of frequencies are summarized.

The ability to control the location and localization of energy and current deposition in fusion plasmas with electron cyclotron waves is unmatched by any other auxiliary heating and current drive method. The establishment of the physics basis of the wave propagation and absorption allows accurate prediction of the deposition given the launcher optics and the profiles of magnetic field, electron density, electron temperature, and impurity density. This, along with the development of the technology of high-power millimeter-wave sources and the means to transmit them to the plasma, has facilitated experiments in present-day fusion devices to demonstrate the utility of heating and current drive with electron cyclotron waves (ECH and ECCD, respectively). Three primary roles are envisioned for ECH or ECCD in burning plasmas. First, all burning plasma scenarios require some access conditions, whether it is merely heating the plasma to fusion-relevant conditions or generating specific profiles of the magnetic field necessary to access steady-state operation in a tokamak. Second, tokamak-based steady-state scenarios require efficient auxiliary current drive to sustain the magnetic configuration. Finally, control of the operating point of a burning plasma is essential. This role includes applications such as response to off-normal events and active control of plasma instabilities. Each of these roles will be discussed using examples from present-day tokamak and stellarator experiments. Prospects for application in ITER and fusion power plants will also be presented.

The ECRH system at ASDEX Upgrade is currently extended from 1.6 MW to 5 MW. The extension so far consists of 2-frequency units, which use single diamond-disk vacuum-windows to transmit power at the natural resonances of these disks (105 & 140 GHz). For the last unit of this extension two additional intermediate non-resonant frequencies are foreseen, requiring new window concepts. For the torus a polarisation-independent double-disk window has been developed. For the gyrotron a grooved diamond disk is actually favoured, for which the grooved surfaces act as anti-reflective coating. Since ASDEX Upgrade operates with completely W-covered plasma facing components, central ECRH is often applied to suppresses W-accumulation in the plasma center. In order to extend the operational range for central ECRH, X3- and O2-heating schemes were developed. Both are characterized by incomplete single-path absorption. For X3 heating, the X2 resonance at the pedestal on the high field side is used as a 'beam-dump', for the O2 scheme a specific reflector tile on the inner heat shield enforces a second path through the plasma center. The geometry for NTM control had to be modified to allow simultaneous central heating. In real-time the ECRH position can be determined either by ray-tracing based on real-time equilibria and density profiles or from ECE for modulated ECRH power. Fast real-time ECE also allows to determine the NTM position. Further major physics applications of the system are summarized.

A demonstration of real-time feedback control for autonomous tracking and stabilization of m/n = 2/1 tearing modes in a tokamak using Electron Cyclotron Resonance Heating and Current Drive (ECRH/ECCD) is reported. The prototype system on TEXTOR combines in the same sight-line an Electron Cyclotron Emission (ECE) diagnostic for tearing mode sensing and a steerable ECRH/ECCD antenna. The mode location is retrieved from the ECE measurements and serves as input for a control loop, which aligns the ECRH/ECCD deposition with the tearing modes by steering of a launcher mirror. The alignment is achieved by matching the mode location in the sensor spectrum with the fixed ECRH/ECCD actuator frequency. The control response is dominated by the response of the mechanical launcher. Analysis of the launcher dynamics receives special emphasis in the control design. In addition, the ECRH/ECCD power is modulated in phase with the rotation frequency of the O-point of the tearing modes using a feedback loop, which extracts the mode's frequency and phase from the ECE data. The experimental results demonstrate the capabilities of the control system to track and suppress tearing modes in real-time. A relatively simple control design suffices to meet the performance requirements demanded for effective tearing mode suppression.

3MW ECRH system with six 68GHz/500kW gyrotrons has been developed on HL-2A. H mode discharges have been realized with ECRH and NBI. NTM has been observed during ECRH heating. Transient ITB after ECRH switch-off has been achieved. Stabilization of tearing mode and sawtooth control with ECRH has been studied

A 110 GHz GYCOM gyrotron, which was loaned from DIII-D in General Atomics (GA) including a matching optics unit (MOU) and a magnet, was successfully commissioned and used for the second harmonic ECH-assisted startup in 2009 Korea Superconducting Tokamak Advanced Research (KSTAR) campaign. The gyrotron was aligned at the magnetic field axis of the magnet by adjusting aligners on top and bottom flanges of the magnet during the installation procedures. The measured images of the output beam profile at the window using a burn paper showed a good agreement with those measured in DIII-D. The maximum available RF power was just about 250 kW, which was measured at the terminal dummy load, due to the limitation of the existing power supply of which nominal beam voltage and current were 63 kV and 20 A, respectively. The 110 GHz, 250 kW EC wave, which corresponds to the second harmonic resonance wave to the toroidal field of 2 T, was injected to KSTAR for the plasma start-up and current ramp-up. The plasma start-up was successfully and reliably achieved through the second harmonic ECH pre-ionization. The injection mode was the X-mode with oblique launch angle to the toroidal magnetic field. This paper reports the initial commissioning and operation results of the 110 GHz ECH system. Moreover, the experimental results of the ECH-assisted start-up during the 2009 KSTAR campaign are presented and discussed.

The spectral characteristics of the large scale (MHD) plasma oscillations were investigated. ECH was used for a modification of plasma parameters. Main tool of the analysis was the high space resolution ECE method. The selection of different modes of oscillations was fulfilled. The simple relations between the eigen-frequencies of oscillations and the radii of the corresponding rational magnetic surfaces were discovered. The absolute values of all measured eigen-frequencies coincide well with the calculation by the introduced formula.

A study has been conducted to evaluate the feasibility of installing an ECRH system on the JET tokamak. This paper presents an overview of the studies performed in this framework by an EU-Russia project team. The motivations for this major upgrade of the JET heating systems and the required functions are discussed. The main results of the study are summarised. The usefulness of an EC system for JET is definitely confirmed by the physics studies. No strong limitations for any of the functions envisaged have been found. This has led to a preliminary conceptual design of the system.

Investigation of electron cyclotron wave propagation, power absorption, and current drive has been performed for a set of JET scenarios, aiming to assess the optimal wave frequency, launching position, and injection angles to achieve the various physics goals of an EC system in JET. EC power absorption and current drive have been computed for three values of the EC frequency, namely, 113 GHz, 150 GHz, and 170 GHz. On the basis of extensive beam tracing calculations performed in a wide range of magnetic fields (2.5 T – 3.4 T), the frequency of 170 GHz has been chosen, since it covers the wider magnetic field range of operation in JET and corresponds to that foreseen in ITER.

A study has been conducted to evaluate the feasibility of installing an ECRH plant on the JET tokamak. The possible options for the wave launching system for JET have been investigated, assuming a frequency of 170 GHz, the use of an evacuated transmission line and the availability of an entire JET mid-plane port for the launching system. Applications include NTM and sawteeth control, core heating and current drive, current profile tailoring.

In the framework of the study of the feasibility of an ECRH system for JET, the aim of this work is to verify that the foreseen 10 MW–170 GHz Electron Cyclotron (EC) input wave power would be sufficient for Neoclassical Tearing Modes control, crucial issue for operation at high β and to determine how much the required power might be further reduced in the case of the microwave source modulation. The stabilization of low order (m,n) modes is discussed using a Generalized Rutherford equation and JET ELMy H-mode scenarios are considered in a wide range of operational magnetic field.

A study conducted over the last year to asses the desirability and feasibility of installing an ECRH system on the JET tokamak has concluded that such a system is indeed both desirable and feasible. Details of physics studies, launcher and transmission line design, and power supplies are presented elsewhere in these proceedings. This paper concentrates on the logistical implications of installing this system at JET. The paper addresses issues such as port allocation and plant location. The study has concluded that a new building will be needed to house the ECRH plant. Building layout proposals are presented together with considerations regarding the required auxiliary equipment.

Quasi-optical (QO) and evacuated waveguide (EWG) transmission lines (TL) have been analyzed as possible solutions to transfer the power from the gyrotrons to the launcher. The EWG solution has been chosen as the reference TL solution due to the achieved space saving, its flexibility and its ITER relevance. The proposed EWG routing is compatible with the use of standard components, a small number of mitre bends and <5% of expected attenuation. Concerning the vacuum window, the only material currently available giving the power/pulse length combination is based on the use of disks in synthetic diamond (CVD). This choice gives the opportunity to adopt the window design proposed for the ITER project. A technical solution exploiting two separate single disk windows rather than a double window has been analyzed in order to fulfill safety requirements and to take into account problems arising in transmitting high power.

The future JET programme, after the installation of the ITER-like wall, will be mainly focused on the consolidation of the physics basis of the three main ITER scenarios. These scenarios will make substantial use of Electron Cyclotron (EC) waves, for heating as well as for control of both the MHD activity and the current density profile. Therefore, a programme for preparation, validation and optimization of the ITER scenarios in present tokamaks would strongly benefit from an ECRH/ECCD system. A study has been conducted to evaluate the feasibility of installing an ECRH system on the JET tokamak. An important intention of the study was to investigate the feasibility to utilise some unused conventional NBI – power supplies for the ECRH project.

The electron cyclotron heating/current drive (ECH/ECCD) system has become an essential tool for the fusion plasma research in toroidal devices. In Korea Superconducting Tokamak Advanced Research (KSTAR) tokamak, development of high power and multi-frequency ECH/ECCD system is in progress. The frequencies employed in KSTAR are 84 GHz, 110 GHz, and 170 GHz. Multiple frequency sources can easily support the wide range of operating regimes from 1.5 T to 3.5 T in KSTAR tokamak. In particular, the 170 GHz source, that will be adapted to the ITER, corresponds to the second harmonic frequency of the KSTAR operating range from 2.6 T to 3.5 T. This frequency will be mainly used for the control of the local plasma current profile to manipulate the internal MHD instabilities such as the neoclassical tearing mode (NTM) critical in high-beta plasma operation. This paper presents simulated ray tracings of the 170 GHz EC waves for a various plasma conditions in KSTAR. The TORAY-GA ray tracing code is used, along with Interactive Data Language (IDL) procedures that create the input files, to study the effect of ECH/ECCD on the plasma equilibrium profiles as a function of the initial density and temperature profiles and of toroidal field.

The improved H-mode in ASDEX Upgrade (AUG) is an operation regime with high confinement and densities near the Greenwald limit. Since the first wall in AUG is completely coated with tungsten, the ECRH is needed to control the tungsten accumulation in H-modes [1], therefore the routinely used X2 mode must be deposited in the plasma centre [2]. For ITER-relevant plasma discharges a safety factor of q₉₅ ≈ 3 must be achieved. At B = 2.5 T plasma currents of > 1.2 MA corresponds to a q₉₅ ≈ 3, which results in densities above the X2 mode cutoff. Another way to decrease q₉₅ is to reduce the magnetic field, but then the X2 mode is not resonant in the plasma centre. For these two cases new ECR heating scenarios using X3 and O2 mode were developed and are presented here.

The central electron temperature of more than 15 keV is achieved in LHD as a result of increasing the injection power and the lowering the electron density. Such collision-less regime is important from the aspect of the neoclassical transport and also potential structure formation. The creation of the high energy electrons and the transport of them can trigger the potential structure formation. Evidences of the presence of high energy electrons are indicated from hard X-ray PHA, and the discrepancy between the stored energy and kinetic energy estimated from Thomson scattering. ECE spectrum in such low density regime under the presence of high energy electrons are discussed by comparing the calculated one that solves the radiation transfer equation. Such investigation might be used for the estimation of high energy electrons as an inverse process of the ECRH.

Second harmonic X-mode electron cyclotron current drive (ECCD) experiments have been made in Heliotron J by using an upgraded EC launching system. A focused Gaussian beam is injected with the parallel refractive index, N_‖, ranging from -0.05 to 0 6. According to ray tracing calculations, the focused Gaussian beam makes the EC power absorption localized, Δρ<0.2, modifying the rotational transform profile. The experimental results show that the EC driven current can be controlled by N_‖ and it depends on the local magnetic field structure where the EC power is deposited. A large increase in ECE signals has been observed when the EC current was driven, indicating important role of high-energy electrons on the ECCD.

Access to the H-mode regime of improved confinement and good global confinement when the plasma heating is dominantly of the electrons is critical to the success of ITER, since the proposed heating schemes for ITER, including heating by fusion products, deposit most of their heat in the electron fluid. Most of the world database for the L-H transition and for confinement is derived from discharges with high power positive-ion neutral beam injection (NBI), which primarily heats the ions. Issues for dominant electron heating include the H-mode power threshold and effect on rotation, density profile, global confinement, pedestal height, and edge localized mode characteristics. Experiments have been performed on DIII-D using electron cyclotron heating (ECH) to simulate heating in ITER. These experiments suggest that the H-mode transition power for ECH is significantly lower than that for NBI in deuterium plasmas but about the same for helium plasmas. The global confinement with ECH relative to the H98(y,2) scaling is around 75% under the conditions of these discharges. The pedestal with pure ECH has a higher electron temperature and lower density than for NBI, and the width of the pedestal region is nearly identical.

At the EC-16 workshop there were 17 presentations primarily on ECE and an invited talk on EBE. There was also a discussion session on the ITER ECE diagnostic system design. ECE imaging, correlation ECE, oblique ECE and EBE imaging diagnostic performance has continued to improve since EC-15. There have been some interesting developments in ECE receiver technology and data analysis that show promise for the future. There is still a need to agree on some potentially critical details of the ITER ECE diagnostic design, and it remains unclear how important the Thomson scattering/ECE discrepancy, seen previously on TFTR and JET, will be for ITER.

Program of ECH of 4MW at 140 GHz is launched for pressure and current density profile control on EAST. Several ECE diagnostics are under development as important ingredient of the research program of EAST. HT-7 is equipped with a heterodyne radiometer containing 16 channels and a ECE image system with 8(radial)x16(vertical) channels. Physical issues including fluctuation by electron and ion modes, low frequency Zonal Flow, magnetic reconnection mechanism, anomalous Doppler resonance effect, etc were investigated on HT-7. These two systems have been moved to EAST after some modifications. New ECE systems including a 32-channel ECE system covering 104–168 GHz and a ECEI system of 24(radial)×16(vertical) channels are under developing. These two systems are designed to fit the ECH plasma regimes and synergetic work for long range correlation research of plasma turbulence. A grating polychromator ECE system will be installed soon for Te profile measurement covering whole operation range of toroidal magnetic field on EAST.

This paper describes measurements of long wavelength, turbulent electron temperature fluctuations in the core plasma of the DIII-D tokamak made with a correlation electron cyclotron emission (CECE) radiometer-based diagnostic. Experimental and simulation results indicate that long wavelength electron temperature fluctuations (1) are similar in amplitude and spectrum to density fluctuations, (2) can be associated with both ITG and TEM turbulence, (3) exhibit changes in the relative fluctuation level that correlate with changes in electron thermal transport, and (4) are correlated, but out of phase, with density fluctuations measured simultaneously with reflectometry.

The Tokamak à Configuration Variable, TCV, is equipped with a moveable ECE receiving antenna, identical to the 6 second harmonic (X2) ECH/ECCD launchers, which can track the plasma at any position within the vacuum vessel in real time. In contrast to this poloidal plane viewing, the receiver can be rotated to obtain an oblique view. In this configuration, measurements of the asymmetry of the electron distribution function, EDF, are performed during co/counter ECCD sweeps at constant input power. Direct evidence of the driven current is provided by the ratio of radiation temperatures from co and counter views of identical plasmas. The results are simulated by the NOTECTCV radiation-transfer code in which current profile broadening can be included to reproduce the measurements. Studies of core broadband temperature fluctuations, induced by plasma turbulence, are performed with a high-resolution X2 correlation ECE diagnostic. ECE correlation is measured by two frequency-tunable YIG filters that can be placed between r/a = 0 - 0.9 using both their wide tuning range, and plasma geometry changes from shot to shot. Evidence of broadband (20–150 kHz) fluctuations with peak frequencies ranging from 20 kHz up to 90 KHz at r/a = 0.3 - 0.8 in Ohmic sawtooth-free discharges was obtained. The amplitude of the temperature fluctuations decreases with increasing density and thus, increasing collisionality, which is in qualitative agreement with predictions from quasi-linear gyrokinetic calculations performed with the gyrokinetic code GS2. The mixing length heat diffusivity calculated from GS2 decreases with increasing collisionality, as does that obtained from a power balance analysis. The real frequency of the broadband turbulence stays positive over the range of collisionalities explored, indicating dominant TEM turbulence.

Multiple angle (0, 10, 20 degrees with respect to the radial direction) and polarization (X, O modes) ECE spectra of JET plasmas with significant Lower Hybrid additional power were obtained with the Oblique ECE diagnostics. Such data have been analyzed with the emission code SPECE that encompasses a multi-Maxwellian model of the fast electron tail driven by Lower Hybrid waves. The model has been used to fit, varying the control parameters, the five experimental signals of the ECE diagnostic aiming to characterize the LH power absorption and driven current.

Microwave imaging reflectometry (MIR) system and electron cyclotron emission imaging (ECEI) system are under development for the simultaneous reconstruction of the electron density and temperature fluctuation structures in the Large Helical Device (LHD). The MIR observes three-dimensional structure of disturbed cutoff surfaces by using the two-dimensionally distributed horn-antenna mixer array (HMA) of 5 × 7 channels in combination with the simultaneous projection of microwaves with four different frequency components (60.410, 61.808, 63.008 and 64.610 GHz). The ECEI is designed to observe two-dimensional structure of electron temperature by detecting second-harmonic ECE at 97–107 GHz with the one-dimensional HMA (7 channels) in the common optics with MIR system. Both the MIR and the ECEI are realized by the HMA and the band-pass filter (BPF) arrays, which are fabricated by micro-strip-line technique at low-cost.

This paper reports on the current status of integration of ITER microwave diagnostics, such as ECE, reflectometry systems and Collective Thomson scattering, and gives an outlook on the upcoming technical and design activity. Some open issues are addressed and discussed.

The development of variable-resolution Electron Cyclotron Emission (ECE) diagnostics for Tokamaks based on the digitization and subsequent Fast Fourier Transformation (FFT) of the intermediate frequency signal [1] has enabled the exploration of the space-time domain of ECE diagnosed phenomena. This development depends on advances made in fast multi -Gigahertz sampling ADCs that have recently become available. One important application is the feedback control of neo-classical tearing-modes (NTMs) in Tokamaks by Electron Cyclotron Heating and Current Drive (ECH&CD) [2, 3 and 4]. This requires both a detection of the full mode content in the plasma and an accurate radial localization and poloidal phase of the magnetic islands. An FT ECE system has the possibility to optimize time and frequency resolution (spatial resolution). It could observe the plasma cross-section and then zoom-in on the detailed structure of the island. The scrutiny of the plasma phenomena at variable temporal and spatial scales could be extended by means of wavelet analysis.

A proof of principle on TEXTOR employing an FFT-ECE [1] system in-line with the ECH&CD system [5] enabled detailed observations of scattering of the high power mm-waves on rotating tearing modes [6]. The observed scattering is found to be in phase with the NTM island rotation. The medium and long-term objective is to develop FFT-ECE for NTM control on AUG and ITER.

The abrupt steep jump of electron cyclotron emission (ECE) signals during current ramp down has been observed and explained by anomalous Doppler resonance effect (ADR). The identifying process of ADR was presented based on fast Fourier transform (FFT) technique.

The RAYTEC code for electron cyclotron (EC) wave radiative transport modelling of fusion plasmas has been generalised to cover EC radiative transport in the presence of an anisotropic distribution of suprathennal electrons. More specifically, superposed on a Maxwellian bulk, the population of suprathermals is taken to be the sum of a Maxwellian and a distribution which is Maxwellian in energy and has a distribution in the form of a one-sided loss-or anti-loss-cone in pitch angle, such that suprathermals with an excess of momentum either perpendicular or parallel to the magnetic field (as characteristic, respectively, for EC cyclotron wave heating and current drive) can be dealt with. To display the impact of anisotropy, the profile of the net EC wave power density lost from an ITER-like plasma is evaluated as a function of the cone angle for suprathemals localized either at or off the plasma centre. The results thus obtained are discussed in respect to those for an isotropic distribution of the suprathennals as well as those for solely the bulk plasma.

We have tested a MATLAB version of the ECESIM code [1] The ECESIM code, originally in IDL, calculates the Electron Cyclotron Emission (Radiation Temperature) given the electron temperature, density and magnetic field radial profiles of a tokamak plasma. This was developed for the analysis of DIII-D ECE and has been shown to be appropriate for the mildly relativistic finite density regime of ITER [2]. The physics of code is based on the theoretical formulation by Bomatici [3]. The MATLAB version of the ECESIM code has been used to calculate the X-and O-mode ECE emission for ITER Scenario-2. From the X and O mode emissivities for ITER, we have identified the frequencies which may be particularly vulnerable to any polarization scrambling which might take place prior to the polarizations being separated.

Notch filters are the most important mm-wave components to protect front-end receivers from intensive gyrotron stray radiation in fusion plasmas. Here we describe a notch filter design with 105 GHz center frequency and 200 MHz rejection bandwidth. The design is based on a fundamental rectangular waveguide with cylindrical cavities coupled by narrow iris gaps, i.e. small elongated holes of negligible thickness. We use numerical simulations to study the sensitivity of the notch filter performance to changes in geometry and in material properties within a total bandwidth of ±10 GHz. The typical insertion loss in the passband is below 1.5 dB, and the attenuation in the stopband is approximately 40 dB.

A 20-channel grating polychromator transferred from PPPL, has been re-built for electron cyclotron emission measurements on EAST. This instrument measures the second harmonic electron cyclotron emission from plasma with frequency range from 90 GHz to 250 GHz, which corresponds to a central magnetic field (R₀=1.7 m) of 2-3.5 T. The radial resolution is around 2.5 cm. New pre-amplifiers are made and tested, based on the electronics of GPC-II on TFTR. These amplifiers have a gain of around 520, with a 400 kHz 3 dB roll off frequency.

The ECE diagnostic system on KSTAR tokamak has been upgraded in order to follow an increase of the operational magnetic field of KSTAR after the 1^st plasma. A new 48CHs ECE radiometer with frequency range of 110 GHz to 162 GHz has been installed and the waveguide system was also replaced by corrugated circular over-mode waveguides. But the ECE collecting optics, which consists of two metallic mirrors, was not changed. With this radiometer, some measurements of the electron temperature at the high field side were carried out during the 2^nd KSTAR campaign, when the tokamak was operated with 2T of toroidal magnetic field. The electron temperature as well as its radial profile was measured and sawtooth phenomena were also observed.

Angular scanning of EBW emission (EBE) has been conducted in MAST. From EBE measurements over a range of viewing angles the angular position and orientation of the B-X-O mode conversion (MC) window can be estimated giving the pitch angle of the magnetic field in the MC layer. The radial position of the corresponding MC layer is found from Thomson scattering measurements. Measurements at several frequencies can provide a pitch angle profile. Results of pitch angle profile reconstruction from EBE measurements are presented in comparison with motional Stark effect measurements. Microwave imaging of the B-X-O Me window is proposed as an alternative to the angular scanning. The proposed scheme is based on an imaging phased array of antennas allowing the required angular resolution. Image acquisition time is much shorter than MHD time scales so the EBE imaging can be used for pitch angle measurements even in the presence of MHD activity.

The electrostatic electron Bernstein wave (EBW) can provide localised on- and off-axis heating and current drive in typically overdense (high-β) spherical tori (ST) where the usual electromagnetic EC modes are cut-off. Hence, the EBW is a candidate for plasma control and stabilisation in such devices. We present here a modelling of EBW heating and current drive in realistic ST conditions, particularly in typical NSTX equilibria and in model equilibria for NHTX [1] and MAST Upgrade [2,3]. The EBW injection parameters are varied in order to find optimized scenarios and possible ways to control the deposition location and the driven current. It is shown that EBWs can be deposited and efficiently drive current at any radial location.

This paper reports on detailed investigation of a fully 28 GHz EBW (electron Bernstein wave) heated plasma in the WEGA stellarator. The plasma shows a fast transition into the "OXB-state" when the threshold density is reached. The profiles become peaked. The EBW emission diagnostic measures a radiation temperature of several keV, which origins from a supra-thermal electron population. The angular dependence of the mode conversion could be confirmed with a movable launching mirror. The toroidal current and the plasma conductivity were measured for different microwave launch positions.

The prototype phased-array antenna system has been developed to control the incident angle and polarization to conduct the Electron Bernstein Wave Heating and Current Drive (EBWH/CD) experiments on the QUEST. The two orthogonal fields measured at the low power level were in excellent agreement with those evaluated by a developed Kirchhoff code. The elliptical polarization in two orthogonal fields can be controlled to excite pure O-mode in the oblique injection. The non-inductive plasma current of 10 kA was ramped up and sustained for 0.7 s. The phased-array antenna system for the reflectometry and the EBW radiometry has been also develoloped concerning the EBWH/CD experiments, and was confirmed to work well in the low power tests.

The power deposition profiles were analyzed with a multiple ray tracing code for the Electron Bernstein Wave Heating and Current Drive (EBWH/CD) experiments in the QUEST. In the EBWH/CD experiments in the QUEST, the O-X-B mode conversion scenario was selected for the plasma current sustainment in the rather low-density case. The algorithm for the wave penetration through evanescent layer beyond a O-mode cutoff position was developed for the multiple-ray analysis. The launching antenna positions were considered to obtain the significant wave absorption in the specific propagating direction using the developed ray-tracing code.

The presentations specifically devoted to the theory of Electron Cyclotron waves are summarized here, although many other presentations included theoretical aspects. The main topics covered are: wave propagation and absorption, cyclotron emission, current drive effects, control of MHD activity.

The recent progress in electron cyclotron current drive calculations with the adjoint technique is reviewed. The main attention is focused on such points as parallel momentum conservation in the like-particle collisions and finite collisionality effects. For high-temperature plasmas with significant relativistic effects, the effectiveness and accuracy of the developed numerical models are demonstrated by ray-tracing calculations.

A fully relativistic theory of electron cyclotron current drive (ECCD) efficiency based on Green's-function techniques is considered. Numerical calculations of the current drive efficiency in a uniform magnetic field are performed. The numerical results with parameter regimes relevant to ITER operations are compared with those of two simplified models in which the electron-electron Coulomb collision operator is respectively approximated by its high-velocity limit and a semi-relativistic form. Our results indicate that the semi-relativistic approximation of the collision operator should be appropriate for modeling the ECCD efficiency under ITER conditions.

We present recent numerically well resolved ECRF 3D STELEC toroidal full wave code [1] modelling results for fundamental and second harmonics scenarios in several tokamaks and ITER. Improved numerical resolution for middle size tokamaks further solidly confirms previously discovered O- and X- modes strong coupling at fundamental harmonic leading to broadened power deposition profiles, in compare with ray tracing predictions, due to influence of Upper Hybrid Resonance (UHR). For the T-10/DIII-D tokamaks we consider O-mode outside launch cases with EC resonance in plasma with UHR usual "moon serp" surface and out off plasma EC resonance at High Field Side when UHR surface is in-plasma internally closed one with Electron Bernstein Waves (EBW) being excited inside of it due to mode conversion process. Combined self consistent dynamic O-mode, X-mode and EB waves structure is intriguing one and is shown. This out off plasma EC fundamental resonance scenario was discovered in WEGA stellarator [2]. In second harmonic scenarios we are concentrating on X-mode outside launch at sufficiently large plasma densities for JET, some times close (but lower) to this mode density cut off. Exact boundary problem EC wave solution again shows that simultaneously is exciting also the O-mode (with smaller amplitude), presumably due to reflection effects and wave depolarization at the wall.

In the technology sessions of EC-16, 24 talks and posters were presented, six on gyrotrons, seven on the system design, transmission lines, components, and the launcher for ITER, three on vacuum windows, seven on new ECRH systems. Additionally, a discussion of future requirements was held…

Recent progress on the development of a high power 170 GHz gyrotron obtained in Japan Atomic Energy Agency (JAEA) is presented. Firstly, a repetitive operation of 800 kW/600 s with an interval of 20-30 min was performed. The electrical efficiency was 52-57 % with a depressed collector. The 72 shots of 88 shots was very stable 600 s oscillation. No damage was found on the gyrotron after the test. Secondly, 5 kHz-full power modulation was demonstrated with pulse duration of 60 s. For this purpose, a full beam current modulation was realized to minimize the collector heat load by adopting an anode voltage switching. Thirdly, in the dual frequency gyrotron development, the 1.3 MW oscillations at 170 GHz and 136.8 GHz were successfully demonstrated at short pulse operation by changing the cavity field and the anode voltage keeping other parameters constant.

Europe is developing a gyrotron capable of delivering 2 MW RF power at 170 GHz in continuous operation (CW) for the ITER EC H&CD system. This paper discusses the advantages and risks of the 2 MW project, the status of the development, and the expected results from the tests planned to start during the 2nd half of 2010 on the industrial gyrotron prototype, which will provide essential elements for the decision between the 2 MW (coaxial cavity) and 1 MW (cylindrical cavity) gyrotron option placed along the track of the European project plan.

The gyrotron complex on the DIII-D tokamak now comprises six gyrotrons in the 1 MW class with pulse lengths during plasma operations up to 5 s. The system performance, representative experiments, gyrotron related tests, diagnostics and long term plans are presented.

The following sections are included:

• Introduction

• Experimental Set-up and Measurement System

• Experimental Results with Reference Beam Tunnel

• Analysis using the Brillouin-Diagram

• Experimental Results with Improved Corrugated Beam Tunnel

• Conclusions

• References

A 24MW CW Electron Cyclotron Heating and Current Drive (EC H&CD) system operating at l70GHz is to be installed for the ITER tokamak. The EC system will represent a large step forward in the use of microwave systems for plasma heating for fusion applications; present day systems are operating in relatively short pulses (≤10s) and installed power levels of ≤4.5MW. The magnitude of the ITER system necessitates a worldwide collaboration. This is also reflected in the EC system that is comprised of the power supplies, sources, transmission line and launchers. A partnership between Europe, India, Japan, Russia, United States and the ITER organization is formed to collaborate on design and R&D activities leading to the procurement, installation, commissioning and operation of this system.

The ITER ECH&CD system will have an installed power of 24 MW at 170 GHz delivered to the launchers at the plasma side through a transmission line sub-system constituted by evacuated HE₁₁ waveguides, DC breaks, power monitors, mitre bends, polarizers, switches, loads and pumping sections. Each line will be typically about 160 m in length and will connect the RF power sources alternatively to the equatorial launcher or to one of the upper launchers in order to accomplish the various physics requirements: heating, current drive and instability control. Two different source configurations are at the moment under study, pending the final decision about the European 2 MW coaxial gyrotron development. Each configuration will imply a dedicated transmission line layout. An overview of the actual design is presented and the technical requirements are discussed.

The following sections are included:

• Introduction

• Numerical analysis

• Conclusions

• Acknowledgements

• References

The paper describes a possible scheme of the transmission line for the ITER ECE diagnostic. This includes wire grid polarisers, straight jointed sections of waveguide, mitre bends and other optical components. The brief description of each component is given. Information on the transmission efficiencies of various components available in the literature is summarised, which indicates that the number of mitre bends may be a concern. The paper also describes our study of the mitre bend through simulation and the results of the simulation are presented.

High-power diplexers can be used in ECRH systems as power or beam combiners (BC), slow and fast directional switches (FADIS) to toggle the power from continuously operating gyrotrons between two launchers, and discriminators of low-power ECE signals from high-power ECRH in launchers used for in-line ECE. In the paper, design options for resonant diplexers are presented, and detailed low-power investigations on transmission characteristics and insertion losses are discussed. Two types, a purely quasi-optical and a compact waveguide-compatible diplexer, respectively, have been tested with high-power in the 140 GHz ECRH system for the stellarator W7-X. Fast switching, arbitrary distribution of the gyrotron power to two outputs, as well as power combination could be demonstrated with the first prototype. In recent experiments with a compact design, a mirror drive for tracking of the resonator to the gyrotron frequency was implemented; first long-pulse tests on transmission characteristics are shown. Finally, plans for implementation of this diplexer in the ECRH at ASDEX Upgrade are described.

A combined Porcelli-Kadomtsev numerical sawtooth instability model is analyzed using control oriented identification techniques. The resulting discrete time linear models describe the system's behavior from crash to crash and is used in the design of a simple discrete time feedback controller, which is successfully applied in simulation.

The following sections are included:

• Introduction

• EU CVD Diamond Window (Prototype I)

• EU CVD Diamond Window (Prototype II)

• Evaluation of H-terminated CVD Diamond Disk Quality

• References

The production of high power mm-wave radiation is a key technology in large fusion devices, since it is required for localized plasma heating and current drive. Transmission windows are necessary to keep the vacuum in the gyrotron system and also act as tritium barriers. With its excellent optical, thermal and mechanical properties, synthetic CVD (Chemical Vapor Deposition) diamond is the state of the art material for the cw transmission of the mm-wave beams produced by high power gyrotrons.

The gyrotrons foreseen for the W7-X stellarator are designed for cw operation with 1 MW output power at 140 GHz. The output window unit is designed by TED (Thales Electron Devices, France) using a single edge circumferentially cooled CVD-diamond disc with an aperture of 88 mm. The window unit is cooled by de-ionized water which is considered as chemical aggressive and might cause corrosion in particular at the brazing. The use of a different coolant such as silicon oil could prevent this issue.

The cooling circuit has been simulated by steady-state CFD analysis. A total power generation of 1 kW (RF transmission losses) with pure Gaussian distribution has been assumed for the diamond disc. The performance of both water and the industrial silicon oil DC200(R) have been investigated and compared with a focus on the temperature distribution on the disc, the pressure drop across the cooling path and the heat flux distribution. Although the silicon oil has a higher viscosity (~x5), lower heat capacity (~x1/2) and lower thermal conductivity (~x1/3), it has proven to be a good candidate as alternative to water.