High-power millimeter wave sources are a key enabling technology in fusion energy research. The present state of the art of application of these sources to the areas of heating, current generation, and scattering for diagnostic purposes in fusion plasmas is reviewed. The extrapolation of these applications to future devices and the requirements which they place on sources and transmission lines are also discussed.

Applications of high-power millimeter waves in fusion energy research

The main goal of this thesis is to demonstrate the capability of magneto-hydrodynamic (MHD) instability control, particularly sawteeth and neoclassical tearing modes (NTMs), in order to achieve high performance operation. Experiments and simulations have been carried out to pursue this purpose on different tokamaks: TCV (in Switzerland), KSTAR (in Korea), AUG (in Germany) and ITER (in construction in France). Each tokamak has different features such as machine size, heating systems, operation scenarios and energy confinement time scale, all the tokamaks are equipped or will be equipped with an electron cyclotron heating/current drive (ECH/ECCD) system for plasma heating/current drive and control of MHD instabilities. Therefore, this work focusses on the feasibility of using the localised ECH/ECCD beams to control the instabilities; sawteeth and NTMs. For the experimental part, sawtooth and NTM control experiments have been carried out. In TCV, novel ways of sawtooth period control - sawtooth pacing and locking - have experimentally been demonstrated using the TCV real-time control system. Based on the successful application of these methods to sawtooth control in TCV, we have next focussed on the extension of these new sawtooth period control methods to other tokamaks: KSTAR and AUG. In the 2013 KSTAR experimental campaign, the applicability of sawtooth locking using EC power modulation has been tested for sawtooth period control in the presence of fast particles generated by neutral beam injection (NBI). The KSTAR real-time control system was not ready for sawtooth pacing thus only locking has been examined. These preliminary KSTAR experimental results have shown the possibility of sawtooth period control using sawtooth locking, although proper locking was not obtained yet. The locking parameters would still need to be adjusted for single period locking to occur. In order for the investigation of the capability of sawtooth locking on KSTAR tokamak to be complete, more experiments with different locking parameters should be carried out. The sawtooth locking technique has also been applied to AUG plasmas. As in the KSTAR tokamak, the real-time control for sawtooth pacing was not available, thus sawtooth locking has been tested. The AUG plasmas were more complicated compared to TCV and KSTAR cases due to the fast particles effect on the evolution of sawtooth from both NBI and ion cyclotron heating (ICH). Sawteeth did not lock to the EC modulation in AUG experiments, though in some discharges they became somewhat more regular. However, the application of sawtooth locking to the AUG tokamak has been well initiated and more experiments will follow to understand better the behaviour of sawteeth and to determine the sawtooth locking range. In addition, sawtooth control was demonstrated and used in other experiments studying the role of sawteeth on impurity transport. Concerning the NTM control experiments, we have focussed on the enhancement of the NTM control strategy, which has been achieved in two ways. In previous TCV experiments, NTM stabilisation was obtained as ECH/ECCD deposition was swept in one direction until the mode disappeared. In order to ameliorate the control of NTMs, as a first improvement, a real-time version of the equilibrium reconstruction code LIUQE (RT-LIUQE) has been implemented in the TCV real-time control system. [...]

Real-Time Control of Sawteeth and NTMs in TCV and ITER

Poloidally asymmetric plasma response with ECH deposition near q=1 in TCV

To achieve reactor-relevant conditions in a tokamak plasma, auxiliary heating systems are required and can be realized by waves injected in the plasma that heat ions or electrons under certain conditions. Electron cyclotron resonant heating (ECRH) is a very flexible and robust technique featuring localized power deposition and current drive (CD) capabilities. Its fundamental principles such as damping on the cyclotron resonance are well understood and the application of ECRH is a proven and established tool; electron cyclotron current drive (ECCD) is regularly used to develop advanced scenarios and control magnetohydrodynamics (MHD) instabilities in the plasma by tailoring the current profile. There remain important open questions, such as the phase space dynamics, the observed radial broadening of the suprathermal electron distribution function (e.d.f.) and discrepancies in predicted and experimental CD efficiency. These are addressed in this thesis. One of its main goals is indeed to improve the understanding of wave-particle interaction in plasmas and current drive mechanisms. This was accomplished by combined experimental and numerical studies, strongly based on the conjunction of hard X-ray (HXR) bremsstrahlung measurements and Fokker-Planck modeling, characterizing the suprathermal electron population. The hard X-ray tomographic spectrometer (HXRS) diagnostic was purposely developed to perform these studies, in particular by investigating spatial HXR emission asymmetries in the co- and counter-current directions and within the poloidal plane. The system uses cadmium-telluride (CdTe) detectors and digital acquisition to store the complete time history of incoming photon pulses. An extensive study of digital pulse processing algorithms was performed and its consequent application allows the HXRS to handle high count rates in a noisy tokamak environment. Numerous other numerical tools were developed in the course of this thesis, among others to improve the time resolution by conditional averaging and to obtain local information with the general tomographic inversion (GTI) package. The interfaces of the comparatively new LUKE code and well-established CQL3D Fokker-Planck (F-P) code to the tokamak a configuration variable (TCV) data were refurbished and a detailed benchmarking of these two codes was performed for the first time. Indeed, the theory-predicted toroidal and poloidal emission asymmetries could be consistently verified by experiment and modeling in many cases, including scans of a variety of plasma and wave parameters. The effects of supra\-thermal electron diffusion and radio frequency (RF) wave scattering, both resulting in a radial broadening of the HXR emission, were separated by a poloidal deposition location angle scan. Furthermore, previous results on anomalous diffusion and CD efficiency were reproduced with increased confidence arising from enhanced diagnostic specifications. The plasma response to electron cyclotron (EC) absorption and the role of quasi-linear effects were investigated using the coherent averaging capabilities of the HXRS. Several MHD instabilities can occur in the plasma center and better understanding of these modes and events is indispensable for their mitigation in order to prevent their negative effects on confinement and stability. Sawtooth crashes are such a major instability and localized at the q=1 surface. They can be described as the evolution of an internal m=1 kink mode leading to [...]

Suprathermal electron studies in Tokamak plasmas by means of diagnostic measurements and modeling

Keywords: ECE ; Oblique ECE Reference EPFL-ARTICLE-169374 URL: http://epubs.ans.org/rip/index.cgi?j=fst URL: http://crpplocal.epfl.ch/pinboard/jpapers/1104901.pdf Record created on 2011-10-14, modified on 2017-05-12

First measurements of oblique ece with a real-time movable line of sight on tcv

Centre de Recherches en Physique des Plasmas, Ecole Polytechnique Federale de Lausanne,Association EURATOM-Confederation Suisse, CH-1015 Lausanne EPFL, Switzerland Introduction: Plasma experiments using absorption of radiation in the range of the electroncyclotron frequency are often grouped under two separate headings: electron cyclotron heating(ECH) or electron c yclotron current dri ve (ECCD). The division is based, roughly , on the toroi-dal angle-of-incidence between the beam and the toroidal magnetic ﬁeld direction. In practice,ECH experiments are those in which there is no projection of the k-vector on the toroidal ﬁeld, B

Poloidally asymmetric plasma response during ECH experiments in TCV

Current and pressure profile control using ECCD and ECH in TCV

1. IntroductionA multichannel hard X–ray (HXR) diagnostic system de-veloped for the Tore Supra tokamak [1] has been employed onthe TCV tokamak with the aim of characterising the spectraland spatial distribution of fast-electron bremsstrahlung emis-sion during electron cyclotron heating (ECH) and current drive(ECCD). The system consists of a vertically viewing pinholecamera equippedwith anarray ofCdTe detectors. CdTe technol-ogy was chosen for this system in order to satisfy the combinedrequirements of good temporal and spatial resolution, of efﬁ-cient–rayrejection and of compactness. On TCV, 14 partiallyoverlapped viewing chords span the entire outer minor radius ofthe plasma, with a radial resolution of2 cm on the midplane(Fig. 1). The intrinsic energy resolution is5–7keV. After am-pliﬁcation,each signal is distributed to 8 discriminator-counterchains, generating spectra in the range 10–150keV. Count ratesup to 1.510 s can be detected before the onset of pileup.The time resolution, determined by the requirement of a relativestatistical noise10%, is in the order of 1–5ms.The ECH and ECCD experiments described in this pa-per have been carried out with up to three 0.5 MW gyrotrons,operating in X-modeat the second harmonic (82.7 GHz) [2].The launching mirrors can be independently rotated in both thepoloidal and the toroidal direction, providing great ﬂexibility inthe choice of heating locations and parallel wave numbers. TheHXR camera constitutes a crucial tool for investigating the loca-tionofthepowerdepositionandthedistributionanddynamicsofsuprathermalelectrons. Initial results are presented in this paper.2. Suprathermal electron population during ECH and ECCDTheparallelwave numberoftheelectroncyclotron(EC) wavewasscannedinaset ofsimi-lar dischargesby varyingthe toroidal launching anglefrom -35 to+35 (this angle is deﬁned

http://epsppd.epfl.ch/Maas/web/pdf/p3039.pdf

Measurements of hard X-ray emission profiles in the TCV tokamak during electron cyclotron heating and current drive

Evolution of Te and ne profiles during ECH and ECCD in TCV

Note: Proceedings of the 2nd Europhysics Topical Conference on RF Heating and Current Drive of Fusion Devices - part 1: Proceedings of the 2nd Europhysics Topical Conference on RF Heating and Current Drive of Fusion Devices, Brussels, Belgium, January 1998 (see also #3637) Reference CRPP-CONF-1998-052 Record created on 2008-05-13, modified on 2017-12-10

Preliminary confinement studies during ECRH in TCV

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