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

Note: Proceedings of the IAEA Technical Committee Meeting on ECRH Physics and Technology for Fusion Devices and the 11th Joint Workshop on Electron Cyclotron Resonance Heating (EC-11), Oh-Arai, Japan, October 1999, JAERI-memo 12-041, 338 - 349 (March 2000) Reference CRPP-CONF-2000-075View record in Web of Science Record created on 2008-05-13, modified on 2017-05-12

Sustained fully non-inductive scenarios using pressure and current profile control with ECCD

This workshop was organised by the CRPP from 15 to 19 February 1999 in Saillon in thecanton of Valais and was the third biennial meeting in the series following Les Houches,France (1995) and Bad Honnef, Germany (1997). The theme was “Diagnostics of IndustrialPlasmas”. The targets of 10, internationally-renowned invited speakers and 60 registeredparticipants were reached, and industrial sponsorship was obtained. The scientificcommittee, speakers and participants represented a mix from university and industrialbackgrounds to discuss the specific question of university/industry exchange and transfer.The workshop proceedings of 67 papers are available as Lausanne Research PaperLRP629/99 and on the conference website http://crppwww.epfl.ch/LTPD99.

APPENDIX B Conferences and Seminars

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

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