Speaker
Prof.
Kenji Tanaka
(National Institute for Fusion Science)
Description
Collective thomson scattering (CTS) is a powerful diagnostic to measure the bulk and fast ion tempertures, densities and ion density ratios A 77 GHZ CTS system has been developed in LHD with a 1 MW gyrotron for electron heating and succesful results have been obtaned [1,2,3]. Use of the frequency of 77 GHz has an advantage of strong signal but suffers from refraction, which makes adjustment of the scattering volume difficult. In addition, multiple scattering occurs due to the wave reflected off the vaccume chamber wall. Since the multiple scattering makes interpretation of the signal difficult, it shoudl be elminated or mimized [4]. In order to solve these problems, a new CTS system with a 1 MW 154 GHz gyrotron for electron heating has been developed and installed in LHD. Both 77 and 154 GHz CTS systems are usualy operated with the electron cyclotron reasonance layer inside the plasma. Electron cyclotron emmision (ECE) from the resonance layer becomes a huge noise source. In particular, the ECE around 154 GHz becoems strong at 2.75 T-operation of LHD. ECE noise can be elminated by power modulation in principle, however, too strong ECE causes saturation of the detectors and amplifiers. To reduce ECE noise, LHD is operated at 1.375 T corresponding to 4th harmonic cyclotron resonance. Preliminary data at 1.375 T showed good signal to noise ratio and the scannable injection antenna was suscessfuly adjusted to obtaine the maximum scattering volume. Detailed spectrum analysis will be presented.
1. S. Kubo et al, Rev. Sci. Instrum. 81, (2010) pp. 10D535-1-10D535-6
2. M. Nishiura et al, Nucl. Fusion 54 (2014) 023006.
3. K. Tanaka et al, Journal of Instrumentation, 10 ,(2015),C12001
4. S. Kubo et al, Journal of Instrumentation, 11 ,(2016),C06005
Primary author
Prof.
Kenji Tanaka
(National Institute for Fusion Science)
Co-authors
Dr
Dmitry Moseev
(Max-Planck-Institut für Plasmaphysik)
Mrs
Ivana Abramovic
(Max-Planck-Institut für Plasmaphysik)
Dr
Masaki Nishiura
(Univeristy of Tokyo)
Prof.
Shin Kubo
(National Institute for Fusion Science)
Prof.
Takashi Shimozuma
(National Institute for Fusion Science)
Prof.
Teruo Saito
(University of Fukui)
