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  4. Third harmonic X-mode absorption in a top-launch configuration on the TCV tokamak
 
research article

Third harmonic X-mode absorption in a top-launch configuration on the TCV tokamak

Arnoux, G.  
•
Alberti, S.  
•
Porte, L.  
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2005
Plasma Physics and Controlled Fusion

In addition to the second harmonic X-mode (X2) electron cyclotron heating (ECH), the TCV ECH system has been completed with three 450 kW gyrotrons operating at the frequency of 118 GHz for third harmonic X-mode (X3) in a top-launch configuration. In the relatively low magnetic field of TCV (1.45 T), the X2 cutoff density is n(e,cutoff)((X2)) = 4 x 10(19) m(-3) and X3 extends the accessible plasma density range up to n(e,cutoff)((X3)) = 11.5 x 10(19) m(-3). The X3 absorption coefficient is lower than that for, X2 by a factor (k(B)T(e))/(m(e)c(2)) and a top-launch injection system has been installed to maximize the beam path along the resonance layer, thus maximizing the optical depth. Theoretical considerations based on a one-dimensional slab geometry model show that the X3 absorption depends mainly on the temperature and the density. It is shown, using a simple two-dimensional model, that in the presence of a suprathermal electron population, the resonance layer width is significantly increased owing to the relativistic shift. The specificity of the top-launch configuration implies that the absorption strongly depends on the propagation direction of the beam. Experimental results are compared with calculations using the linear ray-tracing code TORAY-GA. At the maximum available X3 injected power (1350M), full single-pass absorption is measured, increasing the global electron energy by a factor of 2.5, whereas TORAY-GA predicts only 50% absorption.

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Type
research article
DOI
10.1088/0741-3335/47/2/007
Web of Science ID

WOS:000227287600008

Author(s)
Arnoux, G.  
Alberti, S.  
Porte, L.  
Nelson-Melby, E.  
Hogge, J. P.  
Date Issued

2005

Published in
Plasma Physics and Controlled Fusion
Volume

47

Issue

2

Start page

295

End page

314

Editorial or Peer reviewed

REVIEWED

Written at

EPFL

EPFL units
CRPP  
SPC  
Available on Infoscience
April 16, 2008
Use this identifier to reference this record
https://infoscience.epfl.ch/handle/20.500.14299/22244
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