Observation of parametric decay instability during ion Bernstein wave heating experiments on HT-7

Citation
J. Li et al., Observation of parametric decay instability during ion Bernstein wave heating experiments on HT-7, PLASMA PHYS, 43(9), 2001, pp. 1227-1238
Citations number
30
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Physics
Journal title
PLASMA PHYSICS AND CONTROLLED FUSION
ISSN journal
0741-3335 → ACNP
Volume
43
Issue
9
Year of publication
2001
Pages
1227 - 1238
Database
ISI
SICI code
0741-3335(200109)43:9<1227:OOPDID>2.0.ZU;2-I
Abstract
The parametric decay processes with a power threshold of 70 kW have been ob served on the HT-7 tokamak. Two types of parametric decay instabilities hav e been identified. The pump wave decays into an ion cyclotron quasi-mode an d an ion Bernstein wave, or decays into a low-frequency electron Landau dam ped quasi-mode and an ion Bernstein wave. The experimental observation show s good agreement with theoretical prediction. Other peaks at a frequency of n Omega (D) are also observed. The main features of the observed radiofreq uency spectra is due to the parametric decay instability of the launched sl ow electron plasma pump wave into an ion cyclotron quasi-mode and an electr on plasma wave, dominated by plasma inhomogeneity convective loss. As the p lasma displacement shifts towards the antenna, a higher omega/Omega value a t the antenna position and a higher wave frequency are used to reduce the p ossibility of parametric decay instability (PDI) production. The experiment al evidence clearly shows that a higher wave frequency, edge density and va lue of omega/ Omega in the scrap-off layer are favourable to prevent the pr oduction of PDIs. The PDI was effectively reduced and successfully avoided with a power level up to 300 kW.