Observation of the parametric decay instability during electron cyclotron resonance heating on the Versator II tokamak

Abstract

Observations are reported on a nonlinear, three-wave interaction process occurring during high-power electron cyclotron heating in the Versator II tokamak. The measured spectra and the threshold power are consistent with a model in which the incident power in the extraordinary mode of polarization decays at the upper-hybrid resonance layer into a lower-hybrid wave and an electron Bernstein wave.

Parametric decay instability near the upper hybrid resonance and anomalous mm-wave scattering in tokamak and stellarator plasmas

“…1, and the LHD stellarator [2,3]. Furthermore, similar observations have been made during 1st harmonic electron cyclotron resonance heating (ECRH) experiments at the Versator II, FT-1 and TCA tokamaks [4][5][6], as well as at the W VII-A stellarator [7,8].…”

“…For the PDI in which an electromagnetic X-mode pump wave decays into a warm UH and a warm LH wave near the UHR of the pump wave, we have generalized the results of [4,9,10]; the details are given in [11]. The dispersion relations describring the warm LH and warm UH waves in a simple plasma are given by [10,11], for vanishing k || (with respect to the equilibrium magnetic field B) they become, , indicating that propagating warm UH waves only exist on the same side of the UHR as the propagating X-mode, for which ω 2 < ω 0 < ω UH , when ω pe 2 < 3ω ce 2 , generally limiting the occurrence of this kind of PDI to underdense and weakly overdense plasmas, e.g.…”

Measurements of ion cyclotron range of frequencies mode converted wave intensity with phase contrast imaging in Alcator C-Mod and comparison with full-wave simulations

“…Parametric decay instabilities (PDI) 62,63 may reduce the pump wave intensity without significantly affecting the electron heating. In the electron cyclotron frequency regime, PDI was observed around the upper hybrid resonance 64 . Upper hybrid soliton can also form around the resonance 65,66 , which may have implications for the mode conversion physics.…”

Feasibility of electron Bernstein wave coupling via O-X-B mode conversion in the RFX-mod reversed field pinch device

“…With the antenna on the low-field side this scheme suffers from the serious limitation of the evanescence layer between the X-cutoff (right cutoff ω R = 4 ω 2 pe + Ω 2 ce /2 + Ω ce /2) and the UHR. In Tokamaks [12,13] and Stellarators [14], the X-mode does not encounter cutoffs up to the UHR if launched from the high field sides. However, as discussed later, RFPs cannot take advantage of the high-field-side launch of the X wave.…”