Nonlinear wave phenomena measured by capacitive probes during auxiliary heating in the SOL of TEXTOR

Abstract

Measurements of different wwe phenomena at the plasma boundary during auxiliary heating (ICRH and combined JCRH-NBI) experiments on TEXTOR were performed to elucidate some of the mcchanisms responsible for ICRF-induced effects on the edgc plasma and on plasma-wall interactions. Capacitive probes capable of withstanding high heat loads were used. Excited waves were studied during carbonized and boronized wall conditions in TEXTOR. Apart from at the r.f. generator frcquency, waves were also detected at thc harmonic frequencies due to sheath effeas 81 thc ICRF antenna. Furthermore. waves at half-harmonic frequencies were also excited under Certain conditions. During carbonized machine operation conditions, wares at half-harmonic frequencies were always observed except during thc combined healing phase. Under normal boronized opcration generally no waves at half-harmonic frequencies wcre observed during neutral beam-ICRH combined heating of deuterium plasma. Howevcr, waves at halfharmonic frequencies were observed at higher toroidal magnetic field values as well as during D neutral beam-ICRH combined heating at high H concentration and high r.f. power. Wave amplitudes at the different frequencies were studied as a function of different plasma and machine parametcrs.

Particle-in-cell simulations of parametric decay instability of radiofrequency wave in the ion cyclotron range of frequency in an inhomogeneous plasma

“…With the input power increasing to a few hundreds of kilowatts, our simulations demonstrate similar parametric decay channels as those observed in the HT-7 IBW experiments [17]. It is suggested that the peaks of half-, second-and third-harmonic frequencies of the pump wave observed in the experiments on HT-7 [17] as well as TEXTOR [13] and DIII-D [15] might be generated by resonant PDI processes. In a tokamak plasma, inhomogeneity always exists especially near the plasma edge.…”

“…With more and more applications of rf waves for plasma heating and current drive on tokamak devices, the interactions between waves and plasmas have been investigated extensively [9][10][11][12][13][14][15][16][17][18]. When the input power of the incident wave reaches a megawatt, nonlinear phenomena occur and cannot be ignored.…”

“…When the input power of the incident wave reaches a megawatt, nonlinear phenomena occur and cannot be ignored. The observations of PDI during the ion cyclotron range of frequency (ICRF) heating experiments have been reported on different tokamak devices, such as ASDEX [10], JET [11], TEXTOR [12,13], JT-60 [14], DIII-D [9,15,16], HT-7 [17], Alcator C-Mod [18], etc. In these experiments, the observed decay processes involved (1) resonant decay into two ion Bernstein waves (IBWs), (2) nonresonant decay into an ion cyclotron quasimode (ICQM) plus an IBW, and (3) nonresonant decay into a low-frequency electron quasimode (EQM) and an IBW.…”

Eigenmode analysis of the ITER ICRF antenna plug and electrical solution to the grounding of the antenna

“…on TEXTOR and ASDEX [15,16]). Voltages comparable to those at the fundamental frequency f 0 have been observed by means of a capacitive probe (located close or far from the ICRF antenna) at the fundamental and harmonic frequencies nf 0 and even at half-harmonics nf 0 /2 (in the case of carbonized wall conditions in TEXTOR for pure ICRH [17]). The magnetic perturbation at nf 0 is one order of magnitude lower than at f 0 .…”

“…IBW waves) excited in the SOL by sheath effects and parametric decay. These signals saturate rapidly when the RF power is increased [17]. Their occurrence and relative amplitude depends on the experimental conditions (heating scenario, wall conditioning, position of antenna in the SOL, etc).…”