Investigation of electrostatic waves in the ion cyclotron range of frequencies in L-4 and ACT-1

Abstract

Electrostatic waves in the ion cyclotron range of frequencies (ICRF) were studied in the Princeton L-4 and ACT-I (the Advanced Concept Torus-1) devices for approximately ten years, from 1975 to 1985. The investigation began in the L-4 linear device, looking for the • parametric excita.'ion of electrostatic ion cyclotron waves in multi-ion-species plasmas. In addition, this investigation verified multi-ion-species effects on the electrostatic ion cyclotron wave dispersion relation including the ion-ion hybrid resonance. Finite-Larmor-radius modification of the wave dispersion relation was also observed, even for ion temperatures of , Ti = 1/40 eV (~the room temperature!). Taking advantage of the relatively high field and long device length of L-4, the existence of the cold electrostatic ion cyclotron wave (CES ICW) was verified. This branch occurs below the ion cyclotron frequency and, in a two-ion-lP species plasma, shows a resonance at the ion-ionhybrid frequency. With the arrival of the ACT-1 toroidal device, finite-Larmor-radius (b'LR) waves were studied in a relatively collisionless warm-ion hydrogen plasma. Detailed investigations of ion Bernstein waves (IBW) included the verification of mode-transformation in their launching, their wave propagation characteristics, their absorption, and the resulting ion heating. This basic physics activity played a crucial role in developing a new reactor heating concept termed ion Bernstein wave heating 0BWH).Experimentalresecach in the lower hybrid frequency range confirmed the existence of FLR effects near the lower hybrid resonance, predicted by Stix in 1965. In a neon plasma with a carefully placed phased wave exciter, the neutralized ion Bernstein wave was observed for the f'u'sttime. Using a fastwave ICRF antenna, two parasitic excitation processes for IBW -parametric instabilityand density-gradient-drivenexcitation --were also discoverezLIn the concluding section of this paper, a possible application of externally launched = electrostatic waves is suggested for helium ash removal from fusion reactor plasmas.

Shear Alfven wave excitation by direct antenna coupling and fast-wave resonant-mode conversion

“…The directly excited SQEW is, therefore, similar to that of an infinite homogeneous plasma. This also shows that the resonance cone predicted by cold plasma theory with finite electron mass and verified experimentally by Ono (1979) and the guided beams of Borg et a1 (1985,1987) are as expected for an inhomogeneous plasma. Work has only just begun to investigate the applications of slow waves to fusion plasmas.…”

“…As kA approaches zero the dispersion relation (4d) reads kJk1 = y where k i = kg+ky' and, as for the lower hybrid wave, the SQEW excited by a localized antenna propagates along the magnetic field with a resonance cone of angle 0 = tan-'(y) (Ono 1979). Similarly one may show using ( 4 4 that the group velocity of the SQEW is directed mainly along the magnetic field of a homogeneous plasma.…”

“…The WKB approximation (Fejer and Lee 1967) cannot be applied in these cases because the perpendicular wavefield scale is of the same order as the density gradient scale and the parallel wavelength much longer than the radius of field line curvature. Nonetheless, conditions have been obtained in a laboratory plasma where the WKB approximation applies (Ono 1979). Moreover, under special conditions, the shear Alfvdn wave propagation characteristics are quite simple.…”

Electron Inertial Effects on Linearly Polarized Electromagnetic Ion Cyclotron Waves at Earth's Magnetosphere

“…In hot plasmas, the FW mode can be converted into the short wavelength ion Bernstein wave or ion cyclotron wave modes (or their higher harmonics) at the IIH resonance (e.g., Wright et al, ; Wukitch et al, ). In addition, such short wavelength waves can easily Landau damped (Ono, ). Therefore, in order to consider the exact nature of the resonant absorption it needs to be clarified by a kinetic approach.…”

“…As the EIW approaches the BB resonance, K ⊥ grows and reaches the electron inertial scale. A similar but inverse mechanism also converts incoming EIWs into IIHWs or ion Bernstein waves (Ono, ).…”