Slow- and helicon-wave sustained discharges in HF/VHF bands of radio frequency

Abstract

Helicon-wave sustained (HW) and slow-wave sustained (SW) discharges are studied in a whistler- or helicon-wave range of frequency using high-frequency (13.56 MHz) and very-high-frequency (50 and 144 MHz) bands of rf. For 13.56 and 50 MHz, in addition to capacitive-coupling (E) discharge and the HW discharge, the SW discharge is observed at an extremely low rf power and plasma density; lower than the E discharge region. For 144 MHz, no E discharges appear and the transition from the SW discharge to the HW discharge occurs. In the SW discharge, both the electromagnetic and electrostatic waves are observed. The results of two-dimensional wave code and analytic calculation indicate that the electrostatic component of the electric field parallel to a static magnetic field is dominant in plasma production in the SW discharge.

Experimental characterization of a density peak at low magnetic fields in a helicon plasma source

“…In general, the fast wave is called helicon wave, and the other is called Trivelpiece-Gould (TG) mode (or wave) because the slow wave is close to an electrostatic wave for a large wavenumber perpendicular to B 0 [13,14]. The two waves behave differently for a conventional higher B 0 around a few hundred G and a radio frequency (RF) band of 13.56 MHz, where the fast and slow waves are theoretically and experimentally found to be excited only in high-density (>10 12 as given cm −3 ) and low-density (<10 10 cm −3 ) plasmas, respectively, by Sakawa et al [15]. In low B 0 yielding the density peak, however, the two waves are merged and both the fast and slow waves are observed in a moderate density (∼10 11 cm −3 ) plasma for some cases [6,16].…”

Development of a strong field helicon plasma source

“…7 A helicon wave scheme has the advantages of an easy operation and a wide range of operational parameters, e.g., the magnetic field due to nonresonant wave characteristics and the fill pressure. To further develop this source, it will be necessary to extend conventional parameter regimes such as the plasma size, e.g., very large [8][9][10] or small, 11,12 the applied magnetic field B, the excitation frequency f, e.g., higher frequency, 13 and the fill pressure, as well as novel ideas and technologies to control the plasma performance such as the density profile. 8,9 According to a dispersion relationship of the helicon wave, [1][2][3][4][5][6] f lies between the ion and electron cyclotron frequencies, and the electron density is proportional to B if the parallel wave number is fixed.…”