A higher-order radial mode of helicon waves

Abstract

The axial profile of the axial component of the wave magnetic field B z has been measured for m = 0 helicon waves. A dip in B z is observed at z 25 cm from the antenna, and is explained as a result of the beat between the fundamental and the second-order radial modes of the m = 0 helicon wave. The measured imaginary part of B z , which consists only of the wave field, is compared with that of the calculated wave field using the theory of the uniform plasma case. It is found that 40% of the amplitude arises from the second-order mode and the axial damping length of the fundamental mode 1/k iz 1 70 cm.

Contribution of slow waves on production of high-density plasmas by m=0 helicon waves

“…Figure 1͑a͒ ͑second-order radial mode͒, 18 and N Ќ ϭ539 (N Ќ ϭ989) for rf frequency f ϭ13.56 MHz and aϭ2.5 cm. The LH resonance frequency LH is expressed as…”

“…Very few experimental investigations were conducted to find an optimum B 0 in helicon wave discharges using molecular gases such as H 2 and N 2 . 14 In this article, we investigate the contribution of the SW on high-density plasma production by mϭ0 helicon waves 14,[16][17][18][19][20] using several gases such as H 2 , D 2 , He, N 2 , Ne, Ar, and Xe.…”

High-density hydrogen-plasma production in a simple torus using helicon waves

“…͉B z ͉ increases when helicon waves are excited because the toroidal damping of helicon wave is smaller than that of the antenna field. 15 Therefore, it is postulated that whereas no waves are excited in the L region, helicon waves are excited in the M and H regions. In the H region, ͉B z ͉ tends to saturate.…”

Control of antenna coupling in high-density plasma production by m=0 helicon waves

“…10 Once the density jump occurs, a high-density ͑HD͒ mode is achieved, in which plasmas are produced by helicon waves. 10,11 Because of the axial symmetry, the mϭ0 mode can produce azimuthally symmetric plasmas using simple one-turn or double-loop antennas. If P th can be reduced, the mϭ0 mode is desirable in applications.…”

“…In the uniform cylindrical plasma model, kӍk Ќ for a small diameter plasma and k Ќ is determined by the radius of the discharge tube a as k Ќ ϭ3.83/a (k Ќ ϭ7.02/a) for the fundamental mode ͑second-order radial mode͒. 11 Therefore, when B 0 and are fixed, n p is proportional to k z . We have tried to control k z in the mϭ0 helicon wave discharges by using two or three single-loop antennas and by varying the phase of the rf current and the distance between antennas, for the purpose of controlling n p .…”