A planar inductively coupled radio-frequency magnetic neutral loop discharge

Abstract

A planar inductively coupled radio-frequency (rf) magnetic neutral loop discharge has been designed. It provides diagnostic access to both the main plasma production region as well as a remote plane for applications. Three coaxial coils are arranged to generate a specially designed inhomogeneous magnetic field structure with vanishing field along a ring in the discharge—the so-called neutral loop (NL). The plasma is generated by applying an oscillating rf electric field along the NL, induced through a four-turn, planar antenna operated at 13.56 MHz. Electron density and temperature measurements are performed under various parameter variations. Collisionless electron heating in the NL region allows plasma operation at comparatively low pressures, down to 10−2 Pa, with a degree of ionization in the order of several per cent. Conventional plasma operation in inductive mode without applying the magnetic field is less efficient, in particular in the low pressure regime where the plasma cannot be sustained without magnetic fields.

Electron transport in carbon tetrafluoride along a magnetically neutral plane between constant gradient antiparallel magnetic fields

“…The linearity of a B component was also seen in a calculation result of the B field distribution around the NL by Gans et al (2007). Here, note that there are two possible arrangements for the B z (x) orientation relative to the direction of E; whether the sign ofB z is positive or negative.…”

Wave propagation and noncollisional heating in neutral loop and helicon discharges

“…The detailed distributions of the measured and calculated static magnetic field strength and the field lines are described previous papers. 28,29 Except for a narrow region around the NL, the field structure is practically identical to the helicon case. Figure 13͑a͒ shows a view on the NLD from the discharge bottom taken by a digital camera.…”

“…Details of the NLD static magnetic field configuration are described in previous papers. [28][29][30] Finally, by using only the bottom coil, the helicon discharge is generated. 33,34 A similar helicon configuration is reported by Stevens et al 35 Time-varying magnetic fields are measured via a bare single induction loop ͑B-dot probe͒.…”

“…In our discharge, it turned out that Landau damping is the dominant heating mechanism leading to efficient plasma ionization. Additionally, we present results in a so-called neutral loop discharge [24][25][26][27][28][29][30][31][32] ͑NLD͒ operated in the same setup with a null point configuration of the magnetic field. Theoretical investigations on the heating mechanisms in the NLD are limited to single particle pictures with simple geometry.…”

Characterization of neutral loop discharges in the VINETA device

“…Such a configuration can easily be created by arranging at least three magnetic field coils with opposing currents around a cylindrical vacuum vessel, thus creating an azimuthal X-line [1,2]. If a radio frequency (rf) antenna is operated in the vicinity of the NL, a so-called neutral loop discharge (NLD) is started.…”