An experimental study of waveguide coupled microwave heating with conventional multicusp negative ion sources

Abstract

Negative ion production with conventional multicusp plasma chambers utilizing 2.45 GHz microwave heating is demonstrated. The experimental results were obtained with the multicusp plasma chambers and extraction systems of the RFdriven RADIS ion source and the filament driven arc discharge ion source LIISA. A waveguide microwave coupling system, which is almost similar to the one used with the SILHI ion source, was used. The results demonstrate that at least one third of negative ion beam obtained with inductive RF-coupling (RADIS) or arc discharge (LIISA) can be achieved with 1 kW of 2.45 GHz microwave power in CW mode without any modification of the plasma chamber. The co-extracted electron to H − ratio and the optimum pressure range were observed to be similar for both heating methods. The behaviour of the plasma implies that the energy transfer from the microwaves to the plasma electrons is mainly an off-resonance process.

VUV irradiance measurement of a 2.45 GHz microwave-driven hydrogen discharge

“…Microwave discharge plasmas are typically heated with electron cyclotron resonance (ECR) heating. However, it is possible to sustain the discharge without fullfilling the ECR condition in the plasma chamber [19]. The ECR heating requires the electron gyrofrequency to nearly correspond with the microwave frequency, i.e.…”

A study of VUV emission and the extracted electron-ion ratio in hydrogen and deuterium plasmas of a filament-driven H−/D− ion source

“…21 and 22) that virtually all excitations emitting VUV-photons are caused by the high energy tail of the EED. Due to the large discharge volume and the multicusp magnetic field increasing rapidly toward the chamber wall, 23 the high energy electrons are well confined and dissipate their energy very efficiently, thus producing a uniform plasma emission volume in the driver region. The effect of the uniform tail of the electron energy distribution function (EEDF) on the ionization and excitation rate coefficients is discussed thoroughly in Ref.…”