Experiment Study Of Magnetized Radio Frequency Plasma Discharge

With the development of plasma fusion reactors, plasma material processing andplasma space propulsion, magnetized radio frequency plasma has been the focus of concernas its excellent properties.Wall cleaning has been used popularly on tokamaks to reduce impurities and fuelrecycling. Plasma-associated cleanings has been used and proven to be effective by runninglow energy conditioning plasmas such as glow discharge cleaning (GDC), as well as variousother methods based on RF techniques at electron cyclotron resonance (ECR) and ioncyclotron resonance (ICR).Compare to electron cyclotron resonance (ECR) and ioncyclotron resonance (ICR) helicon wave plasma (HWP) has higher cleaning effect and wideroperational region.AS it is impossible to operate and study HWP on EAST for long periodsof time and the conditions of plasma can’t be controlled easily, we designed a new heliconplasma source.An experimental study of a helicon plasma source was performed during the period05/2012-03/2014at the Department of Physics, Soochow University, under a support byNational Magnetic Confinement Fusion Program of China. With Prof. X M Wu as aPrincipal Investigator, Dr. C G Jin and two students from Soochow University were involvedinto this project. This experiment allows study of the intrinsic advantages of efficient heliconplasma production for use in plasma-material interaction. Historical helicon experiment datahave been applied to help size the experiment. The goal was to create a robust and flexibleexperiment system which would allow optimization of the source and system parameters forefficient helicon wave plasma generation, verify the higher cleaning effect of HWP andwould permit for correlation between helicon theory and experiment. During the past one and half a year, a vacuum chamber was built and a13.56MHz RFpower system was tried to achieving the first inductively coupled discharge. In order toexcite the helicon mode, high-current electromagnets with water cooling system was built.Various RF antenna designs, materials and connections were tested. The RF-delivery andmatching networks were re-designed to minimize losses and gain control. With a self-designed internal antenna the parasitic discharge is successfully suppressed, and the heliconmode discharge was first realized in09/2013. In order to get a steady operating in heliconmode discharge, many efforts were made to gain required controllability of the dischargeparameters. A Langmuir probe and an optical spectrometer system were used to get detailedcharacterization of two operation modes: Inductively Coupled Plasma (ICP) and HWP. Atlast, wall material were processed by the new source, and plasma-material interaction wasstudied.The result of the design and construction effort is a working, reliable, and flexiblehelicon plasma source system. This system provides the capability for futureexperimentation and helicon plasma cleaning method development.