Probe experiment on basic plasma parameter investigation in a quasi-gasdynamic ion source GISMO

Abstract

Plasma parameters in a 28 GHz gasdynamic continuous electron cyclotron resonance discharge (ECR) with a high volumetric energy input were investigated with a Langmuir probe. The knowledge of the dependencies of plasma density and temperature on external parameters is useful for tuning the ECR source to the desired mode of operation. The design features of the plasma chamber and the configuration of the magnetic field made it possible to use the approximation a non-magnetized flat probe to calculate the temperature and electron density at various gas pressures and power of the heating microwave. A movable tungsten probe was used, allowing for studying plasma parameters along the magnetic field at various distances from the plasma electrode. At high powers, the electron density in the plug turned out to be close to the cutoff density (about 10 13   cm − 3). A fraction of warm ( > 30 eV) electrons, appearing at high powers, was found, which explains the formation of a pure proton beam in a number of experiments at the same facility. The abrupt increase in the temperature of the warm fraction with power was also found, which makes it of great interest to perform experiments on a multi-charged ions production in heavy gases.