A new plasma potential measurement instrument for plasma ion sources

Abstract

A very efficient and fast instrument to measure the plasma potential of ion sources has been developed at the Department of Physics, University of Jyväskylä (JYFL). The operating principle of this novel instrument is to apply a decelerating voltage into a mesh located in the beamline of the ion source. The plasma potential is determined by measuring the current at the grounded electrode situated behind the mesh as a function of the voltage. In this article, we will introduce the instrument and the first results. In the experiments, the instrument was connected to the beamline of the JYFL 6.4 GHz electron cyclotron resonance ion source. The plasma potential was measured with different source conditions and it was observed to vary between 30-65 V. The plasma potential tended to increase as the microwave power, or the gas feed rate, was increased. These results are consistent with earlier observations and estimations. It was also noticed that the value of the plasma potential changed when the negative voltage applied to the biased disk at the injection of the ion source was varied. Complementary to optical plasma diagnostics, such an instrument can be used as a very efficient tool to get a precise relationship between plasma conditions and extracted beams.

Measurement of plasma potential of liquid-He-free superconducting electron cyclotron resonance ion source

“…4. Additionally, we investigate the effect of gas mixing on the plasma potential with the same method.…”

“…Recently, several laboratories measured the plasma potential and reported the importance of the measurement, because the lower plasma potential gives us the higher beam intensity of the highly charged heavy ions. [3][4][5] One of the new methods for plasma potential measurement is based on the retarding electric field and successfully applied to measure the plasma potential of ECR ion sources under various conditions ͑gas pressure, rf power, and gas mixing͒. 4,5 In our previous work, we observed that the beam intensities of the highly charged heavy ions are strongly dependent on the B min .…”

“…[3][4][5] One of the new methods for plasma potential measurement is based on the retarding electric field and successfully applied to measure the plasma potential of ECR ion sources under various conditions ͑gas pressure, rf power, and gas mixing͒. 4,5 In our previous work, we observed that the beam intensities of the highly charged heavy ions are strongly dependent on the B min . 6 However, we have just a few experiments for investigating B min effect on the plasma parameters ͑elec-tron density, temperature, and ion confinement time͒.…”

Effect of source tuning parameters on the plasma potential of heavy ions in the 18 GHz high temperature superconducting electron cyclotron resonance ion source

“…Since a significant energy spread can influence the longitudinal optics, it was felt necessary to measure the plasma potentials for various ions and its dependance on source tuning parameters. Tarvainen et al, 6 have measured plasma potentials using the retarding field technique and observed the plasma potentials to increase with RF power and gas pressure and the values changed when the negative dc bias was varied. Tarvainen et al, 7 also measured the the effect of the gas mixing technique on the plasma potential, energy spread, and emittance of the beam under various source conditions.…”

Recent ECRIS Related Research And Development Work At JYFL

“…One interesting part of our work is the plasma potential measurements [1]. The main object of the JYFL ion source group is to serve the research program of the laboratory.…”