Comparative study of positive and negative ion flows extracted from downstream plasmas beyond magnetic and electrostatic electron filters

摘要

In the present paper we compare the positive and negative ion flows created using a recently developedudelectrostatic grid-type filter with the flows formed using a magnetic filter. Langmuir probe measurementsudshow electron cooling with both filters, allowing effective formation of negative ions via electronuddissociative attachment in the region of low electron temperature. The energy distribution functionsudof positive and negative ions extracted from the filtered plasmas are measured in both systems showingudan almost monoenergetic nature of the ions with the energy corresponding to the imposed extractionudpotential. It is shown that in both cases strongly electronegative plasmas where the negative ionuddensity is much larger than the electron density can be formed downstream of the filter. Biasing anudinternal electrode or the electrostatic filter grid allows control of the plasma potential. In the case ofudthe electrostatic filter the plasma could be biased negatively compared to ground and effective extractionudof negative ion was achieved.