Progress in the Understanding of Gridded Inertial Electrostatic Confinement Devices at the University of Wisconsin

For nearly two decades, as many as 4 Inertial Electrostatic Confinement (IEC) devices have been operated simultaneously at the University of Wisconsin-Madison.  Over that time period we have learned that the early perceptions of how IEC devices operate are quite different from the actual performance in the Laboratory.  Over the past 2 years we have gained even more understanding of IEC physics and technology.  Experimental measurements and theoretical improvements have better characterized both the negative ions that contribute up to ~10% of the fusion rate in some cases and the neutral energy distributions in IEC devices at moderate pressure (0.07-0.7 Pa ≈ 0.5-5 mTorr).  We also now understand more of why operation with helium plasmas has such a detrimental effect on high voltage performance of the traditional tungsten alloy grid wires.  Most of the previous IEC work had been confined to < 100 kV with short operation times up to 150 kV.  We have recently expanded our operating regime to ≈ 200 kV  anode-cathode potential difference, which is, to our knowledge, the highest-voltage IEC operation reported in the worldwide IEC literature.  Several design modifications were required to achieve steady state operation at these high voltages and some are described in this article.