Exploratory test of utility of magnetic insulation for electrostatic accelerators

A recent paper L. R. Grisham, Phys. Plasmas 16, 043111 (2009) proposed that a magnetic field which enveloped each of the electrodes in an electrostatic accelerator, along with their support structures, might suppress field emission of electrons and thus allows a higher electric field gradient to be applied between accelerator stages without the onset of vacuum electrical breakdown. Such a magnetic field configuration might be produced by flowing a substantial electric current through each accelerator grid and its support from high current low voltage supplies floated at each accelerator grid potential. This experimental note reports a preliminary exploratory test of whether this magnetic insulation approach might be of benefit at a modest magnetic field strength which could be suitable for practical accelerator applications. This experiment did not find evidence for an increase of the electrostatic potential gradient which could be sustained across a vacuum gap when the cathodic (electron-emitting) electrode was enveloped in a magnetic field of about 240 G. This note discusses a number of possible explanations for this observation as well as the inherent limitations of the experiment.