Determining the electric field in a plasma by measuring the deflection of an ion beam*

A design study has been completed on reconstructing the electric field in magnetically confined plasma by measuring the deflection of a non-confined heavy ion beam. The concept is to send an ion beam through a plasma device where the magnetic field $\mathord{\buildrel{\lower3pt\hbox{$\scriptscriptstyle\rightharpoonup$}}\over {B}} $ is well known and to measure the beam position change at a detector. Either the injection angle or the energy of the ion beam can be changed to allow multiple measurements with differing amounts of plasma penetration. Calculations using a simple geometry show that the reconstruction is reasonable when the electric field $\mathord{\buildrel{\lower3pt\hbox{$\scriptscriptstyle\rightharpoonup$}}\over {E}} $ is relatively strong (at least 1 percent of $\mathord{\buildrel{\lower3pt\hbox{$\scriptscriptstyle\rightharpoonup$}}\over {v}} \times \mathord{\buildrel{\lower3pt\hbox{$\scriptscriptstyle\rightharpoonup$}}\over {B}} )$. Results of the design study are presented for both a slab and a cylindrical geometry. The electric field is reconstructed from a series of measurements using a simple layer model. This diagnostic is simple and inexpensive compared to standard electric field diagnostics such as a Heavy Ion Beam Probe. Future work will be to model an existing device such as HSX.