Miniature magnetic field probes for use in high temperature plasmas

An ideal internal magnetic probe would provide high temporal and spatial resolution, without perturbing the plasma. Optimizing the following moves towards this ideal: Size - as small as possible; Plasma facing material - insulating, difficult to ablate, low Z; Shielding - electrostatic, short field penetration time; Electronics - high gain integration, long term stability. Over the years, significant improvements in these areas have been made. The latest probe, built for TCSU, is 3 axis with 96 windings. It is BN clad with a 6 mm outside diameter, is UHV compatible, and can be baked to 200 C. The integrators used are gated, with a 10 usec RC time, and have less then a 10 mV drift per second. Plasmas with widely varying parameters have been probed. A few hundred eV, 1e20 m-3 density plasma with a 1 msec duration represents a reasonable upper limit for probe usability. Plasma duration, density, and temperature can be traded for each other. Design criterion and construction details will be presented, with a focus on the ``how to'' of actually building one.