Hypervelocity dust beam injection for internal magnetic field mapping

Abstract

Injecting neutral atoms into high-temperature plasmas forms the basis for several important diagnostics, such as motional Stark effect and charge exchange recombination spectroscopy. We describe an alternative approach to seeding the plasma with neutrals, via “hypervelocity dust beam injection” (HDBI), using micron-sized dusts. Among its many potential applications, HDBI mapping of two-dimensional internal magnetic fields inside medium-sized (50–500 eV) plasmas is discussed in detail. Electrostatic acceleration at ∼100–200 kV will launch a stream of (0.2–10 μm-sized) dust grains of lithium or carbon to hypervelocities (1–10 km/s). Each dust grain, acting as a “microcomet” in the plasma, forming a plume (tail), which if photographed, will reveal the direction of the local magnetic field, with anywhere from 10–100 microcomets in the plasma at any time, a full profile of the B-field direction could be obtained per high resolution image. Due to the small dust grain size, the perturbation to the plasma will be minimal. HDBI could be a simple low cost approach to obtain internal magnetic field information in plasmas with magnetic field structures that are significantly different than vacuum fields, such as in spherical tokamaks, FRC's, RFP's, and spheromaks.