Plasma dragged microparticles as a method to measure plasma flows

Abstract

The physics of microparticle motion in flowing plasmas is studied in detail for plasmas with electron and ion densities ne,i∼1019m−3, electron and ion temperatures of no more than 15eV, and plasma flows on the order of the ion thermal speed, vf∼vti. The equations of motion due to Coulomb interactions and direct impact with ions and electrons, of charge variation, as well as of heat exchange with the plasma, are solved numerically for isolated particles (or dust grains) of micron sizes. It is predicted that microparticles can survive in plasma long enough, and can be dragged in the direction of the local ion flow. Based on the theoretical analysis, we describe a new plasma flow measurement technique called microparticle tracer velocimetry (mPTV), which tracks microparticle motion in a plasma with a high-speed camera. The mPTV can reveal the directions of the plasma flow vectors at multiple locations simultaneously and at submillimeter scales, which is hard to achieve by most other techniques. Thus, mPTV can be used to study plasma flows produced in the laboratory.