Laser Assesses Particle Charge in Plasma

Understanding the charge carried by particles in plasma is of keen interest to those investigating plasma environments ranging from thin-film production to interstellar clouds. However, most experimental methods of testing this property require a plasma field with a low neutral gas pressure of 10^-2 to 10^-1 t.

Researchers from the Institute for High Energy Densities in Moscow have developed a method to test dust particle charges in a glass discharge tube with a DC glow discharge produced in neon at 0.5 to 1.5 t. They use a 2-W argon-ion laser from Plasma in Ryazan, Russia, to move an individual dust particle out of a cloud suspended in the discharge without changing the particle's charge. When the particle leaves the beam and returns to the cloud, the researchers determine its charge by measuring its trajectory with the aid of a 670-nm laser diode and a high-speed CCD camera.

The process, reported in the Nov. 12 issue of Physical Review Letters, shows that, while the dependence of the dust particle charge on its size is nonlinear, the surface potential does increase with volume.