Expansion rate measurements at moderate pressure of non-neutral electron plasmas in the Electron Diffusion Gauge (EDG) experiment

Abstract

Measurements of the expansion rate of pure-electron plasmas have been performed on the Electron Diffusion Gauge (EDG) device at background helium gas pressures in the 5×10 −8 Torr to 1×10 −5 Torr range, where plasma expansion due to electron-neutral collisions dominates over plasma expansion due to trap asymmetries. It is found that the expansion rate, defined as the time rate of change of the particles' mean-square radius, scales approximately linearly with pressure and inversely as the square of the magnetic field strength in this regime, in agreement with classical predictions.

Measurements of Plasma Expansion due to Background Gas in the Electron Diffusion Gauge Experiment

“…Malmberg-Penning traps have a uniform magnetic field parallel to the common axis of several cylindrical electrodes, and particles with the same sign of charge can be confined by charging two nonadjacent electrodes to a sufficiently large voltage. Previously reported experimental results [2] from the EDG experiment indicate that the plasma expansion rates measured in the high-vacuum regime (where asymmetry-induced expansion is negligible) are in good agreement with with the predicted expansion rates [13] derived using a warm fluid treatment of the plasma. The evolution of the inferred perpendicular temperature during this expansion, however, did not account for the clear decrease in electrostatic potential energy, prompting improvements to the EDG diagnostic systems.…”

“…Pure electron plasmas are trapped in the Electron Diffusion Gauge (EDG) experiment device [1][2][3][4], a cylindrically symmetric, Malmberg-Penning trap [5][6][7][8][9][10][11][12] with inside diameter I.D. 2 ¡ R w 5.08 cm.…”

Experimental Investigation of m=1 Diocotron Mode Growth at Low Electron Densities

“…• The diocotron mode can be made to grow in response to electron-neutral collisions without resistive forcing by employing low filament bias voltages that produce a low-density (N L • The sensitivity of mode growth to pressure for P § 10¤ 9 Torr is much greater than that previously observed for mode damping.…”

“…The expansion of the plasma column has been related theoretically to the rate of collisions between the electrons and the neutrals [5,6]. The expansion rate has also been measured experimentally on the EDG experiment [7,8] using a Faraday cup collector and observed to scale classically [9] at relatively high neutral pressures (P £ 10¤ 6 ), but this method requires hundreds of repeated discharges to determine the expansion rate. This approach was not only time-consuming, but required excellent plasma reproducibility and low measurement noise.…”

Electron plasma expansion rate studies on the Electron Diffusion Gauge experimental device

“…Pure electron plasmas are trapped in the Electron Diffusion Gauge ͑EDG͒ experimental device, [1][2][3][4] a cylindrically symmetric, Malmberg-Penning trap [5][6][7][8][9][10][11][12] with inside diameter I.D.= 2 ϫ R w = 5.08 cm. Malmberg-Penning traps have a uniform magnetic field parallel to the common axis of several cylindrical electrodes, and particles with the same sign of charge can be confined by charging two nonadjacent electrodes to a sufficiently large voltage.…”