Cooled electrostatic probe.

Abstract

Experiments were performed to evaluate the ability of a water-cooled electrostatic probe to measure local electron temperature, electron density, floating potential, and saturation current ratio in dense plasmas (argon up to 20,000°R at 1 atm). The measurements of electron temperature were calibrated against temperatures obtained from simultaneous local measurements of total plasma enthalpy at different temperatures under conditions of known equilibrium by use of a proven calorimetric probe technique and were found to be in agreement within normal experimental error (3% standard deviation from the mean). Using this electron temperature, the measurements of floating potential and saturation current ratio were found to agree with a first-order theoretical approximation to within the accuracy of the approximation. The cooled calorimetric-electrostatic probe was then used to measure the degree of nonequilibrium in a reduced-pressure argon plasma in terms of the difference between local electron and heavy-particle temperatures. Results were in agreement with analytical predictions of a simple "freezing" criterion. The probe also provided a semiquantitative measurement of plasma turbulence. Nomenclature C = most probable particle speed, cm/sec d = Bohm transition region thickness, cm E -electron kinetic energy, ergs E n -electron kinetic energy after n collisions, ergs &E = change in electron kinetic energy, ergs e -electronic charge, esu (also base of natural logarithms) h = Debye length, cm 7 = current density, amp/cm 2 k = Boltzmann constant L = probe diameter, cm m = particle mass, g n = number of collisions in boundary layer N = number density per cm 3 p = pressure, atm Re = Reynolds number T = temperature, °R or °K U = mean flow velocity, cm/sec V = applied potential, v x = axial distance from arcjet nozzle, cm or in. y = distance from probe surface, cm a. = degree of ionization, N € /(NA + N e ) 8 = boundary-layer thickness, cm X = mean free path, cm /z = mobility <p = probe potential relative to plasma, v <PF -floating potential relative to plasma, v X = deflection angle, rad a-= effective collision cross section, cm 2 SubscriptsA = neutral atoms H = heavy particles (atoms or ions) 0 = initial conditions random saturation freestream conditions electrons r sat e = Presented as Preprint 66-73 at the AIAA 3rd Aerospace

Theory of Ion Boundary Layers

“…= (95/2) 1 ' 4 (16) Expressions (16) agree with the leading terms of the corresponding results (49) and (46) of Ref. 21, and are identical to the results for; and q s obtained using the qUasi-one-dimensional method.…”

The effect of ionization on heat transfer to wires immersed in a highly thermallyionized plasma

“…A more direct treatment of the interaction between a plasma and a solid is available in the literature in conjunction with electrostatic probes [7][8][9][10][11]. The purpose of these probes is to infer, from the probe response, some properties of the plasma surrounding the probe.…”

“…The purpose * Numbers in brackets refer to entries in References. of the recent literature on electrostatic probes [8][9][10][11] is to theoretically account for the disturbance of the plasma by the probe and to predict the currentvoltage characteristic as a function of conditions in the undisturbed plasma. Interpretation of the currentvoltage characteristic in terms of plasma properties is possible only under very simplified theoretical assumptions for the charge carrier flow to the probe.…”

Emission of ions as a result of laser heating of electrolyte drops

“…For the other extreme limit of A,$AD, all the dominant electrical field effects may be assumed to be confined to a region within one mean free path from the probe. For such dense plasmas, the rough analysis of the problem of cooled electrostatic probes has been done by Grey and Jacobs (1967) on the assumption that the electron density remains constant up to the last mean free path from the probe surface, i.e. there is no electrical field in almost all of the thermal sheath.…”