Probe Measurements in a Beam Plasma Discharge

Abstract

The influence of the beam energy and beam current density on the parameters of the plasma is investigated. The efficiency of carrier generation by collective interactions (Langmuir-oscillations) is compared with that by the single collision mechanism. The additional negative charging of the static probe caused by the beam electrons is used for the determination of the beam electron density. , IntroductionAboiit 15 or 20 pears ago the beam generated plasma got importance as a means of generating high frequency oscillations. Another interesting feature of this plasma is the possibility of plasma heating by the beam plasma interaction. For about 5 years attempts have been made to use the anisothermal plasma produced by passing an electron beam through a working gas for substance transformation.The construction and modes of operation of the plasmachemical reactor "MINI-PLAST", used in our experiments, are described in [l]. As working gases we used air and argon. Our paper deals with the spatial distribution of such parameters as plasma potential, mean energy of plasma electrons, number density and energy distribution of the electron gas. From this, statements are to be deduce .-about the range of existence of a working regime favourable to the beam plasma energy input, -about the relations between beam intensiby and plasma properties, and between number density of plasma elect.rons and number density of beam electrons,-about the efficiency of carrier generation by collective interactions as compared to the single ionization by collisions and -about the comparison between inert gas and molecular gas concerning the energy capacity of the electron component of the plasma for argon and air respectively.Several probe techniques were used in our investigations. The systematic error of results and the influence of the weak magnetic field existing in the reactor on the probe characteristic and its 2nd derivative are discussed. fj Beitr. P!asmsphys., Bd. 32, H. 2

The Influence of the Fluctuation Amplitude on the Probe Characteristic

“…1 the electrons in the beanigenerated plasma have a Maxwellian velocity distribution. This has been confirmed experimentally up to about q = 12 [15]. It is possible to regulate the electron temperature by varying the distance between probe and beam axis [15].…”

“…(In order to bring the floating potentials given by formula (6) in coincidence with the measured ones, cf. [15], ni must be fitted to to be found where the probe current of the single probe characteristic has the same amount but the opposite sign. Then the function i(ql + qr) yields one branch of the double probe characteristics, the other one is obtained by reflection.…”

Spatial Characteristics of the Beam Plasma Discharge in Crossed Electric and Magnetic Fields

“…5 presents the plasma density radial distributions while neon density grows from zero up to 3. 5 . 1013 with crypton density equal to 2.5 .…”

“…3a, 3b show plasma density and space potential in dependenoe on the distance from the chamber axis ( r ) a t the discharge with crypton as a working gas, crypton density is no = 7. 5 . lola ~m -~, Ub = 4.5 kV, Ib = 0.7 A, radial voltage u, changes from zero to 50 V. Fig.…”

“…the device can be of interest for practical applications. 1 -the working chamber, 2 -face insulators, 3 -electron gun, 4 -central electrodes, 5 -magnetic coils, 6 -sampler of mass-analyzer, 7 -electron beam collector, 8 -single Langmuire probe…”