INVESTIGATION OF THE ELECTRON ENERGY DISTRIBUTION FUNCTION IN KRYPTON AFTERGLOW PLASMA

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Submitted on 1 Jan 1979

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INVESTIGATION OF THE ELECTRON ENERGY DISTRIBUTION FUNCTION IN KRYPTON

AFTERGLOW PLASMA

O. Angelov, A. Blagoev, Tc. Popov

To cite this version:

O. Angelov, A. Blagoev, Tc. Popov. INVESTIGATION OF THE ELECTRON ENERGY DIS- TRIBUTION FUNCTION IN KRYPTON AFTERGLOW PLASMA. Journal de Physique Colloques, 1979, 40 (C7), pp.C7-19-C7-20. �10.1051/jphyscol:1979709�. �jpa-00219068�

JOUEiNAL DE PHYSIQUE CoZZoque C7, suppZ6ment am n07, Tome 40, JuiZZet 1979, paae ~ 7 , 19

UWESTIGATIONS OF THE ELECTRON ENERGY DISTRIBUTION FUNCTION IN KRYPTON AFTERGLOW PLASMA

0. Angelov, A. Blagoev, Tc. Popov.

Sofia University.

Several previous works /I -3/ made i n the afterglow of helium, neon and argon ~ o s i - tive column show out that in the initial period of the plasma decay, when the quantity of the excited atoms and charged particles has not yet been substantially decreased, the electron energy distribu- tion function ( E E D F ) may substantially deviate from the Maxwellian distribution function in the high energy region: 1.The fast electrons number could be ma.ny or- ders higher than i n a Maxwellian distri- bution with the temperature of the main group of electrons Te. 2.This number de- creases i n time such more slowly than usually presumed.

This work gives the results of similar investigations i n the krypton afterglow for wnich n o previous data exists a s far a s we know.

T h e measurements were carried out o n the same experimental device, used and de- scribed i n details earlier / I / . Short, rectangular voltage pulses at repetition frequency 1,5 kHz were applied o n the electrodes of the discharge tube. T h e experimental conditions were: discharge pulse current I = 6 t 60 mh, gas pres- sure about 0 , 7 torr, tube diameter r = 2,6 cm, radius of cylinurical probe 4.10-3 cm.

I n a selected moment after the cesation of the aischarge current were made both electrical probe and optical absorbtion measurements. A s it is well known EEDF

i s connected with the second derivative of the probe current i;(v) by Druvestain relation. We used the time-resolving method for obtaining i" (v) in a plasma.

with periodically changing parametersjl, .

On fig.1 are shown experimental EEDF il:

absolute units measured at delay t i m e c = 2 0 0 and 540 mks after the uischarge pulse end.

U 4 5 6 7 &C&vI

T h e maximum at 5,8 volts is due to the electrons, created i n the chemoionize- tion reactions:

K~'P,+K~~P~- K r S rnri+e(6 ,47ev) 1 ( i ) Kr3p 2 +~r%,-Kr 1 so+Krf+e(5,94ev) (2) K ~ ~ P , , + K ~ ~ P ~ - K ~ _C. 1 S + ~ r + + e(5,82e~) ( 3 )

I 0

These reactions may also produce ~ r + + e . 2 I n the processes ( 1 ) - ( 3 ) the electrons are created with definite energies., but experimental maximums are broadened and fused by the influence of the finite amplitude of the imposed modulating voltage.

T h e density n2 o f the excited krypton

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979709

atoms L ~ ~ n l of the ICr3p1 atoms and P ~ , n of the K ~ atoms, which are vital ~ P ~

0

for the fast e1ectro:ls creation, was determined by measuring the fractional absorbtion of the spectral lines Kr7694A, Kr5870 A.and Kr.7854 A connected with these levels. The line strength values Were taken from the works /4,5/.

At our experimental conaitions of low gas pressure and discharge currents, the behaviour of fast electrons is governed by Psee diffusien towards the tube walls.

In this case theoretical calculations

/I/ for the EEDF give the following expression for the total density of e1,ectrons in the energy range about

&m=5,,8 eV at the tube axis

w h - ~ r e f, ^{2 0 ,}

P21

A is th,e dzfusion length,. c ( & ) is the fvee diffusion coefficient of an elec- tron witri e.nergy & , ^J04 r/l

,

Bessel funct ion-

Because of the small density of the 'po and levels signit'icant contribution

i n the Sm have exclusivelly reactions including 3 ~ 2 level, namely ( 1 ) - ^{(3 ).}

For the determination of the rate con- stants of Penning ionizations were made complex measurements at 40 different discharge conditions and delay times. A system of inaependant equations in the form of relation (4) was set up froit1 the results of these measurements. It was solvea by the smallest sqha7.-e methoa.

I n this way it was found out that the 3 3 rate constant for the reaction ( P

- 1

2' P2) is (322 = (9,3 + o , ~ ) . I o - ~ cmJs , ^for

I 3

the reaction ( P2,'P1 ) i s p Z 1 =

( 1 + 0,5).10-8 cm3s-I and for the reac-

tion ( 3 ~ 2 , 3 ~ 0 ) is

PZ0

em's-I.

The gas temperature at these small discharge currents is about 300°~, so the corresponuing cross-sections for these processes at the energy 0,026 eV are:

vzZ

rz0 = (8,3 + 2 , 6 ) . 1 0 - ~ ~ c m ~ The results strongly depend on the line strength values.

1. Blagoev A.B. et all. ,Zh.Tekh.Fiz. , 4k, 333, 338, 1974;42, 1160, 1977.

2. Kolokolov N .B. et all. ,Zh.Tekh .Fiz. , 48, 1044, 1832, 1978.

3. Blagoev A. and Popov Tc. -- , ^Physics

Letters A 66, 213, 1978; i n print 79 4. A.P.Thorne, J.E.Charnberlain, Proc.

Phys. Soc. , 82, 1963.

5. R.A.Lilly, JOSA, 66, 245, 1976.