VISIBLE AND INFRARED CONTINUUM RADIATION FROM A LOW TEMPERATURE Cl2-ARC

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VISIBLE AND INFRARED CONTINUUM RADIATION FROM A LOW TEMPERATURE

Cl2-ARC

J. Schmitt, M. Neiger

To cite this version:

J. Schmitt, M. Neiger. VISIBLE AND INFRARED CONTINUUM RADIATION FROM A LOW TEMPERATURE Cl2-ARC. Journal de Physique Colloques, 1979, 40 (C7), pp.C7-279-C7-280.

�10.1051/jphyscol:19797137�. �jpa-00219110�

JOURNAL DE PHYSIQUE CoZZoque C7, suppldment au n07, Tome 40, ~ u i Z l e t 1979, page C7- 279

VISIBLE AND IWRARED CONTINUUM RADIATION FROM A LOW TEMPERATURE Ct TARC

J. Schmitt and M . Neiger.

Ruhr University B o c h , AZZgemeine EZektrotechnik und EZektrooptik 4630 Bochwn, F . R. G.

INTRODUCTION

Continuum visible and especially infrared emission of plasmas is of interest be- cause of its advantages for diagnostic purposes of dense low temperature plas- mas and for the investigation of proper- ties of nonideal plasmas. Continuum ra- diation has been extensively studied in hydrogen and inert gases and to a lesser extent in other atmospheric gases, alkali metal vapors, mercury and the halogens /I/.

In the latter case the measured visible continua were found greater than expected by factors 5-50, but the observed radia-

Fig. 2

Fig. 1

tion has not beenunambiguously identified /I/. It is the aim of the present work to perform quantitative measurements of

the visible and infrared continuum ra- diation of a chlorine arc plasma.

EXPERIMENT

The C12-arc is operated in a water cooled quartz tube of 8 mrn inner diameter and

10 cm length at atmospheric pressure with dc-currents of 4-15 A. Both ends of the drc are submerged in argon gas to prevent re- absorption of radiation by C12-molecules in regions of lower temperature and thus to make possible end-on observation of the arc axis. The detectors used at the exit slit of a McPherson 2051 monochro- mator are photomultipliers (S20, SI), a PbS - cell and a cooled InSb - photocon- ductive detector, whcse signals are fed into a lock-in detection system. A stan-

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19797137

dard carbon arc is used for absolute in- tensity calibration.

MEASUREMENTS

Fig. 1 shows absolute spectral continuum intensities emitted end-on from the arc axis in the wavelength range 0.4

pm - 3Cun

for 4 different arc currents. These curves are c$mposed from those experimental points, which seemed to be unaffected by any atomic line radiation. Simultaneous determination of the axis temperatures as a function of discharge current by abso- lute intensity measurements of C1I spec- tral lines allows conversion of the data of Fig. 1 into absolute absorption coeffi- cients via Kirchhoffs law. The experimen- tal points of Fig. 2 show this absorption coefficienta4(%, 8200 K).

DISCUSSION

Fig. 2 shows a comparison of absolute mag- nitudes and A -dependences of our data with the calculated electron-ion contri- bution (Kramers-Unsbld, S ^{-factor I )} * ^KU

(solid curve) and the electron-atom brems-

&ra&Xang f.frs&-.fred+tnus) (dotted.

curve), which was calculated according to th& ~+an/Kivel approximation /2/. The sum ae KU+ atf (dashed curve in Fig. 2) agrees fairly well with our data in the range 2 p m < 9 < 3pm. On the other hand, fairly large differences exist for 3 < 2 m, t

especially near 2 ^{e I. 7pm and} % ^R+ 0. 5rm, where the experimental data lie high by

factors 2 and 5 respectively. The maximum at 3 w 5300 2 may be interpreted as due to a series of electron-ion recombination

2 4

thresholds into C1I 3s 3p 4p levels. A g - factor /3/ of 5 at maximum, comparable to Xe g-factors at 6000 2 / 4 / , results from this interpretation. Moreover, the depen- dence ae(T, 5300 2) of our data on tempe- rature, which is shown in Fig. 3 and com- pared with both aeKU and 5xaeKU, is also in agreement with this. Fig. 4 shows ex- perimental data ofae(T, 2.9pm) together with the contribution aeKU (%=I ^{) and Se}

as a function of temperature. The steeper increase, whibh is observed in experiment, indicates that an additional radiation mechanism becomes important at higher tem- peratures. A possible process would be

strongly broadened C1I spectrum lines from energy levels close to the ionisation thre- shold which merge into a quasi-continuum.

LITENLTURE

/I/ H.-P. Popq: Phys. Rep. E, 170(1975) /2/ H.A. Hyrnan and B. Kivel: JQSRT 13, 699

(1973)

/3/ L.M. Bibermann and G.E. Norman: Opt.

Spectr. 8, 230 (1960)

/4/ D. Meiners and C.O. Weiss: JQSRT 16,

273 (1976)

Fig. 3

Fig. 4