PLASMA DIAGNOSTICS IN HORIZONTALLY BURNING METAL HALIDE DISCHARGES

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PLASMA DIAGNOSTICS IN HORIZONTALLY BURNING METAL HALIDE DISCHARGES

H. Beyer, W. Funk, H. Kloss

To cite this version:

H. Beyer, W. Funk, H. Kloss. PLASMA DIAGNOSTICS IN HORIZONTALLY BURNING METAL HALIDE DISCHARGES. Journal de Physique Colloques, 1979, 40 (C7), pp.C7-325-C7-326.

�10.1051/jphyscol:19797160�. �jpa-00219136�

JOURNAL DE PHYSIQUE C o l l o q u e C7, supplgment a u n 0 7 , Tome 40, J u i Z Z e t 1979, page C7- 325

PLASMA DIAGNOSTICS IN HORIZONTALLY BURNING METAL HALIDE DISCHARGES

H. Beyer, W. ~ u n k ' and H.G. Kioss.

Akademy d e r ~ i s s e n s & h a f t e n der DDR, Z e n t r a Z i n s t i t u t fur E Z e k t r o n e n p h y s i k , I T 111 DDR-1017 B e r l i n , XWarschauer PZatz 9/10.

VEB Kombinat NARVA, DDR-1017 B e r l i n , E h r e n b e r g s t r . 11-14.

1

.

Introduction The coefficient In(M.Y) essentially Metal halide discharges in horizontal po- the popitione the 'pectral

line levels only and can be easily deter- show a Of the arc from mined in good approximation. For instance the tube axis caused by convection. De-

pending on the value of this deflection for the T1 line 535 nm it equals to 0.85.

more or less deviations from the cylindri- cal symmetry occur so that the measure- ments of temperature and partial pres-

sures by means of the emission coefficient of optically thin spectral lines often can not be accomplished because in this case a cylindrical symmetry is demanded for the Abel inversion. On the other hand all the methods based on the measurement of para- meters of an optically thick spectral line are suitable for the diagnoetics of such non-cylindrical discharges. In this case the experimental results only depend on the conditions along the line of observa- tion and do not depend on the geometry in the other arc zones. The methods to be recommended can be considered as being universal for this type of discharges, because from the malorits of lidtina additives in metal Galid; dis~h&~es-(~a, Ce,Tl,In,Al,Sn,Sc,Be with exception of the rare earths) optically thick spectral lines are available for measurements.

2. Experimental methods

The plasma temperature can be determined by the method developed in [I] and used for the first time in this type of dis- charge in [2]. In this method the tempere- ture is meaeured by means of the intensity of the reversal maxima of em optically thick line, but only much spectral lines can be used the lower level of which lies sufficiently above the ground level.

According to Wients formula

one can get a tWien's temperatmet TW(x,y) according to the position x=O for each intensity of the reversal maxima Imax(y>

(x

-

coordinate along the line of

observation,; y

-

position of the line of observation above the tube axis; x=O, y=O

-

coordinates of the tube axis). The real temperature maximum T(0,y) along the line of observation is determined by the

relation

The distance of the line maximaah can be used for the determination of the partial pressurea p of the lighting additives.

Thie method was proposed in [3] for opti- cally thick resonance lines and extended in 141 for optically thick non-resonance linee. According to C3,41 it follows

a is a coefficient depending only' on the spectral line under consideration and the broadening mechanism. If the broadening parameters are unknown only the relative partial pressure can be measured, n is the broadening exponent equated 1 in 131. In our conditions (broadening of the spectral line by a forei gas) it is better to equate n.1.6 14r The integral

E,

-

^{x o}

(En

-

energy of the lower level of the spectral line, -xo,+x0

-

entrance and exit of the line of observation) has only a relatively weak dependence on the axis temperature and the form of the tempera- ture profile. For many purposes it can be sufficiently exactly determined by assu- ming an approximated profile along the line'of observation (for example a para- bolic profile with TO=5000 K and

TW=lOOO K. )

3. Results

Metal halide discharges with various lighting additives were run in a horizon- tal position with d.c. and s.~., and the- temperature and partial pressures in the plasma were measured by means of optically thick lines of various elements.

For example fig. 1 shows the temp'erature profile in an a.c. halide discharge with NaJ, T1J and InJ as lighting additives and Hg as buffer gas for various powers in the middle of the electrodes (the die- tance between the electrodes 1 = 42 mm the tube radius R = 9,25 mm). Using (If

and ( 2 ) the plasma temperature was

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19797160

determined by means of the intensity of Fig. 2 shows the temperature dependence the reversal maxima of the T1 line 535 nm. in z-direction (z-coordinate in direction It was found out that the deflection of of the tube axis, z = 0

-

middle between the temperature maximum from the tube the both electrodes) for the same dis- axis is nearly independent of the power. charge like in fig. 1 , but burning with

d.c. The temperature at the centre of the deflected arc was measured by means of the intensity of the reversed T1 line 535 nm. Furthermore fig. 2 shows the vari- ation of the partial pressurea of Na, T1 and In along the z-axis obtained from the distances of their maxima of the lines

589,0/589,6, 535 and 451 nm.

Fig, 1: Temperature arid Na partial pres- sure in vertical direction (a.c.) Furthermore, fig. 1 shows the dependence of the Na partial pressure in relative units on the vertical position of the line of observation wi.thin the tube which was measured from the distance of the rever- sed maxima of the Na lines 589,0/589,6 nm using (3). The variation of the pressuxe with various powers was caused by the various temperatures of the tube wall, For a certain power the Na partial pres- sure slowly increased from the upper wall to the tube axis, but this effect is of the order of the measuring error. In the lower part of the discharge St is not possible to get data because the dis- charge is cooler and there are no emisoion of optically thick lines.

In metal halide discharges burning in a horizontal position with d.c. strong cataphoretic effects occur [5]. This means that the partial pressure of the lighting additives rapidly decreases from the cathode to the anode while the plasma temperature increases in this direction.

Fig. 3: Na partial pressure in vertical direction (d.c.)

The measurement of the Na partial pressure in y direction shows an effect of vertical segregation in the d,c. discharge as is demonstrated in fig. 3 for various z-positions. An explanation for this effect can be given in the following manner: There is a field-driven flow of additive ions through the arc to

the cathode, a back diffusion of additive neutrals mainly through the cold gas at the bottom of the tube, and the circle is closed by the transport of the additives according to this vertical partial pres- sure gradient from the bottom back into the arc. For Tl and In this effect is perceptible to a smaller extent.

For Na this effect was obtained in d.c.

discharges with other additives too, for example in discharges with CeJ and NaJ.

In an a.c. discharge there is a sui- 3 ficiently homogeneous Na distribution, while in the case of d.c. a segregation in the vertical direction occurs.

I;

^{max -}

^{-. \}

^{- 2}

^-

^a

^-.-

_P- ^r

^+.

^,-*-*-*-

-1

Literature

[I ] Bartels, H.; 2s. Physik 127 (1950) 243 and 128 (1950) 546

C23 Funk, W.; Kloss, H.-0.; Serick, F.;

Beitr. Plasmaphysik 13 (1973) 101 [33 Teh-Sen Jen; Hoyaux, M.F.; Frost, L3.;

JQSRT 9 (1969)

487

Fig. 2: Temperature and partial pressures of the li tin additives along the axis

g.c.7

[ 4 ] Funk, W.; Kloss, He-G.; ICPIG XIII,

Berlin 1977, p.

149

[51 Beyer, H.; Funk, W.; Kloss, H.-G.;

2nd Int. Symp. on Incoherent Light Sources, Enschede, Netherlands, 1979