1HP12 1HP13

Characterisation of Plasmas produced by the “Torche A Injection Axiale”

3. JONKERS, L.J.M. SELEN, J A M . VAN DER MULLEN, J.M. DE REGT, E.A.H. TIMMERMANS AND D.C. SCHRAM

Eindhoven University of Technology, Department of Applied Physics,

P.O. Box 5 13,5600 MB Eindhoven, The Netherlands

The Torche a Injection A i d e (TIA), i.e. torch with axial gas injection, was developed by the group of Moisan in 1993 [l]. Here, we report on the investigations on two different kind of plasmas created by the TIA: one with helium and the other with argon as main gas.

Using absolute line intensity measurements the densities of the excited states are determined. Applying the ideal gas law yields the ground state density. It is found that the excitation temperature ranges from 3000 to 11000 K. Apparently the atomic state distribution function (ASDF) does not obey the Saha-Boltzmann law. This indicates that these plasmas are far from local thermal equilibrium (LTE). From the shape of the ASDF it can be conclu- ded that the plasma is ionising 121.

The electron temperature and the electron density are determined using Thomson scattering. In the plasma with helium as main gas, tem eratures around 25000 K and densities between 0.64 and 5.1 x 10 m are found. In an argon plasma the electron temperature is lower and the electron density is higher: 17000 K and around lo2’ m-’ respectively [3].

Using the electron temperatures and densities as found by Thomson scattering, it can be established that the ionisation rates of both plasmas are much larger than the recombination rates, which means that the plasmas are far from Saha equilibrium. Moreover, the production of new ions and free electrons outranges by two orders the estimated “classical” losses due to flow and diffusion. The actual losses can be higher due to:

a smaller gradient length, due to a donut like radial distribution of the electron density, mixing with the surrounding air, e.g. charge transfer between an argon ion and molecular nitrogen followed by dissociative recombination, formation of molecular argon ions or an underestimation of the escape of resonance radiation.

2lF -

M. Moisan, G . Sauve, Z. Zakrzewski and J. Hubert, Plasma Sources, Sci. and Technol. 3, 584 (1994) J. Jonkers, H.P.C. Vos, J.A.M. van der Mullen and E.A.H. Timmermans, “On the Atomic State Densities of Plasma produced by the Torche ri Injection Axiale”, accepted for publication In Spectrochim. Acta B. J. Jonkers, J.M. de Regt, J.A.M. van der Mullen, H.P.C. Vas, F.P.J. de Groote and E.A.H. Timmermans, “On the Electron Temperatures and Densities in Plasmas produced by the Torche d lnjecrion hiale”. submitted for publication in Spectrochim. Acta B.

X-RAY TOMOGRAPHY ON IR-T1 TOKAMAK M GHORANNEVISS M MASNAVI A KHADEMIAN AND

A R K TAFRESHI PLASMA PHYSICS RESEARCH CENTER OF(1 A U )

TEHRAN. IRAN POONAK. HESARAK,P 0 BOX 14835-159

ABSTRACT

Measurements of soft X-ray emission from the IR-T1 Tokamak plasma have been analysed with tomographic reco- nstruction methods. IR-T1 is a small air core transformer to- kamak with circular cross-section and without copper shell and divertor ( R = 45 cm , a = 12.5 cm , Bt < 1 T, Ip = 20-40, Ne = ( 0.7 - 2.5 )x 1013 cm” , Te = 150 - 200 ev ),

The detector system is on a circular arc view IR-T1 To- kamak plasmas through a thin berylium window ( in a fashion similar t o that of a pin - hole camera ) , to provide poloidal imaging of soft X-ray emission ( SXR ) in the 600 ev - 20 Kev range. Each detector has an active area 3 x 20 “’.The signals are digitized every 4 ps or 8 ps by use of 8 bit transient recor- ders and the frequency response of detector - preamplifier sy- stem is from 10 Hz - 200 kBz.

The tomography method ( cormack’s method ) is used for reconstructing the images of SXR emissivity distribution in the poloidal cross - section of IR - T1 Tokamak. X - ray im- aging ( XIS ) diagnostics of the Sawtooth oscillation have ten- ded to emphasize the coincidence between magnetic surfaces and the contours of equal X-ray emissivity Because there is a detector array, one - dimensional images of SXR emissivity are obtained with having to resort to rotation models.

Ths method has been used to study the internal disrup- tions and m = 1 oscillation The reconstructed images in the

phase before a Sawtooth crash have shown the hot plasma core move gradually toward one side, this is considered that as the increasing m = 1 kink mode

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