On a heating mechanism for cold hydrogen and deuterium atoms produced at the edge of a tokamak plasma

Abstract

Spectroscopic measurements of the D α and H α line profiles emitted within the edge region of a tokamak plasma, have revealed the existence of a cold central component, broadened mainly by the Zeeman effect arising from the confining magnetic field. Evaluation of the Doppler broadening suggests that the cold component is probably produced by electron impact-induced molecular dissociation, dissociative excitation being one of the few mechanisms which can explain the formation of atoms of kinetic energy around 0.2 eV against a background of comparatively hot electrons and ions. Further analysis of these line profiles, observed along different directions in the equatorial plane and under various tokamak discharge conditions, reveals, in addition to this effective 'cold temperature', an effective 'lukewarm temperature', which we explain in terms of an appreciable collisional heating mechanism. Estimates of the rates for ion-induced dipole and ioninduced quadrupole collisions with excited atoms, yield values of the correct order of magnitude for this observed 'lukewarm temperature'. In addition, measurements of Balmer-α line profiles, radiated from a gas discharge in a magnetic field of similar magnitude, are analysed and their shapes compared with those from the tokamak plasma.

Polarization resolved Hα spectra from the large helical device: Emission location, temperature, and inward flux of neutral hydrogen

“…͑18 and 30 allowed, 2 and 4 ⌬J forbidden͒. [5][6][7] The corresponding perturbed line strengths are calculated according to the method described in Ref. 23.…”

“…1,2 Its quantitative estimate is required for the purpose of evaluating the particle fueling rate and controling the recycling neutrals in the long pulse discharge operation. 3,4 Information on neutral atoms has been obtained from spectroscopic measurements of the Zeeman ͑Paschen-Back͒ split profiles of lines emitted from the divertor or the periphery region in TEXTOR ͑Tokamak-Experiment for Technology Oriented Research͒, [5][6][7][8] JT-60U ͑Japan atomic energy research institute Tokamak-60 Upgrade͒, 9,10 Alcator C-Mod, [11][12][13] Doublet III-D, [14][15][16] ASDEX-U ͑Axially Symmetric Divertor Experiment Upgrade͒, 17,18 Tore Supra, 19,20 TRIAM-1M ͑Torus of Research Institute for Applied Mechanics͒ ͑Ref. 21͒ for hydrogen/deuterium, and in LHD ͑Large Helical Device͒ for helium.…”

Effect of argon additive on H− density and temperature in volume negative ion source

“…͑2͒ the H Ϫ on their way to center can be cooled by excited argon atoms by the mechanism analogous to the one described in Ref. 8. The authors of Ref.…”

“…The authors of Ref. 8 showed that the heating of excited (nϭ3) hydrogen atoms by a hot deuteron background is ϳ10 times more effective than the heating of the atoms in ground state. In other words, the heat transfer between an excited atom and a hot background is much more effective than for the atom in ground state.…”

Influence of non-local thermodynamic equilibrium and Zeeman effects on magnetic equilibrium reconstruction using spectral motional Stark effect diagnostic

“…So for instance, it is an established fact that the Zeeman effect, or more precisely the Paschen-Back effect, dominates the fine-structure splitting of the Balmer-α line emission at the plasma edge of fusion devices 27 . In case of Maxwellian distribution function of atoms every magnetic component of the spectral line is described using a Doppler profile taking into account the different source of excited atoms 27,28 . In the case of MSE measurements the emissions takes place predominantly in the static crossed electric and magnetic fields, being a subject of studies for high Rydberg states 26,29 .…”