Speaker
Mr
Igor Poznyak
(SRC RF TRINITI)
Description
Tungsten is foreseen presently as the main candidate armour material for the divertor targets in ITER. During tokamak transient processes, such as Edge Localized Modes (ELMs) and mitigated disruptions, the armour material is exposed to intense streams of hot plasma that can cause a severe erosion of the exposed material. Erosion restricts lifetime of the divertor components and leads to production of impurities, which can penetrate into the hot fusion plasma causing its radiative cooling [1]. The properties of the eroded materials are critically important to analysis of tokamak-reactor.
The plasma heat loads, which are expected in ITER, are not achieved in the existing tokamak machines. Erosion of candidate armour materials is studied in the laboratory experiments by use of other devices such as plasma guns and electron beams, which are capable to simulate, at least in part, the loading condition of interest. In the present work, the tungsten targets have been tested by intense plasma streams at the pulsed plasma gun MK-200UG [2]. The targets were exposed to the plasma heat fluxes relevant to ITER ELMs and mitigated disruptions.
The targets were irradiated by hot magnetized hydrogen plasma streams with impact ion energy Ei = 2 - 3 keV, pulse duration t = 0.05 ms and energy density varying in the range q = 0.1 – 1 MJ/m$^2$. The plasma stream diameter is d = 6 – 8 cm and the magnetic field is B = 0.5 – 2 T. Primary attention has been focused on investigation of impurity formation due to tungsten evaporation and on investigation of impurity transport along the magnetic field lines from the irradiated target. Optical and EUV spectroscopy was applied to determine the chemical composition and ionization state of near-surface plasma. A pinhole camera equipped with absolutely calibrated AXUV photodiodes was used to study the dynamics of tungsten plasma. A foil bolometer was used to measure the absolute radiation loss of tungsten impurity in hydrogen plasma.
The following points were studied:
- energy threshold for tungsten evaporation;
- velocity of tungsten impurities;
- effective thickness of the near-surface plasma layer;
- tungsten plasma radiation as a function of distance to the target surface.
The obtained spectral data were compared with the numerical calculations [3].
References:
1. Pitts R.A., Carpentier S., Escourbiac F. et al. // J. Nucl. Mater., 2013, v.438, p.S48-S56.
2. Arkhipov N.I., Bakhtin V.P, Kurkin S.M. et al. // J. Nucl Mater. 1996, v.233-237, p.767-770.
3. Pestchanyi S., Arkhipov N., Landman I. // J. Nucl Mater., 2013, v.438, p.S459-S462.
Primary author
Mr
Igor Poznyak
(SRC RF TRINITI)
Co-authors
Mr
Dmitrii Toporkov
(SRC RF TRINITI, Troitsk, Moscow)
Mr
Nikolai Arkhipov
(Project Center ITER, Moscow)
Mr
Sergei Karelov
(SRC RF TRINITI, Moscow, Troitsk)
Mr
Valerii Safronov
(Project Center ITER, Moscow)
