8-12 August 2016
Novosibirsk
Asia/Novosibirsk timezone
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Contribution Oral

Novosibirsk
Plasma-wall interaction

NOVEL ELECTRON BEAM BASED TEST FACILITY FOR OBSERVATION OF DYNAMICS OF TUNGSTEN ERROSION UNDER INTENSE ELM-LIKE HEAT LOADS

Speakers

  • Dr. Leonid VYACHESLAVOV

Primary authors

Co-authors

Content

L.N. Vyacheslavov$^{1,2}$, A.S. Arakcheev$^{1,2,3}$, A.V. Burdakov$^{1,2,3}$, I.V. Kandaurov$^{1,2}$, A.A. Kasatov$^{1,2}$, V.V. Kurkuchekov$^{1}$, V.A. Popov$^{1,2}$, A.A. Shoshin$^{1,2}$ , D.I. Skovorodin$^{1,2}$, Yu.A. Trunev$^{1}$, A.A.$~$Vasilyev$^{1,2}$

1 Budker Institute of Nuclear Physics of Siberian Branch Russian Academy of Sciences, vyachesl@gmail.com; vyachesl@inp.nsk.su

2 Novosibirsk State University

3 Novosibirsk State Technical University

Tungsten erosion is greatly increased under impact of intense transient heat loads corresponding to unmitigated ELM type I events and major disruptions in ITER. The enhanced erosion is associated with melt layer creation, its splashing and ejection of dust particles. In addition to the increase of erosion, tungsten dust particles can penetrate to the plasma core and greatly raise plasma radiation cooling, which harms plasma confinement. Dust accumulation in the ITER vessel leads to increase of tritium retention so the total dust amount stored in the vessel is strictly limited by radiation hazard requirements. Present tokamaks or specially worked out test facilities are still unable to completely reproduce conditions in the ITER divertor associated with transient heat loads. The novel test facility developed at the Budker Institute of Nuclear Physics in Novosibirsk is intended to simulate ELM-like heat loads without too high plasma pressure on the tungsten melt layer typical for QSPA plasma guns. It is especially designed for studies of dynamics of tungsten erosion. The facility is based on electron beam (70-90 keV, 40-80A) with nearly rectangular pulse of 0.1-0.3 ms duration for heating of the tungsten target. Good angular characteristics permit compressing the beam in converging magnetic field and delivering a heat load near 10 GW/m$^2$ on the target with an area of $sim$1 cm$^2$. The ablation plume created by the heat load of tungsten target emits only spectral lines of neutral and single ionized tungsten according to spectral measurements. Relatively weak WI and WII spectral lines in the near infrared (NIR) region above 865 nm permits imaging of the tungsten target in the NIR spectral range during process of it heating and cooling. Fast CCD cameras with minimal exposure time of 7 $mu$s are used for visualization of dynamics of target erosion by recording of 1.4 megapixel frames during a single heating pulse. These cameras are applied for observation of dynamics of tungsten target in the NIR as well as in in the light of 532 nm continuous laser during the heating process and after it. Additionally, tungsten microparticles ejected from the target are analyzed experimentally. Images of these particles are recorded by fast CCD cameras. Besides, we use scattering of light of continuous laser (532 nm, 0.8 W) for the observation of dust particles in the size range of 2-30 microns, emitted from the surface of tungsten under the influence of transient heat load.