Speaker
Alexander Vasilyev
(Budker Institute of Nuclear Physics, Novosibirsk State University)
Description
Plasma-facing components undergo severe transient heat loads (up to 10 MJ/m$^2$) in the reactor-size tokamaks caused by the various plasma instabilities (type I ELMs, VDEs, etc.) and disruptions. Such conditions lead to erosion of the divertor material (cracks, melting, dust formation, droplet ejection, etc.) and can induce mechanical destruction of the tungsten plates and plasma cooling due to the radiation losses.
Specialized test facility with a novel long-pulse electron beam injector with the plasma emitter was developed in BINP SB RAS for simulating ITER-relevant ELM-like heat loads. The beam generator applies acceleration voltage up to 100 kV to electrons with a total current 40 – 80 A and a pulse duration 0.1 – 0.3 ms. After compression in the converging magnetic field it delivers heat load up to 10 GW/m$^2$ on the target with an area of $\sim$1 cm$^2$. Heating by the electron beam creates a relatively low plasma radiation intensity (comparing with QSPAs), that allows a direct target imaging during the heat load.
A set of in-situ optical target surface diagnostics is used for research of the target surface modification. The high-speed cameras gather target surface thermal radiation in near infrared range. Surface temperature field is recovered by an absolute calibration by a ribbon tungsten lamp. One dimensional thermal radiation distribution during the beam impact is obtained by the fiber optics. Lightening with a continuous wave laser light (Nd:YAG, 2$\omega$) is used for an observation of melted layer dynamics. The target surface was pictured in the scattered cw laser light by camera with a narrowband interference filter.
Research on crack formation and melted layer motion with the heat loads near and above melting threshold was carried out on this facility. Surface of the tungsten target was imaged during and after (more than 5ms) electron beam exposure. Detached parts of the target and crack edges were pictured through their higher thermal radiation in comparison with surrounding surface. In addition, local hot spots (few mm$^2$) were found after more than 5 ms heating ending. Specific crack net formation was observed after the first pulse and developed with subsequent exposures. Post-mortem analysis of damaged surface included scanning electron microscopy and standard cross-section cutting procedure. Matching of the NIR surface pictures and SEM and cross-section revealed connection of the horizontal crack propagation and the local hot areas, that can be explained with suppressed thermal conductivity. Motion of the melted layer was found through comparison of serial pictures of the target surface under the heat load far above melting threshold.
Primary author
Alexander Vasilyev
(Budker Institute of Nuclear Physics, Novosibirsk State University)
Co-authors
Dr
Aleksey Arakcheev
(Budker Institute of Nuclear Physics)
Prof.
Alexander Burdakov
(Budker Institute of Nuclear Physics)
Mr
Alexandr Kasatov
(Budker Institute of Nuclear Physics)
Dr
Andrey Shoshin
(Budker Institute of Nuclear Physics)
Dr
Dmitriy Skovorodin
(Budker Institute of Nuclear Physics)
Mr
Igor Kandaurov
(Budker Institute of Nuclear Physics)
Dr
Leonid Vyacheslavov
(Budker Institute of Nuclear Physics)
Mr
Victor Kurkuchekov
(Budker Institute of Nuclear Physics)
Mr
Vladimir Popov
(Budker Institute of Nuclear Physics)
Mr
Yuriy Trunev
(Budker Institute of Nuclear Physics)
Peer reviewing
Paper
Paper files:
- Observation_of_the_tungsten_surface_damage_under_ITER-relevant_transient_heat_loads_during_and_after_electron_beam_pulse;_AIP_Conf._Proc.;_Vasilyev_et_al._postreview.pdf
- Observation_of_the_tungsten_surface_damage_under_ITER-relevant_transient_heat_loads_during_and_after_electron_beam_pulse;_AIP_Conf._Proc.;_Vasilyev_et_al._postreview.docx
- Observation_of_the_tungsten_surface_damage_under_ITER-relevant_transient_heat_loads_during_and_after_electron_beam_pulse;_AIP_Conf._Proc.;_Vasilyev_et_al._postreview.pdf
