[en] We report on the generation of high transient heat and particle fluxes in a linear plasma device by pulsed operation of the plasma source. A capacitor bank is discharged into the source to transiently increase the discharge current up to 1.7 kA, allowing peak densities and temperature of 70x10²⁰ m^-3 and 6 eV corresponding to a surface power density of about 400 MW m^-2.

[en] Full text: Edge Localized Modes (ELMs) in ITER will lead to material erosion, cracking, melting and vaporization. During an ELM, the divertor surfaces are submitted to both the steady state detached divertor plasma and the intense heat and particle fluxes during ELMs. Such a situation will lead to synergistic effects which might strongly affect the material damage threshold. In this contribution we describe a new experimental setup for ELM simulation experiments with relevant steady-state plasma conditions and transient heat/particle source. The Pilot-PSI linear device produces plasma parameters relevant to the study of plasma-surface interactions in the ITER divertor. In parallel to the DC power supply, the plasma source is also connected to a capacitor bank (5 kV, 8.4 mF, 100 kJ) which is discharged in the plasma source to create a transient increase of the discharge current. The pulse duration is about 1 ms. This allows the superimposition of a transient heat and particle pulse to the steady-state plasma. The plasma parameters are measured by Thomson scattering and the sample temperature during the pulse is monitored by a fast infrared camera. The plasma source can be operated in pulsed mode in a variety of gases (Ar, H, He, N) as well as with mixed gases. So far, discharge currents of up to 11.6 kA have been achieved, which represents a peak power in the plasma source of about 5 MW. The highest plasma density of 1.5 x 10²² m^-3 and temperature of 4.5 eV leads to a surface peak heat flux of 0.9 GW·m^-2. The temperature rise time is in the range 300 - 500 μs, comparable to that observed during Type-I ELMs in JET. With higher gas flow, it is anticipated that peak heat fluxes in the range 1 - 3 GW·m^-2 will be reached. Exposure of tungsten targets to hydrogen plasma with transient revealed an abrupt increase of the plasma density after the pulse at the location of the TS system (17 mm from the target). The influence of such heat pulses on the deuterium retention in tungsten will be described. In addition, the pulsed plasma source has been used to assess the effect of transient heat/particle pulses on the growth of helium-induced nanostructure and characterize the generated dust. (author)

[en] A high-power edge-localized mode (ELM) striking onto divertor components presents one of the strongest lifetime and performance challenges for plasma facing components in future fusion reactors. A high-repetition-rate ELM replication system has been constructed and was commissioned at the Magnum-PSI linear device to investigate the synergy between steady state plasma exposure and the large increase in heat and particle flux to the plasma facing surface during repeated ELM transients in conditions aiming to mimic as closely as possible those in the ITER divertor. This system is capable of increasing the electron density and temperature from ∼1 × 10²⁰ m⁻³ to ∼1 × 10²¹ m⁻³ and from 1 to 5 eV respectively, leading to a heat flux increase at the surface to ∼130 MW m⁻². By combining Thomson scattering measurements with heat fluxes determined using the THEODOR code, the sheath heat transmission factor during the pulses was determined to be ≈7.7, in agreement with sheath theory. The heat flux is found to be linearly dependent upon the strength of the magnetic field at the target position, and, by adapting the system to Pilot-PSI, tests at 1.6 T showed heat fluxes of more than 600 MW m⁻². This gives confidence that with the installation of a 2.5 T superconducting magnetic solenoid at Magnum-PSI the heat flux will reach the ITER-relevant gigawatt per square metre heat flux regime. (paper)

[en] In this paper we report on the generation of high transient heat and particle fluxes in Pilot-PSI. A capacitor bank (8400 μF, 37.8 kJ) is coupled to the plasma source to superimpose the pulsed plasma on the top of steady-state plasma beam. Discharge currents up to 11.6 kA were reached corresponding to an input power in the source of 4.5 MW. By varying the discharge current and the gas flow, electron density and temperature during the pulse were varied in the range 40-120 x 10²⁰ m^-3, and 2-6 eV, respectively. The current rise time is about 300-500 μs while the pulse duration is 1-1.5 ms. Thermal response of a tungsten target was monitored by fast infrared camera. The temperature rise time is about 0.5 ms and the heat flux to the target was up to 1 GW/m².

[en] The FOM-Institute for Plasma Physics Rijnhuizen is constructing Magnum-PSI; a magnetized (3 T), steady-state, large area (80 cm²) high-flux (up to 10²⁴ H⁺ ions m^-2 s^-1) plasma generator. Magnum-PSI will be a highly accessible laboratory experiment in which the interaction of magnetized plasma with different surfaces can be studied. This experiment will provide new insights in the complex physics and chemistry that will occur in the divertor region of the future experimental fusion reactor ITER. Here, extremely high power and particle flux densities are predicted at relatively low plasma temperatures. Magnum-PSI will be able to simulate these detached ITER divertor conditions in detail. In addition, conditions can be varied over a wide range, such as different target materials, plasma temperatures, beam diameters, particle fluxes, inclination angles of target, background pressures, magnetic fields, etc., making Magnum-PSI an excellent test bed for high heat flux components of future fusion reactors. The design phase of the Magnum-PSI device has been completed. The construction and assembly phase of the device is in progress. In this contribution, we will present the design and construction of the Magnum-PSI experiment. The status of the vacuum system, the 3 T superconducting magnet, the plasma source, the target plate and manipulator, and additional plasma heating will be presented. The plasma and surface diagnostics that will be used in the Magnum-PSI experiment will be introduced.