A differentially pumped argon plasma in the linear plasma generator Magnum-PSI: gas flow and dynamics of the ionized fraction

Magnum-PSI is a linear plasma generator designed to reach the plasma–surface interaction (PSI) regime of ITER and nuclear fusion reactors beyond ITER. To reach this regime, the influx of cold neutrals from the source must be significantly lower than the plasma flux reaching the target. This is achieved by a differential pumping scheme, where the vacuum vessel is divided by skimmers into separate chambers which are individually pumped. The non-magnetized expansion of 5 Pa m3 s-1 (3 slm) argon in a low background pressure was studied in the differentially pumped vacuum vessel fitted with non-cooled flat skimmers. The behavior of the neutral component was studied with direct simulation Monte Carlo simulations and Rayleigh scattering measurements. Thomson scattering and double Langmuir probe measurements were performed on the ionized fraction. It was found that the electrons and neutral particles are not completely coupled in the shock front. The neutral fraction shows clear signs of invasion from hotter background gas, causing the average temperature and density to increase before the shock. This is also shown in the ionization ratio, which has been determined in front of and behind the first skimmer. This study helps us to understand the behavior of the gas flow in the machine and validates our modeling

Operational characteristics of the high flux plasma generator magnum-PSI

\u3cp\u3eIn Magnum-PSI (MAgnetized plasma Generator and NUMerical modeling for Plasma Surface Interactions), the high density, low temperature plasma of a wall stabilized dc cascaded arc is confined to a magnetized plasma beam by a quasi-steady state axial magnetic field up to 1.3 T. It aims at conditions that enable fundamental studies of plasma-surface interactions in the regime relevant for fusion reactors such as ITER: 10\u3csup\u3e23\u3c/sup\u3e-10\u3csup\u3e25\u3c/sup\u3e m \u3csup\u3e-2\u3c/sup\u3e s\u3csup\u3e-1\u3c/sup\u3e hydrogen plasma flux densities at 1-5 eV. To study the effects of transient heat loads on a plasma-facing surface, a high power pulsed magnetized arc discharge has been developed. Additionally, the target surface can be transiently heated with a pulsed laser system during plasma exposure. In this contribution, the current status, capabilities and performance of Magnum-PSI are presented.\u3c/p\u3

High-fluence and high-flux performance characteristics of the superconducting Magnum-PSI linear plasma facility

\u3cp\u3e The Magnum-PSI facility is unique in its ability to produce and even exceed the heat and particle fluxes expected in the divertor of a fusion reactor, combined with good access to the plasma-material interaction region for diagnostics and relatively easy sample manipulation. In addition, it is possible to study the effects of transient heat loads on a plasma-facing surface, similar to those expected during so called Edge Localized Modes. By virtue of a newly installed superconducting magnet, Magnum-PSI can now maintain these conditions for hours on end for truly long term tests of candidate plasma facing materials. The electron density and temperature in the plasma beam center as a function of different magnetic fields up to 1.6 T, gas flow and source current are determined: particle fluxes greater than 10 \u3csup\u3e25\u3c/sup\u3e m \u3csup\u3e−2\u3c/sup\u3e s \u3csup\u3e−1\u3c/sup\u3e and heat fluxes of up to 50 MW m \u3csup\u3e−2\u3c/sup\u3e are obtained. Linear regression and artificial neural network analysis have been used to gain insight in the general behavior of plasma conditions as a function of these machine settings. The plasma conditions during transient plasma heat loading have also been determined. These capabilities are now being exploited to reach fluence of up to 10 \u3csup\u3e30\u3c/sup\u3e particles m \u3csup\u3e−2\u3c/sup\u3e at ITER-relevant conditions, equivalent to a significant fraction of the divertor service lifetime for the first time. \u3c/p\u3

Operational characteristics of the superconducting high flux plasma generator Magnum-PSI

\u3cp\u3eThe interaction of intense plasma impacting on the wall of a fusion reactor is an area of high and increasing importance in the development of electricity production from nuclear fusion. In the Magnum-PSI linear device, an axial magnetic field confines a high density, low temperature plasma produced by a wall stabilized DC cascaded arc into an intense magnetized plasma beam directed onto a target. The experiment has shown its capability to reach conditions that enable fundamental studies of plasma-surface interactions in the regime relevant for fusion reactors such as ITER: 10\u3csup\u3e23\u3c/sup\u3e–10\u3csup\u3e25\u3c/sup\u3e m\u3csup\u3e−2\u3c/sup\u3es\u3csup\u3e−1\u3c/sup\u3e hydrogen plasma flux densities at 1–5 eV for tens of seconds by using conventional electromagnets. Recently the machine was upgraded with a superconducting magnet, enabling steady-state magnetic fields up to 2.5 T, expanding the operational space to high fluence capabilities for the first time. Also the diagnostic suite has been expanded by a new 4-channel resistive bolometer array and ion beam analysis techniques for surface analysis after plasma exposure of the target. A novel collective Thomson scattering system has been developed and will be implemented on Magnum-PSI. In this contribution, the current status, capabilities and performance of Magnum-PSI are presented.\u3c/p\u3