The Magnum-PSI facility is available for plasma-material interaction studies. • Magnum-PSI is capable to reach relevant plasma parameters for the ITER divertor. • Particle fluxes over 10 25 m-2 s-1 and heat fluxes of up to 50 MWm-2 are obtained. • Particle fluences of up to 10 30 particles m-2 have been achieved. • Linear regression and artificial neural network analysis have been applied.

Tin (Sn) is an attractive option for a liquid metal wall material for future fusion reactors. Control of tritium inventory is key for the successful operation of these reactors, but little data exists up until now on hydrogen isotope retention in Sn. Free surface Sn targets and Sn-based capillary porous structure targets were exposed to deuterium (D) plasma in nano-PSI and magnum-PSI respectively. The retained D inventory was determined using the methods of thermal desorption spectroscopy and nuclear reaction analysis. The retention dependence is somewhat complex due to the mixed composition of the exposed samples as well as their liquid nature. The D retained in both types of Sn targets was found to increase with increasing D plasma fluence. For free surface liquid Sn targets, both thermal desorption spectroscopy and nuclear reaction analysis measurements showed a negative relationship between D retention and sample temperature. For capillary porous structure Sn targets, D retained in the top layer measured by nuclear reaction analysis decreased with temperature while the total D retained measured by thermal desorption spectroscopy remained approximately constant. By extracting pure Sn pieces from the targets it was found that the amount of D retained in pure Sn was much lower than that in the whole Sn-based targets and was estimated to be about 10 −7 -10 −4 D/Sn. D retained at the Sn-wall interface was found to dominate the total amount of D retained in the whole sample and observed cavities between deposited Sn droplets and the wall are the leading candidates responsible for this. Cavity formation is proposed to be the main retention mechanism for D in liquid Sn targets, although enhanced solubility leading to supersaturation under a D plasma environment is mainly responsible for the observed higher D retention in pure Sn compared with normal solubility under D gas. When compared with tungsten, D in Sn samples is of the same order of magnitude at temperatures below 300 °C, but at higher temperatures at least one to two orders of magnitude higher, most likely due to D trapped in cavities.

An advanced Thomson scattering system has been built for a linear plasma generator for plasma surface interaction studies. The Thomson scattering system is based on a Nd:YAG laser operating at the second harmonic and a detection branch featuring a high etendue (f /3) transmission grating spectrometer equipped with an intensified charged coupled device camera. The system is able to measure electron density (n e ) and temperature (T e ) profiles close to the output of the plasma source and, at a distance of 1.25 m, just in front of a target. The detection system enables to measure 50 spatial channels of about 2 mm each, along a laser chord of 95 mm. By summing a total of 30 laser pulses (0.6 J, 10 Hz), an observational error of 3% in n e and 6% in T e (at n e = 9.4 × 10 18 m −3 ) can be obtained. Single pulse Thomson scattering measurements can be performed with the same accuracy for n e > 2.8 × 10 20 m −3 . The minimum measurable density and temperature are n e < 1 × 10 17 m −3and T e < 0.07 eV, respectively. In addition, using the Rayleigh peak, superimposed on the Thomson scattered spectrum, the neutral density (n 0 ) of the plasma can be measured with an accuracy of 25% (at n 0 = 1 × 10 20 m −3 ). In this report, the performance of the Thomson scattering system will be shown along with unprecedented accurate Thomson-Rayleigh scattering measurements on a low-temperature argon plasma expansion into a low-pressure background.

No abstract

The linear plasma generator Magnum-PSI was designed for the study of plasma-surface interactions under relevant conditions of fusion devices. A key factor for such studies is the knowledge of a set of parameters that characterize the plasma interacting with the solid surface. This paper reports on the electrical diagnosis of the plasma beam in Magnum-PSI using a multi-probe system consisting of 64 probes arranged in a 2D square matrix. Cross-section distributions of floating potential and ion current intensity were registered for a hydrogen plasma beam under various discharge currents (80-175 A) and magnetic field strengths (0.47-1.41 T in the middle of the coils). Probe measurements revealed a high level of flexibility of plasma beam parameters with respect to the operating conditions.