Plasma radiation studies in Magnum-PSI using resistive bolometry

Abstract

Both the physics of divertor detachment and vapour shielding are characterized by a relatively large amount of radiation produced in the divertor. The linear plasma generator Magnum-PSI is well-suited to study such processes due to its ITER-divertor relevant plasma conditions, simplified geometry and diagnostic accessibility. The need the quantify the plasma radiated power close to the target surface motivated the development of a 4-channel resistive bolometer for Magnum-PSI, and marks the first deployment of such a diagnostic on a linear device. An axially resolved measurement of plasma emission at arbitrary distances from the target surface is now possible. The radial position of the detector can be varied, hereby viewing the full diameter of the plasma column or down to a central region. The overall system design is discussed alongside a comparison of the spectral absorbance of carbon-coated versus non-coated Au/Al bolometer sensors. Despite low electron temperatures of the plasma (1-5 eV), the observed power densities were found to be 10-37 times the sensor noise floor of ∼0.1 W m −2. A synthetic diagnostic based on collisional radiative model calculations from ADAS could well match observed values from H and Ne plasmas while the measured values for Ar and He were more difficult to reproduce. The obtained findings allow for approximate power balance calculations in Magnum-PSI indicating that maximally ∼47 % and ∼14 % of the total power is lost by radiation in the cases of Ar and Ne/He respectively. The results demonstrate the feasibility of resistive bolometry in low temperature high density plasma regions and on long timescales (>450 s) which is of relevance to ITER. Due to long-term temperature drifts which were observed, a planned upgrade involves the installation of a shutter and FPGAbased electronics for increased accuracy.

Studying divertor relevant plasmas in the Pilot-PSI linear plasma device: experiments versus modelling

“…Further possibilities to study plasmas relevant to detachment are offered by the Magnum-PSI linear plasma device, with a better diagnostic coverage. Target calorimetry and a newly installed bolometric diagnostic [49] could shed more light on studies of the power balance, while a collective Thomson scattering diagnostic [50] (under development) could give axial velocity information.…”

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

“…Recently several new diagnostics have been installed. The ion temperature and axial/rotational velocity of the plasma beam can be measured with Collective Thomson scattering (CTS) [10], while a 4-channel resistive foil bolometer is now available for quantitative measurement of the plasma radiated power [11]. Information on the composition of the plasma in front of the target is obtained from single channel survey optical emission spectroscopy (Avantes AvaSpec-2048-USM2-RM) covering the range 299-950 nm, while spatially resolved spectroscopy can be performed with the aid of a 1 m Jarrell-Ash spectrometer with a flexible spectral range 175 nm wide.…”

Growth mechanism of subsurface hydrogen cavities in tungsten exposed to low-energy high-flux hydrogen plasma

“…Polycrystalline W (99.99 wt% purity) was supplied by Plansee Gruppe, Austria and heat-treated under vacuum at 1873 K for 2 h after electro-polishing. The samples were exposed to a high-flux H plasma beam in the Magnum-PSI linear plasma device (DIFFER, Eindhoven, the Netherlands) for steady-state exposure in ITER-relevant conditions [26][27][28]. The electron temperature and density were measured by Thomson scattering.…”