Collective Thomson scattering for ion temperature and velocity measurements on Magnum-PSI: a feasibility study

Abstract

In this paper, collective Thomson scattering (CTS) is proposed for measuring the ion temperature and axial/rotational velocity of a plasma jet in the linear plasma generator Magnum-PSI, where ITER-relevant plasma conditions will be simulated. CTS is feasible at Magnum-PSI, because high electron densities (n e ) can be obtained at low electron temperatures, which means that small Debye lengths are achievable. Calculations show that CTS is possible at the fundamental wavelength (1064 nm) of a Nd : YAG laser. At this wavelength, a scattering angle of 17-35 • is sufficiently small to achieve a scattering parameter 1 < α < 3. The estimated observational error in the ion temperature T i is expected to be below 10% at n e = 5.0 × 10 20 m −3 and T i = 2.5 eV, for a scattering volume with a length of 2.4 mm using an accumulated scattering energy of 12 J (10 pulses of 1.2 J at 10 Hz). The accuracy in the determination of axial velocity is expected to be about 15%. Setting the required accuracy for ion temperature measurements at 15%, single pulse CTS is expected to be feasible for n e > 1.5 × 10 21 m −3 . The design considerations of the CTS diagnostic are described in this paper.

B2.5-Eunomia simulations of Magnum-PSI detachment experiments: I. Quantitative comparisons with experimental measurements

“…Additional diagnostics can further provide input for B2.5-Eunomia in the future and thus can limit the necessary adjustment or assumptions, and subsequently improved the discrepancies found in this paper. One example is the usage of Collective TS [30] to measure the plasma flow velocity near the source, hence eliminating the need to use homogeneous Neumann boundary condition for the momentum equation. Another important example is the ability to simultaneously measure the electron density and temperature near the source and target, thus the effect of significant gas pressure addition to the source plasma parameters can be directly observed.…”

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.…”

Collective Thomson scattering system for determination of ion properties in a high flux plasma beam

“…16 The scale difference in velocity between ions and electrons is large, and the Salpeter approximation 12,13 can be applied to describe the TS form factor S(k,x) of the observed scattering spectrum as the sum of two separate contributions…”