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 (ne) 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 Ti is expected to be below 10% at ne = 5.0 × 1020 m−3 and Ti = 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 ne > 1.5 × 1021 m−3. The design considerations of the CTS diagnostic are described in this paper.