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

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.