Bayesian inference of plasma parameters from collective Thomson scattering technique on a gas-puff near stagnation

Abstract

AbstractThe Collective Thomson scattering technique has been implemented to study the stagnation of a single liner gas-puff. The plasma parameters are determined by theoretically modelling the scattering form factor in combination with Bayesian inference to provide the set of the most probable parameters that describe the experimental data. Analysis of the data reveal that incoming flows are able to interpenetrate partially. Estimation of the mean free path shows a gradual transition from a weakly collisional to a collisional regime as the plasma gets to the axis. Furthermore, we find that the ion energy at $$\mathrm{r}=2.5\,\mathrm{mm}$$ r = 2.5 mm is $${13.6}_{-0.9}^{+1.0}\,\mathrm{keV}$$ 13.6 - 0.9 + 1.0 keV and is mostly kinetic in nature and represents $${98}_{-9}^{+10} \%$$ 98 - 9 + 10 % of the total energy. This kinetic energy is far greater than the value on axis of $${3.7}_{-0.5}^{+0.4}\,\mathrm{keV}$$ 3.7 - 0.5 + 0.4 keV which is $${84}_{-14}^{+15} \%$$ 84 - 14 + 15 % of the total energy. Energy transfer to the electrons and radiation losses are found to be negligible by this time. A possible explanation for this energy imbalance is the presence of an azimuthal magnetic field larger than $$\sim 4.7\,\mathrm{T}$$ ∼ 4.7 T that deflect the ions vertically. The uncertainties quoted represent 68% credible intervals.