Electron heating in collisional shocks

Thomson scattering of ruby laser light at 90° was used to obtain electron temperature and density profiles for plasmas produced by strong collisional shock waves. Transverse (B1 ≠ 0) shocks of speed 3−25 cm/μsec in 50−100 mTorr deuterium were studied. Plasma created by reflecting a strong shock from a dielectric wall was also studied. It is found, in agreement with theoretical expectations, that the electron temperature (10−30 eV) is much lower than the ion temperature (100−500 eV) immediately after shock heating of the plasma. Temperature equilibration between ions and electrons, however, does not take place in the times of observation (2−4 μsec). It is shown that initial electron heating in the plasma is caused primarily by Ohmic dissipation of currents in the shock structure. For pure gas ionizing shocks (B1 = 0), the measured electron temperature is in good agreement with theory.