An electromagnetic shock tube of new design was used to produce highly ionized helium and argon plasmas. The electron number density ne was determined spectroscopically from line broadening and line shifts, while the temperature kT was found from the relative intensities of HeI and HeII lines and of AII and AIII lines, respectively. The spectroscopic values were compared with predictions from shock theory. It was assumed that the shock-heated plasma reached thermal equilibrium before the first spectroscopic measurements were made (i.e. in a time of order 1 μsec after the onset of luminosity). For helium, with a shock speed of 4.8 cm/μsec and an initial particle density of 1.2 × 1016 cm−3, the spectroscopic temperature (3.7 ev) is in good agreement with the value expected from shock theory (3.8 ev). Line broadening indicates ne = 5 × 1017 cm−3, which is much higher than the shock theory value (1.5 × 1017 cm−3). For argon, with a shock speed of 1.9 cm/μsec and an initial particle density 2.1 × 1016 cm−3, the electron number densities (8, 6 × 1017 cm−3) agree within the experimental errors, but the spectroscopic temperature (2.5 ev) is substantially lower than the shock temperature (3.3 ev).

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