Spectroscopic Survey of Self-Compressed Electron Beam Produced Plasmas

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Abstract
The application of 1500‐J self‐focused 1.5‐MeV electron pulses of 25‐nsec duration to production of energetic plasmas has been studied by time resolved emission spectroscopy. In Ar and He at pressures of from 0.15 to 1.5 Torr a high‐energy plasma is formed which continues radiating for up to 500 μsec. Under drifting electron beam conditions the He plasma appears to be doubly ionized. Measurements of excitation temperature from the relative intensities of neutral He lines fit an equilibrium model 2 μsec after the electron passage and indicate a temperature of 10 000°K falling to 5000°K by 400 μsec. A measurement of the width of the He(I)4921‐Å line indicates an electron density of 1.2×1015 cm−3 at 70 μsec, falling to 3.4×1014 cm−3 by 200 μsec. Studies of an Ar plasma have shown the emission at peak excitation to be in the Ar(IV) spectrum. When the beam exceeds its critical current and is stopped by its own magnetic compression, in Ar, the quenching of the Ar(IV) emission indicates that the plasma reaches an energy which is high compared to the 145 eV necessary to four times ionize and remains above this level for 8 μsec.

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