RESEARCH ON VOLTAGE GRADIENTS FROM ELECTRONACOUSTICAL WAVES.
Final technical rept.,
AEROJET-GENERAL NUCLEONICS SAN RAMON CALIF
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Experimental work was conducted on an energetic argonfed hollow cathode arc. The arc column had a diameter of 1.27 cm and a length of 60 cm. Microwave interferometer measurements at 1.20 x 10 to the 11th power cps gave a plasma density of 1.8 x 10 to the 14th power electronscu cm, and spectroscopic line intensity measurements yielded an electron temperature of 1.1 ev. The voltage gradient along the arc was less than 0.1 vcm. Since a voltage gradient of 10 to 20 vcm would be required to produce current densities of the observed magnitude in a plasma with an electron temperature of 1.1 ev by ordinary conduction, it is believed that the arc current is carried by electrons which are trapped in electron plasma waves and accelerated to high velocity by the waves. Attempts to detect radiation emitted by the plasma at the electron plasma frequency gave inconclusive results. Strong signals were detected at frequencies below 500 kc. The arc column was found to radiate as much as 73 of the input power in the vacuum ultraviolet region between 400 A and 1000 A, with a large fraction concentrated between 430 A and 540 A. Many lines of singly through quadruply ionized argon were identified. Doubly ionized argon appeared to be the most abundant species.