Reaction processes of molecular activated recombination leading to detachment of divertor simulation plasma in GAMMA 10/PDX

Abstract

Reaction processes of molecular activated recombination (MAR) have been investigated using end loss plasma in GAMMA 10/PDX. A tungsten V-shaped target in a divertor simulation experimental module (D-module) is exposed to the end loss plasma. The additional hydrogen gas is supplied into the D-module, leading to the plasma detachment by MAR. The vibrational temperature (Tvib) of H2(X1Σg+) increased up to ∼10,000 K with increasing the hydrogen gas pressure, and the Ha line intensity (IHa) continued to increase even though the electron density decreased after the electron density rollover. The increase in Tvib should be caused mainly by the increase in the number of vibrationally excited molecules which are produced by the molecular ion conversion process in MAR. The continuous increase in IHa is attributed to the dissociative attachment in MAR. When the hydrogen gas pressure was more than 12 Pa, Balmer emissions from highly excited atom suddenly increased and a population inversion with nH(n = 5) larger than nH (n = 4) was observed although Tvib became rather low (∼2,000 K). The formation of population inversion and increase in highly excited Balmer line intensity are considered to be caused by the reaction of mutual neutralization between molecular ion and negative ion, since the cross section of H(n = 5) production is the largest in the reaction. The negative ion should be produced by the resonant ionization process between H(2s), since the negative ion production by the dissociative attachment reaction cannot be expected due to low Tvib. Keywords: GAMMA 10/PDX, Divertor-simulation experiment, Plasma detachment, Molecular activated recombination, Molecular vibrational temperature, Population inversion