The plasma volume recombination associated with vibrationally excited hydrogen molecules, that is, Molecular Assisted Recombination (MAR) is important in the divertor plasma because the recombination process is expected to lead to an enhancement of the reduction of ion particle flux[1]. From results of the probe-assisted laser photodetachment method, Langmuir probe, the visible and VUV spectra (Lyman-band system: B¹Σ_u⁺→X¹Σ_g⁺) and the mass-analysis, spatial structure of MAR with vibrational hydrogen molecules has been observed in the linear plasma simulator, TPD-SheetIV (Test Plasma produced by Direct current for Sheet plasma IV). A small amount of hydrogen gas puffed into a hydrogen plasma reduced the heat flux to the target, while the radiative and three-body recombination processes disappeared[2]. In this range of hydrogen pressure (<4mTorr), the vibrationally excited hydrogen molecules are produced by the collision of hydrogen with hot electron (T_e=10-15 eV) in the central region and move to the circumferential region of the sheet plasma. Therefore, the negative ions of hydrogen atoms are produced by the dissociative electron attachment to the vibrationally excited hydrogen molecules at the circumferential region of plasma with cold electron (T_e = 2-3 eV). After that, these the negative ions of hydrogen atoms recombine with hydrogen ion (mutual neutralization) over the range of low hydrogen pressure (2-4mTorr). It is also shown from the results of the mass-analysis (H⁺, H₂⁺, H₃⁺) that other recombination (dissociative recombination) is taking place in the central region of the sheet plasma over the range of hydrogen pressure (<4mTorr).

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