A. Takayama

D. Kamata

H. Fujiwara

H. Kambe

H. Nakamura

K. Sawada

M. Goto

N. Ezumi

S. Nakauchi

T. Fujimoto

Y. Tomita

National Institute for Fusion Science (NIFS-Repository)

§42. Effect of Vibrational Excitation of Molecular Hydrogen on Hydrogen Recycling in LHD Edge Plasma Sawada, K., Nakauchi, S., Kambe, H., Fujiwara, H., Kamata, D. (Shinshu Univ.), Ezumi, N. (Nagano National College of Technology), Fujimoto, T. (Kyoto Univ.), Goto, M., Takayama, A., Tomita, Y., Nakamura, H. In divertor study, one of the key issues is the molec-ular assisted recombination (MAR), which was first pro-posed by Krashenninikov et al. l ). They found that the MAR may enhance the plasma recombination in the high-er temperature region where the conventional collisioanl-radaitive recombination becomes ineffective. The MAR consists of two series of processes. The first starts with the charge exchange between H2 and H+ (eX MAR): H2 (X l L::, v) + H+ ~ Hi (X2 L::, v') + e ~ Hi (X 2 L::, v") + e ~ H(p) ~ H(q) Hi (X2 L::, v') + H(l) Hi (X 2 L::, v") + e H(l) + H(p) ~ H(l) where p and q denote the principle quantum number of atomic hydrogen. The second is a process which starts with the dissociative attachment (DA MAR): H2 (X l L::,v)+e ~ H- +H+ ~ H(2or3) ~ H(q) H- + H(l) H(l) + H(2or3) ~ H(l) The MAR rate coefficient has been calculated in Ref.l as a function of the electron density and electron tem-perature. Unfortunately, however, in their original pa-pers, they have not investigated the dependence of MAR on the initial vibrational excitation of molecular hydro-gen. We have independently calculated it using our own collisional-radiative model with recent atomic and molec-ular data. Figure 1 shows an example of the MAR rate coefficients for various initial vibrational level v. The vi-brational excited molecules have higher rate coefficients, sometimes by more than an order. This strong v depen-dence stems mainly from the v dependence of the (eXl) and (DAl) cross sections. The goal of our study is to include the recent atom-ic and molecular data especially concerning the MAR in the neutral particle transport code EIRENE and to analyze the LHD plasmas by using the code. As one step to the goal, we have built a rf plasma source at shinshu university which can be used to verify the code before applying it to the LHD. We have produced hy-drogen plasmas (Prj ::; 2.0kW, f = l3.56MHz) with ne = 1010 - 1012cm-3, Te = 2.0 - 6.0eV, where atomic emission lines of Balmer Q, {3", 0, and molecular band (d3IIu-a3L:; fulcher transition) have been observed. 252 o 0 0 o IJ o o C [] Hz(v) + H' -> Hz' + H H2' +e->H+H' H -> H o 0 0 o 0 0 0 c 0 C H2(v) + e -> H- + H H- + H' -> H + H' H'-> H 0 o C C ~ ~ Te 2eV ne 1015cm-3 IO- "LL~_--L._--'-_-'l_--'-_--L __ l....-I~r o 10 12 v Fig.I. The MAR rate coefficients from various initial vibrational levels in H2(X l L:;). Figure 2 shows the populations of excited levels of atomic hydrogen determined from the intensities of the Balmer lines from a plasma with ne = 2.5 x 101lcm-3 , Te = 3.0eV, the gas pressure 0.015Torr. Figure 2 also shows population coefficients Ro(p) , Rl (p), and RM AR(p, v) which are defined by n(p) = Ro(p)nzne + Rl (p)n(l)ne +L:vRMAR(p, v)nH2(V)ne, (1) where p is the principal quantum number. The experi-mental populations were well fitted by eq.(l) with nH = 2.7 x 1014cm-3, nH2(V=0) = 1.0 x 1014cm-3. In order to verify these values, we are planning the studies of the influence of radiation trapping on the atomic emissions, and the analysis of the molecular band emissions. 4 10 Principal Quantum Number Fig.2. The population coefficients of the atomic hydro-gen (open circle). Populations of excited atoms deter-mined from the Balmer line intensities are also shown (closed square). Reference 1) A.Yu.Pigarov and S.I.Krasheninnikov, PFCjJA-96-7 (1996). 

Effect of Vibrational Excitation of Molecular Hydrogen on Hydrogen Recycling in LHD Edge Plasma

Effect of Vibrational Excitation of Molecular Hydrogen on Hydrogen Recycling in LHD Edge Plasma

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