K. Sato

K. Takahara

S. "Namba

S. Kusakabe

T. Katsuta

T." Oda

National Institute for Fusion Science (NIFS-Repository)

§ 17. Observation of Population Inversion in He I due to a Double Electron Capture Process Namba, S., Kusakabe, S., Takahara, K. (Dept. Energy Eng. & Sci., Nagoya Univ.) Sato, K. Katsuta, T., Oda, T. (Dept. Applied Phys. & Chern. Fac. Eng., Hiroshima Univ.) Investigations of recombination processes in high density plasmas were started after remodelling of the TPD-11 device for higher discharge current operation. Observations of inverted population density due to a double electron capture has been performed for He plasma in contact with Hz molecular gas. The following charge transfer process into a selected state, HeZ+ +Hz--> He*(ls 31) + 2H+ (1) is found to have a very large cross section (~1o- 15cmz) in low collision energies(<1eV), due to an orbiting effect and accidental resonance. In order to observe a double electron capture process by spectroscopic methods, a gas puffing system with a piezo valve was installed. A pulsed supersonic Hz molecular gas has been introduced into the He plasma for a duration of 12.5ms. 2m VUV and 75cm visible monochromators have been used to observe He I resonance spectra (np1 P --> 1s1S n=2,3,4,5). Figure 1 and 2 show typical results of the time evolution of the population density under the discharge current 120A, the discharge voltage 130V, magnetic flux density 0.2T, He gas flow rate for discharges 150cc/min and 270cc/min respectively. Apparently from Fig.1, population density of only n=3 appears anomalous enhancements immediately after a Hz gas injection and population inversion between 2p1 P and 3p1 P is obtained,. The reason of the enhancements of He I n=3 is concluded as the process of eq. (1), because its cross section is very large and a cross section of the other single electron capture process, such as He+ + H2 --> He*(nl) + H2 + (2) is small (<10- 18cm2) at low collision energy. On the other hand, Fig. 2 shows the unexpected results. In contrast to the temporal behaviors of populations in Flg.1, population densities of low 132 excited states increase quickly. One possible explanation would be considered by the following processes. That is, firstly excitation of vibrational states of hydrogen molecule, (3) secondary, double electron charge transfer HeZ+ + H2v --> He*(1s, n=2,3,4,5) + 2H+ (4) The injected hydrogen molecules are excited into vibrational states by electron or ion impact. Next, these vibrational excited Hz v would collide alpha particles. Also in this case, the inverted population has been observed. ...... 10 ·a :l 8 .£ ~ 0 6 ·oo ----- n=2 c:: Q,) 4 -···- n=3 "0 c:: -n=4 0 2 -~ ········- n=5 "3 0.. 0 0 0.. 55 60 65 70 time [ms] Fig.l Time evolution of He I population density under He gas flow rate 150cc/min. ';::' ·a 8 :l ..ci ~ 6 0 ·oo 4 c:: Q,) "0 c:: 0 2 ·~ "3 0.. 0 8. 55 60 65 70 time [ms] Fig. 2 Time evolution of He I population density under He gas flow rate 270cc/min. 

Observation of Population Inversion in He I due to a Double Electron Capture Process

Abstract

Similar works

Full text

Available Versions

National Institute for Fusion Science (NIFS-Repository)