Measurement of Electron Collision Cross Section in Shock-Wave Heated MHD Plasma by an FIR Laser

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To estimate the performance of a large scale MHD generator, it is necessary to develop the theoretical methods that can predict correctly the plasma behavior in the MHD channel.In these methods, the accuracy of the estimation depends strongly on the data of the fundamental plasma parameters ; one of these is the collision cross-section for momentum transfer of electrons to the neutral particles, which is directly related to the conductivity of the plasma. This cross-section has been measured by electrostatic or RF probes. However, these probes inevitably disturb the flow field and the obtained values are thought to have large errors. In addition, the cross-section data currently used inthe analyzes are based on the experimental and/or theoretical values obtained over 20 years ago, and the accuracy of these has not been confirmed by the recent diagnostic technique.In the present research, the electron collision cross-section against the neutral argon atom is evaluated experimentally by using the HCN far-infrared (FIR) laser. The target plasma is obtained with the shock tunnel. The driver and driven sections of the shock tunnel are filled with helium and argon, respectively. The shock Mach number is varied by changing the gas pressure, and the plasma generated in the stagnation section upstream of the channel is used as a target. The Michelson interferometer is used to measure the fringe shift due to the plasma, from that the electron density is calculated. Also, the transmissivity of the FIR laser beam through the plasma is measured, and the electron collision cross-section is determinedfrom the measured electron density and transmissivity.