A. Tsushima

M. Machida

M.Y. Tanaka

National Institute for Fusion Science (NIFS-Repository)

§8. Measurement of Neutral Particles by Means of Sound Wave Tsushima, A., Machida, M. (Yokohama National Univ.), Tanaka, M.Y. In a large diameter plasma such as the HYPER-I device 1), the spatial distribution of neural particles is expected to be important for a plasma production. In order to measure the local properties of the neutral particles, we have developed a new method using sound waves with two different frequencies. Figure 1 shows that the propagation speed of the pressure perturbation caused by the vibrating prate depends on the gas parameter r ( = p I /.1 w ) where p is the ambient pressure in Pa, /.1 is the viscosity in Pas, and w is the angular frequency of the perturbation in rad/s. Here, the propagation speed, v, is normalized by sound speed Cs [ = ( y p I p ) 112 , p : the mass density in kglm3, y : the specific heat ratio]. The open circles and the open squares are the measurements by Greenspan in helium with w 12 n = 1 MHz 2) and in argon with w 12 n = 11 MHz 3), respectively. The closed squares and triangles are our measurements in helium with w 12 n =120 kHz and 40kHz, respectively. The solid curve, vies = (r+0.3) I (r+0.15), Is found to fit these measured measurements. 4 3 1/) 2 u "'-.. :> 1 0 10-2 10-1 10° 101 102 103 r Fig. I Propagation speed versus gas parameter. Now, we suppose that we have measured the propagation speeds of the pressure perturbation with different frequencies, say, w 1 and w 2 ( w 1> w 2), and the results are v1 and v2 , respectively. Then, we can find the ratio pi /.1 by the following equation: pI /L ={ {J.)/[40(Rv-1)}} [[ (JORw + 3)-(3Rw + 10)Rv +{[(10Rw+3)- (3Rw+l0)} 2 - 120 Rw(Rv-1//12 }}, for pI JL > (3 w 1 w z/40) 112 • Here, R w = {J.) / {J.) 2 and Rv=v /v2• We also find the ambient gas temperature, T, using the equation: T = (m v /I y kB) • [(pI JL) +0.15 {J.) J}2 /[(pIp )+0.5 (JJ J] 2• From this value of T, we can estimate the viscosity, given by 4) and, simultaneously, the pressure p, since we have the value of pi /.1 in the procedure. In summary, by measuring the propagation speeds of the pressure perturbation with different two frequencies, we can estimate both p and T of the low pressure ambient gas. References 1) Tanaka, M. : J. Phys. Soc. Jpn. 60(1991)344. 2) Greenspan, M. : J. Acoust. Soc. Am. 22 (1950) 568. 3) Greenspan, M. : J. Acpust. Soc. Am. 28 (1956) 644. 4) Reid, R. C. Sherwood, T. K.: The Properties of Gas and Liquids (McGraw-Hill, New York, 1958). 307 

Measurement of Neutral Particles by Means of Sound Wave

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