Orthobaric Density ofHe3in the Critical Region

Abstract

also measured the (limiting) thickness of the shock as a function of plasma density. At pressures p ^ 10~2 mm Hg, with *U<l<*i n , £ being the thickness of the shock and >^ and >^n the i-i and i-n collision mean free paths, respectively, we expect I to be determined entirely by >^-, i.e., Z~ 1/n. That this is the case can be seen from the data of Fig. 3(b), where I is shown as a function of the plasma density n ahead of the shock for a He gas pressure of ~10~2 mm Hg.In conclusion, our results indicate that in plasmas of comparable ion and electron temperatures Landau damping prevents the formation of a shock wave by overcoming the sharpening effect of the nonlinearities. Landau damp ing can, however, be "switched-off" by increasThe coexistence curve of 3 He has been measured by a dielectric constant technique in the neighborhood of the critical point. The parameters in the relation | (p-p c )/p c | =A[{T C~T )/T C ]P are found to be p c = 0.04134 g/cm 3 , T C =3.3095°K, A = 1.323, and /3 = 0.362. Our value of T c is some 14 mdeg lower than previous measurements indicate, and our value of j3 more nearly in agreement with values characteristic of other fluids than was previously found.ations from the law of corresponding states. Recent work by Roach and Douglass 11 casts doubt on this suggestion. They find that for 4 He, 0 = 0.352±0.003, which is to be compared with an earlier estimate 9 of 0.46. Such quantum deviations, if present, should be largest of all for 3 He. We have accordingly measured its coexistence curve by means of a dielectric constant technique, using an improved version of an apparatus previously described, 12 and find j3 = 0.362± 0.001. Any such deviations are therefore substantially smaller than earlier data suggested. We also find that T c is some 14 mdeg lower than previously reported. This correction is largely responsible for our smaller value of /3, since far from the critical point our data agree well with the results of others. 6 ' 13 151 ing T e /T^ from unity to about 10 or so. Further details on our measurements will be presented at a later date.Finally, it should be noted that our results may be relevant to shock formation in interplanetary plasmas.

Critical-Point Behavior of a Model Describing a System of Interacting Fermions

“…17 More recent experiments by Zimmerman and Chase, 26 however, seem to indicate that the exponent j3, which characterizes the coexistence curve singularity, may be closer to the value of i obtained for the heavier elements 27 than it is to the, classical value of \ as obtained in the present model. Evidently, much further experimental work is required before we can say whether or not the present model is in harmony with the laboratory determination of )3 for He 3 .…”

“…362 quoted by Zimmerman and Chase. 26 This value, ]3 = i, is identical again to that of a van der Waals gas and may also be contrasted with the Ising-model values of -|-and 0. 32 in two and three dimensions, respectively.…”

Velocity of Sound at 1 MHz Near theHe4Critical Point

“…10, together with corresponding results for hydrogen 41 and He 3 . 42 "" 44 The presence of a logarithmic singularity in the He 4 data is clearly indicated, and the results are well represented by the equation…”

Density Equation for Saturated 3He

“…In 1973, by measuring the capacitance of a parallel-plate capacitor filled with 3 He as a function of temperature and pressure, Chase and Zimmerman [10,11] determined the dielectric constant of 3 He along 28 isotherms between 3 K and the critical temperature for both saturated liquid and vapor. Then, assuming the Clausius-Mossotti relation holds, they calculated the density along these same trajectories.…”

“…Following the work of Kerr [3,7] and Zimmerman [10], a dimensionless form for the density equation was selected;…”