which replaces the usual relation for dE. All the thermodynamic calculations will go through as before 1 with -n replacing V and \i replacing P. No instability occurs if C^ becomes infinite along a X line, but instability will occur if C n tends to become infinite.We speculate now that at the end of the X line, where the phase separation starts to take place, an infinity in C^ tends to go over to an infinity in C w . This seems a fairly reasonable hypothesis. As long as 3 He is in low concentration, the interaction between rotons, which is responsible for the X transition, would be expected to depend upon an intrinsic property of the 4 He part, such as its chemical potential. But as the concentration of 3 He increases and 3 He itself becomes more intimately concerned in the transition, the dependence might well go over into one on concentration.Some measurements on the specific heat at constant composition C n have been made on 3 He-4 He mixtures. 4 In general, C n reaches a peak at the X line, but does not appear at become infinite, as, of course, it should not. It would be much more difficult to obtain measurements of C^, which should become infinite. Relationships analogous to those with pressure and volume as the parametric variables should hold.The peak of C n along the X line becomes lower as the temperature X is lowered. This pre-This Letter presents a picture of the nonlinear development of a two-stream instability that has resulted from numerical experiments with the one-dimensional Vlasov-Poisson equations. The motion of the electrons is described by Vlasov's equationThere is a uniform neutralizing background, sumably occurs because the decrease in the temperature is correlated with a decrease in the concentration of 4 He. The X transition thus becomes "diluted." Also, at a composition very close to that of the top of the phase-separation curve, the order-disorder changes in the phase separation and in the X transition tend to overlap in the curve of C n vs T, which gives an appearance of rounding off. These phenomena are probably not connected particularly with the change in the character of the transition. But it would be very interesting to have complete thermodynamic data in this region, in order to be able to test and analyze the thermodynamic relationships.

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Purely alpha-particle-driven Toroidal Alfvén Eigenmodes (TAEs) with toroidal mode numbers n=1-6 have been observed in Deuterium-Tritium (D-T) plasmas on the Tokamak Fusion Test Reactor [D.J. Grove and D.M. Meade, Nucl. Fusion 25, 1167 (1985)]. The appearance of mode activity following termination of neutral beam injection in plasmas with q(0)>1 is generally consistent with theoretical predictions of TAE stability. [G.Y. Fu et al., Phys. Plasmas 3, 4036 (1996)] Internal reflectometer measurements of TAE activity is compared with theoretical calculations of the radial mode structure. Core localization of the modes to the region of reduced central magnetic shear is confirmed, however the mode structure can deviate significantly from theoretical estimates. The peak measured TAE amplitude of δ n/n~10-4 at r/a~0.3-0.4 corresponds to δB/B~10-5 , while δB/B~10-8 is measured at the plasma edge. Enhanced alpha particle loss associated with TAE activity has not been observed.