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276MAO, BASSETT, AND TAKAHASHI graph, cannot be evaluated independently but together influence the scatter for the lattice parameters as a function of pressure. The standard deviations for the lattice parameter and volume data are 0.15% and 0.3%, respectively. The c/ a ratio, however, is not influenced by sources (2), (3), and (4). Therefore, the standard deviation for c/ a determinations as a function of pressure remains at 0.1 %.Bundy4 compiled published values for the change in molar volume of iron between bcc and hcp, hcp and fcc, and fcc and bcc phases. He found that no combination of those values met the thermodynamic requirements at the triple point: LLlV=O, andLLlS= LLlV(dP/dT) =0.He attempted to resolve the inconsistency by distributing the error among the volume data around the triple point. However, the volume change between bcc and hcp iron reported in this paper obviates such an adjustment. The following values now seem to be the most reliable and to satisfy the triple point con-ditions:and Ll V (bcc-hcp) = -0.34 cm 3 /mole, Ll V (hcp-fcc) = +0.13 cm 3 /mole,15Ll V (fcc-bcc) = +0.21 cm 3 /mole. 15 ,16 ACKNOWLEDGMENTSThe authors wish to thank Francis P. Bundy of the General Electric Company for providing a sample of pure iron foil which was used in his resistivity experiments, and Larry Kaufman of ManLabs Inc.for critical reading of manuscript. J. Dean Barnett and Daniel L. Decker of the Bringham Young University kindly provided tabulated data of lattice parameter versus pressure for sodium chloride.Experimental results indicate that, under certain conditions, ion beams undergo severe deflection preceding the region where neutralization of the beam occurs. It is believed that this effect is related to the existence of a conducting plasma which forms in the neutral region of the beam. This effect is analyzed in terms of an axially symmetric model. The plasma is simulated by assigning appropriate boundary conditions at the plasma surface. The method consists of specifying the electric field on a trial boundary, then examining the resulting potential distribution for a unipotential surface on this boundary. A sequence of numerical solutions is found in which the trial boundary is perturbed for each iterate until the Cauchy conditions are satisfied. After the location and shape of this boundary are determined, the effect of variations in electrode potentials is examined and compared with observation. It is shown that under some conditions the plasma can significantly influence the structure of the ion beam.

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The paper is concerned with the problems associated with matching the output of a large nuclear-electric power source to the requirements of contact ion thrusters. The factors that influence the design requirements and the technical approach to power conditioning, switching, and control (PCSC) subsystems are discussed. Thruster requirements, power source characteristics, and environmental constraints are analyzed from the standpoint of their relationships to power conditioning. In addition, the results of the development of a breadboard PCSC unit at a 30-kw power level are described. This work gives an insight into the problems and the possible solutions that will result in the realization of power conditioning equipment whose specific weight, efficiency, and reliability are compatible with requirements of large scale nuclear-electric rockets of the future. In particular, one of the most promising experimental results is a 30-kw breadboard whose components exhibit a total weight of 3.2 lb/ kw. The results of a design study for a 300-kw system show that it is feasible to build a PCSC system weighing 9.1 Ib/kw input power including radiators and shadow shielding with a power efficiency of 93%.

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