Monte Carlo calculations have been carried out on Z , lattice gauge theories in d = 3 and d = 4 space-time dimensions. For d = 3, for the gauge-Higgs system, the results show a phase diagram in which the Higgs and confined regions are smoothly connected. There are lines of phase transitions surrounding the unconfined region; first-order behavior occurs on and near the self-dual line. For d = 4, for the pure gauge system, we confirm the results of Creutz et a[., that the transition between confined and unconfined regions is first order.

A new model of the plasma plume from Hall Effect Thrusters (HET's) is presented. The model includes the self-expansion of the main beam by density gradient electric fields, lowenergy ions produced by resonant charge exchange between beam ions and neutral atoms (ambient and thruster-induced), and angle-dependent elastic scattering of beam ions off neutral atoms. The variation of radial velocities across the annular thruster beam is also included. The model is an advance over previous plume models in the way it numerically models the self-expansion of the main beam, and in particular, the treatment of elastic scattering using recently calculated differential cross sections. The results are compared with recent measurements of the energy and angledependent plume from the BPT4000 Hall-Effect Thruster. Both the intensity and energy dependence of the scattering peaks are compared. The principal result is that elastic scattering is the source of the majority of ions with energy greater than E/q=50V that are observed at angles greater than 45° with respect to the thrust axis. The model underscores the need for elastic scattering cross sections for multiply charged ions, as well as a better understanding of HET propellant utilization.

The Space Power Experiment Aboard Rockets I (SPEAR I) biased two 10‐cm radius spheres as high as 46,000 V positive with respect to an aluminum rocket body. The experiment measured the steady state current to the spheres and the floating potential of the rocket body. Three‐dimensional calculations performed using NASCAP/LEO and POLAR 2.0 show that both ion‐collecting and electron‐collecting sheaths were formed. The rocket body potential with respect to the ionospheric plasma adjusted to achieve a balance between the electron current collected by the spheres and the secondary electron‐enhanced ion current to the rocket body. This current balance was obtained with a large ion‐collecting sheath that enveloped most of the electron‐collecting sheath and reduced the area for collection of ionospheric electrons. The calculated current is in agreement with the flight measurement of a steady state current of less than 1/10 A. The calculations show that the rocket body was driven thousands of volts negative with respect to the ionospheric plasma. The calculated rocket potential is within the uncertainty of that inferred from ion spectrometer data. The current flowed through the space plasma. There was almost no direct charge transport between the spheres and the rocket body.

Spacecraft charging has commonly been attributed to electrons with several kilovolts of energy impinging upon spacecraft surfaces. Recent experimental evidence from the SCATHA satellite has shown that charging correlates well with electrons of energies greater than 30 keV. In this paper it is shown that the SCATHA observations are consistent with the model of charging in which a satellite is immersed in a Maxwellian plasma, particle collection is orbit limited, and dominant surface effects are the emission of secondary and backscattered electrons. The energy dependence of the secondary yield for multikilovolt incident electrons determines the charging threshold. In the past, inadequate representations of the secondary yield have led experimenters to question the validity of the charging model. The accuracy of the secondary electron yield formulation based on electron stopping power, such as the one in NASA Charging Analyzer Program (NASCAP), gives good agreement with the SCATHA results. A Maxwellian representation of the magnetospheric plasma is justified by choosing effective temperatures and densities that minimize the error in calculating charging current densities.

A hollow cathode-based plasma contactor will be own on the international space station to control the station's potential to within 40 V of the local ionosphere. Extensive testing of the plasma contactor has been conducted in vacuum facilities at the NASA Lewis Research Center. Signi cant performance differences were observed between tests of the same plasma contactor in different facilities. Why measured plasma contactor performance differs in the laboratory in different tank environments and how the plasma contactor performance measured in the laboratory relates to expected performance in space is addressed. Presented are models of plasma contactor plasma generation and interaction in a laboratory environment, including anode area limiting. These models were integrated using the Space Station Environment Work Bench to predict plasma contactor operation, and the results are compared with the laboratory measurements. Nomenclature F= gas ow rate, standard cubic centimeter per minute I D = total ori ce electron current, A I emission = ori ce current emitted, A I keeper = keeper electrode current, A I loss = ion loss rate, A I max = maximum possible electron current, A I prod = total ion production rate, A J e = electron current density, A m 2 L = ori ce length, m m = neutral atom mass, kg m e = electron mass, kg m i = ion mass, kg N n = neutral density, m 3 r = ori ce radius, m W conv = power loss by electron convection, W W ion = power loss by ionization, W W rad = power loss by radiation, W e = ori ce electron temperature, eV i = ion temperature, eV in = insert region electron temperature, eV n = neutral gas temperature, eV = electrical conductivity, ohm m 1 ion = ionization cross section, m 3 rad = inelastic cross section, m 3 p = electron plasma frequency, rad s 1