[en] A large number of simulations have been performed to establish a database of simulations for use in accelerator designs, and to compare the simulated emittance growths with the threshold for emittance growth actually measured in the Single Beam Transport Experiment (SBTE) at LBL. These simulations show substantial agreement with the experiment. They also extend into the parameter regime, where emittance growths are slower than could be measured in SBTE, but which may still be important to a driver system several times longer. Also demonstrated by these simulations, is that, even for beams which are not in detailed space-charge equilibrium and can therefore be subject to substantial nonlinear space-charge forces, emittance growths are restricted to what is consistent with energy conservation provided that the instability threshold is not crossed. This occurs even though energy need not be conserved in alternating gradient systems. Major modifications have been made to the two dimensional SHIFT-XY (Simulation of Heavy Ion Fusion Transport) code to add some of the three-dimensional physics associated with the transverse variation of the longitudinal fields in a long beam. Enhancements to the code have also been implemented which can decrease running times as much as 30% for typical parameters. 13 refs., 7 figs

[en] Particle simulations are used to examine the behavior of an intense beam propagating down an alternate gradient focusing channel. In order to examine the dependence of emittance growth on the particle distribution function, an initially low current, non K-V, matched distribution is established. The current is then slowly increased as the beam propagates down the channel. Differences are observed in both the current at which emittance growth begins, and the rate at which the emittance grows, when the form of the initial distribution is changed. But this emittance growth still limits the intensity of the beam being transported

[en] Computer calculations were used to investigate the behavior of a periodic solenoidal thin-lens focusing system with 90⁰ phase advance. Despite strong similarities in the behavior predicted by the linear theory, a 90⁰ solenoidal system does not appear to exhibit the emittance growth characteristic of the similar 90⁰ alternate gradient system. In other ways, however, behavior is observed which is similar to the analagous alternate gradient system

[en] Progress during the FY83/84 period has involved both the use of existing numerical tools to investigate current issues, and the development of new techniques for future simulations of increasing sophistication. A balance has been sought with a view towards maximizing the utility of simulations to both present and future decisions in accelerator design. Emphasis during this contract has centered on investigating the nonlinear dynamics of a very low emittance beam with a realistic distribution function - especially when complications such as the image forces from a nearby conducting electrode are considered. A significant part of the effort during this period was also expended in spreading the simulation capabilities already developed. Versions of the SHIFT (Simulation of Heavy Ion Fusion Transport) series of computer codes have been installed on machines available to the HIF community. The enhanced availability of these codes has facilitated their use outside of NRL. For example, simulation results with a significant impact on MBE design were obtained at LBL using the MFECC Version of SHIFT-XY

[en] The current research program is aimed toward the ultimate use of computer simulations to aid in accelerator design and the interpretation of experimental results. Though full three dimensional simulations which can reliably describe all complexities of an actual accelerator remain in the future, useful progress has been made by employing simplified models to understand the scaling of the relevant physics and to conduct simulations specific to those problems which can be examined by less than a full three-dimensional model. During the past year transverse simulations have been performed to further refine the understanding of the transport of intense beams in an alternate-gradient channel and to determine, for a test case, the importance of space-charge aberrations on a final focusing system. The numerical limitations of a longitudinal simulation model have been determined. This longitudinal code has also been used to investigate both the fundamental scaling of the beam dynamics and the non-linear propagation and growth of a perturbation on a bunched beam in the presence of wall impedances approximating those expected in various accelerator systems

[en] A brief discussion is given of instabilities in the presence of space charge which can limit the power transported in a focused channel. Plots of the four-dimensional phase space are given

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[en] The temporal evolution of the temperature profile of an rf heated plasma torus is calculated. The model includes the following effects: (1) inward energy transport by externally launched lower hybrid waves which Landau damp and heat the plasma as they propagate from the plasma edge to the vicinity of the lower hydrid resonance where the remainder of their energy is deposited; (2) quasilinear plateau formation and the competing effect of Fokker-Planck collisions; (3) electron and ion thermal conductivity; and (4) temperature equilibration. The implications of various models of the thermal conductivity (neoclassical, pseudoclassical, and anomalous) and of the heat deposition near the resonance (mode conversion, parametric instabilities, etc.) are investigated. It is found that quasilinear flattening is effective in reducing the Landau damping of the lower hybrid waves and thereby prevents large amounts of energy from being deposited in the outer regions of the plasma

[en] The induction linac bunches of heavy-ion-fusion scenarios are strongly influenced by the longitudinal space-charge impedance. This is in distinct contrast to relativistic bunches in storage rings where most of the data on stability have been obtained. Simulation results reveal that when space-charge effects are large, the stability requirement of small growth rate relative to the synchrotron frequency for relativistic bunches is replaced by the relaxed condition of small growth rate relative to the frequency spacing of the space charge wave modes on the bunch. Dispersive effects from finite pipe size tend to make the lower frequencies less susceptible to instability than higher frequencies. Since induction modules have a high resistive component only for the lowest bunch modes, stability is better than would occur for a broadband impedance of comparable magnitude. These results indicate that long-term longitudinal bunch stability is realizable for induction-linac drivers for heavy-ion fusion