Publications

Abstract not provided.

Abstract not provided.

Intense ion beams may be the best option for an Inertial Fusion Energy (IFE) driver. While light ions may be the long-term pulsed power approach to IFE, the current economic climate is such that there is no urgency in developing fusion energy sources. Research on light ion beams at Sandia will be suspended at the end of this fiscal year in favor of z-pinches studying ICF target physics, high yield fusion, and stewardship issues. The authors document the status of light ion research and the understanding of the feasibility of scaling light ions to IFE.

We describe measurements, modeling, and mitigation experiments on the effects of anode and cathode plasmas in applied-B ion diodes. We have performed experiments with electrode conditioning and cleaning techniques including RF discharges, anode heating, cryogenic cathode cooling and anode surface coatings that have been successful in mitigating some of the effects of electrode contamination on ion diode performance on both the SABRE and PBFA accelerators. We are developing sophisticated spectroscopic diagnostic techniques that allow us to measure the electric and magnetic fields in the A-K gap, we compare these measured fields with those predicted by our 3-D particle-in-cell (PIC) simulations of ion diodes, and we measure anode and cathode plasma densities and expansion velocities. We are continuing to develop E-M simulation codes with fluid-PIC hybrid models for dense plasmas, in order to understand the role of electrode plasmas in ion diode performance. Our strategy for improving high power ion diode performance is to employ and expand our capabilities in measuring and modeling A-K gap plasmas and leverage our increased knowledge into an increase in total ion beam brightness to High Yield Facility (HYF) levels.

Significant progress in the generation and focusing of ion beams generated by PBFA-II has enabled us to begin experiments in ion beam coupling and target physics. Data from these experiments indicates that we can reproducibly deliver 50 KJ of 5 MeV protons at an average power intensity of 3.5 TW/cm 2 to a 6 mm diameter by 6 mm tall cylindrical target. The implosion of spherical exploding pusher targets and the radiation production from foam-filled cylindrical thermal targets were studied in these experiments. They demonstrated that high quality target data can be obtained on PBFA-II. Specific deposition rates of about 100 TW/g were achieved in these experiments. This deposition rate marks the boundary between the regime where enhanced ion deposition and equation-of-state (EOS) physics are studied (10-100 TW/g) and the regime where radiation-conversion and radiation-transport physics are studied (100-1000 TW/g). Experiments in the radiation-conversion regime are now of primary importance in our program because these experiments will test the target physics basis for ion-driven ICE Experiments using a thin film LiF source have produced an intensity of 1 TW/cm 2 of lithium ions. This beam has a potential specific deposition rate of 300-400 TW/g in hydrocarbon foams. However, radiation conversion experiments will require an increased total energy content of this beam in order to overcome the specific internal energy of the foam. Further increases in ion beam intensity and energy content are being pursued in a multi-pronged attack. Understanding and controlling ion beam divergence is the highest program priority. Present understanding indicates that instabilities in the electron sheath cause significant ion beam divergence. Our understanding suggests that this contribution to the ion divergence can be decreased by operating the diode at a low enhancement through the use of high applied magnetic fields or by modifying the electron distribution near the anode via electron limiters. The new 9 cm radius Compact Diode has the capability of generating 8 T applied magnetic fields which will enable divergence experiments in the low-enhancement, high-B regime. Experiments with the LEVIS (Laser Evaporation Ion Source) lithium source have demonstrated the existence of a preformed plasma, as determined by visible-emission spectroscopy of the anode plasma. Work on improving lithium purity with this source is in progress. This active anode plasma will be used in experiments testing the effectiveness of electron limiters in controlling ion beam divergence. We are also working to understand the interrelation between accelerator coupling, diode physics, and ion beam focusing in order to optimize the diode configuration to maximize the power intensity on target. Success in these experiments will provide an adequate lithium beam for performing target experiments exploring radiation conversion and radiation transport physics in ion-driven ICF. © 1992 National Technical Information Service.

UPEML is a machine-portable program that emulates a subset of the functions of the standard CDC Update. Machine-portability has been achieved by conforming to ANSI standards for Fortran-77. UPEML is compact and fairly efficient; however, it only allows a restricted syntax as compared with the CDC Update. This program was written primarily to facilitate the use of CDC-based scientific packages on alternate computer systems such as the VAX/VMS mainframes and UNIX workstations. UPEML has also been successfully used on the multiprocessor ELXSI, on CRAYs under both UNICOS and CTSS operating systems, and on Sun, HP, Stardent and IBM workstations. UPEML was originally released with the ITS electron/photon Monte Carlo transport package, which was developed on a CDC-7600 and makes extensive use of conditional file structure to combine several problem geometry and machine options into a single program file. UPEML 3.0 is an enhanced version of the original code and is being independently released for use at any installation or with any code package. Version 3.0 includes enhanced error checking, full ASCII character support, a program library audit capability, and a partial update option in which only selected or modified decks are written to the complete file. Version 3.0 also checks for overlapping corrections, allows processing of pested calls to common decks, and allows the use of alternate files in READ and ADDFILE commands. Finally, UPEML Version 3.0 allows the assignment of input and output files at runtime on the control line.

The nominal 1000-MJ yield of a Laboratory Microfusion Facility (LMF) pellet requires at least a 1.5-m-radius target chamber to contain the blast. A geometry has been identified that uses an annular ion beam with a center plug, has a total transport length of 4 m, and allows no direct line of sight from the target blast to the ion diode. An analytic model for an achromatic, two-lens system that is capable of transporting a 30-MV, 1-MA Li ion beam over this distance has been developed. The system uses both self-Bθ and solenoidal magnetic lenses. The beam microdivergence requirement is minimized by locating the final solenoidal lens at the target chamber wall. In the present work, the analytic model was verified by PIC (particle-in-cell) transport calculations. A realistic coil system has been designed to supply the required 2-T solenoidal fields. Simulations show that a lithium beam can be transported over the 4-m distance with better than 70% energy and power efficiency, delivering roughly 1 MJ/beam to the target if a 6-mrad microdivergence is achieved at the diode.