Three-dimensional particle-in-cell simulations of applied-B ion diodes on PBFA II

Conference · Sun Dec 31 04:00:00 EST 1995

OSTI ID:178219

Pointon, T D ^[1]

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1. Sandia National Labs., Albuquerque, NM (United States)

The authors are using the 3-D, particle-in-cell code QUICKSILVER to simulate applied-B ion diodes on the PBFA II accelerator at Sandia. Typical diodes use an A-K gap of {approximately} 2 cm, anode area of {approximately}1,000 cm{sup 2}, and insulating fields of {approximately} 3 T. The accelerator delivers a 20 TW, 40 ns pulse, producing a {approximately} 10 MeV, {approximately} 1 MA Li{sup +1} beam. Spectroscopic diagnostics indicate that the LiF ion source used on most shots is not a space-charge-limited emitter; the normal electric field at the anode is 8--10 MV/cm. The field emission algorithm in QUICKSILVER has been modified to model this. The authors have also developed a transmission line algorithm, allowing them to crudely model the accelerator. The simulations show good agreement with experiment early in the pulse, but differ substantially as the ion beam current increases. Despite the limited success modeling actual PBFA diode shots, the simulations have substantially improved the understanding of instabilities in the applied-B diode. They show the same qualitative instability evolution seen in earlier idealized Cartesian coordinate simulations. Early in time they see a diocotron instability at a high frequency relative to the ion transit time, f{tau}{sub i} > 1, followed by a transition to an ion mode instability at much lower frequency, f{tau}{sub i} {approximately} 1. A new diagnostic shows that the spatial structure of the diocotron and ion mode are distinctly different.

• Research Organization: Sandia National Laboratory
• DOE Contract Number: AC04-94AL85000
• OSTI ID: 178219
• Report Number(s): CONF-950612--; ISBN 0-7803-2669-5
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
COMPUTERIZED SIMULATION
ION SOURCES
LITHIUM IONS
PARTICLE BEAM FUSION ACCELERATOR
PLASMA DIAGNOSTICS
PLASMA INSTABILITY
THERMIONIC DIODES