Lithium beam generation and focusing on PBFAII
- Sandia National Labs., Albuquerque, NM (United States)
The time resolved size and position of the Li beam focus from a 15-cm-radius radial focusing applied-B field ion diode on PBFAII are examined to separate the effects of source divergence, virtual cathode instabilities, charge-exchange, and canonical angular momentum. The diode used {approximately}1,000 cm{sup 2} area LiF anodes to generate 6 TW, 10 MeV Li beams. The focus of a 64{degree} sector of the annular beam, on a gold foil target at the center of the diode, was observed with two ion pinhole cameras (IPCs) and a spatially resolved magnetic spectrometer. The Li beam energy agreed with the diode voltage early in time but was generally about 1 MeV below the diode voltage late in time. About 40% of this is attributed to range shortening in the gold target. The remainder could be due to charge-exchange of Li beam ions in gas desorbed from the anode surface or virtual cathode instability waves selectively accelerating Li ions at the rear of the waves. The focus measurements show a horizontal beam focus size that increases with time consistent with a beam with constant transverse temperature of 5 keV. Calculations with the program, SOPHIA, using constant 25 mR source divergence give good agreement to the focus throughout the pulse. The horizontal focus position often moves {approximately}2 mm to the left during the power pulse. This could be due to movement of applied B-field through the gas cell during diamagnetic compression of the field lines toward the anode by the virtual cathode, charge-exchange of beam ions with desorbed gas from the anode, or virtual cathode instability waves selectively accelerating Li ions at the trailing portion of the waves.
- Research Organization:
- Sandia National Laboratory
- DOE Contract Number:
- AC04-94AL85000
- OSTI ID:
- 182755
- Report Number(s):
- CONF-950612--; ISBN 0-7803-2669-5
- Country of Publication:
- United States
- Language:
- English
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