Development of beam position monitors for heavy ion recirculators
Work is underway at the Lawrence Livermore National Laboratory to design and build a small-scale, heavy ion recirculating induction accelerator. An essential part of this design work is the development of small non-intercepting diagnostics to measure beam current and position. This paper describes some of this work, with particular emphasis on the development of a small capacitive probe beam position monitor to resolve beam position to the 100 /spl mu/m level in a 6 cm diameter beam pipe. Initial measured results with an 80 keV potassium ion beam are presented.
K+ diode for the LLNL heavy ion recirculator accelerator experiment
An 80 keV K+ diode source that will deliver up to 9 mA of beam current has been developed for the LLNL Small Recirculator experiment. The diode consists of a hot plate alumino-silicate (Zeolite) source, a graphite Pierce electrode, and an exit extraction electrode. The K+ source emitting surface is planar, and one inch in diameter. A fine (70 line/inch) high transparency (90%) mesh is placed in the exit beam extraction electrode. The exit mesh reduces the sensitivity of the diode optics to possible variations in the diode gap and exit aperture shape, without a growth in the beam emittance. Numerical EGUN simulations were used for the diode physics design. The simulations showed that the diode can deliver a uniform 9 mA K+ beam with a normalized emittance of about 0.05 mm-mr, resulting mainly from the source temperature at 1000 /spl deg/C. The beam at the diode exit is aperture to a diameter of 11 mm to meet the recirculator experiment requirements of a 2 mA beam with 0.01 mm-mr normalized emittance. The 80 kV source acceleration potential is provided by a thyratron switched, 4 /spl mu/S long 8-section PFN which drives a 1:10 step-up pulse transformer. We shall report on the source performance including measurements of the beam total current, current density profile, phase space profile, angular divergence, and transverse emittance.
Recirculating induction accelerators as drivers for heavy ion fusion
A two‐year study of recirculating induction heavy ion accelerators as low‐cost driver for inertial‐fusion energy applications was recently completed. The projected cost of a 4 MJ accelerator was estimated to be about $500 M (million) and the efficiency was estimated to be 35%. The principal technology issues include energy recovery of the ramped dipole magnets, which is achieved through use of ringing inductive/capacitive circuits, and high repetition rates of the induction cell pulsers, which is accomplished through arrays of field effect transistor (FET) switches. Principal physics issues identified include minimization of particle loss from interactions with the background gas, and more demanding emittance growth and centroid control requirements associated with the propagation of space‐charge‐dominated beams around bends and over large path lengths. In addition, instabilities such as the longitudinal resistive instability, beam‐breakup instability and betatron‐orbit instability were found to be controllable with careful design.