PPPL, Princeton, New Jersey
The Paul Trap Simulator Experiment is a compact laboratory Paul trap that simulates a long, thin charged-particle bunch coasting through a kilometers-long magnetic alternating-gradient (AG) transport system by putting the physicist in the beam's frame-of-reference. The transverse dynamics of particles in both systems are described by the same sets of equations, including all nonlinear space-charge effects. The time-dependent quadrupolar electric fields created by the confinement electrodes of a linear Paul trap correspond to the axially-dependent magnetic fields applied in the AG system. Results are presented from experiments in which the lattice period and strength are changed over the course of the experiment to transversely compress a beam with an initial depressed-tune of 0.9. Instantaneous and smooth changes are considered. Emphasis is placed on determining the conditions that minimize the emittance growth and the number of halo particles produced after the beam compression. The results of PIC simulations performed with the WARP code agree well with the experimental data. Initial results from a newly installed laser-induced fluorescence diagnostic will also be discussed.
PPPL, Princeton, New Jersey
LLNL, Livermore, California
LBNL, Berkeley, California
Voss Scientific, Albuquerque, New Mexico
Intense heavy ion beam pulses need to be compressed in both the transverse and longitudinal directions for warm dense matter and heavy ion fusion applications. Previous experiments and simulations utilized a drift region filled with high-density plasma in order to neutralize the space-charge and current of a 300 keV K+ beam, and achieved transverse and longitudinal focusing separately to a radius < 2 mm and pulse width < 5 ns, respectively. To achieve simultaneous beam compression, a strong solenoid is employed near the end of the drift region in order to transversely focus the beam to the longitudinal focal plane. Simulations of near-term experiments predict that the ion beam can be focused to a sub-mm spot size coincident with the longitudinal focal plane, reaching a peak beam density in the range 1012 - 1013 cm-3, provided that the plasma density is large enough for adequate neutralization. Optimizing the compression under the appropriate experimental constraints offers the potential of delivering higher intensity per unit length of accelerator to the target, thereby allowing more compact and cost-effective accelerators and transport lines to be used as ion beam drivers.
LBNL, Berkeley, California
LLNL, Livermore, California
PPPL, Princeton, New Jersey
UCB, Berkeley, California
Voss Scientific, Albuquerque, New Mexico
This work was supported by the Office of Fusion Energy Sciences, of the U. S. Department of Energy under Contract No. DE-AC02-05CH11231, W-7405-Eng-48, DE-AC02-76CH3073 for HIFS-VNL.
PPPL, Princeton, New Jersey
Installation of a laser-induced fluorescence (LIF) diagnostic system has been completed and initial measurement of the beam density profile has been performed on the Paul trap simulator experiment (PTSX). The PTSX device is a linear Paul trap that simulates the collective processes and nonlinear transverse dynamics of an intense charged particle beam propagating through a periodic focusing quadrupole magnetic configuration. Although there are several visible transition lines for the laser excitation of barium ions, the transition from the metastable state has been considered first mainly because an operating, stable, broadband, and high-power laser system is available for experiments in this region of the red spectrum. The LIF system is composed of a dye laser, fiber optic cables, a line generator, which uses a Powell lens, collection optics, and a CCD camera system. Single-pass mode operation of the PTSX device is employed for the initial tests of the LIF system to make optimum use of the metastable ions. By minimizing the background light level, it is expected that enough signal to noise ratio can be obtained to re-construct the radial density profile of the ion beam.
PPPL, Princeton, New Jersey
LBNL, Berkeley, California
Plasmas are sources of electrons for charge neutralizing ion beams to allow them to focus to small spot sizes and compress their axial pulse length. Sources must operate at low pressures and without strong electric/magnetic fields. To produce meter-long plasmas, sources based on ferroelectric ceramics with large dielectric coefficients were developed. The sources use BaTiO3 ceramic to form plasma. The drift tube inner wall of the Neutralized Drift Compression Experiment (NDCX) is covered with ceramic and ~7 kV is applied across the wall of the ceramics. A 20-cm-long prototype source produced plasma densities of 5·1011 cm-3. It was integrated into the Neutralized Transport Experiment and successfully neutralized the K+ beam. A one-meter-long source comprised of five 20-cm-long sources has been tested and characterized, producing relatively uniform plasma over the length of the source in the 1·1010 cm-3 range. This source was integrated into NDCX for beam compression experiments. Experiments with this source yielded compression ratios ~80. Future work will consider longer and higher plasma density sources to support beam compression and high energy density experiments.