LBNL, Berkeley, California
PPPL, Princeton, New Jersey
Funding: This work was supported by the Director, Office of Science, Office of Fusion Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
Recent changes to the NDCX beamline offer the promise of higher current compressed bunches, with correspondingly larger fluences, delivered to the target plane for ion-beam driven warm dense matter experiments. We report modeling and commissioning results of the upgraded NDCX beamline that includes a new induction bunching module with approximately twice the volt-seconds and greater tuning flexibility, combined with a longer neutralized drift compression channel.
PPPL, Princeton, New Jersey
LBNL, Berkeley, California
Funding: Research Supported by US Department of Energy.
Plasma are a source of unbound electrons for charge netralizing intense heavy ion beams to focus them to a small spot size and compress their axial length. To produce long plasma columns, sources based upon ferroelectric ceramics with large dielectric coefficients have been developed. The source utilizes the ferroelectric ceramic BaTiO3 to form metal plasma. The drift tube inner surface of the Neutralized Drift Compression Experiment (NDCX) is covered with ceramic material. High voltage (~8kV) is applied between the drift tube and the front surface of the ceramics. A BaTiO3 source comprised of five 20-cm-long sources has been tested and characterized, producing relatively uniform plasma in the 5x1010 cm-3 density range. The source has been integrated into the NDCX device for charge neutralization and beam compression experiments. Initial beam compression experiment yielded current compression ratios ~ 120. Recently, an additional 1 meter long source was fabricated to produce a 2 meter source for NDCX compression experiments. Present research is developing higher density sources to support beam compression experiments for high density physics applications.
LBNL, Berkeley, California
LLNL, Livermore, California
PPPL, Princeton, New Jersey
Voss Scientific, Albuquerque, New Mexico
The Heavy-Ion Fusion Sciences Virtual National Laboratory is pursuing an approach to target heating experiments in the warm dense matter regime, using space-charge-dominated ion beams that are simultaneously longitudinally bunched and transversely focused. Longitudinal beam compression by large factors has been demonstrated in the Neutralized Drift Compression Experiment (NDCX) with controlled ramps and forced neutralization. Using an injected 30 mA K+ ion beam with initial kinetic energy 0.3 MeV, axial compression leading to ~100X current amplification and simultaneous radial focusing to a few mm have led to encouraging energy deposition approaching the intensities required for eV-range target heating experiments. We discuss the status of several improvements to NDCX to reach the necessary higher beam intensities, including:
- greater axial compression via a longer velocity ramp;
- beam steering dipoles to mitigate aberrations in the bunching module;
- time-dependent focusing elements to correct considerable chromatic aberrations; and
- plasma injection improvements to establish a plasma density always greater than the beam density, expected to be >1013 cm-3.
Fermilab, Batavia
PPPL, Princeton, New Jersey
Funding: Research supported by the U.S. Department of Energy.
Understanding the effects of random errors in machine components such as quadrupole magnets and RF cavities is essential for the optimum design and stable operation of high-intensity accelerators. The effects of random errors have been studied theoretically, but systematic experimental studies have been somewhat limited due to the lack of dedicated experimental facilities. In this paper, based on the compelling physics analogy between intense beam propagation through a periodic focusing quadrupole magnet system and pure ion plasma confined in a linear Paul trap, experimental studies of random error effects have been performed using the Paul Trap Simulator Experiment (PTSX). It is shown that random errors in the quadrupole focusing strength continuously produce a non-thermal tail of trapped ions, and increases the rms radius and the transverse emittance almost linearly with the amplitude and duration of the noise. This result is consistent with 2D WARP PIC simulations. In particular, it is observed that random error effect can be further enhanced in the presence of beam mismatch.
PPPL, Princeton, New Jersey
Funding: Research supported by the U.S. Department of Energy.
The Paul Trap Simulator Experiment (PTSX) 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 frame-of-reference of the beam. Results are presented from experiments in which the axial distribution function is modified by lowering the axial confinement barrier to allow particles in the tail of the axial distribution function to escape. Measurements of the axial energy distribution and the transverse density profile are taken to determine the effects of the modified distribution function on the charge bunch. It is observed that the reduced axial-trapping potential leads to an increase of the transverse effective temperature.