• R.C. Davidson, S.R. Hudson, I. Kaganovich, H. Qin, E. Startsev
  PPPL, Princeton, New Jersey

In application of heavy ion beams to high energy density physics and fusion, background plasma is utilized to neutralize the beam space charge during drift compression and/or final focus of the ion beam. It is important to minimize the deleterious effects of collective instabilities on beam quality associated with beam-plasma interactions. Plasma electrons tend to neutralize both the space charge and current of the beam ions. It is shown that the presence of the return current greatly modifies the electromagnetic Weibel instability (also called the filamentation instability), i.e., the growth rate of the filamentation instability greatly increases if the background ions are much lighter than the beam ions and the plasma density is comparable to the ion beam density. This may preclude using underdense plasma of light gases in heavy ion beam applications. It is also shown that the return current may be subject to the fast electrostatic two-stream instability.

• I. Kaganovich, R.C. Davidson, E. Startsev
  PPPL, Princeton, New Jersey

Ion-atom ionization cross sections are needed in many applications employing the propagation of fast ions through matter. When experimental data or full-scale theoretical calculations are non-existent, approximate methods must be used. The most robust and easy-to-use approximations include the Born approximation of quantum mechanics and the quasi-classical approach utilizing classical mechanics together with the Bohr-Sommerfeld quantization rule.* The simplest method to extend the validity of both approaches is to combine them, i.e., use the two different approaches but only for the regions of impact parameters in which they are valid, and sum the results to obtain the total cross section. We have recently investigated theoretically and experimentally the stripping of more than 18 different pairs of projectile and target atoms in the range of 3-38 MeV/amu to study the range of validity of various approximations. The results of the modified approach agree better with the experimental data than either the Born approximation or the quasi-classical approach, applied separately.

*I. D. Kaganovich et al., "Formulary and scaling cross sections for ion-atom impact ionization," http://arxiv.org/abs/physics/0407140.

• I. Kaganovich, R.C. Davidson, E. Startsev
  PPPL, Princeton, New Jersey

Background plasma can be used as an effective neutralization scheme to transport and compress intense ion beam pulses, and the application of a solenoidal magnetic field allows additional control and focusing of the beam pulse. Ion beam pulse propagation in a background plasma immersed in an applied solenoidal magnetic field has been studied both analytically and numerically with three different particle-in-cell codes (LSP, OOPIC-Pro and EDPIC) to cross-check the validity of the results. Very good charge and current neutralization is observed for high values of the solenoidal magnetic field.* However, for intermediate values of the solenoidal magnetic field, current neutralization is a complex process, and a sizable self-magnetic field is generated at the head of the beam. Collective wave excitations are also generated ahead of the beam pulse.

*I. D. Kaganovich, E. A. Startsev and R. C. Davidson, Nuclear Instruments and Methods in Physics Research A, in press (2004).

• A. Friedman, J.J. Barnard, D. A. Callahan, G.J. Caporaso, D.P. Grote, R.W. Lee, S.D. Nelson, M. Tabak
  LLNL, Livermore, California
• R.J. Briggs
  SAIC, Alamo, California
• C.M. Celata, A. Faltens, E. Henestroza, E. P. Lee, M. Leitner, B. G. Logan, G. Penn, L. R. Reginato, A. Sessler, J.W.  Staples, W. Waldron, J.S. Wurtele, S. Yu
  LBNL, Berkeley, California
• R.C. Davidson, L. Grisham, I. Kaganovich
  PPPL, Princeton, New Jersey
• C. L. Olson, T. Renk
  Sandia National Laboratories, Albuquerque, New Mexico
• D. Rose, C.H. Thoma, D.R. Welch
  ATK-MR, Albuquerque, New Mexico

The Heavy Ion Fusion Virtual National Laboratory (HIF-VNL) is developing the intense ion beams needed to drive matter to the High Energy Density (HED) regimes required for Inertial Fusion Energy (IFE) and other applications. An interim goal is a facility for Warm Dense Matter (WDM) studies, wherein a target is heated volumetrically without being shocked, so that well-defined states of matter at 1 to 10 eV are generated within a diagnosable region. In the approach we are pursuing, low to medium mass ions with energies just above the Bragg peak are directed onto thin target "foils," which may in fact be foams or "steel wool" with mean densities 1% to 100% of solid. This approach complements that being pursued at GSI, wherein high-energy ion beams deposit a small fraction of their energy in a cylindrical target. We present the requirements for warm dense matter experiments, and describe suitable accelerator concepts, including novel broadband traveling wave pulse-line, drift-tube linac, RF, and single-gap approaches. We show how neutralized drift compression and final focus optics tolerant of large velocity spread can generate the necessarily compact focal spots in space and time.

• P.K. Roy, A. Anders, D. Baca, F.M. Bieniosek, J.E. Coleman, S. Eylon, W.G. Greenway, E. Henestroza, M. Leitner, B. G. Logan, D. Shuman, D.L. Vanecek, W. Waldron, S. Yu
  LBNL, Berkeley, California
• R.C. Davidson, P. Efthimion, E.P. Gilson, I. Kaganovich, A.B. Sefkow
  PPPL, Princeton, New Jersey
• D. Rose, C.H. Thoma, D.R. Welch
  ATK-MR, Albuquerque, New Mexico
• W.M. Sharp
  LLNL, Livermore, California

Ion beam neutralization and compression experiments are designed to determine the feasibility of using compressed high intensity ion beams for high energy density physics (HEDP) experiments and for inertial fusion power. To quantitatively ascertain the various mechanisms and methods for beam compression, the Neutralized Drift Compression Experiment (NDCX) facility is being constructed at Lawrence Berkeley National Laboratory (LBNL). In the first compression experiment, a 260 KeV, 25 mA, K+ ion beam of centimeters size is radially compressed to a mm size spot by neutralization in a meter-long plasma column and beam peak current is longitudinally compressed by an induction velocity tilt core. Instrumentation, preliminary results of the experiments, and practical limits of compression are presented. These include parameters such as emittance, degree of neutralization, velocity tilt time profile, and accuracy of measurements (fast and spatially high resolution diagnostic) are discussed.