• P.A. Seidl, A. Anders, F.M. Bieniosek, J.E. Coleman, J.-Y. Jung, M. Leitner, S.M. Lidia, B.G. Logan, P.N. Ni, D. Ogata, P.K. Roy, W.L. Waldron
  LBNL, Berkeley, California
• J.J. Barnard, R.H. Cohen, D.P. Grote
  LLNL, Livermore, California
• M. Dorf, E.P. Gilson
  PPPL, Princeton, New Jersey
• D.R. Welch
  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:

1. greater axial compression via a longer velocity ramp;
2. beam steering dipoles to mitigate aberrations in the bunching module;
3. time-dependent focusing elements to correct considerable chromatic aberrations; and
4. plasma injection improvements to establish a plasma density always greater than the beam density, expected to be >10¹³ cm^-3.

Slides

• S.M. Lund, J.E. Coleman, S.M. Lidia, P.A. Seidl, C.J. Wootton
  LBNL, Berkeley, California

Funding: This research was performed under the auspices of the U.S. DOE at the Lawrence Livermore and Lawrence Berkeley National Laboratories under Contracts No. DE-AC52-07NA27344 and No. DE-AC02-05CH11231.

A recent theory in Ref. * analyzes small-amplitude oscillations of the transverse beam centroid (center of mass) in solenoidal transport channels. This theory employs a transformation to a rotating Larmor frame to simply express the centroid response to mechanical misalignments (transverse center displacements and tilts about the of the longitudinal axis of symmetry) of the solenoid and initial centroid errors. The centroid evolution is expressed in terms of a superposition of the centroid evolving in the ideal aligned system plus an expansion in terms of "alignment functions" that are functions of only the ideal lattice with corresponding amplitudes set by the solenoid misalignment parameters. This formulation is applied to analyze statistical properties of beam centroid oscillations induced by solenoid misalignments. Results are compared to experiments at the NDCX experiment at the LBNL. It is found that contributions to oscillation amplitudes from tilts are significantly larger than contributions from offsets for expected parameters. Use of the formulation to optimally steer the centroid back on-axis with limited diagnostic measurements is also discussed.

* S.M. Lund, C.J. Wootton, and E.P. Lee, "Transverse centroid oscillations in solenoidally focused beam transport lattices," accepted for publication, Nuc. Inst. Meth. A.