Simulations and experiments of intense ion beam current density compression in space and time

The Heavy Ion Fusion Science Virtual National Laboratory has achieved 60-fold longitudinal pulse compression of ion beams on the Neutralized Drift Compression Experiment (NDCX) [P. K. Roy, Phys. Rev. Lett. 95, 234801 (2005)]. To focus a space-charge-dominated charge bunch to sufficiently high intensities for ion-beam-heated warm dense matter and inertial fusion energy studies, simultaneous transverse and longitudinal compression to a coincident focal plane is required. Optimizing the compression under the appropriate constraints can deliver higher intensity per unit length of accelerator to the target, thereby facilitating the creation of more compact and cost-effective ion beam drivers. The experiments utilized a drift region filled with high-density plasma in order to neutralize the space charge and current of an ∼300 keV K⁺ beam and have separately achieved transverse and longitudinal focusing to a radius <2 mm and pulse duration <5 ns, respectively. Simulation predictions and recent experiments demonstrate that a strong solenoid (B _z <100 kG) placed near the end of the drift region can transversely focus the beam to the longitudinal focal plane. This paper reports on simulation predictions and experimental progress toward realizing simultaneous transverse and longitudinal charge bunch focusing. The proposed NDCX-II facility would capitalize on the insights gained from NDCX simulations and measurements in order to provide a higher-energy (>2 MeV) ion beam user-facility for warm dense matter and inertial fusion energy-relevant target physics experiments.