Final focus system for high intensity beams

Abstract

The NTX experiment at the Heavy Ion Fusion Virtual National Laboratory is exploring the performance of neutralized final focus systems for high perveance heavy ion beams. The NTX final focus system produces a converging beam at the entrance to the neutralized drift section where it focuses to a small spot. The final focus lattice consists of four pulsed quadrupole magnets. The main issues are the control of emittance growth due to high order fields from magnetic multipoles and image fields. We will present experimental results from NTX on beam envelope and phase space distributions, and compare these results with particle simulations using the particle-in-cell code WARP.

Overview of theory and simulations in the Heavy Ion Fusion Science Virtual National Laboratory

“…However, transport using solenoids scales well to high line charge densities and low kinetic energies, and is currently preferred for the HEDP mission. Analysis and simulations have been clarifying this physics [32] and were applied to the design and interpretion of the STX [33]. Alignment requirements in solenoid systems have been assessed via WARP runs [34].…”

US Heavy Ion Beam Research for High Energy Density Physics Applications and Fusion

“…For fusion energy applications, either un-neutralized [29 -31] or neutralized [32][33][34][35][36][37][38][39] compression may be considered. In the un-neutralized case, to describe the drift compression dynamics and the final focus of the beam particles to a common axial plane and prescribed focal spot size, a warm-fluid model has been employed to describe the longitudinal dynamics of drift compression, coupled nonlinearly to envelope equations that describe the self-consistent transverse dynamics and focusing of the ion beam as it propagates through the quadrupole focusing lattice [30,31].…”

“…Simulations and analysis have also been carried out [33 -35] in support of the Neutralized Drift Compression Experiment (NDCX) described in Sec. III, and neutralized transverse focusing has been studied in simulations for the general case [36] and for experiments in the Neutralized Transport Experiment (NTX) [37,38] described in Sec. III.…”

Focusing and neutralization of intense beams

“…The second phase of NTX consists of magnetic transport with 4 pulsed quadrupoles [9] enclosing a thinwall stainless steel tube approximately 26 cm in diameter. The half-lattice period is 60 cm.…”

“…These changes were measured optically, and found to be in excellent agreement with predictions of WARP3D, a 3-D particle-in-cell code for space charge dominated beam transport. [9] In Figure 5 we show the variations with beam energy (in steps of 3%) of the measured beam image (bottom row) against WARP3D simulations (top row). …”