New developments in WARP: Progress toward end-to-end simulation

Ion beams (including protons) with low emittance and high space-charge intensity can be propagated with normal incidence through a sequence of thin metallic foils separated by vacuum gaps of order the characteristic transverse beam extent to transport/collimate the beam or to focus it to a small transverse spot. Energetic ions have sufficient range to pass through a significant number of thin foils with little energy loss or scattering. The foils reduce the (defocusing) radial electric self-field of the beam while not altering the (focusing) azimuthal magnetic self-field of the beam, thereby allowing passive self-beam focusing if the magnetic field is sufficiently strong relative to the residual electric field. Here we present an envelope model developed to predict the strength of this passive (beam generated) focusing effect under a number of simplifying assumptions including relatively long pulse duration. The envelope model provides a simple criterion for the necessary foil spacing for net focusing and clearly illustrates system focusing properties for either beam collimation (such as injecting a laser-produced proton beam into an accelerator) or for magnetic pinch focusing to a small transverse spot (for beam driven heating of materials). An illustrative example is worked for an idealization of a recently performed laser-produced proton-beam experiment to provide guidance on possible beam focusing and collimation systems. It is found that foils spaced on the order of the characteristic transverse beam size desired can be employed and that envelope divergence of the initial beam entering the foil lens must be suppressed to limit the total number of foils required to practical values for pinch focusing. Relatively modest proton-beam current at 10 MeV kinetic energy can clearly demonstrate strong magnetic pinch focusing achieving a transverse rms extent similar to the foil spacing (20-50 m gaps) in beam propagation distances of tens of mm. This is a surprisingly optimistic result since placing many foils per characteristic beam radius, which one might expect to be necessary to strongly attenuate the self-electric field, would likely result in excessive scattering and loss of focusing from the current neutralization due to the beam propagating too far through solid metal. Results from the envelope model are compared with particle-in-cell simulations to help clarify limits related to envelope-model idealizations. Possible degradations of focusing in situations where strong halo can be generated and where pulse duration is short are clarified.

Section: Particle-in-cell Simulationsmentioning

confidence: 99%

Envelope model for passive magnetic focusing of an intense proton or ion beam propagating through thin foils

Lund

Cohen

2013

“…Using the WARP [14] particle-in-cell computer code, simulations for a wide range of injected beam current showed that there is no expected particle loss as the beam drifts to the diagnostics in the absence of solenoid focusing. The diagnostics include a large Faraday cup with a negatively biased cylindrical electrode upstream of the collector to suppress the secondary e À yield due to ion impact, known to be significant at this energy [15].…”

Section: B Diagnosticsmentioning

confidence: 99%

Development and testing of a lithium ion source and injector

Seidl

Greenway

Grote

et al. 2012

We report on the development and testing of an intense lithium ion source and injector for an ion induction accelerator designed for warm, dense matter target heating experiments. The source is a 10.9-cm diameter aluminosilicate emitter on a porous tungsten substrate. For an injector voltage pulse of 120 kV, pulse duration of 1:0-s FWHM, and an operating temperature of 1250 C, the source emits 35 mA of Li þ ions. The results follow experimental studies with much smaller sources. The key challenges included beam quality, source lifetime, and heat management.

“…Numerical simulations were also performed in WARP [27][28][29][30] and LSP [23] to model the longitudinal dynamics. Both PIC methods used the experimental Marx waveform as an input to calculate the beam dynamics.…”

Section: Correlation Of the Longitudinal Measurements With The Mmentioning

confidence: 99%

Single-pulse and multipulse longitudinal phase space and temperature measurements of an intense ion beam

Coleman

Seidl

Bieniosek

et al. 2012

Longitudinal phase space and temperature measurements were conducted on a 2-3 s long, singly charged K þ ion bunch with an ion energy of $0:3 MeV and current of 30 mA. The principal objective of these experiments was to measure the longitudinal beam dynamics and study the limits of axial compression. The differences between the measured beam energy, longitudinal beam dynamics, and the amplitude and time history of the Marx voltage waveform were all quantified. Longitudinal phase space measurements indicate a slight chromaticity ( < 1%) in the beam from head to tail. Record low longitudinal temperatures of T z ¼ 2-4 Â 10 À2 eV were measured for a beam bunch of this intensity with negligible effects from neutralizing the beam space charge with a background plasma. A qualitative comparison of experimental and calculated results are presented, which include time resolved longitudinal distributions, and phase space of the beam at 430 cm.