Beam Dynamics in a Long-pulse Linear Induction Accelerator

2014

Beam dynamics issues are assessed for a new linear induction electron accelerator being designed for flash radiography of large explosively driven hydrodynamic experiments. Special attention is paid to equilibrium beam transport, possible emittance growth, and beam stability. It is concluded that a radiographic quality beam will be produced possible if engineering standards and construction details are equivalent to those on the present radiography accelerators at Los Alamos.* The cathode emission surface to anode shroud dimension should not be confused with the actual anodecathode (AK) gap, which is defined by a virtual anode located in the exit pipe somewhat downstream of the anode shroud. However, it is a convenient dimension for diode simulation comparisons, so it is frequently called the "AK gap," and that common usage is preserved in this article.

Section: A Beam Breakupmentioning

confidence: 99%

Beam Dynamics for ARIA

2014

“…Only the diode voltage and beam current are measured on DARHT-II. Therefore, we rely on computer simulations the injector for the initial conditions and emittance [3]. The DARHT-II injector is based on a diode with a hot, dispenser cathode as the source of electrons.…”

Section: Introductionmentioning

confidence: 99%

Fidelity of hot-cathode injector simulations

2018

It is presently planned to use a hot-cathode injector for the new multi-pulse Scorpius linear induction accelerator (LIA). Design of this multi-pulse hot-cathode diode at LLNL might use the Trak gun-design code. This code has been used extensively for simulations of the DARHT-II long-pulse hotcathode diode. Comparison of Trak simulations with PIC code simulations and experimental data have been in excellent agreement, over a broad range of beam energy, from nonrelativistic to fully relativistic. This is largely due to the hot dispenser cathode physics, which ensures that an adequate source of electrons is available at any applied voltage, so long as the cathode is at operating temperature. This fact, and the agreement of Trak with experimental data and PIC simulations, provides confidence in the ability of Trak to accurately predict the diode current resulting from an applied voltage waveform for a Scorpius pulse format.

“…The 2-kA, 20-MeV Axis-I LIA creates a single 60-ns radiography pulse. The 1.7-kA, 16.5-MeV Axis-II creates multiple radiography pulses by kicking them out of a 1600-ns long pulse from the LIA [3,4,5].…”

Section: Introductionmentioning

confidence: 99%

Emittance growth in the DARHT Axis-II Downstream Transport

Schulze

2015

Using a particle-in-cell (PIC) code, we investigated the possibilities for emittance growth through the quadrupole magnets of the system used to transport the high-current electron beam from an induction accelerator to the bremsstrahlung converter target used for flash radiography. We found that even highly mismatched beams exhibited little emittance growth (< 6%), which we attribute to softening of their initial hard edge current distributions. We also used this PIC code to evaluate the accuracy of emittance measurements using a solenoid focal scan following the quadrupole magnets. If the beam is round after the solenoids, the simulations indicate that the measurement is highly accurate, but it is substantially inaccurate for elliptical beams.