[en] The Diagnostic X (D-X) beamlines will transport the DARHT-II beam from the end of the accelerator to the Diagnostic X firing point providing four lines of sight for x-ray radiography. The design goal for the Diagnostic X beamline is to deliver four x-ray pulses with the DARHT-II dose format and time integrated spot size on each line of sight. The D-X beamline's final focus should be compatible with a range of first conjugates from 1 m-5 m. Furthermore, the D-X beamline operational parameters and the beamline layout should not preclude a possible upgrade to additional lines of sight. The DARHT-II accelerator is designed to deliver beams at a rate of 1 pulse per minute or less. Tuning the D-X beamline with several hundred optical elements would be time consuming. Therefore, minimizing the required number of tuning shots for the D-X beamline is also an important design goal. Many different beamline configurations may be able to accomplish these design objectives, and high beam quality (i.e., high current and low emittance) must be maintained throughout the chosen beamline configuration in order to achieve the DARHT-II x-ray dose format. In general, the longer the distance a beam travels, the harder it is to preserve the beam quality. Therefore, from the point of view of maintaining beam quality, it is highly desirable to minimize the beamline length. Lastly, modification to the DARHT-II building and the downstream transport should be minimized. Several processes can degrade beam quality by increasing the beam emittance, increasing the time-varying transverse beam motion, creating a beam halo, or creating a time-varying beam envelope. In this report, we consider those processes in the passive magnet lattice beamline and indicate how they constrain the beamline design. The physics design considerations for the active components such as the kicker system will be discussed in Ref. 2. In Sec. I, we discuss how beam emittance affects the x-ray forward dose. We also establish a physics design goal for the emittance growth budget. In Sec. II, we discuss how the conductivity and size of the beam pipe affects the transverse beam motion. We also discuss the emittance growth arise from the beam centroid offset. In Sec. III, we discuss the background gas focusing effects and establish the vacuum requirements. In Sec. IV, we consider the emittance growth in a bend. In Sec. V, we discuss the misalignment and corkscrew motion. The design specifications for misalignment are established. In Secs. VI and VII, we discuss the design objectives on how to extract beams from the DARHT-II beamline and how to minimize the tuning shots. The integrated spot size and final focusing are discussed in Sec. VIII. A conclusion will be presented in Sec. IX

[en] At LLNL resistive wall monitors are used to measure the current and position used on ETA-II show a droop in signal due to a fast redistribution time constant of the signals. This paper presents the analysis and experimental test of the beam bugs used for beam current and position measurements in and after the fast kicker. It concludes with an outline of present and future changes that can be made to improve the accuracy of these beam bugs. of intense electron beams in electron induction linacs and beam transport lines. These, known locally as beam bugs, have been used throughout linear induction accelerators as essential diagnostics of beam current and location. Recently, the development of a fast beam kicker has required improvement in the accuracy of measuring the position of beams. By picking off signals at more than the usual four positions around the monitor, beam position measurement error can be greatly reduced. A second significant source of error is the mechanical variation of the resistor around the bug

[en] The DARHT-II beam line utilizes a fast stripline kicker to temporally chop a high current electron beam from a single induction LINAC and deliver multiple temporal electron beam pulses to an x-ray converter target. High beam quality needs to be maintained throughout the transport line from the end of the accelerator through the final focus lens to the x-ray converter target to produce a high quality radiographic image. Issues that will affect beam quality such as spot size and emittance at the converter target include dynamic effects associated with the stripline kicker as well as emittance growth due to the nonlinear forces associated with the kicker and various focusing elements in the transport line. In addition, dynamic effects associated with transverse resistive wall instability as well as gas focusing will affect the beam transport. A particle-in-cell code is utilized to evaluate beam transport in the downstream transport line in DARHT-II. External focusing forces are included utilizing either analytic expressions or field maps. Models for wakefields from the beam kicker, transverse resistive wall instability, and gas focusing are included in the simulation to provide a more complete picture of beam transport in DARHT-II. From these simulations, for various initial beam loads based on expected accelerator performance the temporally integrated target spot size and emittance can be estimated

[en] Advanced radiographic systems for stockpile stewardship require very small x-ray sources to achieve the required resolution. Focusing multi-kiloampere beams to diameters on the order of 1 mm onto a Bremsstrahlung target leads to the generation of axial electric fields on the order of several MV/cm which act to extract ions out of the surface plasma and accelerate them upstream into the beam. These backstreaming ions act as a distributed electrostatic lens which can perturb the focus of the electron beam in a time varying manner during the pulse. An analytic model of the ion extraction is presented for a particular target geometry along with scaling laws for the perturbation of the focal spot

[en] Results are presented for the 500 GeV/c pion production asymmetry and polarization of the Λ_c (bar Λ_c) charmed baryon from Fermilab experiment E791. An analysis of the decay to the pbar K

[en] A fast stripline beam kicker is used to dynamically switch a high current electron beam between two beamlines. The transverse dipole impedance of a stripline beam kicker has been previously determined from a simple transmission line model of the structure. This model did not include effects due to the long axial slots along the structure as well as the cavities and coaxial feed transition sections at the ends of the structure. 3-D time domain simulations show that the simple transmission line model underestimates the low frequency dipole beam coupling impedance by about 20% for our structure. In addition, the end cavities and transition sections can exhibit dipole impedances not included in the transmission line model. For high current beams, these additional dipole coupling terms can provide additional beam-induced steering effects not included in the transmission line model of the structure

[en] In phase two of the Dual-Axis Radiographic Hydrodynamic Test facility (DARHT-II), four electron beam pulses of variable pulse length strike an X-ray converter target to produce time-resolved X-ray image. An important requirement for the converter target is to minimize the hydrodynamic expansion of the converter material so that there is enough material to generate the required X-ray dose for all four pulses. Minimizing the hydrodynamic expansion is also important from the standpoint of beam transport. If there is too much expansion of the converter material, the spot-size of the beam will deteriorate due to the charge neutralization of the beam by the target plasma. The beam spot size can also be deteriorated by backstreaming ions. However, this effect can be minimized by placing a barrier foil in front of the target. In this paper, we present a converter target design, based on the simulations using the radiation hydrodynamics code LASNEX and the Monte Carlo radiation transport code MCNP, that can produce the required X-ray dose for all four pulses with tolerable X-ray spot size variation. Our calculations also show that the barrier foil may block the backstreaming ions for all four pulses

[en] The accelerator on the second-axis of the Dual-Axis Radiographic Hydrodynamic Test (DARHT-II) facility will generate a 20 MeV, 2-4 kA, 2 s long electron beam with an energy variation ≤ 0.5%. Four short current pulses with various lengths will be selected out of this 2 s long current pulse and delivered to an x-ray converter target. The DARHT-II radiographic resolution requires these electron pulses to be focused to sub-millimeter spots on Bremsstrahlung targets with peak-to-peak transverse beam motion less than a few hundred microns. We have modeled the transverse beam motion, including the beam breakup instability, corkscrew motion, transverse resistive wall instability and beam induced transverse deflection in the kicker system, from the DARHT-II injector exit to the x-ray converter target. Simulations show that the transverse motion at the x-ray converters satisfies the DARHT-II radiographic requirements

[en] A fast stripline beam kicker and septum are used to dynamically switch a high current electron beam between two beamlines. The transport of the beam through these structures is determined by the quality of the applied electromagnetic fields as well as temporal effects due to the wakefields produced by the beam. In addition, nonlinear forces in the structure will lead to emittance growth. The effect of these issues is investigated analytically and by using particle transport codes. Due to the distributed nature of the beam-induced effects, multiple macro-particles (slices) are used in the particle transport code, where each slice consists of an ensemble of particles with an initial distribution in phase space. Changes in the multipole moments of an individual slice establish electromagnetic wakes in the structure and are allowed to interact with subsequent beam macro-particles to determine the variation of the steering, focusing, and emittance growth during the beam pulse

[en] Recent progress in the development and understanding of linear induction accelerator have produced machines with 10s of MeV of beam energy and multi-kiloampere currents. Near-term machines, such as DARHT-2, are envisioned with microsecond pulselengths. Fast beam kickers, based on cylindrical electromagnetic stripline structures, will permit effective use of these extremely high-energy beams in an increasing number of applications. In one application, radiography, kickers were an essential element in resolving temporal evolution of hydrodynamic events by cleaving out individual pulses from long, microsecond beams. Advanced schemes are envisioned where these individual pulses are redirected through varying length beam lines and suitably recombined for stereographic imaging or tomographic reconstruction. Recent advances in fast kickers and their pulsed power technology are described. Kicker pulsers based on both planar triode and all solid-state componentry are discussed and future development plans are presented