UCI, Irvine, California, USA
LLNL, Livermore, California, USA
The mean energy, energy spread and divergence of the electron beam can be deduced from laser-Compton scattered X-rays filtered by a material whose K-edge is near the energy of the X-rays. This technique, combined with a spot size measurement of the beam, can be used to measure the emittance of electron bunches, and can be especially useful in LWFA experiments where conventional methods are unavailable. The effects of the electron beam parameters on X-ray absorption images are discussed, along with experimental demonstrations of the technique using the Compact Laser-Compton X-ray Source at LLNL.
LLNL, Livermore, California, USA
UCI, Irvine, California, USA
LLNL's compact laser-Compton based x-ray source is currently producing up to 35 keV photons, with the capability to upgrade to 250 keV. Increasing the average brightness of such sources requires increasing the electron beam current. To avoid degradation of the narrow-bandwidth performance of the source, the per-bunch charge shouldn't increase; the effective repetition rate of the electron beams must be raised. It has been proposed* to generate bunch trains of several hundred pulses spaced by the period of X-band RF (~87 ps), which raises questions about beam-loading effects on the energy uniformity of the bunches and wakefield effects degrading the emittance of later bunches, compromising the x-ray quality. As a first test of this concept, we have installed into the electron-generating laser of our system optical pulse-stacking hardware to allow generation of 16-electron-bunch trains. Here we present the current status of our x-ray source, along with initial results using this new multi-bunch train. This includes characterization of collective electron beam energy spread and emittance growth.
* D.J. Gibson, et al., IPAC2012.
LLNL, Livermore, California, USA
Lawrence Livermore National Lab (LLNL) is developing an intense, high-brightness fast neutron source to create sub-mm-scale resolution neutron radiographs and images. A pulsed 7MeV, 300μA average-current commercial deuteron accelerator will produce an intense source (1011 n/s/sr at 0 deg) of fast neutrons (10MeV) using a novel neutron target with a small (1.5mm diameter) beam spot size to achieve high resolution. A highly flexible multi-accelerator beamline has been developed allowing for the use of both 4MeV and 7MeV RFQ/DTL deuteron accelerators. TRACE3D has been used to model the beam transport and design the quadrupole lattice and results will be presented including iterated design within beamline mechanical constraints, sensitivities, and multiple use of the magnets. Because of the high power density of such a tightly focused, modest-energy ion beam, intercepting beam diagnostics are extremely challenging, motivating novel concepts and extensions of current techniques to higher average power densities. Full duty factor beamline diagnostics will be discussed including charge, position, emittance via beam-induced fluorescence, and a full power beam dump and Faraday cup.
LLNL, Livermore, California, USA
Lawrence Livermore National Lab (LLNL) is building an intense, high-brightness fast neutron source to create millimeter-scale neutron radiographs and images. An intense source (1011 n/s/sr at 0 degrees) of fast neutrons (10 MeV) allows for penetrating very thick, dense objects while preserving the ability to create good image contrast in low density features within the object and maintaining high detector response efficiency. Fast neutrons will be produced using a pulsed 7 MeV, 300 microamp average-current commercial ion accelerator that will deliver deuteron bunches to a 3 atmosphere deuterium gas cell target to produce neutrons by the D(d, n)3He reaction. Due to the high power density of such a tightly focused, modest-energy ion beam, the transport, controls, diagnostics, and in particular the neutron production gas target and beam stop approaches present significant engineering challenges. Progress and status on the building and early commissioning of the lab-scale demonstration machine shall be presented.
UCI, Irvine, California, USA
LLNL, Livermore, California, USA
Compton scattering of laser photons by a relativistic electron beam produces monoenergetic, tunable and small source size X-rays similar to synchrotron light sources in a very compact setting, due to the shorter undulator period of lasers. These X-ray sources can bring to every hospitals advanced radiology and radiotherapy that are currently only being conducted at synchrotron facilities. Few examples include phase contrast imaging utilizing the micron-scale source size, K-edge subtraction imaging from two monoenergetic X-rays at different energies and radiation therapy using radiosensitization of high-Z nanoparticles. At LLNL, 30 keV X-rays have been generated from the 30 MeV X-band linac, and the X-rays have been characterized and agree with the modeling very well. This source is being used to study the feasibility of aforementioned medical applications. Experimental setup of K-edge subtraction of contrast agents are presented, demonstrating the low-dose, high-contrast imaging potential of the light source. Plans to study enhanced radiotherapy using Gold nanoparticles with the upgrade of the machine to higher energies are discussed.