An X-band multi-bunch test station is being built at LLNL to investigate the science and technology paths required to boost the current mono-energetic gamma-ray (MEGa-Ray) brightness by orders of magnitude. The test station will consist of a 5.5 cell X-band RF photoinjector, single accelerator section, and beam diagnostics. Beam quality must be exceedingly high in order to produce narrow-bandwidth gamma-rays, requiring a robust state of the art photoinjector. The photoinjector will be a high gradient (200 MV/m peak surface field on the cathode) standing wave structure, featuring a dual feed racetrack coupler, elliptical irises, and an optimized first cell length. A solidstate Scandinova modulator will power a single SLAC XL4 11.424 GHz 50 MW klystron. RF distribution will allow for full powering of the photoinjector with the balance of the RF powering a single accelerator section so that the electron parameters can be measured. The status of the facility will be presented including commissioning schedule and first experiment plans. Future experimental programs pertinent to Compton scattering R&D, high gradient structure testing, and light source development will be discussed.

A design for an X-band rf photoinjector that was developed jointly by SLAC National Accelerator Laboratory (SLAC) and Lawrence Livermore National Laboratory (LLNL) is presented. The photoinjector is based around a 5.59 cell rf gun that has state-of-the-art features including: elliptical contoured irises; improved mode separation; an optimized initial half cell length; a racetrack input coupler; and coupling that balances pulsed heating with cavity fill time. Radio-frequency and beam dynamics modeling have been done using a combination of codes including PARMELA, HFSS, IMPACT-T, ASTRA, and the ACE3P suite of codes developed at SLAC. The impact of lower gradient operation, magnet misalignment, solenoid multipole errors, beam offset, mode beating, wakefields, and beam line symmetry have been analyzed and are described. Fabrication and testing plans at both LLNL and SLAC are discussed.

Received 28 February 2011DOI:https://doi.org/10.1103/PhysRevLett.106.109903© 2011 American Physical Society

We demonstrate the hohlraum radiation temperature and symmetry required for ignition-scale inertial confinement fusion capsule implosions. Cryogenic gas-filled hohlraums with 2.2 mm-diameter capsules are heated with unprecedented laser energies of 1.2 MJ delivered by 192 ultraviolet laser beams on the National Ignition Facility. Laser backscatter measurements show that these hohlraums absorb 87% to 91% of the incident laser power resulting in peak radiation temperatures of T(RAD)=300 eV and a symmetric implosion to a 100 μm diameter hot core.

We present an optimized 5+ 1 cell, X-band photoinjector designed to produce 7 MeV, 250 pC, sub-micron emittance electron bunches for the LLNL Mono-Energetic Gammaray (MEGa-ray) light source. This LLNL/SLAC collaboration modifies a design previously demonstrated to sustain 200 MV/m on-axis accelerating fields [1]. We present the photoinjector operating point, optimized by scaling beam dynamics from S-band photo-guns and by evaluation of the MEGa-Ray source requirements.

Feasibility studies and manufacturing experience on the GEM Magnet conductor are presented, including all components-NbTi strand, cable, conduit manufacture, cable pulling, and aluminum sheath application.<>

This paper outlines a design technique for attaining much larger on-axis magnetic field tuning ranges in accurate, high magnetic field electromagnetic wigglers than have been heretofore possible. The general theory of ''tunability enhancement'' is described, followed by specific application to the magnetics design of the wiggler for the intense microwave prototype (IMP) free electron laser at the Lawrence Livermore National Laboratory.

Lawrence Livermore National Laboratory (LLNL) joined the multi- national L* Detector collaboration in early 1990. The L* Detector has been described in great detail in a number of documents submitted to the Superconducting Super Collider (SSC) Laboratory. LLNL`s participation in the L* collaboration consisted of a multi- disciplinary effort involving a number of physicists, engineers and technologists from different areas of the laboratory who came together to identify areas of research, development and engineering on the L* Detector where LLNL`s expertise and technological capabilities could best be utilized. Among these capabilities, superconducting magnet technology, chemistry and materials science, and design of new types of physics detectors were deemed areas of LLNL expertise best suited to the R&D effort needed for L*. This paper will describe the work carried out at LLNL on muon chamber R&D for the L* detector in FY 1991. Because of the L* proposal rejection in May 1991, and the subsequent restructuring to form the GEM detector collaboration in July 1991, the work described in this paper will also be seen to the applicable to the envisioned muon chamber subsystem for GEM.

We present here a conceptual design for an X-ray FEL operating at 45 Å and producing 0.1–1.0 GW of power. Its architecture is a single-pass amplifier with growth from spontaneous noise. It uses an electron beam of about 1.5 GeV and with a normalized emittance of about 20 mm mrad, a beam which may be accelerated in a relatively short length of a high-gradient accelerator driven by an X-band relativistic klystron. Examination of sensitivity of the FEL performance to energy spread, wiggler field errors, jitter in the positioning of the electron beam, and finite steering accuracy indicates that the requisite technologies for this design are imminently available.

Experimental work is being performed by collaborators at LLNL, SLAC, and LBL to investigate relativistic klystrons as a possible rf power source for future high-gradient accelerators. We have learned how to overcome or previously reported problem of high power rf pulse shortening and have achieved peak rf power levels of 330 MW using an 11.4-GHz high-gain tube with multiple output structures. In these experiments the rf pulse is of the same duration as the beam current pulse. In addition, experiments have been performed on two short sections of a high-gradient accelerator using the rf power from a relativistic klystron. An average accelerating gradient of 84 MV/m has been achieved with 80-MW of rf power.

Tapering a free electron laser (FEL) amplifier to improve extraction after gain saturation can be accomplished by varying both the wiggler period and the wiggler field. This paper considers specific FEL designs and demonstrates the improvement in extraction efficiency that can be achieved by utilizing both variations. Fabrication considerations make a continuously varying wiggler period impractical for long wigglers, and so this technique entails discontinuous steps in the wiggler period. Such steps in wiggler period must be introduced in a manner such that they do not induce steering in the electron beam for reasonable ranges of transverse velocities and energies nor induce a large spread in phase shifts. We discuss such techniques.