A. Zholents

Generation of subpicosecond X-ray pulses using RF orbit deflection

Abstract A technique is proposed for producing high average intensity X-ray radiation from a storage ring for studies of the ultrafast phenomena on a subpicosecond time scale. Two RF cavity accelerating structures excited in the E 110 mode can be installed in a storage ring to create vertical displacements of electrons correlated with their longitudinal position in the bunch. The magnitude of these displacements can be sufficient for the X-ray radiation of the electron bunch between accelerating structures to be viewed as produced by a large number of independent sources, each of a subpicosecond duration.

Design Studies for a VUV–Soft X-ray Free-Electron Laser Array

Several recent reports have identified the scientific requirements for a future soft X-ray light source [1, 2, 3, 4, 5], and a high-repetition-rate free-electron laser (FEL) facility responsive to them is being studied at Lawrence Berkeley National Laboratory (LBNL) [6]. The facility is based on a continuous-wave (CW) superconducting linear accelerator with beam supplied by a high-brightness, high-repetition-rate photocathode electron gun operating in CW mode, and on an array of FELs to which the accelerated beam is distributed, each operating at high repetition rate and with even pulse spacing. Dependent on the experimental requirements, the individual FELs may be configured for either self-amplified spontaneous emission (SASE), seeded high-gain harmonic generation (HGHG), echo-enabled harmonic generation (EEHG), or oscillator mode of operation, and will produce high peak and average brightness X-rays with a flexible pulse format ranging from sub-femtoseconds to hundreds of femtoseconds. This new light source would serve a broad community of scientists in many areas of research, similar to existing utilization of storage ring based light sources.

Science and Technology of Future Light Sources

Science and Technology of Future Light Sources A White Paper Report prepared by scientists from ANL, BNL, LBNL and SLAC. The coordinating team consisted of Uwe Bergmann, John Corlett, Steve Dierker, Roger Falcone, John Galayda, Murray Gibson, Jerry Hastings, Bob Hettel, John Hill, Zahid Hussain, Chi-Chang Kao, Janos Kirz, Gabrielle Long, Bill McCurdy, Tor Raubenheimer, Fernando Sannibale, John Seeman, Z.-X. Shen, Gopal Shenoy, Bob Schoenlein, Qun Shen, Brian Stephenson, Joachim Stohr, and Alexander Zholents. Other contributors are listed at the end of the document. Argonne National Laboratory Brookhaven National Laboratory Lawrence Berkeley National Laboratory SLAC National Accelerator Laboratory December 2008

Design Studies for a High-Repetition-Rate FEL Facility at LBNL

Lawrence Berkeley National Laboratory (LBNL) is working to address the needs of the primary scientific Grand Challenges now being considered by the U.S. Department of Energy, Office of Basic Energy Sciences: we are exploring scientific discovery opportunities, and new areas of science, to be unlocked with the use of advanced photon sources. A partnership of several divisions at LBNL is working to define the science and instruments needed in the future. To meet these needs, we propose a seeded, high-repetition-rate, free-electron laser (FEL) facility. Temporally and spatially coherent photon pulses, of controlled duration ranging from picosecond to sub-femtosecond, are within reach in the vacuum ultraviolet (VUV) to soft X-ray regime, and LBNL is developing critical accelerator physics and technologies toward this goal. We envision a facility with an array of FELs, each independently configurable and tunable, providing a range of photon-beam properties with high average and peak flux and brightness.

Longitudinal phase space control in the Berkeley Femtosecond X-ray light source LUX

LUX, the proposed Berkeley Femtosecond X-ray light source, is a /spl sim/2.5 GeV recirculating linear accelerator, where electrons reach their final energy in four passes through a 600 MeV superconducting linac after injection at /spl sim/120 MeV. An important consideration for this machine is the preservation of the electron beam longitudinal emittance through the various stages of acceleration including injection linac, bunch compression, and various passages through the linac and magnetic arcs. In this paper we analyze the longitudinal dynamics of electrons and define a strategy for the electron beam manipulation leading to a successful conservation of the longitudinal emittance. Particular attention is given to the management of the correlated energy spread induced by collective effects such as longitudinal wake fields and coherent synchrotron radiation (CSR).

Critical issues for high-power FEL based on microtron recuperator/electron out-coupling scheme

The FELs based on the rf accelerator-recuperator and the electron outcoupling is promising for obtaining average output power of hundreds of kilowatts. We present basic considerations for the system stability and performance optimization for this scheme.

Low Energy Ring lattice of the PEP-II asymmetric B-factory

Developing a lattice that contains a very low beta value at the interaction point (IP) and has adequate dynamic aperture is one of the major challenges in designing the PEP-II asymmetric B-factory. For the Low Energy Ring (LER) we have studied several different chromatic correction schemes since the conceptual design report (CDR). Based on these studies, a hybrid solution with local and semi-local chromatic sextupoles has been selected as the new baseline lattice to replace the local scheme in the CDR. The new design simplifies the interaction region (IR) and reduces the number of sextupoles in the arcs. Arc sextupoles are paired at /spl pi/ phase difference and are not interleaved. In this paper we describe the baseline lattice with the emphasis on the lattice changes made since the CDR.

Current-enhanced SASE using an optical laser and its application to the LCLS

We propose a significant enhancement of the electron peak current entering a SASE undulator by inducing an energy modulation in an upstream wiggler magnet via resonant interaction with an optical laser, followed by microbunching of the energy-modulated electrons at the accelerator exit. This current enhancement allows a reduction of the FEL gain length. The x-ray output consists of a series of uniformly spaced spikes, each spike being temporally coherent. The duration of this series is controlled by the laser pulse and in principle can be narrowed down to just a single, ~;200-attosecond spike. Given potentially absolute temporal synchronization of the x-ray spikes to the energy-modulating laser pulse, this scheme naturally makes pump-probe experiments available to SASE FELs. We also study various detrimental effects related to the high electron peak current.

Initial feasibility study of a dedicated synchrotron radiation light source for ultrafast X-ray science

We present an initial feasibility summary of a femtosecond synchrotron radiation x-ray source based on a flat-beam rf gun and a recirculating superconducting linac that provides beam to an array of undulators and bend magnets. Optical pulse durations of < 100 fs are obtained by a combination of electron pulse compression, transverse temporal correlation of the electrons, and x-ray pulse compression. After an introduction and initial scientific motivation, we cover the following aspects of the design: layout and lattice, ultra-fast x-ray pulse production, flat electron-beam production, the rf gun, rf systems, cryogenic systems, collective effects, photon production, and synchronization of x-ray and laser pulses. We conclude with a summary of issues and areas of development that remain to be addressed.

FEL design for power beaming

We are reporting on the current design status of the 200 kW average power FEL at a 0.84 micron wavelength for power beaming of satellites. The project includes a cw RF photocathode gun injector, a cw linear accelerator, achromatic beam transport lines and an FEL amplifier. Problems that are specific to our design are considered.