Fernando Sannibale

VHF-band Photoinjector

New generation accelerator-based x-ray light sources require high quality electron beams. Parameters such as transverse emittance (projected or “sliced”), energy spread and bunch length for beams in the nC charge range, need to be pushed beyond their present limits for the successful operation of light sources such as Energy Recovery Linacs (ERL) and Free Electron Lasers (FEL). At the same time, the demand for a high average brightness is also driving towards technologies capable of very high repetition rate operation. The overall performance is greatly determined at the accelerator injector and in particular, at the electron gun. In this note, we present a new concept for a high repetition-rate photoinjector, capable of providing pulses up to at least 1 MHz or more.

Generation of Picosecond X-Ray Pulses in the ALS Using RF Orbit Deflection

A scheme is proposed for producing ps length pulses of x-ray radiation from the Advanced Light Source (ALS) using two RF deflecting cavities. The cavities create vertical displacements of electrons correlated with their longitudinal position in the bunch. The two cavities separated by 180 degrees of vertical phase advance. This allows the vertical kick from one cavity to be compensated by the vertical kick of the other. The location of the cavities corresponds to the end of one straight section and the beginning of the following straight section. Halfway between the cavities a bending magnet source is located. The radiation from the bend can be compressed to ∼ 1 ps in duration.

Science and Technology of Future Light Sources: A White Paper

Many of the important challenges facing humanity, including developing alternative sources of energy and improving health, are being addressed by advances that demand the improved understanding and control of matter. While the visualization, exploration, and manipulation of macroscopic matter have long been technological goals, scientific developments in the twentieth century have focused attention on understanding matter on the atomic scale through the underlying framework of quantum mechanics. Of special interest is matter that consists of natural or artificial nanoscale building blocks defined either by atomic structural arrangements or by electron or spin formations created by collective correlation effects (Figure 1.1). The essence of the challenge to the scientific community has been expressed in five grand challenges for directing matter and energy recently formulated by the Basic Energy Sciences Advisory Committee [1]. These challenges focus on increasing our understanding of, and ultimately control of, matter at the level of atoms, electrons. and spins, as illustrated in Figure 1.1, and serve the entire range of science from advanced materials to life sciences. Meeting these challenges will require new tools that extend our reach into regions of higher spatial, temporal, and energy resolution. X-rays with energies above 10 keV offer capabilities extending beyondmorexa0» the nanoworld shown in Figure 1.1 due to their ability to penetrate into optically opaque or thick objects. This opens the door to combining atomic level information from scattering studies with 3D information on longer length scales from real space imaging with a resolution approaching 1 nm. The investigation of multiple length scales is important in hierarchical structures, providing knowledge about function of living organisms, the atomistic origin of materials failure, the optimization of industrial synthesis, or the working of devices. Since the fundamental interaction that holds matter together is of electromagnetic origin, it is intuitively clear that electromagnetic radiation is the critical tool in the study of material properties. On the level of atoms, electrons, and spins, x-rays have proved especially valuable. Future advanced x-ray sources and instrumentation will extend the power of x-ray methods to reach greater spatial resolution, increased sensitivity, and unexplored temporal domains. The purpose of this document is threefold: (1) summarize scientific opportunities that are beyond the reach of todays x-ray sources and instrumentation; (2) summarize the requirements for advanced x-ray sources and instrumentation needed to realize these scientific opportunities, as well as potential methods of achieving them; and (3) outline the R&D required to establish the technical feasibility of these advanced x-ray sources and instrumentation.«xa0less

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 of a VHF-band RF photoinjector with megahertz beam repetition rate

New generation accelerator-based X-ray light sources require high quality beams with high average brightness. Normal conducting L- and S-band photo injectors are limited in repetition rate and D-C (photo)injectors are limited in field strength at the cathode. We propose a low frequency normal-conducting cavity, operating at 50 to 100 MHz CW, to provide beam bunches of up to the cavity frequency. The photoinjector uses a re-entrant cavity structure, requiring less than 100 kW CW, with a peak wall power density less than 10 W/cm2. The cavity will support a vacuum down to 10 picoTorr, with a load-lock mechanism for easy replacement of photocathodes. The photocathode can be embedded in a magnetic field to provide correlations useful for emittance exchange. Beam dynamics simulations indicate that normalized emittances smaller than 1 mm-mrad are possible with gap voltage of 750 kV, with fields up to 20 MV/m at the photocathode, for 1 nanocoulomb charge per bunch after acceleration and emittance compensation. Long-bunch operation (10s of picosecond) is made possible by the low cavity frequency, permitting low bunch current at the 750 kV gap voltage.

A high repetition rate VUV-soft X-ray FEL concept

We report on design studies for a seeded FEL light source that is responsive to the scientific needs of the future. The FEL process increases radiation flux by several orders of magnitude above existing incoherent sources, and offers the additional enhancements attainable by optical manipulations of the electron beam: control of the temporal duration and bandwidth of the coherent output, reduced gain length in the FEL, utilization of harmonics to attain shorter wavelengths, and precise synchronization of the X-ray pulse with seed laser systems. We describe an FEL facility concept based on a high repetition rate RF photocathode gun, that would allow simultaneous operation of multiple independent FELs, each producing high average brightness, tunable over the VUV-soft X-ray range, and each with individual performance characteristics determined by the configuration of the FEL. SASE, enhanced-SASE (ESASE), seeded, harmonic generation, and other configurations making use of optical manipulations of the electron beam may be employed, providing a wide range of photon beam properties to meet varied user demands.

A second beam-diagnostic beamline for the Advanced Light Source

A second beamline, BL 7.2, completely dedicated to beam diagnostics is being installed at the Advanced Light Source (ALS). The design has been optimized for the measurement of the momentum spread and emittance of the stored beam in combination with the existing diagnostic beamline, BL 3.1. A detailed analysis of the experimental error has allowed the definition of the system parameters. The obtained requirements found a good matching with a simple and reliable system based on the detection of X-ray synchrotron radiation (SR) through a pinhole system. The actual beamline, which also includes a port for visible and infrared SR as well as an X-ray beam position monitor (BPM), is mainly based on the design of two similar diagnostic beamlines at BESSY II. This approach allowed a significant saving in time, cost and engineering effort. The design criteria, including a summary of the experimental error analysis, as well as a brief description of the beamline are presented.

R&D for a Soft X-Ray Free Electron Laser Facility

R&D for a Soft X-Ray Free Electron Laser Facility A White Paper Report prepared by LBNL and SLAC with contributions from LBNL: David Attwood, John Byrd, John Corlett, Peter Denes, Roger Falcone, Phil Heimann, Wim Leemans, Howard Padmore, Soren Prestemon, Fernando Sannibale, Ross Schlueter, Carl Schroeder, John Staples, Marco Venturini, Tony Warwick, Russell Wells, Russell Wilcox, and Alexander Zholents SLAC: Chris Adolphsen, John Arthur, Uwe Bergmann, Yunhai Cai, Eric Colby, David Dowell, Paul Emma, John Fox, Josef Frisch, John Galayda, Robert Hettel, Zhirong Huang, Nan Phinney, Tom Rabedeau, Tor Raubenheimer, David Reis, John Schmerge, Joachim Stohr, Gennady Stupakov, Bill White, and Dao Xiang Lawrence Berkeley National Laboratory SLAC National Accelerator Laboratory June 2009

Scientific Needs for Future X-ray Sources in the U.S. -- A White Paper

Many of the important challenges facing humanity, including developing alternative sources of energy and improving health, are being addressed by advances that demand the improved understanding and control of matter. While the visualization, exploration, and manipulation of macroscopic matter have long been technological goals, scientific developments in the twentieth century have focused attention on understanding matter on the atomic scale through the underlying framework of quantum mechanics. Of special interest is matter that consists of natural or artificial nanoscale building blocks defined either by atomic structural arrangements or by electron or spin formations created by collective correlation effects (Figure 1.1). The essence of the challenge to the scientific community has been expressed in five grand challenges for directing matter and energy recently formulated by the Basic Energy Sciences Advisory Committee. These challenges focus on increasing our understanding of, and ultimately control of, matter at the level of atoms, electrons, and spins, as illustrated in Figure 1.1. Meeting these challenges will require new tools that extend our reach into regions of higher spatial, temporal, and energy resolution. Since the fundamental interaction that holds matter together is of electromagnetic origin, it is intuitively clear that electromagnetic radiation is the critical tool in the study of material properties. On the level of atoms, electrons and spins, x rays have proved especially valuable.

Measurements of impedance and beam instabilities at the Australian Synchrotron

In this paper we present the first measurements of machine impedance and observed beam instabilities at the Australian Synchrotron. Impedance measurements are made by studying the single bunch behaviour with beam current, using optical and X-ray diagnostic beamlines. An observed coupled-bunch instability, its cause and cure is also discussed.