SLAC, Menlo Park, California, USA
LBNL, Berkeley, California, USA
Five months after first lasing in April 2009, the Linac Coherent Light Source (LCLS) began its first round of x-ray experiments. The facility rapidly attained and surpassed its design goals in terms of spectral tuning range, peak power, energy per pulse and pulse duration. There is an ongoing effort to further expand capabilities while supporting a heavily subscribed user program. The facility continues to work toward new capabilities such as multiple-pulse operation, pulse durations in the femtosecond range, and production of >16 keV photons by means of a second-harmonic “afterburner” undulator. Future upgrades will include self-seeding and polarization control. The facility is already planning to construct a major expansion, with two new undulator sources and space for four new experiment stations.
LBNL, Berkeley, California, USA
UCB, Berkeley, California, USA
ANL, Argonne, USA
The Next Generation Light Source (NGLS) is a design concept, under development at LBNL, for a multi‐beamline soft x‐ray FEL array powered by a 2 GeV superconducting linear accelerator, operating with a 1 MHz bunch repetition rate. The CW superconducting linear accelerator is supplied by a high-brightness, high-repetition-rate photocathode electron gun. Electron bunches are distributed from the linac to the array of independently configurable FEL beamlines with nominal bunch rates up to 100 kHz in each FEL, and with even pulse spacing. Individual FELs may be configured for EEHG, HGHG, SASE, or oscillator mode of operation, and will produce high peak and average brightness x-rays with a flexible pulse format, and with pulse durations ranging from sub-femtoseconds to hundreds of femtoseconds.
FEL/Duke University, Durham, North Carolina, USA
PKU/IHIP, Beijing, People's Republic of China
Recently, the Duke optical klystron FEL (OK-5 FEL) has been commissioned to produce lasing in the VUV region (191 - 193 nm), overcoming substantial laser cavity loss due to low reflectivity of the VUV FEL mirrors. With two OK-5 FEL wigglers separated by more than 20 meters in a non-optimal configuration, an adequate FEL gain was realized by operating the Duke storage ring with a high single-bunch current (30 to 50 mA). This VUV FEL has enabled us to produce circularly polarized Compton gamma-ray beams in the 70 to 100 MeV region at the High Intensity Gamma-ray Source (HIGS), Duke University. This high energy gamma-ray beam capability will create new opportunities for both fundamental and applied research at HIGS. In this work, we report our experience of VUV FEL lasing with a high single-bunch current and first production of gamma-ray beams in the 70 to 100 MeV region.
LANL, Los Alamos, New Mexico, USA
LBNL, Berkeley, California, USA
The proposed Matter-Radiation Interactions in Extremes (MaRIE) facility at the Los Alamos National Laboratory will include a 50-keV X-Ray Free-Electron Laser (XFEL), a significant extension from planned and existing XFEL facilities. To prevent an unacceptably large energy spread arising from energy diffusion, the electron beam energy should not exceed 20 GeV, which puts a significant constraint on the beam emittance. To achieve a sufficiently high gradient of 50 MV/m, an rf frequency of 11.424 GHz is considered. A 100-pC baseline design is presented along with advanced technology options to increase the photon flux and to generate longitudinal coherency through single-bunch optical seeding, pre-bunching the electron beam, and combinations of these techniques.
TUODS3
SLAC, Menlo Park, California, USA
Recently the scheme of echo-enabled harmonic generation (EEHG*) was proposed for short wavelength seeded FELs. This scheme allows far higher harmonic numbers to be accessed and makes the generation of coherent soft x-ray directly from a UV seed laser in a single stage possible**. In this paper we present the experimental demonstration*** of this echo harmonic technique at the Next Linear Collider Test Accelerator (NLCTA) at SLAC, where the coherent radiation at the harmonic frequency of the seed laser is generated using the 120 MeV electron beam. The experiment confirms the physics behind this technique and paves the way for applying it for seeded x-ray FELs.
* G. Stupakov, Phys. Rev. Lett, ZeHn2, 074801 (2009).
** D. Xiang and G. Stupakov, Phys. Rev. ST Accel. Beams 12, 030702 (2009).
*** D. Xiang, at al, Phys. Rev. Lett, ZeHn5, 114801 (2010).
TUODS4
ENEA C.R. Frascati, Frascati (Roma), Italy
INFN/LNF, Frascati (Roma), Italy
Istituto Nazionale di Fisica Nucleare, Milano, Italy
CEA/DSM/DRECAM/SPAM, Gif-sur-Yvette, France
SOLEIL, Gif-sur-Yvette, France
Università di Roma II Tor Vergata, Roma, Italy
LUXOR, Padova, Italy
LOA, Palaiseau, France
UCLA, Los Angeles, California, USA
Rome University La Sapienza, Roma, Italy
INFN-Roma, Roma, Italy
Universita' degli Studi di Milano, Milano, Italy
ISM-CNR, Rome, Italy
ENEA Portici, Portici (Napoli), Italy
ELETTRA, Basovizza, Italy
BNL, Upton, Long Island, New York, USA
There is a need for an Optics-Free FEL Oscillators (OFFELO) to further the advantages of free-electron lasers and turning them in fully coherent light sources. While SASE (Self-Amplified Spontaneous Emission) FELs demonstrated the capability of providing very high gain and short pulses of radiation and scalability to the Xray range, the spectra of SASE FELs remains rather wide (~0.5%-1%) compared with typical short wavelengths FEL-oscillators (0.01% - 0.0003% in OK-4 FEL). Absence of good optics in VUV and X-ray ranges makes traditional oscillator schemes with very high average and peak spectral brightness either very complex or, strictly speaking, impossible. In this paper, we discuss lattice of the X-ray optics-free FEL oscillator and present results of initial computer simulations of the feedback process and the evolution of FEL spectrum in X-ray OFFELO. We also discuss main limiting factors and feasibility of X-ray OFFELO.
RadiaBeam, Santa Monica, USA
PSI, Villigen, Switzerland
YerPhI, Yerevan, Armenia
GPI, Moscow, Russia
Weizmann Institute of Science, Rehovot, Israel
University of North Texas, Denton, Texas, USA
Texas A&M University, College Station, Texas, USA
For a free-electron laser without inversion (FELWI), es- timates of the threshold laser power are found. The large- amplification regime should be used to bring an FELWI above the threshold laser power.
HZB, Berlin, Germany
CLASSE, Ithaca, New York, USA
Hard x-ray Energy Recovery Linacs (ERLs) operate with high-brightness electron beams, matching the requirements for X-ray FELs in terms of emittance and energy spread. We have analyzed in how far it is feasible to include X-ray FELs in ERL facilities. X-ray FEL Oscillators require comparatively low peak currents and are therefore good candidates for FEL sources in ERLs. However, also high-gain FELs do not seem out of reach when bunch-compression schemes for higher peak currents are utilized. Using the proposed Cornell ERL as an example, different FEL concepts are discussed and their suitability as X-ray sources are analyzed.
USTC/NSRL, Hefei, Anhui, People's Republic of China
SLAC, Menlo Park, California, USA
BNL, Upton, Long Island, New York, USA
* T. Watanabe et al, Phys. Rev. Lett. 98, 034802 (2007).
** X.J. Wang et al, Phys. Rev. Lett. 103, 154801 (2009).
BNL, Upton, Long Island, New York, USA
We show that the paraxial field equation for a free electron laser (FEL) in an infinitely wide electron beam with a kappa-2 energy distribution can be reduced to a fourth ordinary differential equation (ODE). Its solution for arbitrary initial phase space density modulation has been derived in the wave-vector domain. For initial current modulation with Gaussian profile, close form solutions are obtained in space-time domain.
PKU/IHIP, Beijing, People's Republic of China
FEL/Duke University, Durham, North Carolina, USA
A well-calibrated spectrometer is critical for measuring the real spectra of spontaneous radiation of an electron beam in undulators (i.e. undulator radiation), which is important for FEL research. A calibration method of spectrometers based upon the known undulator radiation spectrum has been developed at Duke FEL Laboratory (DFELL). It has been used to provide a precise calibration for spectrometers from infrared (IR) to ultraviolet (UV). This calibration method is expected to be useful for the calibration of spectrometers working in the extreme ultraviolet (EUV) and X-ray region. In this work, we present the details of the calibration method and illustrate the usefulness of the method using a portable spectrometer in the visible region as an example.
FEL/Duke University, Durham, North Carolina, USA
PKU/IHIP, Beijing, People's Republic of China
The 53.73 meters long free-electron laser (FEL) resonator at Duke University consists of two concave mirrors with the similar radius of curvature. The downstream mirror receives not only the fundamental but also higher order harmonic radiation (typically in the UV and VUV range) emitted by relativistic electrons in the magnetic field of wigglers. The power load of wiggler radiation on this mirror can thermally deform and permanently damage the multi-layer coating of the mirror, therefore, limiting the maximum power of the FEL operation and reducing the mirror lifetime. To mitigate these problems, a water-cooled aperture system has been installed inside the FEL resonator. This aperture system has been used to prevent most of off-axis helical wiggler radiation from reaching the downstream FEL mirror. It has also been used to manipulate the FEL gain process by increasing the FEL beam diffraction loss inside the resonator. In principle, this aperture system can be used as an independent FEL gain control device for FEL operation. This paper reports our preliminary study of the FEL operation using the in-cavity apertures to manipulate the FEL gain process.
FEL/Duke University, Durham, North Carolina, USA
The Duke FEL and High Intensity Gamma-ray Source (HIγS) are operated in the range of electron beam energies of 0.24 - 1.2 GeV and photon beam wavelengths of 190-1060 nm. The range of gamma-beam energies currently produced by HIγS facility is from 1MeV to about 100 MeV, with the maximum total gamma-flux of up to 3*1010 gammas per second around 10 MeV. Production of this high level gamma-ray flux requires an average FEL photon beam power inside the FEL resonator at one kilowatt or more. The high power FEL operation causes degradation of the FEL mirrors, especially when operating the FEL in the UV and VUV region at a high electron beam energy. To ensure reliable HIγS operation, we developed a comprehensive program to continuously monitor the performance of the FEL mirrors. This program enabled us to use a particular set of FEL mirrors for a few hundreds hours of high gamma-flux operation with predictable performance. In this work, we discuss sources and consequences of the mirror degradation for a variety of wavelengths. We also present estimates of the mirror life time as a function of the FEL wavelength, photon and gamma-ray polarization, and total gamma-flux.
LANL, Los Alamos, New Mexico, USA
There are several schemes currently being investigated which use modulator and dispersive sections to step the coherent bunching of the electron beam up to higher harmonics. X-ray FELs generally operate in a regime where the FEL parameter ρ is equal to or less than the effective energy spread introduced from the emittance in the electron beam. Because of this large effective energy spread, the energy modulation introduced from harmonic generation schemes would seriously degrade FEL performance. This problem can be mitigated by incorporating the harmonic generation scheme at an electron kinetic energy lower than the energy at the final undulator. This will help because the effective energy spread from emittance is reduced at lower energies, and can be further reduced by making the beam transversely large. Then the beam can be squeezed down slowly enough in the subsequent accelerator sections so that geometric debunching is avoided. Here we show analytical results that demonstrate the feasibility of this harmonic pre-bunching scheme.
LANL, Los Alamos, New Mexico, USA
The MaRIE (Matter-Radiation Interactions in Extremes) experimental facility will be used to advance materials science by providing the tools scientists need to develop materials that will perform predictably and on demand for currently unattainable lifetimes in extreme environments. The MaRIE facilities, the Multi-Probe Diagnostic Hall (MPDH), the Fission and Fusion Materials Facility (F3), and the Making, Measuring, and Modeling Materials (M4) Facility will each have experimental needs for one or more high-energy X-ray beam probes. MPDH will also require access to an electron beam probe. These probe beams can be created using a 20-GeV electron linac, both to serve as a source of electrons and as a driver for a set of up to five X-ray undulators for the high-energy X-rays. Because of space considerations at the facility, a high-gradient design is being investigated that will use a normal-conducting linac and X-band RF systems. Experimental requirements are also calling for relatively long pulse lengths, as well as interleaving high- and low-charge electron bunches. This paper will provide an overview of how an XFEL would address the scientific requirements for MaRIE.
UCLA, Los Angeles, USA
SLAC, Menlo Park, California, USA
During commissioning and operation of the Linac Coherent Light Source (LCLS) x-ray Free Electron Laser (FEL) at the SLAC National Accelerator Center electron and x-ray beam size, shape, centroid motion have been studied. The studies, sources, and remediation are summarized in this paper.
SLAC, Menlo Park, California, USA
* D. Xiang et al., "Demonstration of the Echo-Enabled Harmonic Generation Technique for Short-Wavelength Seeded Free Electron Lasers", PRL 105, 114801, 2010.
JLAB, Newport News, Virginia, USA
We report on the performance of a high gain UV FEL oscillator operating on an energy recovery linac at Jefferson Lab. The high brightness of the electron beam leads to both gain and efficiency that cannot be reconciled with a one-dimensional model. Three-dimensional simulations do predict the performance with reasonable precision. Gain in excess of 100% per pass and an efficiency close to 1/2NW, where NW is the number of wiggler periods, is seen. The laser mirror tuning curves currently permit operation in the wavelength range of 438 to 362 nm. Another mirror set allows operation at longer wavelengths in the red with even higher gain and efficiency.
JLAB, Newport News, Virginia, USA
UW-Madison/SRC, Madison, Wisconsin, USA
We describe the operation and commissioning of the Jefferson Lab UV FEL using a CW SRF ERL driver. Based on the same 135 MeV linear accelerator as the Jefferson Lab 10 kW IR Upgrade FEL, the UV driver ERL uses a bypass geometry to provide transverse phase space control, bunch length compression, and nonlinear aberration compensation necessitating a unique set of commissioning and operational procedures. Additionally, a novel technique to initiate lasing is described. To meet these constraints and accommodate a challenging installation schedule, we adopted a staged commissioning plan with alternating installation and operation periods. This report addresses these issues and presents operational results from on-going beam operations.
UCB, Berkeley, California, USA
UESTC, Chengdu, Sichuan, People's Republic of China
LBNL, Berkeley, California, USA
The possibility of implementing echo-enabled harmonic generation* (EEHG) within a single optical resonance cavity is explored both analytically and with numerical simulations. Two modulators of the same frequency are used so that the cavity radiation replaces the two seed lasers of conventional EEHG. Such a scheme has potential** to produce tunable radiation as in EEHG, but with the high repetition rate, longitudinal coherence, and narrow spectral bandwidth of an oscillator. These benefits, however, come with the complication that the beam must generate the radiation that modulates it. Analysis and GINGER simulations are presented for a specific example that takes advantage of robust multilayer mirror performance at 13.4 nm to produce radiation near or possibly even below 1 nm.
* G. Stupakov, Phys. Rev. Lett. 102, 074801 (2009).
** J. Wurtele et al., Proc. of the 2010 FEL Conference, TUOC12.
University of Chicago, Chicago, Illinois, USA
ANL, Argonne, USA
References
* K-J Kim, Y Shvyd'ko and S Reiche, Phys. Rev. Lett 100, 24802(2008)
** S. K. Sinha, E. B Sirota, S. Garoff, Phys. Rev. B38 2297 ((1988)
*** G. Park in preparation
UW-Madison/SRC, Madison, Wisconsin, USA
UW-Madison/PD, Madison, Wisconsin, USA
JLAB, Newport News, Virginia, USA
The University of Wisconsin-Madison/Synchrotron Radiation Center is advancing its design for a seeded VUV/soft X-ray Free Electron Laser facility called WiFEL. To support this vision of an ultimate light source, we are pursuing a program of strategic R&D addressing several crucial elements. This includes development of a high repetition rate, VHF superconducting RF electron gun, R&D on photocathode materials by ARPES studies, and evaluation of FEL facility architectures (e.g., recirculation, compressor scenarios, CSR dechirping, undulator technologies) with the specific goal of cost containment. Studies of high harmonic generation for laser seeding are also planned.