Storage Ring Free Electron Laser Research Articles

High current operation of a storage-ring free-electron laser

The operation of storage-ring free-electron lasers (SRFEL) at high current still represents a challenge because of the growth of longitudinal beam instabilities. One of these, the quadrupolar coherent synchrotron oscillation, is very harmful for free-electron-laser (FEL) operation. On the Super-ACO storage ring, they either prevent the FEL start-up, or result in a very poor stability of the FEL source. A new feedback system to damp the quadrupolar coherent synchrotron oscillation has been installed on the ring and the stabilized beam parameters have been systematically measured. As a result, the FEL gain is higher and the FEL operates more easily and with a higher average power. Its stability, which is very critical for user applications, has been significantly improved as it has been observed via systematic measurements of FEL dynamics performed with a double sweep streak camera.

Implementing storage rings free electron lasers for users on synchrotron radiation facilities: from Super-ACO to SOLEIL

Storage Ring Free Electron Laser (SRFEL) sources can be implemented on synchrotron radiation facilities. Although in the beginning an additional experiment on the accelerator requires specific operating conditions as on Super-ACO at Orsay (France), they can now be conceived as an integral part of the project, providing coherent picosecond tunable light in the UV–VUV range, synchronized with synchrotron radiation for the scientific community, as on the SOLEIL project. Third generation storage ring beam characteristics are discussed in terms of synchrotron radiation and FEL optimization. FEL performances are presented, showing the improvement between the Super-ACO and the SOLEIL cases, including stability issues.

SRFEL, FEL-X project, and applications at the ETL

The present status of the NIJI-IV storage ring free-electron laser (SRFEL) in the visible and ultraviolet region, the design and preliminary experimental results of the generation of quasi-monochromatic X-ray beam by exploiting the laser Compton backscattering using an infrared FEL, and possible application of those beams are presented.

Single-bunch beam property for FEL on the UVSOR storage ring

Single-bunch beam properties such as bunch lengthening and instability that are very important factors to develop storage ring free electron lasers (SRFEL) have been investigated on the UVSOR electron storage ring. Data were analyzed based on a model of potential-well distortion due to the impedance of the vacuum pipe. The inductive impedance was obtained to be 40 nH which is approximately 10 times larger than that of a newly constructed 3rd generation light source. In an operation with negative momentum compaction factor, the bunch shortening was observed which is also explained by which the inductive impedance dominates the single bunch property on the UVSOR ring.

Duke FEL storage ring light sources and applications

In this paper we present the status of the Duke UV FEL (Free Electron Laser) storage ring, ring based light sources, and a related multi-disciplinary application program. Using the OK-4 optical klystron system, we have demonstrated tunable spontaneous radiation from the near Infrared (IR) to UV, coherent laser radiation from 345 to 413 nm, and Compton back-scattered linearly polarized γ-ray radiation from 3 to 16 MeV. We report the progress made in developing new light source capabilities. We also report user interface development for a pilot application program organized to utilize various ring driven sources. We discuss future upgrades and additions to the ring based sources.

Storage-ring free-electron lasers and self-consistent harmonic generation

We employ a semianalytical model to study the self-consistent higher harmonic generation in free-electron lasers operating with storage rings. The model combines the rate equations, governing standard storage-ring free-electron laser dynamics, with the equations describing the evolution of the bunching coefficients. The developed technique is amenable to a straightforward numerical implementation and provided reliable results, whose correctness is proved by means of a more complete numerical procedure.

Spectroscopic Techniques using Synchrotron Radiation and Free-Electron and Conventional Lasers.

Considerable progress in the investigation of the electronic and vibrational properties of atoms, molecules, materials, surfaces and interfaces has been achieved by combining different photon sources of complementary characteristics. In this paper some experimental results obtained recently at LURE by using two synchronized sources, such as the IR free-electron laser (FEL) CLIO, the VUV storage ring FEL, synchrotron radiation and table lasers, are presented. Using CLIO synchronized with a YAG laser allows the investigation of the vibrational properties of adsorbed species by the non-linear optical technique of visible-IR sum (difference) frequency generation, as shown for the adsorption of hydrogen on platinum in the electrochemical environment. The second result reported here relates to the study of the intersubband stimulated emission in GaAs/GaAlAs quantum wells by pump-probe experiments using the two-colour configuration of CLIO. The combination of a mode-locked Ar(+) laser and synchrotron radiation has been used for investigations in a pump-probe arrangement of the ionization of Xe atoms via the resonant state Xe* 5p(5)5d [3/2](1). The final example is a time-resolved core-level spectroscopy study of photoexcited Si(111) 2 x 1 surfaces by using a combination of the naturally synchronized UV storage ring laser and synchrotron radiation.

Design study of a free-electron laser on a storage ring at Tohoku University.

A free-electron laser (FEL) based on the proposed Tohoku Light Source storage ring is discussed. In the first stage the FEL is made to operate in the visible region with a relative low beam energy to avoid the complication of mirrors. Then, with a higher beam energy, the FEL can produce radiation of wavelengths in the UV or VUV region. Some simulation results of the storage-ring FEL with wavelengths of approximately 200 nm are presented.

Gamma rays production by intra-cavity Compton Back Scattering with Super-ACO Storage Ring Free Electron Laser

High-energy γ-photons have been produced by an intra-cavity Compton Back Scattering (CBS) process between the Super-ACO Storage Ring Free Electron Laser, at 350 nm, and an ultra-relativistic (800 MeV) positron bunch. No spatial selection of the beam has been made so a wide energy range of γ-photons has been directly (NaI detector) and indirectly (CBS positrons bunch life-time) investigated. The high intra-cavity laser power leads to a high γ-photons emission rate (5 millions ph/s). Some future possible improvements are proposed.

Study of beam property on a storage ring operated with negative momentum compaction factor

To investigate variations of the bunch length and the energy spread of the electron beam on a storage ring, which are very important beam properties for storage ring free electron lasers, we have measured longitudinal electron distributions and spectra of spontaneous radiation from an optical klystron on the UVSOR storage ring operated with both signs of negative and positive momentum compaction factors. Significant differences in the bunch lengthening and the increase of the energy spread with the beam current have been found between two operations. In a case of the negative momentum compaction, a threshold beam current for the longitudinal microwave instability was observed to be very low, meanwhile “the bunch shortening” was observed.

Initial dual-sweep streak camera measurements on the Duke storage ring OK-4 UV/visible FEL

Initial measurements at the Duke storage ring free electron laser (FEL) of both spontaneous emission radiation (SER) from the OK-4 and FEL radiation outcoupled from the oscillator cavity have been done with a dual-sweep streak camera. In the SER case, ANL's Hamamatsu C5680 streak camera was used to characterize stored electron-beam bunch lengths versus rf gap voltage and single-bunch current. Electron-beam bunch lengths were observed in a range from 50 to 300 ps (FWHM). Particle beam energies of 270 and 500 MeV in the storage ring (SR) were used with the OK-4 to generate SER from 500 nm to less than 200 nm. Sensitivity to single-bunch, single-turn SER was shown down to ∼4 μA beam current at λ=450 nm. By operating in the synchroscan mode and at bunch currents less than 1 mA, beam orbit length vs. the resonator round-trip time was investigated by detecting the relative arrival time of the second pass outcoupled from the resonator at λ≈200 nm. These measurements were used in support of first lasing in the UV-visible regime in November 1996. The dual-sweep streak mode was then used to monitor lasing intensity variations on the 1 and 50 ms time scales, to measure a lasing pulse length as short as ∼3 ps ( σ) at λ=388 nm at low beam current, and to track the orbit length detuning curve.

First UV/visible lasing with the OK-4/Duke storage ring FEL

In this paper, we report first lasing results in the near-UV and visible spectral ranges with the OK-4/Duke storage ring – the first storage ring FEL operating in the United States. The OK-4/Duke FEL was commissioned in November 1996 and demonstrated lasing in the 345–413 nm range with extracted power of 0.15 W. In addition to lasing, the OK-4/Duke FEL generated a nearly monochromatic (1% FWHM) γ-ray beams. In this paper, we describe initial performance of the OK-4/Duke storage ring FEL and γ-ray source in this demonstration experiment. We briefly discuss the present status of the project and its future user program.

Numerical simulation to UV coherent harmonic radiation on Hefei storage-ring FEL

It is a prospective technical route to generate UV coherent radiation using external high-power laser to pre-bunch ultra-relativistic electron beam provided by storage ring and then amplifying its harmonic components with the super-radiation method. In this paper, based on the primary parameters of Hefei Storage Ring (NSRL) FEL system, firstly we made the simulation to the electron beam energy modulation process in an optical klystron, the simulation parameters include: γ=1000, the relativistic factor of the electron beam; the wavelength and power of the injected external laser are, λ s=0.353 μm and 100 MW; the period number and wavelength of the undulators are N u=20, and λ u=7.2 cm (we have the same structure for the modulator and radiator); and the normalized amplitude of the magnetic field is K=4.2. An effective energy modulation can be achieved when the rms energy spread for the electron beam is less than 10 −4, i.e., σ γ / γ⩽10 −4. Then density modulation for the energy-modulated electron beam in the dispersive section is also simulated. Under the above-mentioned conditions when the dispersive parameter N d≅76, a good density modulation results can be obtained. Finally, we also give the harmonic super radiation output power components P 3, P 5, P 7 in the radiator section.

Storage-ring free electron laser interaction and longitudinal phase-space dynamics

We investigate the interplay between storage ring beam dynamics and FEL. It is shown that the on-set of the FEL provide a modification of the longitudinal damping times of the e-beam mode distribution and may act as feedback to inhibit the growth of the instabilities of the microwave type.

OK-4/Duke monochromatic γ-ray source: performance and prediction

A beam of nearly monochromatic γ-rays was produced via intracavity Compton backscattering in the OK-4/Duke storage ring FEL. The OK-4 FEL operated in the near-UV range (345–413 nm) with electron energies of 260–550 MeV. The energy of the produced γ-rays varied from 3 to 16 MeV. In the near future we plan to increase the energy of the γ-rays to 50 MeV by increasing the electron energy and reducing FEL wavelength. Results from direct measurements of the γ-ray flux and energy resolution (using a 3 mm diameter lead collimator) (Litvinenko et al., Phys. Rev. Lett. 78 (1997) 4569) are very close to our theoretical predictions. The energy resolution of the γ-rays was ∼1%. In this paper we present a comparison of our measurements with theoretical predictions and our plans for future improvements. We discuss upgrades of our system to attain an energy resolution down to 0.1% and to increase the flux. A brief description of the experimental program utilizing the OK-4/Duke monochromatic γ-ray source is presented.

Performance and operation modes of the Duke FEL storage ring

We present the recent status and performance of the Duke Free Electron Laser (FEL) storage ring. We report a large transverse and energy aperture observed in the storage ring. We describe the consequences of this large aperture on the operation of the storage ring. Several unusual phenomena are reported in this paper, including large amplitude transverse multibunch coherent oscillations (Saturn rings) and beam capture from outside the RF separatrix. We also present the established operation modes for the storage ring, including energy ramping, working point tuning, and different bunch-mode operations to optimize the ring as a synchrotron light source, an FEL, and a gamma-ray source. Finally, we summarize the achieved storage ring parameters since its first operation in November 1994.

Saturation mechanism of a storage ring free electron laser: An analytic model

An analytical solution of the optical pulse evolution equation in a storage ring free electron laser under the assumption of long electron pulse with parabolic shape is obtained by exploiting recent results in the operational calculus associated to exponential operators. The intracavity laser power is coupled to the induced electron beam energy spread evolution equation. The model also includes other saturation mechanisms: the electron beam bunch lengthening, causing a reduction of the peak current, and the longitudinal synchronism between laser and electron pulses.

Analysis of OK SR FEL devices

We discuss a simple model for the evolution of a Storage-Ring (SR) FEL operating in the optical-klystron (OK) configuration. We analyze the OK gain formula and introduce the parametrizations which account for the inhomogeneous broadening and saturation effects. We also derive a parametrization for the induced energy spread. The OK SR FEL evolution is then described by two coupled rate equations which accounts for the evolution of the intracavity power and the associated e-beam heating and damping. The model allows the derivation of the stationary output and intracavity power and is also a flexible tool for the system optimization. The analytical results are confronted with the available experimental data and the agreement is found more than satisfactory.

Design of an optical cavity in the NIJI-IV for high output power

A new optical cavity system which efficiently takes out intense intracavity power of a storage ring free electron laser (SRFEL) in the visible and ultraviolet (UV) regions are planed. If a cavity mirror is started to rotate at the peak of an SRFEL macro-pulse to rapidly lead an SRFEL micro-pulse to the high transmission area, we can dump a part of the intracavity power sufficiently. A high-speed piezotranslator and a special mirror holder will realize this system, what is called cavity dump. The piezotranslator would make the optical cavity mirror rotate with the angular velocity of 2.52 × 10 −6rad per one round-trip. In the case of NIJI-IV FELs, the output power of the micro-pulse would be estimated at about 7600 times around 488 nm and about 2700 times around 352 nm as strong as that in the normal operation.

Storage rings FELs

Storage ring Free Electron lasers (SRFEL) are reviewed: particular features of undergoing experiments are underlined. The understanding of the SRFEL, dynamics is under progress, especially for the analysis of the FEL interaction with the beam, involving the stored beam dynamics and for stability, which constitutes a critical issue for the users. Finally, future prospects are given.