FEL Experimental Results

WEAIS01 Experimental Demostration of Wavelength Tuning in High-Gain Harmonic Generation Free Electron Laser
Timur Shaftan, Erik Johnson, Sam Krinsky, Henrik Loos, James Murphy, George Rakowsky, James Rose, Brian Sheehy, John Skaritka, Xijie Wang, Zilu Wu, Li-Hua Yu (BNL/NSLS, Upton, Long Island, New York)

We present experimental results on tuning of the HGHG FEL output wavelength while holding the input seed wavelength constant. Using compression of the initially chirped beam in the HGHG dispersion section we have measured the wavelength shift of about 1% around the nominal value of 266 nm. The tuning range is expected to reach 3 % after the dispersive section upgrade at the DUV FEL. An optimized design based on this principle, using additional linac sections, would have the capability of providing full tunability.

WEAOS02 Spectral Phase Modulation and chirped pulse amplification in High Gain Harmonic Generation
Zilu Wu, Erik Johnson, Sam Krinsky, Henrik Loos, James Murphy, Timur Shaftan, Brian Sheehy, Yuzhen Shen, Xijie Wang, Li-Hua Yu (BNL/NSLS, Upton, Long Island, New York)

High Gain Harmonic Generation (HGHG), because it produces longitudinally coherent pulses derived from a coherent seed, presents remarkable possibilities for manipulating FEL pulses. If spectral phase modulation imposed on the seed modulates the spectral phase of the HGHG in a deterministic fashion, then chirped pulse amplification, pulse shaping, and coherent control experiments at short wavelengths become possible. In addition, the details of the “transfer function” will likely depend on electron beam and radiator dynamics and so prove to be a useful tool for studying these. Using the DUVFEL at the National Synchrotron Light Source at Brookhaven National Laboratory, we present spectral phase analyses of both coherent HGHG and incoherent SASE ultraviolet FEL radiation, applying Spectral Interferometry for Direct Electric Field Reconstruction (SPIDER), and assess the potential for employing compression and shaping techniques.

WEAOS04 Study of Coherence Limits and Chirp Control in Long Pulse FEL Oscillator
Avraham Gover, Alon Eliran, Yehoshua Socol, Mark Volshonok (University of Tel-Aviv, Tel-Aviv), Moshe Einat, Miki Kanter, Boris Yu Kapilevich, B. Litvak, Yuri Lurie, Yosef Pinhasi, Asher Yahalom (The College of Judea and Samaria, Ariel)

Electrostatic Accelerator FELs have the capacity to generate long pulses of tens microseconds and more, that in principle can be elongated indefinitely (CW operation). This allows the generation of very coherent radiation. The fundamental linewidth is extremely narrow [1], and in practice the spectral width is limited by the pulse duration (Fourier transform limit) and e-beam stability. Practical problems such as the accelerator terminal voltage drop due to a non-ideal electron beam transport may reduce the length of the radiation pulse and hence create a limiting factor for coherence measurement. The current status of the Israeli Tandem Electrostatic Accelerator FEL allows the generation of pulses of tens microseconds duration. It has been operated recently past saturation, and produces single mode coherent radiation of relative linewidth ~Δf/f=10-5 at frequencies near 100GHz. A clear frequency chirp is observed during pulses of tens of microseconds (0.1-1 MHz/mS), and is directly proportional to the voltage drop rate of the High-Voltage terminal. We will report experimental studies of the spectral linewidth and chirp characteristics of the radiation, along with theory and numerical simulations, carried out using space-frequency model [2], matching the experimental data.

THPOS04 Characterization of Laser-Electron Interaction at the BESSY Femtoslicing Facility
Shaukat Khan, Karsten Holldack, Torsten Kachel, Rolf Mitzner, Torsten Quast, Friedmar Senf (BESSY GmbH, Berlin)

A "femtoslicing" facility to generate ultrashort x-ray pulses by laser-electron interaction [1] is being commissioned at the BESSY II storage ring. The energy modulation of electrons by femtosecond laser pulses of several mJ in an undulator is a good test case for FEL seeding schemes. The dependence of the interaction efficiency on various parameters is measured and compared to simulations and analytical results.

THPOS06 Measurement and Calculation of the 'Electron Efficiency' on the ‘CLIO’ Free-Electron Laser
Rui Prazeres, François Glotin, Jean Michel Ortega (LURE, Orsay)

This paper describe recent measurements which have been performed with the CLIO FEL in the wavelength range 40 to 120µm. The FEL electron efficiency, η, is deduced from the electron energy loss. It gives an absolute measurement of the optical power produced by the electron beam, which is then compared to the extracted power of the FEL measured optically. The ratio is compared to numerical simulation taking into account the diffraction of the optical mode in the optical cavity and in the beam line.

THPOS21 Recent Results of the JAERI Energy-Recovery Linac FEL
Ryoichi Hajima, Hokuto Iijima, Nobuhiro Kikuzawa, Eisuke John Minehara, Ryoji Nagai, Nobuyuki Nishimori, Tomohiro Nishitani, Masaru Sawamura (JAERI/FEL, Ibaraki-ken)

A research program towards a high-power FEL utilizing an energy-recovery linac is carried forward at Japan Atomic Energy Research Institute (JAERI). In this paper, we summarize recent results of the research activity at the JAERI ERL-FEL, which include the reinforcement of the injector, replacement of the RF control system and so on.

THPOS23 JAERI 200 kV Electron Gun with an NEA-GaAs Photocathode
Tomohiro Nishitani, Ryoichi Hajima, Nobuhiro Kikuzawa, Eisuke John Minehara, Ryoji Nagai, Nobuyuki Nishimori, Masaru Sawamura, T. Yamauchi (JAERI/FEL, Ibaraki-ken)

The GaAs photocathode with negative electron affinity surface (NEA-GaAs) has been expected to be low emittance (<0.5 πmm・mrad) electron beam source. In order to generate low emittance electron beam required from ERL-FEL, we have started the developmental program of a 200keV electron gun with the NEA-GaAs photocathode for the first time in JAERI. An NEA surface has the problem that lifetime is limited by gun vacuum condition and by ion back bombardment between anode- and cathode-electrode. In order to long an NEA surface lifetime, the JAERI 200keV electron gun system consists of a 200kV DC-gun chamber on extreme high vacuum condition and an NEA activation chamber with load-lock system.

THPOS28 Performance of the Optical Klystron ETLOK-III for Developing Infrared Storage Ring Free Electron Lasers
Norihiro Sei, Hiroshi Ogawa, Kawakatsu Yamada, Masato Yasumoto (AIST-PRI, Tsukuba, Ibaraki)

Oscillations of free electron lasers (FELs) with the compact storage ring NIJI-IV in a wade wavelength region of 1-12 micron are planned in the AIST. The optical klystron ETLOK-III for developing infrared FELs has been installed in a long straight section of the NIJI-IV. The ETLOK-III has two undulator sections of 7 periods of 20 cm and one 75 cm dispersive section. The maximum K value is about 10. Electron injection to the NIJI-IV with the ETLOK-III is now in progress. Fundamental and higher harmonics of spontaneous emission from the ETLOK-III will be observed in detail. The electron-beam qualities will be also evaluated by using the measurements of the spontaneous emission. In the presentation, we will report the experimental results and discuss the performance of the ETLOK-III.

THPOS29 Improved Performance of the NIJI-IV Compact VUV/IR FEL and its Application to the Surface Observation
Kawakatsu Yamada, Hiroshi Ogawa, Norihiro Sei, Kazutoshi yagi Watanabe, Masato Yasumoto (AIST-PRI, Tsukuba, Ibaraki)

At AIST, efforts to increase the FEL power as well as to shorten the lasing wavelength below 190 nm are being made, to use the NIJI-IV FEL as an intense light source for real-time surface observation using the photoelectron emission microscopy (PEEM). By irradiating a transition-metal surface with the 200-nm FEL, fine structure of one- micron scale was successfully observed with spatial and temporal resolutions of a few hundreds nm and 33 ms, respectively. In addition, a 3.6-m optical klystron for lasing in the infrared was recently installed into the north straight section of the NIJI-IV to extend the lasing wavelength range up to ~ 10 microns. One of our interests in the infrared-FEL application is to utilize it for a Raman spectroscopy which can examine adsorbed molecules and their bonding conditions on the metal surface. Establishment of a total surface analysis system using NIJI-IV compact VUV/IR FEL combined with characteristic surface analysis techniques is one of our goals in the near future. Improved performance of the NIJI-IV FEL obtained this year will be reported. Typical results of the PEEM measurement will be discussed.

THPOS33 A mm-Wave, Table Top Cerenkov Free-Electron Laser
Isabel de la Fuente, Klaus Boller, Peter van der Slot (UTWENTE, Enschede)

We have designed and constructed a compact (0.5 x 1.5 m), 100 kV Cerenkov FEL operating at a frequency of 50 GHz. The electron beam is produced by a gridded thermionic electron gun with a beam current of 800 mA. Simulations shows that 800 mA is sufficient to produce an output power of ~ 1 kW peak at 50 GHz using a total cavity reflectivity of about 10 to 20 %. The average power approaches 1 kW when the electron pulse length is extended to CW. A depressed collector will be used to increase the overall efficiency of this device. Special attention has been given to the outcoupler that has to combine multiple functions. First it has to separate the radiation field from the electron beam. Second it has to be transparent for the electron beam and acts as a partial reflector for radiation. Finally it has to convert the generated TM01 mode in the interaction region into the fundamental TE01 mode of the standard rectangular output port. We will present the overall design and experimental set-up, first experimental results and discuss possible applications for this table-top Cerenkov FEL.

THPOS37 Status of 30 GHz Facility for Experimental Investigation of the Copper Cavity Lifetime (Clic Collider Project)
Alim Kaminsky, Artem Elzhov, Eugene Gorbachev, Vitaly Kosukhin, Elkuno Perelstein, Nikolay Pilyar, Tatiana Rukoyatkina, Sergey Sedykh, Anatoly Sergeev, Alexey Sidorov, Vladimir Tarasov (JINR, Dubna, Moscow Region), Naum Samuilovich Ginzburg, Sergey Kuzikov, Nikolay Peskov, Mikhail Petelin, Alexander Sergeevich Sergeev, Nikolay Zaitsev (IAP RAS, Nizhny Novgorod)

Facility for experimental investigation of a copper cavity lifetime under multiple action of 30 GHz power pulses is now created by the collaboration of CLIC team (CERN) [1], FEM groups of JINR (Dubna) and IAP RAS (Nizhny Novgorod). Design of the test cavity, estimation of the operating parameters of the FEM oscillator and the RF power transmission line was already reported at FEL’03 [2]. Last year was devoted to the achievement of the design parameters of all the elements of the facility. We have developed the equipment and the procedure of RF transmission line adjustment, improved the stability of the linac power supplies, created the new system of data acquisition. Start of the full-scale experiments is planned to the end of 2004.

THPOS54 Characterization of Storage Ring FEL operating in the Giant Pulse Mode
Igor V. Pinayev, Kevin Chalut (Duke University, Durham, North Carolina), Vladimir N. Litvinenko (BNL, Upton, Long Island, New York)

In this paper we present the experimental results on the storage ring free electron laser operating in the giant pulse mode with variable repetition rate. The experiments were conducted in the wide range of the electron beam energies from 270 MeV to 600 MeV with the giant pulses generated using a gain modulator. Dependence of the peak and average power, and the other properties and parameters of giant pulses on the pulse repetition rate are studied. In particular, it is found that the average lasing power in the giant pulse mode reaches levels of 70-90% of that in the CW power mode. Applications of such mode of operation are discussed.

THPOS56 VISA IB: Ultra-High Bandwidth, High Gain SASE FEL
Gerard Andonian, Ronald Barkley Agustsson, Alex Murokh, Claudio Pellegrini, Sven Reiche, James B Rosenzweig, Gil Travish (UCLA, Los Angeles, California), Marcus Babzien, Ilan Ben-Zvi, Jung Yun Huang, Vladimir N. Litvinenko, Vitaly Yakimenko (BNL, Upton, Long Island, New York), Ilario Boscolo, S. Cialdi, Alessandro Flacco (INFN Milano, Milano), Massimo Ferrario, Luigi Palumbo, C. Vicario (INFN/LNF, Frascati (Roma))

The results of a high energy-spread SASE FEL experiment, the intermediary experiment linking the VISA I and VISA II projects, are presented. A highly chirped beam (~1.7%) was transported without correction of longitudinal aberrations in the ATF dogleg, and injected into the VISA undulator. The output FEL radiation displayed an uncharacteristicly large bandwidth (~11%) with extremely stable lasing and measured energy of about 2 microJoules. Start-to-end simulations reproduce key features of the measured results and provide an insight into the mechanisms giving rise to such a high bandwidth. These analyses are described as they relate to important considerations for the VISA II experiment.

THPOS62 Preliminary Measurements of the High-Gain FEL Radiation Properties along the Radiator
Timur Shaftan, Henrik Loos, Brian Sheehy, Li-Hua Yu (BNL/NSLS, Upton, Long Island, New York)

We present experimental results on evolution of properties of the DUV FEL output radiation along the radiator. Intercepting the electron beam at the different locations inside the undulator we recorded and analyzed transverse profiles, spectra and intensity of the FEL output. Shot-to-shot fluctuations of the FEL radiation may significantly affect the accuracy of measurement. In the paper we present and discuss a single-shot measurement technique, based on a special imaging system.