07 Accelerator Technology

T22 Lasers

 
Paper Title Page
TUOCFI02 First Results of SNS Laser Stripping Experiment 980
 
  • V.V. Danilov, A.V. Aleksandrov, S. Assadi, J. Barhen, Y. Braiman, D.L. Brown, W. Grice, S. Henderson, J.A. Holmes, Y. Liu, A.P. Shishlo
    ORNL, Oak Ridge, Tennessee
  
  Thin carbon foils are used as strippers for charge exchange injection into high intensity proton rings. However, the stripping foils become radioactive and produce uncontrolled beam loss, which is one of the main factors limiting beam power in high intensity proton rings. Recently, we presented a scheme for laser stripping of an H- beam for the SNS ring. First, H- atoms are converted to H0 by a magnetic field, then H0 atoms are excited from the ground state to the upper levels by a laser, and the excited states are converted to protons by a magnetic field. This paper presents first results of the SNS laser stripping proof-of-principle experiment. The experimental setup is described, and possible explanations of the data are discussed.  
slides icon Transparencies
THPCH150 Double-pulse Generation with the FLASH Injector Laser for Pump/Probe Experiments 3143
 
  • O. Grimm, K. Klose, S. Schreiber
    DESY, Hamburg
  
  The injector laser of the VUV-FEL at DESY, Hamburg, was modified to allow the generation of double-pulses, separated by a few cycles of the 1.3 GHz radio-frequency. Such double pulses are needed for driving the planned infrared/VUV pump/probe facility. Construction constraints of the facility will result in an optical path length about 80 cm longer for the infrared. Although the VUV can be delayed using normal-incidence multilayer mirrors at selected wavelengths, a fully flexible scheme is achieved by accelerating two electron bunches separated by more than the path length difference and then combine the infrared radiation from the first with the VUV from the second. This paper explains schemes for the generation of double-pulses with the laser system. It summarizes experimental studies of the effect on the operation of diagnostic instrumentation and on the tunability of the machine. Of special concern is the effect of wakefields on the quality of the second bunch, critical for achieving lasing.  
THPCH151 Commissioning of the Laser System for SPARC Photoinjector 3146
 
  • C. Vicario, M. Bellaveglia, D. Filippetto, A. Gallo, G. Gatti, A. Ghigo
    INFN/LNF, Frascati (Roma)
  • P. Musumeci, M. Petrarca
    INFN-Roma, Roma
  
  In this paper we report the commissioning of the SPARC photoinjector laser system. In the high brightness photoinjector the quality of the electron beam is directly related to the features of the laser pulse. In fact the temporal pulse shape, the temporization and the transverse distribution of the electron beam is determined by the incoming laser pulse. The SPARC laser system is based on an amplified Ti:Sapphire active medium and the pulse shape is imposed by a programmable acousto-optics dispersive filter. The transfer-line has been designed to reduce the angular jitter and to preserve to the cathode the temporal and spatial features of the laser pulse. The laser system has been integrated with the accelerator apparatus. The diagnostics and the control system has been completed. We present the measured performances and the simulations we carried out.  
THPCH152 Temporal Quantum Efficiency of a Micro-structured Cathode 3149
 
  • V. Nassisi, F. Belloni, G. Caretto, D. Doria, A. Lorusso, L. Martina, M.V. Siciliano
    INFN-Lecce, Lecce
  
  In this work the experimental and simulation results of photoemission studies for photoelectrons are presented*. The cathode used was a Zn disc having the emitting surface morphologically modified. Two different excimer lasers were employed like energy source to apply the photoelectron process: XeCl (308nm, 10ns) and KrF (248nm, 20ns). Experimental parameters were the laser fluence (up to 70 mJ/cm2) and the anode-cathode voltage (up to 20 kV). The output current was detected by a resistive shunt with the same value of the characteristic impedance of the sistem, about 100 ?. In this way, our device was able to record fast current signals. The best values of global quantum efficiency were approximately 5x 10-6 for XeCl and 1x 10-4 for KrF laser, while the peaks of the temporal quantum efficiency were 8x 10-6 and 1.4x10-4, respectively. The higher efficiency for KrF is ascribed to higher photon energy and to Schottky effect. Several electron-beam simulations using OPERA 3-D were carried out to analyze the influence of the geometrical characteristics of the diode. Simulating the photoemission by cathodes with micro-structures the output current was dependent on cathode roughness.

*L. Martina et al. Rev. Sci. Instrum., 73, 2552 (2002).

 
THPCH153 Production of Temporally Flat Top UV Laser Pulses for SPARC Photoinjector 3152
 
  • M. Petrarca, P. Musumeci
    INFN-Roma, Roma
  • I. Boscolo, S. Cialdi
    INFN-Milano, Milano
  • G. Gatti, A. Ghigo, C. Vicario
    INFN/LNF, Frascati (Roma)
  • M. Mattioli
    Università di Roma I La Sapienza, Roma
  
  In the SPARC photoinjector, the amplified Ti:Sa laser system is conceived to produce an UV flat top pulse profile required to reduce the beam emittance by minimizing the non-linear space charge effects in the photoelectrons pulse. Beam dynamic simulations indicate that the optimal pulse distribution must be flat top in space and time with 10 ps FWHM duration, 1 ps of rise and fall time and a limited ripple on the plateau. In a previous work~\cite{loose} it was demonstrated the possibility to use a programmable dispersive acousto-optics (AO) filter to achieve pulse profile close to the optimal one. In this paper we report the characterization of the effects of harmonics conversion on the pulse temporal profile. A technique to overcome the harmonics conversion distortions on the laser pulses at the fundamental wavelength in order to obtain the target pulse profile is explained too. Measurements and simulations in the temporal and spectral domain at the fundamental laser wavelength and at the second and third harmonics are presented in order to validate our work. It is also described a time diagnostic device for the UV pulses.

*H. Loos et al. "Temporal E-Beam Shaping in an S-Band Accelerator", Proc. Particle Accelerator Conference, p.642, 2005, Knoxville, TN, USA.

 
THPCH154 Development of Pulsed Laser Super-cavity for Compact High Flux X-ray Sources 3155
 
  • K. Sakaue, M. Washio
    RISE, Tokyo
  • S. Araki, Y. Higashi, Y. Honda, T. Taniguchi, J. Urakawa
    KEK, Ibaraki
  • M.K. Fukuda, M. Takano
    NIRS, Chiba-shi
  • H. Sakai
    ISSP/SRL, Chiba
  • N. Sasao
    Kyoto University, Kyoto
  
  Pulsed-laser super-cavity is being developed at KEK-ATF for the application of a compact high brightness x-ray source based on Laser Compton Scattering. We use a Fabry-Perot optical cavity with a pulsed laser. The cavity increases a laser effective power, and at the same time, stably makes a small laser spot in side the cavity. In addition, the pulsed-laser gives much higher peak power. Thus, this scheme will open up a new possibility for building a compact high-brightness x-ray source, when collided with an intense bunched electron beam. We are now planning to build such an x-ray source with a 50MeV multi-bunch linac and a 42cm Fabry-Perot cavity using pulse stacking technology. We actually finished construction of the 50MeV linac and will start its operation in the spring, 2006. Development of the pulsed-laser super-cavity and future plan of our compact x-ray source will be presented at the conference.  
THPCH155 High-quality Proton Beam Obtained by Combination of Phase Rotation and the Irradiation of the Intense Short-pulse Laser 3158
 
  • S. Nakamura, Y. Iwashita, A. Noda, T. Shirai, H. Souda, H. Tongu
    Kyoto ICR, Uji, Kyoto
  • S. Bulanov, T. Esirkepov, Y. Hayashi, M. Kado, T. Kimura, M. Mori, A. Nagashima, M. Nishiuchi, K. Ogura, S. Orimo, A. Pirozhkov, A. Sagisaka, A. Yogo
    JAEA, Ibaraki-ken
  • H. Daido, A. Fukumi
    JAEA/Kansai, Kizu-machi Souraku-gun Kyoto-fu
  • Z. Li
    NIRS, Chiba-shi
  • A. Ogata, Y. Wada
    HU/AdSM, Higashi-Hiroshima
  • T. Tajima
    JAEA/FEL, Ibaraki-ken
  • T. Takeuchi
    AEC, Chiba
  
  Ion production from laser-induced plasma has been paid attention because of its high acceleration gradient (>100GeV/m) compared with conventional RF accelerator. Its energy spectrum is Maxwell-Boltzmann distribution with high-energy cut-off, which limited its application. The phase rotation scheme, which rotates laser produced ions by an RF electric field synchronous to the pulse laser in the longitudinal phase space, was applied to proton beam up to 0.9MeV emitted from Ti foil with 3mm thickness irradiated by focused laser-pulse with peak intensity of 9 ´ 1017W/cm2. Multi-peaks with ~6% width (FWHM) were created and intensity multiplication up to 5 was attained around 0.6MeV region. The proton production process by the intense short-pulse laser has been optimized with use of time of flight measurement of proton beam detected by a plastic scintillation counter, which is specially shielded from the heavy background of electrons and X-rays induced by the intense laser. We have succeeded in on-line measurement of such a proton signal by the detector for the first time, which played an essential role for the investigation of phase rotation scheme.  
THPCH156 SNS Transverse and Longitudinal Laser Profile Monitors Design, Implementation and Results 3161
 
  • S. Assadi
    ORNL, Oak Ridge, Tennessee
  
  SNS is using a Nd:YAG laser to measure transverse profiles at nine-stations in the 186-1000 MeV Super-Conducting LINAC (SCL) and a Ti:Sapphire mode-locked laser to measure longitudinal profiles in the 2.5 MeV Medium Energy Beam Transport (MEBT). The laser beam is scanned across the H- beam to photo-neutralize narrow slices. The liberated electrons are directly collected to measure the transverse or longitudinal beam profiles. We have successfully measured the transverse and longitudinal profiles at all stations. The SCL laser system uses an optical transport line that is installed alongside the 300 meter super-conducting LINAC to deliver laser light at nine locations. Movement of the laser light in the optical transport system can lead to problems with the profile measurement. We are using telescopes to minimize the oscillations and active feedback system on mirrors to correct the drifts and movements. In this paper we present our implementation and beam profiles measured during SCL commissioning. We also discuss future improvements, drift/vibration cancellation system, as well as plan to automate subsystems for both the transverse and the longitudinal profiles.