01 Electron Accelerators and Applications
1D FELs
Paper Title Page
SUPB006 Study of Beam-Based Alignment for Shanghai Soft X-Ray FEL Facility 10
 
  • D. Gu, Q. Gu, D. Huang, M. Zhang, M.H. Zhao
    SINAP, Shanghai, People's Republic of China
  
  In linear accelerators, dispersion caused by quadrupole misalignment and transverse wake-field effect caused by alignment errors of accelerate structures will lead to a significant emittance growth. There are more stringent restrictions on SXFEL, the traditional optical alignment can no longer meet its requirements, but the Beam-Based Alignment(BBA) method allows more precise alignment, further reduce the Linac errors to meet SXFEL requirements .In undulator sections, orbit changes are not only caused by misalignments of quadrupole magnet position ,but also the errors of undulator magnetic. In order to achieve alignment accuracy over longer distance, we measuring BPM data under different conditions and using SVD algorithm for calculation and analysis, we can get the quadrupole magnet errors and BPM offset. With the method above, software based on MATLAB has been designed and compared the results with other software.  
 
MO1A02 Status of the European XFEL – Constructing the 17.5 GeV Superconducting Linear Accelerator 105
 
  • W. Decking
    DESY, Hamburg, Germany
  
  The European XFEL is presently under construction in Hamburg, Germany. It consists of a 1.2 km long superconducting linac serving an about 3 km long electron beam transport system. Three undulator systems of up to 200 m length each produce hard and soft x-rays via the self-amplified spontaneous emission (SASE) process. We will present the status of the civil construction and the accelerator components. The production of the 100 superconducting accelerator modules is distributed between industries and a collaboration of accelerator laboratories. We describe the carefully orchestrated production sequence, quality assurance measures and risk mitigation mechanisms. The last module is scheduled to be installed in the accelerator in spring 2015 and commissioning with beam will start in summer of that year.  
slides icon Slides MO1A02 [8.730 MB]  
 
TU2A01
 Review of FEL Projects  
 
  • J.N. Corlett
    LBNL, Berkeley, California, USA
  
  This talk will review the status of FELs in operation and proposals for major FEL facilities in the world.  
slides icon Slides TU2A01 [18.141 MB]  
 
TU2A02 Overview of SACLA Machine Status 427
 
  • Y. Otake
    RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
  
  SACLA of an X-ray free-electron laser has been constructed and was successfully lased at 0.06 nm in 2011. SACLA mainly comprises a low-emittance thermionic electron gun, an 8-GeV linear accelerator using C-band (5712 MHz) cavities and 18 in-vacuum undulators. The concept to develop this machine is compactness compared with the other machine, such as LCLS with the length of more than 1 km. Stable X-ray lasing up to 0.06 nm as also the concept demands extreme stable accelerator components, such as 50 fs temporal stability at a cavity in an injector. We now realized a 700 m compact machine by a low-emittance at the electron gun, an accelerating gradient of more than 35 MV/m with the C-band accelerator, and the short-period undulators. The continuous lasing for more than several days is strongly supported by these stable components and small operator‘s trimming, and also established by reduction of perturbation sources to laser instability. SACLA is regularly operated for user experiments, such as the imaging with extreme amount of data. This presentation introduces the machine performance, the reduction of the perturbation sources and the operation of SACLA.  
slides icon Slides TU2A02 [28.971 MB]  
 
TU2A03 LCLS Operation Experience and LCLS-II Design 432
 
  • T.O. Raubenheimer
    SLAC, Menlo Park, California, USA
  
  This talk will report the operations experience at LCLS and will describe the LCLS-II, a new X-ray FEL facility that uses the middle 1/3 of the SLAC linac as compared to the LCLS which uses the last 1/3 of the SLAC linac.  
slides icon Slides TU2A03 [4.761 MB]  
 
TUPLB01 The Swiss FEL RF Gun: RF Design and Thermal Analysis 442
 
  • J.-Y. Raguin, M. Bopp, A. Citterio, A. Scherer
    PSI, Villigen, Switzerland
  
  We report here on the design of a dual-feed S-band 2.5 cell RF gun, developed in the framework of SwissFEL, capable of operating at 100 Hz repetition rate. As in the LCLS RF gun, z-coupling, to reduce the pulsed surface heating, and a racetrack coupling cell shape, to minimize the quadrupolar component of the fields, have been adopted. The cell lengths and the iris thicknesses are as in the PHIN gun operating at CERN. However the irises aperture has been enlarged to obtain a frequency separation between the operating π mode and the π/2 mode higher than 15 MHz. An amplitude modulation scheme of the RF power, which allows one to obtain a flat plateau of 150 ns for multibunch operation and a reduced average power is presented as well. With an RF pulse duration of 1μs it is shown that operation at 100 MV/m and 100 Hz repetition rate is feasible with very reasonable thermal stresses.  
slides icon Slides TUPLB01 [1.679 MB]  
 
TUPLB02 Deflecting Structures with Minimized Level of Aberrations 445
 
  • V.V. Paramonov
    RAS/INR, Moscow, Russia
  
  Funding: in part RBFR N 12-02-00654a
Deflecting structures are now widely used for bunch phase space manipulations either in bunch rotation for special bunch diagnostic or in emittance exchange experiments. As a tool for manipulation, the structure itself should provide the minimal phase space perturbations due to non linear additives in the field distribution. Even if the field of synchronous harmonic is aberration free, the higher space harmonics provide significant non linear additives in the field distribution, leading to emittance growth during phase space manipulation. Criterion of the field quality estimation is developed and deflecting structures are considered for minimization of non linear additives. Examples with almost aberration free total field distributions are presented. 		 
slides icon Slides TUPLB02 [0.727 MB]  
 
TUPLB04 Results of Testing of Multi-beam Klystrons for the European XFEL 448
 
  • V. Vogel, L. Butkowski, A. Cherepenko, S. Choroba, I. Harders, J. Hartung
    DESY, Hamburg, Germany
  
  For the European XFEL multi-beam klystrons, which can produce RF power of 10 MW at an RF frequency of 1.3 GHz, at 1.5 ms pulse length and 10 Hz repetition rate, were chosen as RF power sources. Twenty-seven of horizontal multi-beam klystrons (MBK) together with connection modules (CM) will be installed in the XFEL underground tunnel. The CM will be installed on the MBK and connects the MBK to the pulse transformer with only one HV cable, because the CM has a filament transformer inside as well as all diagnostics for HV and cathode current measurements. MBK prototypes together with CM prototypes have been tested for long time at a test stand at DESY, about 3000 hours of operation for each of horizontal MBK with full RF output power, full pulse length and repetition rate of 10 Hz. Testing of first MBKs from series production has been started. In this paper we will give an overview of the test procedure, summarize the current test results and we will give a comparison of the most important parameters.  
 
TUPLB05 Computational Model Analysis for Experimental Observation of Optical Current Noise Suppression below the Shot-Noise Limit 451
 
  • A. Gover
    University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel
  • A. Nause
    University of Tel Aviv, Tel Aviv, Israel
  
  Funding: We acknowledge support of the Israel Science Foundation grant
We report first demonstration of optical frequency current shot-noise suppression in a relativistic e-beam. This process is made possible by collective Coulomb interaction between the electrons of a cold intense beam during beam drift, and is essentially a process of longitudinal beam-plasma oscillation [1]. Suppression of beam current noise below the classical “shot-noise” level has been known in the microwave tubes art [2]. This is the first time that it is demonstrated in the optical regime. We predict that the scheme can be extended to the XUV and possibly to shorter wavelengths with further development of technology. The fundamental current shot-noise determines the level of incoherent spontaneous radiation emission from electron-beam optical radiation sources and SASE-FELs [3]. Suppressing shot-noise would make it possible to attain spontaneous emission sub-radiance [4] and surpass the classical coherence limits of seed-injected FELs. The effect was demonstrated by measuring sub-linear growth as a function of current of the OTR Radiation. This finding indicates that the beam charge homogenizes due to the collective interaction, and its distribution becomes sub-Poissonian.
[1] A. Gover, E. Dyunin, PRL, 102, 154801, 2009
[2] H. Haus, N. Robinson, Proc. IRE, 43, 981 (1955)
[3] P. Emma, et al , Nature Photonics 4, 641 (2010)
[4] A. Dicke, Phys. Rev. 93, 99 (1954)
 		 
 
TUPB001 The Fine Structure of the Zone of Particle Interaction with a Finite Length Periodic Structure 473
 
  • V.V. Paramonov
    RAS/INR, Moscow, Russia
  
  The periodic constant impedance deflecting structures are widely used for a special beam diagnostic in FEL facilities. The method, based on frequency domain approach, was developed to estimate long range wake fields structure parameters in a wide frequency range. It is shown, that regardless to number of cells in the structure, at each passband to the zone of particle effective interaction with the structure belongs several, at least three modes. The usual time domain simulations provide the total estimation for loss factor or kick factor values and modes separation in the time domain approach requires enormous simulations.  
 
TUPB002 Deflecting Structures with Minimized Level of Aberrations 476
 
  • V.V. Paramonov
    RAS/INR, Moscow, Russia
  
  Funding: in part RBFR N 12-02-00654a
Deflecting structures are now widely used for bunch phase space manipulations either in bunch rotation for special bunch diagnostic or in emittance exchange experiments. As a tool for manipulation, the structure itself should provide the minimal phase space perturbations due to non linear additives in the field distribution. Even if the field of synchronous harmonic is aberration free, the higher space harmonics provide significant non linear additives in the field distribution, leading to emittance growth during phase space manipulation. Criterion of the field quality estimation is developed and deflecting structures are considered for minimization of non linear additives. Examples with almost aberration free total field distributions are presented. 		 
 
TUPB004 Results of Testing of Multi-beam Klystrons for the European XFEL 479
 
  • V. Vogel, L. Butkowski, A. Cherepenko, S. Choroba, I. Harders, J. Hartung
    DESY, Hamburg, Germany
  
  For the European XFEL multi-beam klystrons, which can produce RF power of 10 MW at an RF frequency of 1.3 GHz, at 1.5ms pulse length and 10 Hz repetition rate, were chosen as RF power sources. Twenty-seven of horizontal multi-beam klystrons (MBK) together with connection modules (CM) will be installed in the XFEL underground tunnel. The CM will be installed on the MBK and connects the MBK to the pulse transformer with only one HV cable, because the CM has a filament transformer inside as well as all diagnostics for HV and cathode current measurements. MBK prototypes together with CM prototypes have been tested for long time at a test stand at DESY, about 3000 hours of operation for each of horizontal MBK with full RF output power, full pulse length and repetition rate of 10 Hz. Testing of first MBKs from series production has been started. In this paper we will give an overview of the test procedure, summarize the current test results and we will give a comparison of the most important parameters.  
 
TUPB005 Computational Model Analysis for Experimental Observation of Optical Current Noise Suppression Below the Shot-noise Limit 482
 
  • A. Gover
    University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel
  • A. Nause
    University of Tel Aviv, Tel Aviv, Israel
  
  Funding: We acknowledge support of the Israel Science Foundation grant
We report first demonstration of optical frequency current shot-noise suppression in a relativistic e-beam. This process is made possible by collective Coulomb interaction between the electrons of a cold intense beam during beam drift, and is essentially a process of longitudinal beam-plasma oscillation.[1] Suppression of beam current noise below the classical “shot-noise” level has been known in the microwave tubes art [2]. This is the first time that it is demonstrated in the optical regime. We predict that the scheme can be extended to the XUV and possibly to shorter wavelengths with further development of technology. The fundamental current shot-noise determines the level of incoherent spontaneous radiation emission from electron-beam optical radiation sources and SASE-FELs [3]. Suppressing shot-noise would make it possible to attain spontaneous emission sub-radiance [4] and surpass the classical coherence limits of seed-injected FELs. The effect was demonstrated by measuring sub-linear growth as a function of current of the OTR Radiation. This finding indicates that the beam charge homogenizes due to the collective interaction, and its distribution becomes sub-Poissonian.
[1] A. Gover, E. Dyunin, PRL, 102, 154801, 2009
[2] H. Haus, N. Robinson, Proc. IRE, 43, 981 (1955)
[3] P. Emma, et al , Nature Photonics 4, 641 (2010)
[4] A. Dicke, Phys. Rev. 93, 99 (1954) 		 
 
TUPB006 Stability Performance of the Injector for SACLA/XFEL at SPring-8 486
 
  • T. Asaka, T. Hasegawa, T. Inagaki, H. Maesaka, T. Ohshima, Y. Otake, S. Takahashi, K. Togawa
    RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
  
  To realize the SACLA, it is necessary to obtain stabilities of 10-4 and 50 fs in the amplitude and time of an acceleration voltage, respectively. The achievement of the rf stabilities were almost satisfactory for the target values. Consequently, the 7 GeV beam energy stability was 0.02% (std.) or less. However, there was XFEL power variation caused by a variation of a beam position in a 40 MeV injector section. A periodically changed beam position of 40 μm (std.) was found out at a cycle of 2 s by Fourier transform method using BPM data. The temperatures of all the injector rf cavities are controlled within 28±0.04˚C by a controller using the cooling water. The AC power supplies of the controller to heat the cooling water are operated at 0.5 Hz by pulse width modulation control with alternatively turning on or off. The strong correlation between laser intensity variation and the modulation frequency of the AC power supplies was found out. We are planning to improve the cavity temperature variation in the order of less than 0.01˚C with DC power supplies to establish continuously regulated the cavity temperature. This plan will reduce the XFEL power variation.  
 
TUPB008 Major Trends in Linac Design for X-ray FELs 489
 
  • A. Zholents
    ANL, Argonne, USA
  
  Funding: This work was supported by the U.S. Department of Energy under Contract No. DE-AC02-06CH11357.
Major trends in the contemporary linac designs for x-ray free-electron lasers (XFELs) are outlined starting with identification of the key performance parameters, continuing with considerations of the design options for the electron gun and linac, and finishing with electron beam manipulation in the phase space. 		 
 
TUPB009 C-Band Accelerating Structure Development and Tests for the SwissFEL 492
 
  • R. Zennaro, J. Alex, H. Blumer, M. Bopp, A. Citterio, T. Kleeb, L. Paly, J.-Y. Raguin
    PSI, Villigen, Switzerland
  
  SwissFEL requires a 5.8 GeV beam provided by a C-band linac consisting of 104 two-meter accelerating structures. Each structure is of the constant gradient type and is composed of 113 cups. The cup shape is double-rounded to increase the quality factor. No tuning feature is implemented. For this reason ultra-precise turning is exploited. A strong R&D program has been launched on structure fabrication, which will be followed by a future technology transfer to a commercial company. The program includes the production and test of short structures that can be brazed in the existing PSI vacuum oven and will be completed with the production of the full two-meter prototype once the new full scale brazing oven, presently under construction, is operational. The status of the R&D program, including the production and power test results of the first two test structures, is reported here.  
 
TUPB010 The Swiss FEL RF Gun: RF Design and Thermal Analysis 495
 
  • J.-Y. Raguin, M. Bopp, A. Citterio, A. Scherer
    PSI, Villigen, Switzerland
  
  We report here on the design of a dual-feed S-band 2.5 cell RF gun, developed in the framework of SwissFEL, capable of operating at 100 Hz repetition rate. As in the LCLS RF gun, z-coupling, to reduce the pulsed surface heating, and a racetrack coupling cell shape, to minimize the quadrupolar component of the fields, have been adopted. The cell lengths and the iris thicknesses are as in the PHIN gun operating at CERN. However the irises aperture has been enlarged to obtain a frequency separation between the operating π mode and the π/2 mode higher than 15 MHz. An amplitude modulation scheme of the RF power, which allows one to obtain a flat plateau of 150 ns for multibunch operation and a reduced average power is presented as well. With an RF pulse duration of 1μs it is shown that operation at 100 MV/m and 100 Hz repetition rate is feasible with very reasonable thermal stresses.  
 
TUPB011 The Swiss FEL S-Band Accelerating Structure: RF Design 498
 
  • J.-Y. Raguin
    PSI, Villigen, Switzerland
  
  The Swiss FEL accelerator concept consists of a 450 MeV S-band injector Linac at 2998.8 GHz followed by the main linac at the C-band frequency aiming at a final energy of 5.8 GeV. The injector has six four-meter long S-band accelerating structures that shall operate with gradients up to 20 MV/m and with a 100 Hz repetition rate. Each structure has 122 cells, including the two coupler cells and operates with a 2π/3 phase advance. The design presented is such that the average dissipated RF power is constant over the whole length of the structure. The cells consist of cups and the cell irises have an elliptical profile to minimize the peak surface electric field. The coupler cells are of the double-feed type with a racetrack cross-section to cancel the dipolar components of the fields and to minimize its quadrupolar components.  
 
TUPB012 The Swiss FEL C-Band Accelerating Structure: RF Design and Thermal Analysis 501
 
  • J.-Y. Raguin, M. Bopp
    PSI, Villigen, Switzerland
  
  The Swiss FEL accelerator concept consists of a 450 MeV S-band injector linac followed by the main linac in C-band aiming at a final energy of 5.8 GeV. The two-meter long C-band accelerating structures have 113 cells, including the two coupler cells, and operate with a 2π/3 phase advance. The structure is of the constant-gradient type with rounded wall cells and has an average iris radius of 6.44 mm, a radius compatible with the impact of the short-range wakefields on the whole linac beam dynamics. The cell irises have an elliptical profile to minimize the peak surface electric fields and the coupler cells are of the J-type. We report here on the RF design of the structure, as well as on its thermal analysis, to target operational conditions with an accelerating gradient of about 28 MV/m and a repetition rate of 100 Hz.  
 
TUPB013 Update on the Commissioning Effort at the SwissFEL Injector Test Facility 504
 
  • T. Schietinger
    PSI, Villigen, Switzerland
  
  The SwissFEL Injector Test Facility at the Paul Scherrer Institute is the principal test bed and demonstration plant for the SwissFEL project, which aims at realizing a hard-X-ray Free Electron Laser by 2017. Since the spring of 2012 the photoinjector facility has been running with all RF cavities in full operation, allowing beam characterization at energies around 230 MeV with bunch charges between 10 and 200 pC. We give an overview of recent commissioning efforts with particular emphasis on efforts to optimize the emittance of the uncompressed beam.  
 
TUPB014 Comparative Design of Single Pass, Photo-cathode RF-LINAC FEL for the THz Frequency Range: Self Amplification vs. Enhanced Super-radiance 507
 
  • Yu. Lurie, Y. Pinhasi
    Ariel University Center of Samaria, Faculty of Engineering, Ariel, Israel
  
  Self amplified spontaneous emission and enhanced super-radiance are discussed and compared as possible configurations in the construction of a single-pass, photo-cathode RF-LINAC FEL source for THz radiation, being developed in Ariel University Center of Samaria. Numerical simulations carried out using 3D, space-frequency approach demonstrate the charge squared dependence of the radiation power in both cases, the characteristic typical to super-radiant emission. The comparison reveals a high efficiency of an enhanced super-radiance FEL, which however can only be achieved with ultra-short (the radiation wavelength long or shorter) drive electron beam bunches at a proper energy chirping.  
 
TUPB015 Warm Beamlines and Infrastructure in the European XFEL 510
 
  • M. Hüning
    DESY, Hamburg, Germany
  
  The European XFEL is driven by a superconducting linear accelerator. In the main accelerator tunnel the accelerator modules will be suspended from the tunnel ceiling. The warm sections like bunch compressors will be installed on girders supported from the floor. The accelerator infrastructure like klystrons and electronic racks will be installed in the accelerator tunnel in close proximity to the electron beamline.  
 
TUPB018 Study of Beam-Based Alignment for Shanghai Soft X-Ray FEL Facility 513
 
  • D. Gu, Q. Gu, D. Huang, M. Zhang, M.H. Zhao
    SINAP, Shanghai, People's Republic of China
  
  In linear accelerators, dispersion caused by quadrupole misalignment and transverse wake-field effect caused by alignment errors of accelerate structures will lead to a significant emittance growth. There are more stringent restrictions on SXFEL, the traditional optical alignment can no longer meet its requirements, but the Beam-Based Alignment(BBA) method allows more precise alignment, further reduce the Linac errors to meet SXFEL requirements .In undulator sections, orbit changes are not only caused by misalignments of quadrupole magnet position ,but also the errors of undulator magnetic. In order to achieve alignment accuracy over longer distance, we measuring BPM data under different conditions and using SVD algorithm for calculation and analysis, we can get the quadrupole magnet errors and BPM offset. With the method above, software based on MATLAB has been designed and compared the results with other software.  
 
TUPB019 Second CW and LP Operation Test of XFEL Prototype Cryomodule 516
 
  • J.K. Sekutowicz, V. Ayvazyan, J. Branlard, M. Ebert, J. Eschke, A. Gössel, D. Kostin, W. Merz, F. Mittag, R. Onken
    DESY, Hamburg, Germany
  • W. Cichalewski, W. Jałmużna, A. Piotrowski, K.P. Przygoda
    TUL-DMCS, Łódź, Poland
  • K. Czuba, Ł. Zembala
    Warsaw University of Technology, Institute of Electronic Systems, Warsaw, Poland
  • I.M. Kudla, J. Szewiński
    NCBJ, Świerk/Otwock, Poland
  
  In summer 2011, we have performed the first test of continuous wave (cw) and long pulse (lp) operation of the XFEL prototype cryomodule, which originally has been designed for short pulse operation. In April and June 2012, the second test took place, with the next cryomodule prototype. For that test cooling in the cryomodule was improved and new LLRF system has been implemented. In this contribution we discuss results of the second RF test of these new types of operation, which can in the future extend flexibility in the time beam structure of the European XFEL facility  
 
TUPB020 Status of the European XFEL 3.9 GHz system 519
 
  • E. Vogel
    DESY, Hamburg, Germany
  • A. Bosotti, P. Michelato, L. Monaco, C. Pagani, R. Paparella, P. Pierini, D. Sertore
    INFN/LASA, Segrate (MI), Italy
  • E.R. Harms
    Fermilab, Batavia, USA
  
  The third harmonic system at 3.9 GHz of the European XFEL injector section will linearize the bunch RF curvature, induced by first accelerating module, before the first compression stage. This paper presents qualification tests on cavity prototypes and the on-going activities towards the realization of the third harmonic section of the European XFEL in view of its commissioning in 2014.  
 
TUPB021 Study of Plasma Effect in Longitudinal Space Charge Induced Microbunching Instability 522
 
  • D. Huang, Q. Gu
    SINAP, Shanghai, People's Republic of China
  • K.Y. Ng
    Fermilab, Batavia, USA
  
  The longitudinal space charge (LSC) plays an important role in introducing the microbunching instability in the LINAC of a free electron laser (FEL) facility. The current model of LSC impedance [1] derived from the fundamental electromagnetic theory [2] is widely used to explain the growth of the microbunching instability [3]. However, in the case of highly bright relativistic electron beams, the plasma effect starts to play a role. In this article, the basic model of LSC impedance including the plasma effect is built , and the modifications to the microbunching instability based on the new model are discussed in various conditions.
[1] Marco Venturini, Phys Rev. ST Accel. Beams 11, 034401 (2008)
[2] J. D. Jackson, Classical Electrodynamics (Wiley, 1999)
[3] Z. Huang, et. al., Phys, Rev. ST Accel. Beams 7, 074401 (2004) 		 
 
TUPB022 A Passive Linearizer for Bunch Compression 525
 
  • Q. Gu, M. Zhang, M.H. Zhao
    SINAP, Shanghai, People's Republic of China
  
  In high gain free electron laser (FEL) facility design and operation, a high bunch current is required to get lasing with a reasonable gain length. Because of the current limitation of the electron source due to the space charge effect, a compression system is commonly used to compress the electron beam to the exact current needed. Before the bunch compression, the nonlinear energy spread due to the finite bunch length should be compensated; otherwise the longitudinal profile of bunch will be badly distorted. Usually an X band accelerating structure is used to compensate the nonlinear energy spread while decelerating the beam. For UV FEL facility, the X band system is too expensive comparing to the whole facility. In this paper, we present a corrugated structure as a passive linearizer, and the preliminary study of the beam dynamics is also shown.  
 
TUPB023 The Optimization of RF Deflector Input Power Coupler 528
 
  • A.Yu. Smirnov, O.A. Adonev, P.V. Binyukov, N.P. Sobenin
    MEPhI, Moscow, Russia
  
  This paper concerns the investigation of different types of input power cell for S-band RF electron deflector. This device serving for slice emittance diagnostics is a disc-loaded waveguide which operates with TE11-like wave in traveling wave regime with 120 deg phase shift per cell. Since this deflector meets the restriction on its length and has to provide high enough deflecting potential to a particle during its flight time it is significant to increase the transversal field strength in coupling cell or to shorten it so that the deflecting potential remains constant. The total structure consists of 14 regular cells and two couplers. As it is now all cells have the same length equal to D=33.34 mm and the field in couplers is lower than that of regular cells. In this paper different length are considered and numerically simulated in order to choose the best one.  
 
TH2A004 Computational Model Analysis for Experimental Observation of Optical Current Noise Suppression Below the Shot-noise Limit 783
 
  • A. Gover
    University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel
  • A. Nause
    University of Tel Aviv, Tel Aviv, Israel
  
  Funding: We acknowledge support of the Israel Science Foundation grant
We report first demonstration of optical frequency current shot-noise suppression in a relativistic e-beam. This process is made possible by collective Coulomb interaction between the electrons of a cold intense beam during beam drift, and is essentially a process of longitudinal beam-plasma oscillation.[1] Suppression of beam current noise below the classical “shot-noise” level has been known in the microwave tubes art [2]. This is the first time that it is demonstrated in the optical regime. We predict that the scheme can be extended to the XUV and possibly to shorter wavelengths with further development of technology. The fundamental current shot-noise determines the level of incoherent spontaneous radiation emission from electron-beam optical radiation sources and SASE-FELs [3]. Suppressing shot-noise would make it possible to attain spontaneous emission sub-radiance [4] and surpass the classical coherence limits of seed-injected FELs. The effect was demonstrated by measuring sub-linear growth as a function of current of the OTR Radiation. This finding indicates that the beam charge homogenizes due to the collective interaction, and its distribution becomes sub-Poissonian.
[1] A. Gover, E. Dyunin, PRL, 102, 154801, 2009
[2] H. Haus, N. Robinson, Proc. IRE, 43, 981 (1955)
[3] P. Emma, et al , Nature Photonics 4, 641 (2010)
[4] A. Dicke, Phys. Rev. 93, 99 (1954)