Charge by hcj

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									Charge to the Committee
The RF Technical Review for the Linac Coherent Light Source (LCLS) Injector will be
held at Stanford Linear Accelerator Center (SLAC) on November 3, 2004. The reviewers
will be given the LCLS injector performance requirements, and are asked to critically
assess the RF, thermal and mechanical designs for the gun and first accelerator section
which are proposed to meet these requirements. Presentations will cover beam dynamics
and the dual feed and racetrack designs for the gun and L0-1 accelerator section.
Thermal management and RF mode issues for the gun will also be presented. Specific
technical issues include the elimination of dipole and quadrupole field distortions with
dual feed couplers and racetrack shaped coupler cells, thermal distortion of the gun when
operated at 120 Hz, and the excitation of the 0-mode and its effect in the gun during the
RF transient. Specifically we ask the committee to recommend whether or not the 0-pi
mode separation should be increased. Manufacturing, RF testing and tuning procedures
will also be discussed.
The committee is requested to:
        1. Identify and quantify technical issues related to the Injector RF design
        2. Determine if the design will meet LCLS requirements
        3. Identify any technical issues not already included in design
        4. Determine if design, RF tuning and construction plans are reasonable
        5. Make comments and suggestions for improving the RF design
A written report of the committee’s comments and recommendations is requested.

General Description of the LCLS Injector

The last kilometer of the SLAC 3-km linac will be used to provide a 10-15 GeV beam for
the LCLS. A new off-axis injector will be built at Sector 20 in an existing vault. The
injector utilizes an S-band rf gun with a metal photocathode. The laser for exciting the
cathode will be in a laser room which will be inside an existing building above the vault.
Additional information on LCLS can be found at the LCLS web site:

http://www-ssrl.slac.stanford.edu/lcls/



The goal of the LCLS injector is to produce an electron beam bright enough to saturate
the SASE x-ray fel within a 120 meter undulator. The injector parameters needed to
achieve this are given in Table I.

Table I. Parameter goals of the LCLS injector
                             Parameter                        Value

                 Peak current                          100 A
                 Charge                                0.1 – 1 nC
                 Normalized transverse emittance        1.2 / 1.0 m rms
                    projected/slice
                 Rate                                  120 Hz
                 Energy                                135 MeV
                 Energy spread @ 150 MeV                0.1 / 0.01 % rms
                    projected/slice
                 Gun laser timing stability             0.50 ps rms
                 Booster mean rf phase stability       0.1  rms
                 Charge stability                       2.0 % rms
                 Bunch length stability                 5 % rms

The injector consists of an RF photocathode gun and two s-band SLAC-sections to give a
total beam energy of 135 MeV, as shown in the figure below. The photocathode gun
produces electrons using a drive laser located in a room located directly above the gun.
In order to achieve the challenging parameters given in Table I, the injector has been
designed to include features not found in other injectors. These include:
    1. Cathode load lock and a cathode lab located near the injector.
    2. Rf gun with dual rf feeds to minimize field asymmetry.
    3. High-resolution energy diagnostics between the gun and the first linac section.
    4. Dual rf feeds on the first accelerator section to eliminate time-dependent rf kicks.
    5. Transverse rf deflecting cavity for direct measurement of the longitudinal phase
        space and slice emittance.
    6. Electro-optical bunch shape diagnostics.
    7. High-resolution spectrometer for measuring beam properties at 135 MeV.
    8. A ‘laser heater’ is included to allow a controlled increase in the uncorrelated
        energy to suppress coherent synchrotron radiation and longitudinal space charge
        instabilities.



       Presentations will be posted at the web site here below by

http://ssrl.slac.stanford.edu/lcls/photoinjector/reviews/2004-11-
03_rf_review/




See also the two technical notes on the RF system for the LCLS injector related to the
LCLS injector RF systems:

       http://www-ssrl.slac.stanford.edu/lcls/technotes/lcls-tn-04-4.pdf
       http://www-ssrl.slac.stanford.edu/lcls/photoinjector/internals/documents/sband-
l01-section-coupler.doc


                                                                                         RF Gun &
                                                                                         Solenoid




                                                            T
                                                            REA




                                                                              VAC
                                                              TME




                                                                                 UUM
                                                                 NT
                                                       CHA




                                                                                    PU
                                                          MBE




                                                                             M
                                                                             PS
                                                            R
                                                                                                       L0-1 & L0-2


                      ASSEG
                       LON
  Load Lock


                         MB EL
                           B
                            LY LO
                                WS




                                     S OO
                                     EAL LS
                                      SP
                                           FRO
                                              MVAL
                                                                                                    3-m SLAC Sections

                                                  VE




                                                          HO R
                                                           P
                                                           LDER N
                                                           O
                                                             CUPI
                                                                  E CA
                                     GA A
                                      U
                                      TEVALMET
                                      HV




                                                                     THO
                                          L




                                                                        D
                                           L




                                                                         E
                                           VE A
                                             S
                                               L




                                                                                                     Laser Heater & Chicane
              Gun Diagnostics
                                                                                                           Transverse RF Cavity

                                                                                                                Electro-Optic Diagnostic

                                                                                                                OTR Emittance Diagnostics
               Radiation Shield Walls
                                                                                                                         35o Bend



     SLAC Main Linac Beamline



                                                                                                      Straight Ahead Spectrometer

The LCLS Injector at Sector 20

								
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