Linac Coherent Light Source Stanford Synchrotron .Linac Coherent Light Source Stanford Synchrotron

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  • LCLS Laser Heater ReviewLCLS Laser Heater ReviewMarch 1, 2004March 1, 2004

    ZhirongZhirong Huang, SLACHuang, SLAC1zrh@slac.stanford.eduzrh@slac.stanford.edu

    Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center

    Suppression of MicrobunchingInstability in the LCLS

    Z. Huang, M. Borland (ANL), P. Emma, J. WuC. Limborg, G. Stupakov, J. Welch

    Suppression of MicrobunchingInstability in the LCLS

    Z. Huang, M. Borland (ANL), P. Emma, J. WuC. Limborg, G. Stupakov, J. Welch

    Motivation

    CSR/LSC Instability

    Cure (laser heater)

    Motivation

    CSR/LSC Instability

    Cure (laser heater)LCLSLCLS

  • LCLS Laser Heater ReviewLCLS Laser Heater ReviewMarch 1, 2004March 1, 2004

    ZhirongZhirong Huang, SLACHuang, SLAC2zrh@slac.stanford.eduzrh@slac.stanford.edu

    Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center

    IntroductionIntroductionIntroductionFEL instability in the undulator requires a very bright

    electron beam (small emittance and energy spread)

    This beam interacting with self-fields in the accelerator can be sensitive to other undesirable instabilities

    Bunch compressors designed to increase the peak current give rise to a microbunching instability that may degrade the beam quality significantly

    Increasing the local energy spread within the FEL tolerance can damp the instability without degrading the XFEL performance

  • LCLS Laser Heater ReviewLCLS Laser Heater ReviewMarch 1, 2004March 1, 2004

    ZhirongZhirong Huang, SLACHuang, SLAC3zrh@slac.stanford.eduzrh@slac.stanford.edu

    Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center

    How cold is the photoinjector beam?How cold is the photoinjector beam?Parmela at 1 nC TTF measurement at 4 nC

    simulationmeasured

    mean

    E/E

    (sec)

    3 keV Huning and Schlarb, PAC03

    Local rms energy spread ~ 3 keV, could be less!

  • LCLS Laser Heater ReviewLCLS Laser Heater ReviewMarch 1, 2004March 1, 2004

    ZhirongZhirong Huang, SLACHuang, SLAC4zrh@slac.stanford.eduzrh@slac.stanford.edu

    Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center

    Microbunching instabilityMicrobunching instability Initial density modulation induces energy modulation through long. impedance Z(k), converted to more density modulation by a chicane growth of local energy spread/emittance!

    t

    Energybi bf >> bi or G= bf/ bi >> 1

    (k)

    R56

    Current modulation

    1% 10%Gain=10

    t

  • LCLS Laser Heater ReviewLCLS Laser Heater ReviewMarch 1, 2004March 1, 2004

    ZhirongZhirong Huang, SLACHuang, SLAC5zrh@slac.stanford.eduzrh@slac.stanford.edu

    Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center

    LCLS accelerator systemsLCLS accelerator systems

    Linac 1

    BC1 BC2

    SC wiggler at 4.5 GeV

    DL2DL1

    End of injector

    Linac 2 Linac 3Laser heaterat 135 MeV

    At the end of injector, e-beam carries some residual density modulations which can be amplified in the downstream accel.

    Sources of impedance: CSR in dipoles, longitudinal space charge (LSC) and linac wakefields in linacs

    Landau damping options: a SC wiggler before BC2 at 4.5 GeV or a laser heater before DL1 at 135 MeV

  • LCLS Laser Heater ReviewLCLS Laser Heater ReviewMarch 1, 2004March 1, 2004

    ZhirongZhirong Huang, SLACHuang, SLAC6zrh@slac.stanford.eduzrh@slac.stanford.edu

    Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center

    FEL parameter ~ 510-4, not sensitive to energy spread until ~ 110-4

    3 keV initial energy spread after compression = 90 keV,corresponding to < 110-5 at 14 GeV

    M. Xies fitting formula = 1 mIp = 3.4 kA = 25 m quantum diffusion

    can increase by a factor of 10 without FEL degradation

    FEL limit

    0 1 2 3 4f10

    4

    4

    5

    6

    FELPow

    erGainLe

    ngthm

    Heating within FEL toleranceHeating within FEL tolerance

  • LCLS Laser Heater ReviewLCLS Laser Heater ReviewMarch 1, 2004March 1, 2004

    ZhirongZhirong Huang, SLACHuang, SLAC7zrh@slac.stanford.eduzrh@slac.stanford.edu

    Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center

    energy profileenergy profile long. spacelong. space temporal profiletemporal profile

    micro-bunching

    micro-bunching

    33101066

    230 fsec230 fsec

    CSR microbunchingCSR microbunching

    SCSC--wiggler wiggler damps damps

    bunchingbunching 33101055

  • LCLS Laser Heater ReviewLCLS Laser Heater ReviewMarch 1, 2004March 1, 2004

    ZhirongZhirong Huang, SLACHuang, SLAC8zrh@slac.stanford.eduzrh@slac.stanford.edu

    Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center

    SC wiggler increases 10 times at 4.5 GeV (BC2), suppresses the CSR gain

    Landau damping wigglerLandau damping wiggler

    100 200 300

    0

    50

    100

    Gain

    elegant HWiggler onL

    Theory HWiggler onL

    elegant HWiggler offL

    Theory HWiggler offL

    Initial modulation wavelength (m)

    Linac wakefields contribution (2X) included

  • LCLS Laser Heater ReviewLCLS Laser Heater ReviewMarch 1, 2004March 1, 2004

    ZhirongZhirong Huang, SLACHuang, SLAC9zrh@slac.stanford.eduzrh@slac.stanford.edu

    Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center

    LSC instabilityLSC instability

    LSC-induced energy modulation can accumulate in the linacand can dominate the microbunching instability

    SaldinSchneidmillerYurkov

  • LCLS Laser Heater ReviewLCLS Laser Heater ReviewMarch 1, 2004March 1, 2004

    ZhirongZhirong Huang, SLACHuang, SLAC10zrh@slac.stanford.eduzrh@slac.stanford.edu

    Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center

    SDL RF zero-phasing measurementSDL RF zero-phasing measurement RF zero-phasing method can be used to extract LSC-induced energy modulation in the linac (Shaftan/Huang)

    25 35 keV at 200 A

  • LCLS Laser Heater ReviewLCLS Laser Heater ReviewMarch 1, 2004March 1, 2004

    ZhirongZhirong Huang, SLACHuang, SLAC11zrh@slac.stanford.eduzrh@slac.stanford.edu

    Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center

    Space charge oscillationSpace charge oscillationCurrent modulation Energy modulation

    Space charge oscillation in the photoinjector (see C. Limborgs talk). Initial density modulation can be reduced at the expense of increased energy modulation (which is also bad)

  • LCLS Laser Heater ReviewLCLS Laser Heater ReviewMarch 1, 2004March 1, 2004

    ZhirongZhirong Huang, SLACHuang, SLAC12zrh@slac.stanford.eduzrh@slac.stanford.edu

    Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center

    LSC impedanceLSC impedance

    Free-space longitudinal space charge impedance

    At end of photoinjector, beam density modulation freezes and energy modulation accumulates

    rb

    1/

    Evaluate microbunching gain relative to density modulation at injector end, which may over/under estimate gain relative to the drive laser modulation

  • LCLS Laser Heater ReviewLCLS Laser Heater ReviewMarch 1, 2004March 1, 2004

    ZhirongZhirong Huang, SLACHuang, SLAC13zrh@slac.stanford.eduzrh@slac.stanford.edu

    Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center

    3 keV energy spread is too small to suppress high-frequency LSC instability, which can even amplify shot noise

    c13 m from 3 keV SC wiggler does not affect BC1 gain, but can smear out microbunching after BC2

    0 50 100 150 2000 m

    10

    100

    1000

    10000

    Total

    Gain

    SC wiggler on

    SC wiggler off

    20 40 60 80 1000 m

    0

    25

    50

    75

    100

    BC1Gain

    Microbunching gain including LSCMicrobunching gain including LSC

  • LCLS Laser Heater ReviewLCLS Laser Heater ReviewMarch 1, 2004March 1, 2004

    ZhirongZhirong Huang, SLACHuang, SLAC14zrh@slac.stanford.eduzrh@slac.stanford.edu

    Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center

    High BC1 gain significant energy modulation in Linac-2, which can be temporally smeared in BC2 and becomes effective energy spread ( SC wiggler too late) Slice energy spread at undulator (14 GeV), seeded with 1% initial density modulation (see J. Wus talk)

    Growth of energy spreadGrowth of energy spread

    20 30 40 50 600 m

    5

    10

    15

    f10

    4

    FEL limitElegantTheory

    Need < 0.1% initial density modulation or suppress theBC1 gain effectively

  • LCLS Laser Heater ReviewLCLS Laser Heater ReviewMarch 1, 2004March 1, 2004

    ZhirongZhirong Huang, SLACHuang, SLAC15zrh@slac.stanford.eduzrh@slac.stanford.edu

    Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center

    Laser HeaterLaser Heater

    2 cm2 cm

    10 cm10 cm

    10 cm10 cm 50 cm50 cm

    ~120 cm~120 cm

    5.75.7

    Laser-electron interaction in an undulator induces rapid energy modulation (at 800 nm), to be used as effective energy spread before BC1 (3 keV 40 keV rms)

    Inside a weak chicane for easy laser access, time-coordinate smearing