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Activities at the PITZ facility Igor Isaev LaPlas 2017 NRNU MEPhI, 2017.01.25

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  • Activities at the PITZ facility

    Igor IsaevLaPlas 2017NRNU MEPhI, 2017.01.25

  • > The PITZ is a dedicated site to develop and test RF guns for high brightness beams including all subsystems:gun cavity, cathodes, interlock system, water cooling system, RF feed system, photocathode laser, electron beam diagnostics, ...

    > PITZ goals: Development of an electron source for the European XFEL:

    - very small transverse emittance (

  • PITZ facility


    Facility parameters> RF photoelectron gun > Booster> Diagnostics:

    slit scan (transverse phase space) streak camera, TDS, dipole (longitudinal

    phase space) screen stations (beam shape) tomography (transverse phase space)

    Parameter ValueBeam bunch charge, nC 0.001 .. 4Beam momentum after gun / booster, MeV/c 7 / 25

    Number of pulses in a train ≤800

    Repetition rate, Hz 10

    Maximum average beam current, µA ≤32Optimized emittance (1nC ), mm mrad New developments (e.g. plasma acceleration)

  • Photoelectron gun setupPITZ photoelectron gun setup consists of:> RF cavity

    L-band 1.6-cell copper (OFHC) cavity Dry-ice cleaning → low dark current ( Solenoids Dedicated for emittance compensation Max. on-axis field ~0.3 T (500 A in the main solenoid) Bucking solenoid for compensation of field at cathode

    > Photocathode laser Pulse train structure Micropulses temporally and spatially shaped

    Gun parameter Value

    Max. accelerating gradient at the cathode, MV/m 60

    Frequency, MHz 1300

    Unloaded quality factor ~20000

    Beam momentum after gun, MeV/c 7

    RF peak power, MW 6.5

    RF pulse duration, µs ≤650

    Repetition rate, Hz 10

    RF cavity water cooling channels(Gun 4 type)

    Three designs of the cathode area

    Watchband spring design

    Mo plug

    CuBe spring

    Cs2Te cathode

    Watchband Reloaded

    spring design

    Mo plug

    CuBe spring

    Cs2Te cathode

    Contact stripe design

    Mo plug

    CuBe spring

    Cs2Te cathode

    RF gun

    Gun 4.6

  • Ramp-up procedure:• RF power increase by steps of max 0.2 MW every 15 min• vacuum pressure < 10-7 mbar• In case of significant vacuum or other trips:

    • re-ramp RF power from 0 with short pulses (10 µs)• Initially, the rf gun solenoid is off (then sweep)

    Conditioning of the Gun 4.6









    PMTse-det e-det

    IR IR






    dir.cpl. dir.cpl.






  • New developments and technologies3D Ellipsoidal Laser (ELLA) (collaboration with IAP)

    Plasma acceleration

    THz radiation generation based on PITZ facility

    > Fiber-based laser oscillator and amplifier> Multi-pass diode pumped disk amplifier with Yb:KGW crystals> SLM-based spatio-temporal shapers in 4f zero-dispersion layout> Second and fourth harmonic converters> Scanning auto/cross-correlators (diagnostic)

    Status:> Laser is installed > First photoelectrons are produced> Drift correction to be implemented> Adjustments to be done

    The plasma cell is designed as a heat pipe with metal grooves inside the oven acting like a wick.Results of 1st experimental run:•transverse defocusing was observed•time resolved measurement show transverse oscillations•energy spectrum undergo widening •energy modulations via longitudinal phase space measurements were observed•plasma cell still needs further improvements

    Motivation: To be a prototype facility for a proposal to use IR/THz radiation

    generated by a “PITZ-like” accelerator together with X-rays from the European XFEL for pump-probe experiments.

    Studies of radiation-based electron beam diagnostics.

    Outlook for the first half of 2017:•CTR station design and installation•First experimental generation of THz CTR at PITZ

  • > Optimum machine parameters: experiment ≠ simulations

    > The electron beam asymmetry was observed during emittance measurements at PITZ

    Electron beam asymmetries

    E-beam x-y asymmetry (tails)

    Emittance vs. Imain Bunch charge vs. laser energy


    Emittance vs. laser XYrms


    Phase space of the electron beam

    X phase space

    Y phase space

    Optimum: Imain≠MaxB

  • Coupler kick

    > RF field simulations (CST MWS): The full model of the gun:

    − the gun cavity− the coupler − simplified cathode

    Frequency domain solver (F-solver) Tetrahedral mesh (~106 elements) with 2nd order curved elements Half structure symmetry

    E-field distribution: H-field distribution:

  • Larmor angle experiment

    Measurements (29.09.2015M-A):

    • Pgun=5MW (6.1MeV/c max)

    • Launch phase: MMMG• Cathode laser:

    Gaussian 11.5 ps FWHM (expected)

    BSA=1.2mm (VC2)• Charge 0.5 nC

    Beam at High1.Scr1 Main solenoid current is 361 A, opposite polarity, bucking current is 0


    I main = - 361 A, I bucking = 0 A

    I main = + 361 A, I bucking = 0 A

    “Tracking back” towards cathode (M.Krasilnikov)Cathode Z=0.18m EMSY

    I mai

    n =


    AI m


    = -3


    The kick at z=0.18m is oriented by 45°.

    Could it be described by a skew quadrupole?

  • Quads like field from coupler kicker or/and solenoid

    #1 David Dowell, Analysis and Cancellation of RF Coupler- induced Emittance Due to Astigmatism. LCLS-2 TN-15-05 3/23/2015.#2 John Schmerge, LCLS Gun Solenoid Design Considerations. SLAC-TN-10-084.

    Main idea:1. the kick optics can be modeled as a rotated quadrupole with focal length and rotation angle

    given in terms of the (complex) Voltage kicks. 2. a rotated quadrupole near the coupler is effective at compensating for the kick, cancelling both

    the coupler emittance and the astigmatic focusing.

    Simulations: with assumed skew quadrupoles fields at z= 0.18m. These assumptions are also based on other beam asymmetry studies (Larmor angle experiment).All ASTRA simulation set up are same with experiment set up, beam momentum and solenoid current.

    Experimental setup:Pgun=5MW , 6.178 MeV/c, gradient is 54.2 MeV/c, 500 pC no booster 05.09A-06.09N.2015.

    /skew quadrupoleQ_type(1) = 'skew',Q_length(1)=0.01,Q_K(1)= XXX,Q_pos(1)=0.18,

  • Simulations with rotation quads model (Q.Zhao)

    Q_length(1)=0.01,Q_K(1)= +-0.6,Q_pos(1)= x.xx,Q_zrot(1)= y.yy

    Use rotation quads model in ASTRA simulation by scanning the rotation angle and z position. Find the parameters for beam images at High1.Scr1 to fit the experiment images, the direction of the

    beam wings for both solenoid polarity. 2D-3D space charge used in ASTRA simulation, z_trans=0.12m.

    I main = +361A

    ~13 degree ~78 degree

    Images table from simulation analysisI main = -361A

    Summary of the simulations: Position: around z=0.18m Rotation angle: Skew quads: 45 degree( negative polarity) / 135 degree( positive polarity). Polarity: same, not effected by solenoid field polarity.

    Position: around z=0.34m Rotation angle: Normal quads. Polarity: when change the solenoid polarity, the quads polarity also changed.

  • First design of the Gun Quad (4 coils)Parameters:• Aluminum frame• 0.56 mm copper cable• 180 windings per coil• 2 thermal switchers (80 degC max)• Non-magnetic screws• Fixed by radiation-hard cable tie• Q_grad = 0.0207 T/m @ 1A

    Influence on the transverse beam shapeFocused Beam @ High1.Scr1Imain = 335A, Positive polarityGun.Quad is OFF

    Rounded beam @ High1.Scr1Imain = 335A, Normal polarityGun.Quad 0.5A, Normal oriented

    Influence on emittance

    • One quad was able to compensate beam asymmetry, but only for one solenoid polarity• The compensation of the beam asymmetry for both solenoid polarities two quads are needed• Emittance does not get smaller but more equal

    Beam size


    Red- X value, Blue - Y value, Green - XY value

  • Second design of the Gun Quad (8 coils)Parameters:• Combination of a normal and a skew quads• Aluminum frame• 0.56 mm copper cable• 140 windings per coil• 2 thermal switchers (80 degC max)• Non-magnetic screws• Fixed by radiation-hard cable tie• Q_grad = 0.0117 T/m @ 1A

    Influence on emittanceBeam @ LEDA Beam @ High1.Scr1without Gun.Quads

    with Gun.Quads

    Beam is tilted

    No beam tilt

    Sol.pol.=Positive Sol.pol.=Negative


    Xemit=1.60mm mrad

    Xemit=1.34mm mrad

    Yemit=1.23mm mrad

    Yemit=1.47mm mrad

    XYemit=1.41mm mrad

    XYemit=1.41mm mrad

    • Possible to compensate beam asymmetry for all solenoid settings• LEDA tilt can be compensated• Emittance more symmetric, but not smaller

  • Current & future PITZ activities

    A brighter & more robust electron source for FLASH & XFEL➢Gun 4.6 conditioned with higher gradient & stability (2 DESY RF windows)➢Generation of 3D ellipsoidal electron bunches➢Measurements and beam dynamics (e.g. slice energy spread or➢projected/slice emittance vs gun gradient and vs laser shape)➢Studies of beam imperfections and charge stability in bunch train➢Gun 5 development

    New accelerator technology and its application➢Self modulation➢Transformer ratio➢Lab Astrophysics➢Experiments with dielectrics➢THz studies

  • Thank you for your attention.

    Slide 1Slide 2PITZ facilityPhotoelectron gun setupSlide 5Slide 6MotivationCoupler kick studiesLarmor angle experimentQuads like field from coupler kicker or/and solenoidSimulations with rotation quads model (Q.Zhao)First design of the Gun Quad (4 coils)Second design of the Gun Quad (8 coils)Summary and OutlookSlide 15