SLAC Particle Sources Efforts Review/Status and Plans

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SLAC Particle Sources EffortsReview/Status and
Plans

• SLAC HEP Program Review
• June 13th, 2007

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Electron Source Systems
Laser
Injector specific RF structures
Photo cathodes
Gun
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Positron Source Systems
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e/e- Institutions in the US

• SLAC
• Overall coordination leadership
• Define parameters
• Polarized e- Source Laser System
• Photocathode Development
• Target hall, remote handling, activation
• Beamline optics and tracking
• NC L-Band accelerator structures and RF systems
• Experiments E166, FLUKA validation experiment

• LLNL
• Target simulations
• Target design
• Pulsed OMD design
• ANL
• Optics
• Tracking
• OMD studies
• Eddy current calculations
• Jlab
• Polarized gun development
• Cornell
• Undulator design, alternative target concepts

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Collaborating non-US Institutions

• Institutions doing substantial work on ILC
  baseline e development
• CCLRC-Daresbury
• undulator design and prototyping
• beam degradation calculations
• CCLRC-RAL (?)
• remote handling
• eddy current calculations
• target hall activation
• Cockcroft and Liverpool University
• target design and prototyping
• DESY-Zeuthen
• target hall activation
• spin preservation
• photon collimation
• E166

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Electron Source Technical Milestones

• Demonstrate Source Laser System.
• DC Gun Development (HV design).
• Advance Polarized Photocathode Technology.
• Bunching system design.
• Beam Dynamics.
• Demonstrate polarized electron bunch train with
  ILC parameters.

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Source Laser System
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Source Laser System

• Source laser development has started at SLACs
  ILC Injector Development Facility.
• Laser system pushes the state of the art in laser
  technology.
• Collaboration with Kapteyn-Murnane Labs through
  SBIR phase II (pending approval) aids in laser
  development.
• Facility allows use of SLC 120 kV DC gun in
  combination with laser system to generate
  polarized ILC electron bunch train.
• Goal is to demonstrate the operating laser system
  by the end of FY 09.

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DC Gun Development

• Project will start in FY 08 at Jlab.
• 140 kV minimum operating voltage ? 200 kV design.
• Combine features of SLACs 120 kV SLC gun and
  Jlabs 100 kV gun.
• HV design (power supply).
• Optimize electrodes (material and design) for ILC
  conditions.
• Load lock is essential for high reliability.
• Goal is to test the gun with laser system
  developed at SLAC.

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Photocathode RD Program

• Supported by ILC (mostly FTEs, small MS
  contribution)
• Several SBIRs/STTRs in FY07 (all Phase I)
• Activation Layer Stabilization of High
  Polarization Photocathodes in Sub-Optimal RF Gun
  Environments.
• High Polarization and High Peak Current
  Compositionally Graded AlGaAs/GaAs Superlattice
  Photocathodes for RF Gun Applications.
• High Polarization and High Robustness Antimonide
  Based Superlattice Photocathodes for RF Gun
  Applications.
• ? All applicable to DC guns as well
• Collaboration with University of St. Petersburg
  (Russia)
• Study of AlInGaAs/AlGaAs cathodes

Baseline Design Strained GaAs/GaAsP

• RD goals
• Improve robustness and lifetime
• Investigate alternative materials with
• increased polarization and QE
• Maintain and build expertise

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Photocathode RD Program

• Faraday rotation experiment

• Measures Depolarization Dynamics
• Depolarization occurs during transport through
  cathode material
• Interband absorption smearing due to bandedge
  fluctuations
• Hole scattering between the HH and LH states
  causes a broadening of the LH band
• Spin precession due to an effective magnetic
  field generated by the lack of crystal inversion
  symmetry and spin orbit coupling
• Electron hole scattering
• Less polarization selectivity in the BBR
• Scattering and trapping of electrons in the BBR
• SLAC-Pub-11384
• Understanding depolarization allows design of
  optimized photocathodes

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ILC Sources Optics and beam line design
Example Electron Source Optics
Positron beam line geometry
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ILC Polarized Positron System Technical Milestones

• 1. Demonstrate undulator parameters.
• 2. Demonstrate NC SW structure high power rf
  performance.
• 3. Spinning target pre-prototype demonstration.
• 3. Eddy current measurements on spinning target.
• 4. Selection and Technical design of Optical
  Matching Device.
• 5. System engineering for e source remote
  handling.
• 6. System engineering for photon dump.
• 7. System design compatibility with ILC upgrade
  scenarios polarization and energy.

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Undulator Challenges

• High fields
• Pushing the limits of technology
• Short Periods
• Shorter periods imply higher fields
• Narrow apertures
• Very tight tolerances - Alignment critical
• Cold bore (4K surface)
• Cannot tolerate more than few W of heating per
  module
• Minimizing impact on electron beam
• Must not degrade electron beam properties but
  have to remove energy from electrons
• Creating a vacuum
• Impossible to use conventional pumps, need other
  solution
• Minimizing cost
• Minimize total length, value engineering

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UK 4m Prototype Module
50K Al Alloy Thermal shield. Supported from He
bath
U beam Support rod

• Stainless steel vacuum vessel with Central turret

Stainless Steel He bath filled with liquid
Helium.
Magnet support provided by a stiff U Beam
Beam Tube
Superconducting Magnet cooled to 4.2K
Construction has started, will be complete by
Autumn 07
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Undulator Magnet Design Concept
Winding pins
Steel Yoke. Provides 10 increase in field and
mechanical support for former
PC board for S/C ribbon connections
Steel yoke
2 start helical groove machined in steel former
Cu beam pipe, withconductor wound on to tube OD
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Baseline Target Design

• Wheel rim speed (100m/s) fixed by thermal load
  (8 of photon beam power)
• Rotation reduces pulse energy density from
  900J/g to 24J/g
• Cooled by internal water-cooling channel
• Wheel diameter (1m) fixed by radiation damage
  and capture optics
• Materials fixed by thermal and mechanical
  properties and pair-production cross-section
  (Ti6Al4V)
• Wheel geometry (30mm radial width) constrained
  by eddy currents.
• 20cm between target and rf cavity.

T. Piggott, LLNL
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Activation Simulations

• New target geometry (mostly) migrated to FLUKA
• Simulations will begin at DL shortly as well as
  DESY/Z

motor assembly
L. Fernandez-Hernando, DL
NC rf cavity
target wheel (including water channel)
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Experiments at SLAC

• E166 proof of principle Undulator based
  polarized positron production
• Publication is pending (NIM, PRL)
• Validation of FLUKA activation calculations
• SLAC/CERN Collaboration (RP groups)
• 100 W
• 30 GeV electron beam in ESA at SLAC
• Cylindrical copper dump
• Samples around the dump (including a Ti-4V-6Al)
• Look mr/hour and gamma spectrum from irradiated
  samples
• Data taken, analysis in progress
• http//www-group.slac.stanford.edu/esh/rp/rpg/T-48
  9

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Target Remote Handling(conceptual)
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Optical Matching Device

• Optical Matching Device
• factor of 2 in positron yield (3 if immersed
  target)
• DC solenoid before target or pulsed flux
  concentrator after target
• Pulsed device is the baseline design
• Target spins in the magnetic field of the OMD
• Eddy currents in the target need to calculate
  power
• Magnetic field is modified by the eddy currents
  effect on yield??
• Eddy current mitigation
• Reduce amount of spinning metal
• Do experiment to validate eddy current
  calculations
• Look for low electrical / high thermal
  conductivity Ti-alloys
• Other materials such as ceramics
• No OMD
• Use focusing solenoidal lens (1/4 wave) lower
  fields
• OMD is upgrade to polarization!!!!!

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Eddy Current Experiment
Proposed experiment Layout at Cockcroft Institute/
Daresbury (this summer)
Eddy current calculation mesh - S. Antipov, W.
Liu, W. Gai - ANL
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Prototype Positron Capture Section
Design and Prototype
High Power Test using L-band station in SLACs
Endstation B
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Outlook EDR phase for e-/e
Dec 07 EDR Scope definition design depth and
breadth, cost, schedule, staff Dec 09 Freeze
layout, full component and civil
specifications Jan 09 EDR detailed component
inventory May 09 First cost review Dec 09
Deliver EDR and preconstruction work plan
Need Systems Engineering in FY08