Axel Brachmann, John Sheppard, Vinod Bharadwaj SLAC Particle Sources Efforts Review/Status and Plans...

Axel Brachmann, John Sheppard, Vinod Bharadwaj

SLAC Particle Sources EffortsReview/Status and Plans

SLAC HEP Program ReviewJune 13th, 2007

International LinearCollider – Americas

2/24

Gun

Laser

Injector specificRF structures

Photocathodes

Electron Source Systems


3/24

Positron Source Systems


4/24

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


5/24

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


6/24

Electron Source Technical Milestones

1. Demonstrate Source Laser System.

2. DC Gun Development (HV design).

3. Advance Polarized Photocathode Technology.

4. Bunching system design.

5. Beam Dynamics.

6. Demonstrate polarized electron bunch train with ILC parameters.


7/24

Source Laser System


8/24

Source Laser System

• Source laser development has started at SLAC’s 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.


9/24

DC Gun Development

• Project will start in FY 08 at Jlab.

• 140 kV minimum operating voltage 200 kV design.

• Combine features of SLAC’s 120 kV SLC gun and Jlab’s 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.


10/24

Photocathode R&D Program

• Supported by ILC (mostly FTE’s, small M&S contribution)

• Several SBIR’s/STTR’s 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 DesignStrained GaAs/GaAsP

R&D goals:

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


11/24

Photocathode R&D Program

Faraday rotation experimentMeasures 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


12/24

ILC Sources Optics and beam line design

Example: Electron Source Optics

Positron beam line geometry


13/24

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.


14/24

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


15/24

UK 4m Prototype Module

Stainless steel vacuum vessel with Central turret

50K Al Alloy Thermal shield. Supported from He bath

Stainless Steel He bath filled with liquid Helium.

Magnet support provided by a stiff U Beam

U beam Support rod

Superconducting Magnet cooled to 4.2K

Beam Tube

Construction has started, will be complete by Autumn 07


16/24

Undulator Magnet Design Concept

Steel Yoke. Provides 10% increase in field and mechanical support for former

PC board for S/C ribbon connections

Winding pins

Steel yoke

Cu beam pipe, withconductor wound on to tube OD

2 start helical groove machined in steel former


17/24

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 (Ti6%Al4%V)

• Wheel geometry (~30mm radial width) constrained by eddy currents.

• 20cm between target and rf cavity. T. Piggott, LLNL


18/24

Activation Simulations

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

NC rf cavity

motor assembly

target wheel (including water channel)

L. Fernandez-Hernando, D

L


19/24

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-4

89

http://www-group.slac.stanford.edu/esh/rp/rpg/T-489

http://www-group.slac.stanford.edu/esh/rp/rpg/T-489


20/24

Target Remote Handling(conceptual)


21/24

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!!!!!


22/24

Eddy Current Experiment

Eddy current calculation mesh -S. Antipov, W. Liu, W. Gai - ANL

Proposed experimentLayout at CockcroftInstitute/Daresbury(this summer)


23/24

Prototype Positron Capture Section

Design and Prototype

High Power Test using L-band station in SLAC’s Endstation B


24/24

Outlook – EDR phase for e-/e+

Need Systems Engineering in FY08

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

Axel Brachmann, John Sheppard, Vinod Bharadwaj SLAC Particle Sources Efforts Review/Status and Plans...

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