polarized electron source for the ilc

September 10-14, 2007 XIIth International Workshop on Polarized Sources, Targets & Polarimetry, Brookhaven National Laboratory (BNL)

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Polarized Electron Source for the ILC

Axel Brachmann

- SLAC -


2

Overview

ILC and Electron Source Layout ILC e- Source Parameters Reference Design Report Engineering Design Report R&D

Source Laser System Electron Gun Polarized Photocathodes

Summary


3

Current ILC Schematic


4

Overall e- Source Layout Schematic


5

Tunnel Maze (Source, RTML, Main Linac, Damping Ring, Service, Shafts)


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ILC Source Parameters

Parameter Symbol Value UnitElectrons per bunch (at gun exit) ne 3 x 1010 Number

Electrons per bunch (at DR injection) ne 2 x 1010 Number

Number of bunches Ne ~ 3000 Number

Bunch repetition rate Fμb 3 MHz

Bunch train repetition rate Fmb 5 Hz

Bunch length at source t ~ 1 ns

Current in bunch at source Iavg 3.2 A

Energy stability S < 5 % rms

Polarization Pe 80 (min) %

Photocathode quantum efficiency QE 0.5 %

Drive laser wavelength 790 20 nm

Single bunch laser energy E 5 μJ


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Design Process, History and Future

NLC, JLC,TESLA

2005 2007 2010

RDR EDR

Funding Decision

Construction ~ 7 years ILC

?


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Institutions & International Context

Area Systems Groups SLAC JLAB KEK Others TBD

Technical Systems Groups and R&D Projects SLAC, FNAL, JLAB, BNL University of Wisconsin KEK, University of

Hiroshima CERN, DESY Others TBD


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Global Systems:

• Conventional Facilities• Installation• Instrumentation• Controls

Reference Design Reporthttp://www.linearcollider.org/cms/

Area Systems(e.g. e- source)

TechnicalSystems

GlobalSystems

Technical Systems:

• Magnet System• Vacuum System• Cryogenics• RF system• Dumps & Collimators

Cost Reduction

Area Systems:

• Accelerator physics• technical specifications


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RDR Cost of Electron Source

Conventional Facilities

Dumps & Collimators

Vacuum System

Instrumentation

Controls

Magnet System

Cryogenics System

RF SystemCryomodules

e- specific (Gun, laser, etc.)

Overall Total of e- source : ~ 165 M$ILC total: ~ 6.7 B$


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Source Integration example:Damping Ring / Source RF System Compatibility

DR fundamental RF : 650 MHzDR fill patterns provides clearing gaps for electron and ion clod

mini-train gap (e.g. total of 44 bunches in mini-train, 82 mini-trains)

3. Pulse1. Pulse 2. Pulse

t

t must be an integer multiple of SHB periods, most critical for SHB I

Example:

t = 177 DR RF buckets = 272.31 ns SHB frequency of 216.67 MHz

Bunch spacing is 2 RF buckets

First Revolution

Second Revolution


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Engineering Design Report (FY08-FY10)

Next step after RDR Conceptual design Engineered design

Goal is to have a ‘construction ready’ design and submit a construction proposal to funding agencies

Detailed cost analysis In addition to design and engineering:

Conduct required R&D Prototype of critical components


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R&D Focus to support the EDR

Source Drive Laser System Photocathodes DC Gun Accelerator Physics

Alternatives beyond the baseline design: (not currently funded by ILC)

Polarized RF gun e.g. SC polarized RF gun research at BNL

(see J. Kewisch’s talk ‘The polarized SCR gun experiment’; this afternoon)

Demonstrate ILC beam


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Source Laser Requirements

Central wavelength : ~ 790 nm Laser pulse energy is determined by cathode QE

~ 5 μJ mirco pulse energy Tunability of 20 nm Pulse shaping requires bandwidth Availability of high power cw pump source to facilitate

amplification at 3 MHz To tap industrial resources common lasing

medium is required Choice of Ti:Sapphire laser system pumped by solid

state Nd:YAG (or similar)


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Source Laser Schematic


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Gun Development Program

SLC DC gun is baseline design Optimizion for ILC conditions will improve operation

of the source Emittance Energy spread Beam loading Electrode materials and geometry HV power supply

HV 140 – 200 kV Pulsed power supply may be necessary to mitigate

beam loading R&D program starts in FY08


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Comparison of DC Gun Parameters worldwide (compilation courtesy of M. Poelker, JLab)

Facility Beam Structure HV [kV] Avg. Current Bunch Charge Polarization

Bonn – ELSA 50 Hz 50 5 μA 100 nC / 1 μs +

CEBAF cw: 1497 MHz 100 200 μA 0.13 pC +

Mainz Microtron cw: 2450 MHz 100 50 μA 0.02 pC +

MIT Bates 600 Hz, DF=1.5% 60 120 μA 250 nC (25 μs) + (bulk GaAs)

Nagoya/JLC 200 +

NIKHEV 2μs pulses @ 1 Hz 100 0.04 μA

SLAC–fixed Target 0.3μs pulses @ 120 Hz 120 +

SLAC – SLC 2ns pulses @ 120 Hz 120 2 μA 16 nC +

Heidelberg TSR DC <1 1 mA N/A -

JLAB FEL cw: 75 MHz 350 10 mA 135 pC -

Daresbury ERLP cw: 75 MHz 350 -

Cornell cw: 1300 MHz 750 100 mA 77 pC -

JAEA 250 50 mA -

JLab 100kW FEL cw: 750 MHz 500 100 mA 135 pC -

ILC 1ms 3 MHz (1ns) train @ 5Hz 140 - 200 ~100 μA 5 nC +

EIC – ELIC >100 1 mA +

EIC - eRHIC cw >100 25 mA +

Historical or diminished scope Under construction Proposed operating


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Accelerator Physics

95% of electrons produce by the DC gun are captured within 6-D damping ring acceptance: (Ax+Ay)0.09m and E x z (25 MeV) x (3.46 cm)

Beam envelope along the NC injector


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Photocathode Status

Baseline design: strained layer supperlattice GaAs/GaAsPPolarization ~ 85 - 90 % ,QE 1% maximum, 0.3-0.5% routinely

High gradient p-doping increases QE and reduces surface charge limit:5 x 1019 cm-3 5 x 1017 cm-3


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Photocathode R&D program

R&D continues on cleaning and surface preparation techniques (e.g. Atomic Hydrogen Cleaning)

Determine optimum doping level for ILC conditions Investigate depolarization mechanisms using time resolved

Faraday rotation Alternatives are InAlGaAs/GaAs strained supperlatice

photocathodes 91% polarization has been reported, see talk by Y. Mamaev:

‘Record values of polarization and quantum efficiency for semi-conductor photocathodes’

Friday, 10:10-10:40, Plenary Session


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Summary

Reference Design Conceptual Design Engineering Design Construction Proposal in

progress R&D topics:

Source Laser System Electron Gun Photocathodes

International collaboration broad range of expertise can be tapped Logistics of collaboration are challenging

Funding in different regions determine pace of progress


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Contributors

J. Clendenin,

T. Maruyama,

F. Zhou,

J. Sheppard,

K. Ioakeimidi,

R. Prepost,

M. Poelker,

M. Kuriki,

Many more, see RDR author list.

polarized electron source for the ilc

Documents

polarized sources

targets polarimetry

polarized electron source

ilc total

dr rf buckets

ns shb frequency

ilc axel brachmann slac

rd projectsslac