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Polarized Electron Source for ILC in Korea 김귀년 ( 경북대학교 CHEP), 박성주 ( 포항가속기연구소 )

Polarized Electron Source for ILC in Korea 김귀년 ( 경북대학교 CHEP), 박성주 ( 포항가속기연구소 ). 4.0eV. 1.76eV. Polarized photoemission. • Circularly polarized light excites electron from valence band to conduction band • Electrons drift to surface L < 100 nm to avoid depolarization

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Polarized Electron Source for ILC in Korea 김귀년 ( 경북대학교 CHEP), 박성주 ( 포항가속기연구소 )

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  1. Polarized Electron Source for ILC in Korea김귀년(경북대학교 CHEP), 박성주(포항가속기연구소)

  2. 4.0eV 1.76eV Polarized photoemission • Circularly polarized light excites electron from valence band to conduction band • Electrons drift to surface L < 100 nm to avoid depolarization • Electron emission to vacuum from Negative-Electron-Affinity (NEA) surface NEA Surface – Cathode “Activation” • Ultra-High-Vacuum < 10-11 Torr • Heat treatment at 600° C • Application of Cesium and NF3/O2

  3. Polarized Electron Source (Nakanishi’s summary) - DC gun with NEA–GaAs photocathode --------- Goal is not so far ----- ☺ Photocathode ------GaAs–GaAsP strained superlattice----- Pol. ∼ 90%, QE ∼ (0.5∼1.0)% (Nagoya/KEK, SLAC, St. Petersburg,----) ☺ High gradient gun 120 keV (SLAC, worked well for SLC) 200 keV (Nagoya---under test, SLAC---planned) 500 keV (JLAB/Cornell, Nagoya/KEK---planned)

  4. Photocathode R&D in the last 13 years 1978 First GaAs polarized electron source (E122) SLAC – 37% polarization 1991 Strained InGaAs/GaAs (MBE) SLAC/Wisc AlGaAs/GaAs superlattice (MBE) KEK/Nagoya Strained GaAs/GaAsP (MOCVD) Nagoya Strained GaAs/GaAsP (MOCVD) SLAC/Wisconsin 1992 High gradient doping technique applied to AlGaAs/GaAs KEK/Nagoya 1993 Surface photovoltaic effect observed at SLC Strained GaAs/GaAsP used for SLC 1994 InGaAs/GaAs strained-superlattice (MBE) KEK/Nagoya 1995 InGaAs/AlGaAs strained-superlattice (MBE) St. Petersburg 1998 No Charge limit in high gradient doped superlattice Nagoya/KEK 2000 GaAs/GaAsP strained-superlattice (MOCVD) Nagoya/KEK 2001 No charge limit in high gradient doped strained GaAs SLAC/Wisconsin 2003 GaAs/GaAsP strained-superlattice (GSMBE) SLAC/Wisconsin 2004 InAlGaAs/AlGaAs strained-superlattice (MBE) St. Petersburg

  5. GaAs/GaAsP Superlattice Nagoya (MOCVD) SLAC (GSMBE) Polarization 85 – 90% QE 0.5 – 1%  Clear HH and LH transitions.  The step-like behavior of 2D structure is observed.

  6. No Surface Charge Limit SLAC Nagoya p-p : 2.8ns, bunch-width : 0.7ns Charge: 1nC/bunch 11012 e- in 60 ns → 4.51012 e- in 270 ns (×3 NLC train charge)

  7. Clendenin (SPIN2004) Parameter NLC ILC ILC SLC at Source NCRFSCRFNCRF-Inj/Design S-bandL-bandSCRF-Linac(2-cm) ne nC 2.4 6.4 6.4 20 Dz ns 0.5 2 0.5 3 Impulse, avg A 4.8 3.2 12.8 6.7 Impulse, peak A 11 (SCL) Conclusion: Space charge limit a problem for ILC source only if try to operate with NCRF injector S-band linac

  8. 3rd generation polarized gun Inverted gun (SLAC) Nagoya JLAB 3 chambers: HV Gun chamber Inverted or Double insulator Prep chamber Load-lock Atomic hydrogen cleaning

  9. Next generation guns • Polarized RF gun • Holy grail of polarized electron source • UHV requirement precludes current photocathodes • Two photon excitation? • Large band gap materials like strained InGaN • > 500 kV DC gun • Proposal to build 500 kV gun (Nagoya) Higher voltage and smaller emittance vs. Higher leakage current and shorter cathode lifetime

  10. ☻Laser system No complete system exists, considerations are needed. (Homework; Solutions must be proposed before the next WS ?) Bunch–structure depends on the DR scheme (by Urakawa) 1) 2.8ns100bunches (300Hz) ---------- may be no problem 2) 337ns2820bunches (5Hz) ---------- may be not easy ☺ Buncher system (beam–width: 1ns  5ps) depends on bunch structure ------ may be no problem ☺ Important gun performances ○ NEA lifetime---- o.k. by recesiation and reactivation ○ Surface charge limit effect---- may be negligible ○ Gun emittance ( ≤ 10πmm-mrad)--------- may be o.k.

  11. Laser • Laser for the ILC polarized electron source requires considerable R&D Pulse energy: > 5 J Pulse length: 2 ns # pulses/train: 2820 Intensity jitter: < 5% Pulse spacing: 337 ns Rep rate: 5 Hz Wavelength: 750 ~ 850 nm (tunable) • Photoinjector laser at DESY-Zeuthen

  12. Towards ILC Polarized Electron Source • Photocathode R&D • JLAB • Nagoya/KEK • SLAC • St. Petersburg Technical University • Gun R&D • FNAL • JLAB • Nagoya • SLAC • Laser R&D • DESY-Zeuthen • SLAC

  13. Specifications for ILC polarized electron source Parameters units TESLA-TDR NLC/GLC US-COLD Gun bunch charge nC (#e-) 4.5 (2.8×1010) Polarization % > 80 Bunch length ns 2 0.7 Cathode bias voltage kV -120 Beam radius mm 12 # bunches / pulse 2820 192 Bunch spacing ns 337 1.4 Pulse length µs 950 0.27 Repetition rate Hz 5 120

  14. Korea’s Capabilities Relevant to ILC Injcetors • PES Test Stand • GaAs-NEA Photocathode Production • Compact Mott Polarimeter • Electrostatic Bend • PEGGY Source (provided by the SLAC) • PAL XFEL Injector • GTS (Gun Test Stand) • BNL Gun-IV-type 1.6-Cell RF Gun • Ti:Sapphire Laser • Dedicated RF Source • Beam Diagnostics • PPI (Pohang Photo-Injector)

  15. Laser Gun Chamber Mott Chamber Gun Chamber Faraday Cup RGA Mott Chamber Faraday cup RGA e beam O2 leak Valve (120l/s) 1. Polarized Electron Source Test Stand Layout of Test-Stand

  16. Mini-Mott Chamber

  17. Polarization Measurement at Test Stand J. Korean Phys. Soc. 44, (2004) 1303

  18. 2. PPI - PAL XFEL Injector Gun PPI (Pohang Photo-Injector) Experiences from GTS (Gun Test Stand) with modified BNL Gun-IV

  19. Layout of PAL - GTS Laser System

  20. Specification of PAL - GTS Laser System

  21. Layout of GTS (Gun Test Stand) for PAL XFEL & FIR-FED Facilities

  22. 1.6-Cell RF Gun

  23. Fabrication of Aluminum Model Cavity

  24. Emittance Compensating Solenoid

  25. Korea’s Capabilities Relevant to ILC Injcetors - Continued - • Special facilities for klystron fabrication • XHV Baking Station • Various Furnaces • HP Microwave Test-Lab • Infra-Structures • Chemical Cleaning Shop, Plating Facility, Welding Shop, 3D CMM,… • Magnetic Field Measurement Facilities • Full-line of Microwave Equipments • High-Quality Manpowers • Beam-Dynamics Experts • Mechanical Engineers • High-Power Electrical Engineers • RF Engineers (LL & HL) • XHV Experts • were involved in the PLS construction, now in the PAL XFEL project

  26. Polarized Positron Source for ILC

  27. Photons 10-20 MeV Conventional vs. Gamma Based Positron Source Primary Beam Capture Optics Target thin target: 0.4 X0 Electrons 0.1-10 GeV thick target: 4-6 X0

  28. Gamma Based Positron Source For the production of polarized positrons circularly photons are required. • Methods to produce circularly polarized photons of 10-60 MeV are: • radiation from a helical undulator • Compton backscattering of laser light off an electron beam

  29. 1. Undulator Based Positron Source • Undulator length depends on the integration into the system, i.e. the distance between undulator exit and target which is required for the beam separation: • ~ 50-150 m

  30. 2. Polarized Positron based on Laser Compton Gamma

  31. Laser Compton Scattering Beam Line using Pohang Linac Pohang Accelerator Lab.

  32. Summary • Based on R&D work • Polarized Electron : • - 500 keV Gun Development • - Gun Test • 2. Polarized Positron : • - Laser Compton Beam Line • - Test Facility for Positron Target

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