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High Polarization and Low Emittance Electron Source for ILC

High Polarization and Low Emittance Electron Source for ILC. Nagoya University Dept. of Physics (SP-Lab) Masahiro Yamamoto. Collaborators of PES development in Japan. Nagoya University T.Nakanishi, S.Okumi, M.Yamamoto, N.Yamamoto, A.Mano, Y.Nakagawa, T.Konomi

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High Polarization and Low Emittance Electron Source for ILC

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  1. High Polarization and Low Emittance Electron Source for ILC Nagoya University Dept. of Physics (SP-Lab) Masahiro Yamamoto CCAST@Beijing

  2. Collaborators of PES development in Japan Nagoya University T.Nakanishi, S.Okumi, M.Yamamoto, N.Yamamoto, A.Mano, Y.Nakagawa, T.Konomi T.Ujihara, T.Katoh, X.G.Jin, M.Tanioku, Y.Takeda Hiroshima University M.Kuriki Osaka Prefecture University H. Horinaka, T. Matsuyama KEK F.Furuta, T.Omori, H.Mastumoto, M.Yoshioka, Y.Kurihara, J.Urakawa CCAST@Beijing

  3. International Linear Collider INTERACTIONS.ORG—Particle Physics and Resources Polarized electron source • High luminosity Low emittance beam Multi-bunch beam structure • polarized electron (positron) Detail studies of Higgs, SUSY search, … L ~ 1034 cm-2s-1 !! CCAST@Beijing

  4. Polarized (90% right-handed e-) SUSY Search Scalar muon production Suppressed !! Background signal Unpolarized CCAST@Beijing

  5. N↑－N↓ Polarization= < 50 % N↑＋N↓ Because Gpoint of GaAs is degenerated. How to generate polarized electron Photoemission from GaAs Historically, PES using GaAs was developed by Dr. Pierce in 1970s • Using a selection role of photo-excitation at G point • Supplying high intensity polarized electrons D. T. Pierce and F. Meier, Phys. Rev. Lett. B 13, 5484 (1976) Quantum Efficiency CCAST@Beijing

  6. How to generate polarized electron Negative Electron Affinity 1.Making a band bending by p+ doping to the surface 2.Electric dipole layer by vacuum evaporation of Cs and oxygen c≤ -100meV Weak point… NEA surface is extremely delicate in vacuum conditions (harmful residual molecules, surface cleanliness) CCAST@Beijing

  7. Average current Beam Structure for ILC • Muti-bunch Structure 5 nC × 2625 bunch × 5 Hz ~ 65mA peak current ~ 5A, current density ~ 20mA/mm2 CCAST@Beijing

  8. PES Technologies & Challenges Technical Challenges Polarized Electron Source Photocathode • High polarization • Pol.> 80%, QE>0.5% • High beam current • Ipeak > 5A, (>20mA/mm2) • Long lifetime • ≥100 h, ≥ 65mA operation • Low emittance • Norm. ex.rms≤ 10 p.mm.mrad • Multi bunch structure • ≥5nC/micropulse (for laser), • 2860micropulse/train Crystal structure design (strained, superlattice structure) High Voltage Gun Ultrahigh Vacuum ≤ 10-9 Pa vacuum Load-Lock High Field gradient Field emission study Electrode development Laser CCAST@Beijing

  9. 1.Photocathode development CCAST@Beijing

  10. d N↑－N↓ Polarization= > 50 % N↑＋N↓ How to generate “High” polarized electron CCAST@Beijing

  11. m* > m* |Jz|=3/2 |Jz|=1/2 How to generate “High” polarized electron GaAs (compressed) GaAs (well) AlGaAs (barrier) GaAsP (substrate) T. Nakanishi et al., Phys. Letters A158 (1991) 345 T. Omori et al., Phys. Rev. Lett. 67 (1991) 3294 Strained GaAs Superlattice eR: residual strain, Cij: elastic stiffness b: deformation potential CCAST@Beijing

  12. GaAs-GaAsP strained Superlattice Eth=1610 meV 3.5meV 81meV Faculty of Engineering, Nagoya University • Structure of GaAs-GaAsP superlattice Well layer (GaAs) 4nm Barrier layer (GaAsP) 4nm Splitting of HH and LH ~80meV CCAST@Beijing

  13. Nagoya Performance of GaAs-GaAsP superlattice SLAC T.Nishitani et al., J. Appl. Phys. 97, 094907 (2005) T.Maruyama et al., Appl. Phys. Lett. 85, 2640 (2004) GaAs-GaAsP strained SL Polarization ≥ 85% Quantum Efficiency ≥ 0.5% CCAST@Beijing

  14. 2. 200 keV Gun development CCAST@Beijing

  15. Ceramic 200 keV Polarized Electron Gun Photocathode puck (f23mm) • Ultra high vacuum ≤ 10-9Pa • Photocathode preparation • with Load-Lock • (cleaning, NEA activation) • High field gradient ≥ MV/m CCAST@Beijing

  16. -200kV power supply Gun Chamber Preparation Chamber Insulation tank CCAST@Beijing

  17. t QE(t) QE0 ・ exp = t 1 1 1 1 = + + t tgas tDC tion Photocathode Lifetime Measured by 70keV Gun t is determined by ... 1. Adsorption molecules 2. Field emission dark current 3. Ion bombardment CCAST@Beijing

  18. Reducing field emission dark current Nagoya & KEK Electrode shape Gap 0.5mm results Test sample F.Furuta et al., NIM-A 538 (2005) 33-44 Test sample CCAST@Beijing

  19. Electrode Design & Fabrication Mo cathode Material : pure Mo (>99.96%) Size : f 162mm Space Charge Limit: 30A Maximum field gradient: 7.8 MV/m @electrode Ti anode Material : pure Ti (JIS-grade 2) Gap:22mm Mo Cathode Ti Anode CCAST@Beijing

  20. Stable operation > 200 hours Electrode Conditioning Breakdown voltage rises about 0.4kV per one breakdown. After 80 breakdowns, the break- down voltage up to 212kV, and the state of 200kV was main- tained more than 200 hours. (dark current ≤1nA) Advantages of Ti-Mo electrode Darkcurrent characteristic isn’t degraded even if many breakdowns were occurred. M.Yamamoto et al., PST2007@BNL CCAST@Beijing

  21. Photocathode Lifetime Preliminary Base Pressure Gun:2.7x10-9Pa 2NEG:2.0x10-9Pa UHV & Dark current conditions seem no problem. Lifetime measurement of ~100mA operation is under way. CCAST@Beijing

  22. Laser system for nano second pulse generation PD PBS 700~900nm Driver& Pockels cell Ti:Sa filter 2w,532nm Nd:YAG ~1ns pulse is produced by a combination of fast pockels cell and polarized beam splitter. Repetition : 10Hz Transmitted energy : ~10mJ/pulse CCAST@Beijing

  23. ILC:5nC/bunch Nano second bunch generation from superlattice Bunch charge : 8nC Laser spot size : f~20mm, Bunch width(FWHM): 1.6ns Peak current density ~18 mA/mm2 No Charge Limit space-charge-limit was appeared clearly over 6nC/bunch under under condition with -70kV. Photocathode : GaAs-GaAsP strained SL M.Yamamoto et al., SPIN2006 @Kyoto CCAST@Beijing

  24. Solenoid 4.8nC, f16mm 0 0.15 0.5[m] Solenoid anode 200kV,1.0ns,4.8nC Emittance simulation Norm. ex.rms ~ 8.8 p.mm.mrad with optimization emittance compensation by solenoid. CCAST@Beijing

  25. Pepper Pot Mask (f40mm holes) Emittance Measurement System Plastic sintillator CCAST@Beijing

  26. N. Yamamoto et al., J. Appl. Phys. 102, 024904 (2007) Measurement of ~1ns, 5nC bunch is progressing. CCAST@Beijing

  27. Summary(1) Polarized Electron Source Photocathode GaAs-GaAsP strained superlattice Pol ≥ 85%, Q.E ≥ 0.5% are demonstrated. High Voltage Gun Ultrahigh Vacuum UHV (2.2x10-9 Pa) was achieved. Lifetime measurement under progressing… High Field gradient 200kV (3MV/m@photocathode) operation for > 200 hours without breakdown, dark current ≤ 1nA Laser under developing… (Ti-Sapphire laser system is planed by SLAC) CCAST@Beijing

  28. Summary(2) • High polarization Pol.> 80% with high QE • High beam current Ipeak > 5A, (>20mA/mm2) • Long lifetime ≥100 h, ≥ 65mA operation • Low emittance Norm. ex.rms≤ 10 p.mm.mrad • Multi bunch structure ≥5mJ/micropulse, (drive laser development) 2860micropulse/train CCAST@Beijing

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