1. PST ２００７ BNL 1 Development of High- performance Polarized e- source at Nagoya University. Nagoya University M.Yamamoto, S.Okumi, T.Konomi N.Yamamoto, A.Mano, Y.Nakagawa, T.Nakanishi T.Katoh, X.G.Jin, M.Tanioku, T.Ujihara, Y.Takeda KEK M.Kuriki, F.Furuta, H.Matsumoto, M.Yoshioka

2. PST ２００７ BNL 2 Nano second bunch extraction & simulation of space charge limit for ILC. New electrode development for high voltage DC- gun. Outline Summary

3. PST ２００７ BNL 3 Production of nanosecond pol.e - beam for ILC Photocathode: GaAs-GaAsP SL (Pol.max > 85%) Laser energy : 6  J （ 10Hz ） Bunch width(FWHM): 1.6ns Bunch charge : 8nC Laser e - beam The SL active layer grown on a laser cutting GaAs wafer ILC:6.4nC/bunch

4. PST ２００７ BNL 4 Extracted charge of 30nC/bunch was obtained. Space charge limit Experiments & Simulations The experimental data is a measurement of supply current to the electrode. Both results are corresponding well, therefore this simulation is almost appropriate for calculating SC effect. Experimental data Simulation data （ GPT ） Extracted charge is estimated from the number of macro-particles at 10mm downstream PC.

5. PST ２００７ BNL 5 Higher voltage gun operation is better for generating short and low emittance bunches, but operation risks (dark current, breakdown) become higher… These simulations have been done in a situation of the beam emittance minimized at 0.5m downstream from PC by using a solenoid. Small beam radius helps suppressing emittance growth while bunching in the SHBs section. Beam simulations at gun exit (before SHBs) The emittance and beam radius become smaller. z=0.5m 1ns bunch length Advantages of higher voltage Beam loss at injector region become lower.

6. PST ２００７ BNL 6 Gap 0.5mm results Material dependence of dark current Electrode shape F.Furuta et al., NIM-A 538 (2005) 33-44 Nagoya & KEK Test sample

7. PST ２００７ BNL 7 Reduction of primary field emissions Reduction of secondary enhanced emissions Mo Ti e- + Cathode Anode -  Primary field emission Dark current= Enhanced emission + F-N theory Ions emission from the anode, secondary electrons and negative ions emission from the cathode. Material dependence of dark current wisker Enhanced emission current

8. PST ２００７ BNL 8 Fabricating process of Mo Cathode Hot squeezing EB welding Annealing 400 ℃ 1h Electro-buff polishing Pure Mo (99.96%) sheets 2mm thickness e beam rotation

9. PST ２００７ BNL 9 Installation & Vacuum test Pure Titanium > 99.6% Finishing: Electro-buff polish Ti-anode Base pressure : 2.7x10 -9 Pa no vacuum problem

10. PST ２００７ BNL 10 Electrode Conditioning After 80 breakdowns, the break- down voltage up to 212kV, and the state of 200kV was maintained more than 200 hours. ( dark current < 1nA) The breakdown voltage rises about 0.4kV per one breakdown. The unstable problem of 200kV operation was improved ! The vacuum pressure become worse ~10 -7 Pa immediately after breakdown, but it will recover to 10 -9 Pa range in about ten minutes later. Stable operation > 200 hours

11. PST ２００７ BNL 11 Characteristics of SUS and Ti-Mo electrode Dark current characteristic isn’t degraded even if many breakdowns were occurred. Hardly observed dark current until breakdown was occurred. Advantages of Ti-Mo electrode

12. PST ２００７ BNL 12 Photocathode Lifetime Preliminary The photocathode lifetime seems no problem under the condition of a few micro amps beam emission. Gun:2.7x10 -9 Pa 2NEG:2.0x10 - 9 Pa

13. PST ２００７ BNL 13 Summary A large size and a light molybdenum electrode were made by the hot-squeezing and the EB welding. Long-term 200keV operation became possible by employing the titanium anode and molybdenum cathode electrode. The dark current characteristic of the electrode hardly degrades by breakdowns. A higher voltage (>200kV) operation would be possible by continuing additional conditionings.