1. Studies of Emittance & Lifetime
Yan
8/6/18

2. Outline Photocathodes Emittance / Thermal Angle vs Parameters
Gun HV
Laser Spot Size
Laser Spot Location
Damaged Spot
Sb thickness
Lifetime vs Sb thickness
Laser Heating Effect on Photocathodes
Conclusion

3. CsK2Sb Photocathodes Five photocathodes Sb deposition time
Four GaAs substrate photocathodes
One Moly substrate photocathode
Sb deposition time
GaAs substrate: 10, 30, 60 and 90 min
Moly substrate: 10 min

4. CsK2Sb Photocathodes

5. Beam Conditions Gun HV: 200 kV RF pulse Laser
Wave length: 532 nm
Repetition rate: 374 MHz
Pulse width: 50 ps
For emittance measurements
100 nA tune beam, 1.5% duty factor
Lens #1, viewer #3 and Harp
For lifetime measurements
mA cw beam

6. Emittance vs Bunch Charge

7. Normalized Emittance vs Gun HV

8. Thermal Angle vs Gun HV

9. Emittance Across Photocathode

10. Emittance Across Photocathode

11. Emittance across Damaged Spot
Damaged Spot Size

12. X Plane Emittance vs Laser Size

13. Y Plane Emittance vs Laser Size

14. Thermal Angle vs Sb Deposition Time

15. Beam Size vs Laser Size

16. Photocathode’s Lifetime

17. Photocathode’s Lifetime

18. Laser Heating Effect

19. Possible Sources of Errors
Distance between lens and harp (0.5%)
Size of the harp wire (0.1%)
Size of laser spot (5%)
Solenoid field map
Solenoid current (0.1%)
Beam energy (?)
Beam rotation caused by solenoid
Roundness of beam (5%)

20. Conclusion
Normalized emittance does not depend on the gun high voltage
Constant emittance across the whole photocathode (along x axis or y axis, except at the edge) indicates that the electric field in the region between the photocathode and the anode is not significantly affected by the insulator or the shed.
No obvious effect on emittance by damaged spots.
No obvious effect on emittance by Sb thickness or photocathode surface roughness.
Moly substrate and GaAs substrate photocathode show similar emittance.
Moly substrate photocathodes have good lifetimes and much better than those of GaAs substrate photocathodes.
For GaAs substrate photocathodes, the thickness of the Sb layer affects the lifetime. Photocathodes with a very thick Sb layer have good lifetimes.