Studies of Emittance & Lifetime Yan 8/6/18

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

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

CsK2Sb Photocathodes

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 1.0 - 4.5 mA cw beam

Emittance vs Bunch Charge

Normalized Emittance vs Gun HV

Thermal Angle vs Gun HV

Emittance Across Photocathode

Emittance Across Photocathode

Emittance across Damaged Spot Damaged Spot Size

X Plane Emittance vs Laser Size

Y Plane Emittance vs Laser Size

Thermal Angle vs Sb Deposition Time

Beam Size vs Laser Size

Photocathode’s Lifetime

Photocathode’s Lifetime

Laser Heating Effect

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%)

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.