Studies of Emittance Lifetime Yan 8618 Outline Photocathodes

Studies of Emittance & Lifetime Yan 8/6/18

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

Cs. K 2 Sb Photocathodes • Five photocathodes Ø Four Ga. As substrate photocathodes Ø One Moly substrate photocathode • Sb deposition time ØGa. As substrate: 10, 30, 60 and 90 min ØMoly substrate: 10 min

Cs. K 2 Sb Photocathodes Photocathode QE 10 QE (%) 8 6 QE Map, Ga. As substrate 4 Depo chamber, Ga. As substrate Beam Based, Ga. As substrate QE map, Moly substrate 2 beam based, Moly substrate Depo chamber, Moly substrate 0 0 30 60 90 Sb Deposition Time (min) 120

Beam Conditions • Gun HV: 200 k. V • RF pulse Laser Ø Wave length: 532 nm Ø Repetition rate: 374 MHz Ø Pulse width: 50 ps • For emittance measurements Ø 100 n. A tune beam, 1. 5% duty factor Ø Lens #1, viewer #3 and Harp • For lifetime measurements Ø 1. 0 - 4. 5 m. A cw beam

Emittance vs Bunch Charge Gun HV 200 k. V. Laser Size RMS 0. 2 mm. Lens #1 & Harp x y Emittance (mm mrad) 0, 2 0, 1 0 0 10 20 30 40 Bunch Charge (f. C) 50 60 70 80

Normalized Emittance vs Gun HV Laser Spot Size RMS 0. 31 mm X y Emittance (mm mrad) 0, 3 0, 2 0, 1 0 0 50 100 150 200 Gun HV (k. V) 250 300 350

Thermal Angle (mm mrad / mm) Thermal Angle vs Gun HV x 0, 8 y 0, 7 0, 6 0, 5 0, 4 0, 3 0, 2 0, 1 0 0 50 100 150 200 Gun HV (k. V) 250 300 350

Emittance Across Photocathode Normalized Emittance vs Laser Position along X Axis Emittance (mm mrad) 0, 2 x y -2 -1 x_GPT y_GPT 0, 1 0 -6 -5 -4 -3 0 1 2 Laser Position along X Axis (mm), Y=0 3 4 5 6

Emittance Across Photocathode Normalized emittance vs Laser Position along Y Axis Emittance (mm mrad) 0, 2 x y x_GPT y_GPT 0, 1 0 -6 -5 -4 -3 -2 -1 0 1 2 Laser Position along Y Axis (mm), X=0 3 4 5 6

Emittance across Damaged Spot Size

X Plane Emittance vs Laser Size Gun 200 k. V. Lens #1 & Harp 0, 25 Normalized Emittance (mm mrad) 10 min Sb 0, 2 30 min Sb 60 min Sb 0, 15 90 min Sb 10 min Sb Moly 0, 1 Linear(10 min Sb) Linear(30 min Sb) 0, 05 Linear(60 min Sb) Linear(90 min Sb) 0 0 0, 05 0, 15 0, 25 0, 3 Laser Sopt Size RMS (mm) 0, 35 0, 45 0, 5

Y Plane Emittance vs Laser Size Normalized Emittance (mm mrad) Gun 200 k. V. Lens #1 & Harp 0, 25 0, 2 10 min Sb 30 min Sb 60 min Sb 0, 15 90 min Sb 10 min Sb Moly Linear(10 min Sb) 0, 1 Linear(30 min Sb) Linear(60 min Sb) Linear(90 min Sb) 0, 05 Linear(10 min Sb Moly) 0 0 0, 1 0, 2 0, 3 Laser Spot Size RMS (mm) 0, 4 0, 5

Thermal Angle vs Sb Deposition Time Gun 200 k. V. Lens #1 & Harp x Ga. As substrate y Ga. As substrate x Moly substrate y Moly substrate Thermal Angle (mm mrad / mm) 0, 7 0, 6 0, 5 0, 4 0, 3 0, 2 0, 1 0 0 30 60 Sb Deposition Time (min) 90 120

Beam Size vs Laser Size Gun 200 k. V. No Focusing. Viewer #2 8 Beam Size RMS (mm) 7 6 x 30 min Sb x 60 min Sb 5 x 90 min Sb y 30 min Sb 4 y 60 min Sb y 90 min Sb 3 2 0 0, 05 0, 15 0, 25 Laser Spot Size RMS (mm) 0, 35 0, 45

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 Ga. As substrate photocathode show similar emittance. • Moly substrate photocathodes have good lifetimes and much better than those of Ga. As substrate photocathodes. • For Ga. As substrate photocathodes, the thickness of the Sb layer affects the lifetime. Photocathodes with a very thick Sb layer have good lifetimes.