Launch Jitter/Drift Revisited

1. Launch Jitter/Drift Revisited • Wilbert showed the great hardware laser phase feedback system • Does this benefit the drift/jitter seen in the launch phase of P.I.? Revisit beam timing diagnostics: • Laser streak: Monitor centroid of virtual cathode image on streak camera • Charge fluctuation: Set RF gun to sit on rising edge of Q vs. ϕ to map fluctuations in charge (at ICT2) to phase fluctuation. Monitor charge fluctuations with time.

2. Calibration Fine RF gun phase scan over rising edge And for streak camera, calibration of: 0.32 ps/pixel

3. Drift with Wilbert Device on

4. Drift with Wilbert Device on Still have ps-scale launch phase drift in the cave …why?

5. Afternoon drift observations • Continued data taking in afternoon (but yes, with NO Wilbert Device) • Drift quiet from 20 – 60 mins except for discrete jump @ minute 65… • Considered that warehouse door had been closed for a while.

6. Afternoon drift observations • Fiducials mark us opening/closing bay door (Does anyone else see a new relative slew?) Door opened Door re-opened Door closed

7. Anything wrong with Wilbert Device? • Manfred and Wilbert’s feedback circuit uses IR phase in laser room to detect laser phase drifts • There are still some 20 meters of mirrors on steel and concrete between laser room and cathode • Estimate optical path length changes as function of temperature • For α of concrete/steel over 20 meters we get ~1 ps / °C • Spec of climate control in warehouse is only ± 5°C. • If this is adding to drift, must simply include effect in feedback

8. Suggested fix Possible candidate for phase detection of UV at virtual cathode Photek PD025 • 25 mm x 25 mm • (40 mm also available) • 180 – 600 nm • Rise time < 100 ps • Response > 3 GHz • High 5 kV bias • Can push 1.3 GHz harmonic?

9. [Added note] • Yes, these data are not conclusive, only suggestive. • Other potential solutions were discussed, with other challenges, advantages and interoperabilities • Philippe pointed out extended problem: • If thermal fluctuation in optical transport is phase drift suspect, so is RF waveguide (long copper channel) • This may explain noted loss of correlation between data sets in afternoon data taking (relative slew between laser streak and charge fluctuation) • Transport drift-dominated in morning, not so much in afternoon? • “Just” use local gun RF as phase detector ref to fix launch phase? • Must we then also perform phase feedback on RF gun to 9 cell phase, and so on, and on and on…?