Beam Diagnostics and Measurements

1. Beam Diagnostics and Measurements G. A. Krafft*, A. Sievers, and L. Merminga* *Work supported by DOE Contract DE-AC05-84ER40150

2. Presentations Outline • Phase I ERL Device (G. Krafft) • Commissioning Process (G. Krafft) • Diagnostics Requirements (G. Krafft) • Systems Summaries (G. Krafft) • Longitudinal Profiles (A. Sievers) • HOM Studies (L. Merminga)

3. Phase I ERL Device

4. ERL Prototype

5. Stages of Commissioning • Phase 1 Gun/Injector Validation • Stage 1: Electron gun plus solenoid, with diagnostic beamline and 50 kW dump • Stage 2: Gun, two solenoids and buncher, with diagnostic beamline and 50 kW dump • Stage 3: Gun, solenoids, buncher and injector cryomodule, with diagnostic beamline, deceleration structure, and 50 kW dump • Stage 4: Gun, solenoids, buncher, cryomodule, and merger optics, with diagnostic beamline, decelerator, and 50 kW dump

6. Results of Phase 1 • A fully functional and characterized injector by the start of ERL commissioning • A fully functional 500 kW beam dump • Developed injector setup procedures by the start of ERL commissioning • Developed suitable diagnostics to support injector setup by the start of ERL commissioning • Measured injector beam properties, checked performance of emittance compensation and checked merger CSR • Operated injector with low duty factor tuneup beam and high average current

7. Stages of Commissioning • Phase 2 Through the Linac • Stage 5: Injector, Linac cryomodule, diagnostic beamline, decelerator, and dump • Results of Phase 2 • Linac beam properties measured • Completed cavity HOM measurements with beam

8. Stages of Commissioning • Phase 3 Close the Loop • Stage 6: Complete ERL • Results of Phase 3 • Low emittance mode in back leg checked • Highly compressed bunches in back leg checked • BBU stability studies completed • CSR parameter studies utilizing bends • Beam Loss studies completed • HOM cooling studies completed • Surface roughness and resistive wakes measured in experiments on the back leg

9. Diagnostics Requirements Quantity Set Value Range Device Resolution 100 m 5 mm BPM (0,0) Position OTR/SLM 50 m 0.1-5 mm Profile 1 mm Res. Ionization Emittance 2 mm mrad 0.1-5 mm mrad Profile 0.1 mm mrad Charge 77 pC 1-1000 pC Faraday Cup 3 pC Energy 100 MeV 50-140 MeV High BPM 0.1% High OTR 50 keV Energy Spread 100 keV 20-600 keV R56 Design 50 cm RF Phase 1 cm Bunch Length 2.0 psec 0.1-2 psec Coherent IR 0.1 psec

10. BPMs in Phase I ERL Device BPM Location 25 Total

11. Beam Profiling • Two basic tuning modes • Low average power several microsecond/several Hz pulses • CW full current • Pulsed beam analyzed with OTR viewers with cameras • CW beam analyzed by synchrotron light, ionization profiling, or diffraction radiation

12. Beam Profiling Equipment

13. Emittance Measurements • General philosophy: measure the beam optical functions and the beam size • Spot sizes of about 300 microns RMS must be resolved at 1 mm mrad normalized • Injector and end of linac measurements must be done separately (and well!), to ensure the accuracy of the measurement

14. Difference Orbits • Adjust correctors and measure orbit gives the usual transfer matrix elements • Adjust energy and measure orbit gives the dispersion • Data will be automatically gathered and analyzed by computer. • In bigger machines (aka CEBAF), faster 30 Hz toggling measurements are very beneficial • Difference differencing potentially a powerful technique for drift detection • For a 10% emittance measurement on the back-leg need about 100 micron precision in BPMs, assuming a difference orbit amplitude of 3 mm

15. Longitudinal Emittance • Measure bunch length and energy spread at location where you can measure both, and ensure that know the phase ellipse slope. • Best place is in the Bates bends before going onto the back leg. Phase ellipse will not be upright, but should be well-enough known.

16. Some Viewer Details • Viewers tolerate only low current tune-up mode. They provide a check for proper accelerator tune. Useful for gross phasing of linac cavities • Viewers inside the recirculation loop MUST have holes in them to pass the first pass beam • Viewers are shielded, i.e. designed so when retracted the beam-line is smooth

17. Current Measurements • Non-invasive beam current measurements by current transformers and current cavities • Precision beam loss and halo measurement, at the 10-100 nA (0.1-1 ppm) level using (1) absence of 1300 MHz in cavity inside the loop and (2) lock-in detection of beam scraping • Phase transfer verification of the longitudinal phase space setup

18. Beam Current/M56 Current Cavity Faraday Cup

19. Phase Transfer Measurements(Longitudinal dispersion and more) Simultaneously, digitize phase modulation and arrival time determined by a phase detector

20. CEBAF Longitudinal Dynamics

21. One of the Earliest Measurements at CEBAF

22. Phase Space Correction Scheme

23. Path Length Setup • Originally, with low duty factor beam use the cavity beam loading and/or the linac longitudinal cavity • In high current CW mode, as Lia has shown you, just continuously monitor the forward RF power into the linac cavities

24. Conclusions • Our plans on beam diagnostics and commissioning have been presented • Most of the diagnostics devices are straightforward extensions of existing principles • Injector profiling, injector bunch length, and injector emittance measurements may require “new” approaches. Several possibilities exist that need to be explored in detail

25. FEL Phase Transfer Measurements