Breakout Session: Controls

1. Breakout Session: Controls Physics Requirements and Technology Choices for LCLS Instrumentation & Controls

2. Outline • Beam position monitors • Issues for the undulator cavity BPMs • Issues for signal processing • Power supplies and controllers • Pulsed operation of DL1 for diagnostics • Low level RF • Source and synchronization issues • Feedback and x-band regulation • Bunch length monitors

3. Cavity Beam Position Monitors • Frequency choice • Cavity Iris should be masked from SR • Vacuum chamber dimensions for the undulator are now chosen • 12 mm aperture • is close to X-band cutoff • Evaluating two frequency choices (Z. Li) • Issues • BPM location with respect to quadrupoles • Resolution in combination with beam-based alignment with EM quads • Signal processing 5 mm 10 mm

4. Undulator Cavity BPM locations with respect to quadrupoles • Quadrupole and BPM mounted adjacent on the undulator support cradle to ensure 1 um beam based alignment resolution • Also need to keep the distance between the electron beam and the undulator segment axis to less than 70 microns rms • Considering beam position measurement options at downstream end as well QuadBPM assemblies Optional wire monitors, Train-linked undulator sections – see H.-D. Nuhn presentation

5. Cavity BPM Signal Processing • X and Y cavity at each undulator plus ~1 phase reference cavity per girder • High-frequency x-band signal is attenuated in a short distance • Incorporate a local mixer to IF at the cavity • Only a simple passive device in the tunnel • Temperature stable • Relatively low radiation loss environment • Distribution of reference x-band oscillator signal in the tunnel • Choose intermediate frequency to match into the RF front end used for stripline

6. Digital BPM Signal Processing • Use same RF front end for stripline BPMs and output from first mixer for cavity BPMs • Initial desire to use a commercially produced BPM processing module (Libera) • We obtained a try out Libera module • Integration into the control system not proceeding fast enough, e.g. could not access raw data in the module. • Present design solution • Commercial VME 8 channel digitizer • RF front end from discrete, commercial components

7. Power supplies and controllers • Requirements • Stability of 1E-5 for bunch compressors • fast response for feedback correctors • Integrate with epics controls • reliability • Design solution • digital controller/regulator • developed at PSI and further developed at Diamond • commercially supplied power modules

8. Power supplies and controllers • Status • Test power supply delivered from PSI • controlled from an epics IOC • long term current stability tests into resistive load are underway

9. PSI Power Supply 12 hour Test <2.5E-5

10. Pulsed operation of DL1 for diagnostics • Propose to allow option of pulsing DL1 bends • allow pulse stealing at ~1 Hz into the spectrometer line • monitor beam profile and energy spread • Potentially combine with pulsing of the transverse cavity • Laminated magnet • Experience at SLAC with damping ring DRIP magnets • Keep two dipoles in series • Need to maintain 1E-4 stability • Laminate magnets now • Develop pulsed supply later

11. Pulsed operation of DL1 for diagnostics • 1 Hz pulsed into the spectrometer line • monitor beam profile • Investigate further if transverse cavity can be optimized for slice measurements in the spectrometer line • monitor energy spread

12. Low Level RF • Feedback and x-band regulation • Question that arose last time was how to distinguish drift in the X-band system from errors in the S-band system • Solution is to keep X-band regulation fixed, and compensate errors with the S-band system only • See next slide • Source and synchronization issues • noise and stability issues in oscillator and distribution

13. Demonstration of L1 S-band adjustment to compensate Lx errors – courteseyJuhao Wu X-band amplitude error of 5%, fixed with L1 S-band adjustment: phase +0.61°, voltage 0.18 % X-band phase error of + 5o, fixed with L1 S-band adjustment: phase +2.1°, voltage - 2.1 %

14. Low Level RF Source and synchronization • Present design concept: • Microwave crystal oscillator phase locked to SLAC MDL – low noise in the low frequency band • Gun laser oscillator mode locked to crystal oscillator – low noise in the high frequency band • Under evaluation • Derive the LLRF 2856 MHz from crystal oscillator or from laser optical output • Distribute LLRF over copper or optional optical fiber

15. RF/Laser distributionproposed by Ilday et al, MIT at the SLAC Timing workshop Optical-laser synchronization module Upgrade path: Fiber distribution system Master laser oscillator RF-optical synchronization module Low noise crystal microwave oscillator Baseline Cu Coax distribution LLRF to klystron Linac MDL

16. RF stabilization – Ilday et al, MIT

17. Derivation of LLRF from laser – F. Omer Ilday, MIT

18. Synchronizing Gun and User Lasers– F. Omer Ilday, MIT

19. BC1, BC2 Single-shot Bunch Length Detectors • Non-intercepting detector for off-axis synchrotron radiation • Reflected through a port to: • Spectral Power detector • Single shot Autocorrelator THz power detector THz autocorrelator B4 Bend CSR Bunch Compressor Chicane Vacuum port with reflecting foil

20. Bunch Length Monitor Issues • The CSR we now understand is dominated by Coherent Edge Radiation • Same spectral and angular distribution characteristics as transition radiation • Need to account for interference effects from adjacent magnets • Experimental investigation at SPPS planned • Can also learn from UCLA expt at BNL-ATF

21. Bunch Length Monitor Issues • Need practical experience in evaluating • window materials • Detectors (pyrometers, Golay cells, bolometers) • Autocorrelator designs (mirrors, splitters, detectors) • New development of single-shot autocorrelators

22. End of Presentation Backup slides

23. Power supply controller system layout EPICS I O C 8 ch VME card ADCCard Power Supply DSP Controller 5MHz Optical fiber PWM signal Monitor signals DCCT load PWM AC Converter AC line

24. PSI Digital Power Supplies Master Fast Optical Link (5 MHz) DSP Controller ADC/DAC Card Optical Trigger 0..6 Slaves PWM Signal I DIO U1..4 DCCT Magnet Power Converter Courtesy A. Luedeke, PSI

25. P l/4 Stripline f Digital processing ADC x4 700 MHz Control system RF in l 500 MHz BP filter 119 MHz Clock 24th harmonic C-band cavity Mixer IF ~5 GHz Dipole mode coupler LO sync’ed to RF Stripline versus Cavity BPM Signals • noise (resolution) minimized by removing analog devices in front of ADC that cause attenuation • drift minimized by removing active devices in front of ADC

26. SPPS Laser Phase Noise Measurements – R. Akre 476 MHz M.O. fiber ~1 km MDL 3 km Ti:Sa laser osc EO VCO diode 2856 MHz x6 Phase detector 2856 MHz to linac scope

27. Courtesy F. Jenni, PSI

28. E E E Φrf(L2) Φrf(L3) Vrf(L1) DL1 sz Φrf(L1) sz E Φrf(L2) Vrf(L0) DL1 Spectr. BSY 50B1 BC2 BC1 DL2 L1 L2 L3 L0 Energy and Bunch Length Feedback Loops • Beam based feedback will stabilize RF F,A • Against drift and jitter up to ~10 Hz • But no diagnostic to distinguish drift of X-band • Linearization, higher-harmonic RF has the tightest tolerance • No unique beam measurement