Breakout Session SC5 – Control Systems Physics Requirements for Control System P. Krejcik

Goal of diagnostics and controls Introduction Goal of diagnostics and controls Facilitate machine tuning through measurement and data acquisition Maintain stability of operation and diagnose faults Review progress on control system hardware and software Review key diagnostic devices

Controls subsystems Safety systems Personnel protection system, PPS Transverse and longitudinal e-beam diagnostics Machine protection system, MPS Timing system Power supply control Relational database Application software

PPS Zones for LCLS 3. BSY + Sect. 30 gate muon shield gate 1. injector Laser Key entrance gate PPS Key entrance gate Shield wall PPS Key entrance gate PPS Key entrance gate D2 stopper Injector stopper 2. LINAC 3. BSY + Sect. 30 gate muon shield 4. LTU gate 5. undulator gate 6. FEE 20-21 22-23 24-25 26-27 28-29 Equipment & emergency gate BAS II stopper PPS Key entrance gate Sector entrances to be upgraded 7. Near Hall x-ray transport 8. Far Hall

PPS safety zones incorporated at the design stage Design for injector PPS going through approval process Will use certified PLC system rather than older electro-mechanical logic – see talks by P. Bong Linac entryways (safety) upgrades controlled PPS access (fewer searches) Stairway access instead of ladders

Transverse diagnostics Longitudinal diagnostics Diagnostic Systems Beam trajectory Stripline and cavity BPMs Transverse diagnostics Profile monitors and wire scanners Longitudinal diagnostics Coherent radiation single-pulse bunch length monitor at each bunch compressor S-band transverse deflecting cavities Injector and linac

Cavity Beam Position Monitors Frequency choice Cavity Iris should be masked from SR Vacuum chamber dimensions for the undulator are now chosen 10 mm aperture is larger than 8 mm diameter inside quadrupole X-band chosen to maximize resolution and minimize length. Issues BPM location with respect to quadrupoles Resolution in combination with beam-based alignment with EM quads Signal processing 5 mm 10 mm

X-Band Cavity BPM Resolution far exceeds LCLS requirements Zenghai Li feedthrough Ri = 5 mm 18 mm Resolution far exceeds LCLS requirements Sensitivity of 1.6 mV/nC/mm 20 nm demonstrated at KEK/SLAC experiments – S. Smith et al Systematic offsets are of greater concern

BPM Calibration Requirements Offset Absolute position Does minimum signal (zero +noise) correspond to beam at the geometric center of the cavity Test stand measurements Antennae scans on a CMM Beam test measurements Establish beam on apparent electrical center of 3 cavities and compare to alignment data. Use wire fiducilization scheme proposed for undulator to independently measure beam center See presentation in undulator session SC3 Q I

Sources of offset in the cavity BPM lid body Concentric surfaces Calculate effects from errors in Concentricity of 3 surfaces Couple offsets and tilts Parallel surfaces 5 um machining tolerances achievable - C. Pearson

Cavity Electric Center Sensitivity

Tolerance on Coupling Slots

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 Quad BPM assemblies Optional wire monitors, Train-linked undulator sections – see H.-D. Nuhn presentation

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

Cavity BPM Signal Processing Upstairs RF receiver RF in IF ~300 MHz BP filter Dw~5 MHz RF Amp Common Local Oscillator IF ~50 MHz BP filter Dw~10 MHz IF Amp In-tunnel X-band heterodyne receiver ADC 14 bit e.g Echotek Digital processing Control system IF 300 MHz Calibration Pulse 11.42 GHz Local Oscillator 11.1 GHz 119 MHz Clock 24th harmonic

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 See T. Straumann presentation

Cavity BPM Prototyping and Test Plan Components for prototyping and testing divided into (see SC3 session presentation) Cavities Feed-throughs and waveguide RF receiver electronics and reference oscillator Digitizer electronics EPICS integration and application programs Bench tests Beam tests

Transverse Beam Size Monitor Requirements Wire scanners Non-invasive measurement of projected x,y beam size averaged over ~100 beam pulses Resolution <5 mm, offset error <20 mm, jitter <5 mm Profile monitors Invasive measurement of single-shot transverse distribution Optical resolution <5 mm,

Power supplies and controllers Requirements Stability of 2E-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 SLC compatibility Only new LCLS beamlines would be equipped with new supplies Now learning that old linac magnet supplies may not meet requirements

Power supplies and controllers Status – see K. Luchini presentation Test power supply delivered from PSI controlled from an epics IOC long term current stability tests into resistive load are underway

PSI Power Supply 12 hour Test

Feedback and x-band regulation Low Level RF Feedback and x-band regulation Question that arose 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

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

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

Low-noise RF source and distribution ~3 km Main Drive Line 476 MHz Sector 20 Existing SLAC Master Oscillator LCLS Crystal Master Oscillator New master oscillator is located in the sector 20 RF hut Laser oscillator is located at the injector Both coax and fiber run between the two locations Can choose the lowest noise option for distribution 2856 MHz Copper coax Distribution 119 MHz x24 Ti:Sa Laser Oscillator 119 MHz Optical fiber Distribution

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

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

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

End of Presentation