1. Breakout Session SC1/SC2 – Accelerator System
Diagnostics and Controls Overview
P. Krejcik

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. Cavity Electric Center Sensitivity

12. Tolerance on Coupling Slots

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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

20. PSI Power Supply 12 hour Test

21. 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

22. 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 %
X-band amplitude error of 5%, fixed with L1 S-band adjustment: phase +0.61°, voltage 0.18 %

23. 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

24. 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

25. 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

26. 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

27. 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

28. End of Presentation
Backup slides