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

2. Accelerator Physics Driving Controls Design
Precision beams
Low emittance
Short bunch
Single pass
Every shot different
Compatibility
Other programs
Old controls
Simultaneous
Single shot
Read all devices
Process/respond in
< 1/120th sec.
Timing distribution
RF Phase control
Applications
Machine tuning
Feedback
Trajectory
Bunch length
Energy

3. LCLS Machine Stability Tolerance Budget
X-band X-
From P. Emma:
RMS tolerance budget for <12% rms peak-current jitter or <0.1% rms final e− energy jitter. All tolerances are rms levels and the voltage and phase tolerances per klystron for L2 and L3 are Nk larger, assuming uncorrelated errors, where Nk is the number of klystrons per linac.
125 fs tolerance on X-band system

4. Key facility factors driving controls design
Undulator machine protection
Single pulse abort capability
Compatibility with non-LCLS beams
Straight through beams some months of the year
Hybridize new controls with old SLC controls

5. Design solutions for specialized diagnostics
Low emittance beams require
Precision wire scanners
Average projected emittance
Almost non-invasive diagnostic
Profile monitor
Single pulse full beam profile
OTR screens inhibit sase operation
Low energy injector beams require YAG screens
Slice emittance reconstruction
Transverse RF deflecting cavity with profile monitor

6. Accelerator System Diagnostics
180 BPMs at quadrupoles and in each bend system
8 Energy (BPM) E, energy spread (Prof) sE measurements :
5 Emittance gex,y measurements (Profs, Wire Scanners) :
2 Transverse RF deflecting Cavities for slice measurements
5 Bunch length monitors RF
gun L0
upstream linac L1 X L2 L3
DL1
BC1
BC2
DL2
undulator
LTU
Dump

7. Linac stripline BPMs Need to replace old BPM electronics
Commercially available processing units look promising
Beam testing of module as soon as funding available
Must work with existing linac striplines

8. Design solutions for specialized diagnostics
Short bunch, high peak current beams require
Longitudinal bunch profile measurement with sub-picosecond resolution
Transverse RF deflecting cavity
Electro optic bunch length measurement
A non-invasive bunch length monitoring system for pulse-to pulse feedback control
Spectral power detectors for CSR and CDR
A detector sensitive to micro-bunch instabilities
CSR spectrum

9. Timing system requirements
Synchronization of fiducials in low-level RF with distribution of triggers in the control system
360 Hz fiducials phase locked to low level RF
Linac 476 MHz
Main Drive Line
1/360 s
Sector feed
Fiducial
detector
SLC
Control
System
119 MHz
Event
Generator
360 Hz Triggers
8.4 ns±10 ps
Master
Pattern
Generator
128-bit word
beam codes

10. 3 Levels in the Timing System
“coarse” triggers at 360 Hz with 8.4 ns delay step size and 10 ps jitter
Gated data acquisition (BPMs)
Pulsed devices (klystrons)
Phase lock of the low-level RF
0.1 S-band (100 fs) phase stability
Timing measurement of the pump-probe laser w.r.t. electron beam in the undulator
10 fs resolution

11. Bunch length and arrival time from Electro Optic measurements at SPPS
A. Cavalieri
Principal of
temporal-spatial correlation
single pulse
EO xtal
Line image camera
analyzer
polarizer Er
width
centroid
30 seconds, 300 pulses: sz = 530 fs ± 56 fs rms Dt = 300 fs rms

12. Electro-Optical Sampling at SPPS – A. Cavalieri et al.
<300 fs
Single-Shot
200 mm thick ZnTe crystal
Ti:Sapphire laser e-
Timing Jitter
170 fs rms
e- temporal information is encoded on transverse profile of laser beam

13. Closed Loop Response of Orbit Feedback - L. Hendrickson
Undulator trajectory launch loop to operate at 120 Hz, <1 pulse delay
Damps jitter below 10 Hz
Linac orbit loops to operate at 10 Hz because of corrector response time
Antidamp
Damp
Gain bandwidth shown for different loop delays

14. Energy and Bunch Length Feedback Loops
DL1
Spectr.
BC1
BC2 L2 L3
BSY 50B1
DL2
Vrf(L0)
Φrf(L2)
Vrf(L1)
Φrf(L3) E sz
Φrf(L1)
4 energy feedback loops
2 bunch length feedback loops
120 Hz nominal operation, <1 pulse delay
Feedback model (J. Wu)
PID controller (proportional, integral, derivative)
Cascade control for sequential loops (off-diagonal matrix elements)

15. Energy feedback loop response - J. Wu P. Emma
Bode Plot (E/E)
P:0.2
P:0.2; I:0.5
I:0.5
3 different settings of the PID controller
Integral term dominant

16. Bunch length feedback loop response - J. Wu P. Emma
Bode Plot (I/I)
P:0.2
P:0.2; I:0.5
I:0.5
3 different settings of the PID controller
Integral term dominant

17. Controls Issues for Power Supplies
16 types out of a total of 55 power supplies
Tightest regulation tolerance is 5*10-5 (BC’s)
transductor regulation circuit
Able to use commercial supplies, with SLAC engineering effort for: AC
interlocks
regulator circuits
control interface

18. Controls Issues for Power Supplies
A few unique power supplies:
Parallel supplies for linac quads to switch between LCLS operation at low current and HEP operation at full field.
Fast orbit feedback requires power supplies and corrector magnets to respond in <8 ms (120 Hz).
Single Bunch Beam Dumper (SBBD) is a 120 Hz pulsed magnet supply

19. MPS - Beam Rate Limiting
Single bunch beam dumper (SBBD)
Linac beam up to the dog-leg bend in the LTU can be maintained at 120 Hz
Favorable for upstream stability and feedback operation
Pulsed magnet allows
Single shot, 1 Hz, 10 Hz, 120 Hz down the LTU line
Failure in pulsed magnet will turn off beam at gun
Tune-up dump at end of LTU
Max. 10 Hz to tune-up dump
Stopper out will arm MPS for stopping beam with the SBBD

20. MPS - Beam Rate Limiting
Conditions that will stop the beam at the SBBD
Tune-up dump at end of LTU is out, and:
Beam loss at detected by either by PLIC along the undulator chamber, or by the PIC’s between the undulator modules
Invalid readings from undulator
Vacuum
Magnet movers
BPMs
Energy error in the LTU
PIC’s at the collimators
Launch orbit feedback failing
Magnet power supplies for some key elements

21. Summary
LCLS will be a challenging machine to control and operate – dynamic control, not passive operation!
Controls integrated into the LCLS design concept
Single pulse readback of all devices
Fast feedback control essential for stability
New and challenging techniques for timing distribution and measurement.
Diagnostics being developed hand-in-hand with controls and feedbacks