Breakout Session SC5 – Control Systems

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 • Timing distribution • RF Phase control Simultaneous Single shot Read all devices Process/respond in < 1/120th sec. • Feedback • Trajectory • Bunch length • Energy • Applications • Machine tuning

3. X- X-band LCLS Machine Stability Tolerance Budget 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. 5 Emittance gex,y measurements (Profs, Wire Scanners) : Accelerator System Diagnostics • 180 BPMs at quadrupoles and in each bend system 8 Energy (BPM) E, energy spread (Prof) sE measurements : 2 Transverse RF deflecting Cavities for slice measurements 5 Bunch length monitors RF gun L0 L1 L2 L3 X upstream linac BC1 BC2 DL1 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 http://www.i-tech.si

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 1/360 s Linac 476 MHz Main Drive Line 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 Line image camera EO xtal 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. 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 Closed Loop Response of Orbit Feedback- L. Hendrickson Antidamp Damp Gain bandwidth shown for different loop delays

14. 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) 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

15. Energy feedback loop response - J. WuP. 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. WuP. 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