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

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

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

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

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

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

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

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

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

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

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

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

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

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)

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

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

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

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

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

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

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