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Patrick Krejcik
LCLS FAC [email protected]
April 29, 2004
Breakout Session: Controls
Physics Requirements Overview
P. Krejcik
Patrick Krejcik
LCLS FAC [email protected]
April 29, 2004
Key accelerator physics factors driving controls design
Precision beams low emittance, short bunch lengths
Stringent stability requirementsFeedback control of
orbit, charge energy and bunch length
Single pass beams unlike storage ring, every pulse potentially different
Precision timing requirements
Patrick Krejcik
LCLS FAC [email protected]
April 29, 2004
Key facility factors driving controls design
Undulator machine protectionSingle pulse abort capability
Compatibility with non-LCLS beamsStraight through beams some months of the year
Hybridize new controls with old SLC controls
Patrick Krejcik
LCLS FAC [email protected]
April 29, 2004
Design solutions for specialized diagnostics
Low emittance beams requirePrecision 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 reconstructionTransverse RF deflecting cavity with profile monitor
Patrick Krejcik
LCLS FAC [email protected]
April 29, 2004
Design solutions for specialized diagnostics
Short bunch, high peak current beams require
Longitudinal bunch profile measurement with sub-picosecond resolution
Transverse RF deflecting cavityElectro 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 instabilitiesCSR spectrum
Patrick Krejcik
LCLS FAC [email protected]
April 29, 2004
Bunch length diagnostic comparisonDevice Type Invasive
measurementSingle shot measurement
Abs. or rel. measurement
Timing measurement
Detect bunchin
g
RF Transverse Deflecting Cavity
Yes: Steal 3 pulses
No: 3 pulses Absolute No No
Coherent Radiation Spectral power
No for CSR Yes for CTR
Yes Relative No Yes
Coherent RadiationAutocorrelation
No for CSR Yes for CTR
No Absolute(2nd moment
only)
No No
Electro Optic Sampling
No Yes Absolute Yes No
Energy Wake-loss
Yes No Relative No No
Patrick Krejcik
LCLS FAC [email protected]
April 29, 2004
Feedback global requirements
Description of feedback types and locationsOrbit
charge
energy
bunch length
Control system response time120 Hz single pulse data transfer, zero latency
Patrick Krejcik
LCLS FAC [email protected]
April 29, 2004
Energy and Bunch Length Feedback Loops
L0 L1
DL1
DL1Spectr. BC1 BC2
L2 L3
BSY 50B1
DL2
Vrf(L0)
Φrf(L2)Vrf(L1) Φrf(L3)E E E
Φrf(L2) zΦrf(L1) zE
Patrick Krejcik
LCLS FAC [email protected]
April 29, 2004
Antidamp
Damp
Gain bandwidth for different loop delays- L. Hendrickson
Closed Loop Response of Orbit Feedback
Patrick Krejcik
LCLS FAC [email protected]
April 29, 2004
Linac type stripline BPMs
LCLS range
Resolution achievable with existing processor
New BPM processor design challenges:
• large dynamic range• Low noise, high gain• 20 ps timing jitter limit
Patrick Krejcik
LCLS FAC [email protected]
April 29, 2004
Cavity beam position monitors in the undulator and LTU
Coordinate measuring machine verification of cavity interior
• X-band cavity shown
• Dipole-mode couplers
• X-band cavity shown
• Dipole-mode couplers
• Raw digitizer records from beam measurements at ATF
• Raw digitizer records from beam measurements at ATF
R&D at SLAC – S. Smith
Patrick Krejcik
LCLS FAC [email protected]
April 29, 2004
Assembled X-band cavity BPM
Mechanical center of RF BPM well correlated to electrical center – more accurately than for stripline BPMS
Mechanical center of RF BPM well correlated to electrical center – more accurately than for stripline BPMS
Patrick Krejcik
LCLS FAC [email protected]
April 29, 2004
Preliminary beam calibration data from a C-band cavity tested at ATF
• cavity BPM signal versus predicted position
• bunch charge 1.6 nC
• cavity BPM signal versus predicted position
• bunch charge 1.6 nC
• plot of residual deviation from linear response• << 1 m LCLS resolution requirement
• plot of residual deviation from linear response• << 1 m LCLS resolution requirement
25 m
200 nm
R&D at SLAC – S. Smith
Patrick Krejcik
LCLS FAC [email protected]
April 29, 2004
Bunch Length Measurements with the RF Transverse Deflecting CavityBunch Length Measurements with the RF Transverse Deflecting Cavity
yy
Asymmetric parabola indicates incoming tilt to beam
Y = A * (X - B)**2 + CA = 1.6696E-02 STD DEV = 1.3536E-03B = 28.23 STD DEV = 3.084C = 1328. STD DEV = 8.235RMS FIT ERROR = 23.63
-80 -40 0 40 80
SBST LI29 1 PDES (S-29-1)
1.7
1.6
1.5
1.4
1.3
X103
****
***
**
**
*
****
********
-80 -40 0 40 80
SBST LI29 1 PDES (S-29-1)
1.7
1.6
1.5
1.4
1.3
X103
E
-80 -40 0 40 80
SBST LI29 1 PDES (S-29-1)
1.7
1.6
1.5
1.4
1.3
X103
-80 -40 0 40 80
SBST LI29 1 PDES (S-29-1)
1.7
1.6
1.5
1.4
1.3
X103
-80 -40 0 40 80
SBST LI29 1 PDES (S-29-1)
1.7
1.6
1.5
1.4
1.3
X103
-80 -40 0 40 80
SBST LI29 1 PDES (S-29-1)
1.7
1.6
1.5
1.4
1.3
X103
E
MANUAL STEPPING. STEPS = 30
1-APR-03 20:21:16
Cavity on
Cavity off
Cavity on- 180°
Bunch length reconstructionMeasure streak at 3 different phases
z = 90 m
(Str
eak
size
)2
0 180
2.4 m 30 MW
Patrick Krejcik
LCLS FAC [email protected]
April 29, 2004
Calibration scan for RF transverse deflecting cavity
Beam centroid[pixels]
Cavity phase [deg. S-Band]
• Bunch lenght calibrated in units of the wavelength of the S-band RF
Further requirements for LCLS:
•High resolution OTR screen•Wide angle, linear view optics
Patrick Krejcik
LCLS FAC [email protected]
April 29, 2004
OTR Profile Monitor in combination withRF Transverse Deflecting Cavity
Simulated digitized video image
Injector DL1 beam line is shown
Best resolution for slice energy spread measurement would be in adjacent spectrometer beam line.
Patrick Krejcik
LCLS FAC [email protected]
April 29, 2004
400 GHz1.2 mm
BC1 Bunch Length Monitor
CSR Power spectral density signal for bunch length feedback
CSR Power spectral density signal for bunch length feedback
Spectral lines accompanying micro-bunching instability
– Z. Huang.
Spectral lines accompanying micro-bunching instability
– Z. Huang.
Patrick Krejcik
LCLS FAC [email protected]
April 29, 2004
4 THz
BC2 Bunch length monitor spectrum
BC2 bunch length feedback requires THz CSR detector
Demonstrated with CTR at SPPS
Patrick Krejcik
LCLS FAC [email protected]
April 29, 2004
Dither feedback control of bunch length minimization - L. Hendrickson
Dither time steps of 10 seconds
Bunch length monitor response Feedback correction
signal
Linac phase
“ping”
optimum
Jitter in bunch length signal over 10 seconds ~10% rms
Jitter in bunch length signal over 10 seconds ~10% rms
Patrick Krejcik
LCLS FAC [email protected]
April 29, 2004
Timing system requirements
Synchronization of fiducials in low-level RF with distribution of triggers in the control system
1/360 sLinac 476 MHzMain Drive Line Sector feed
Fiducialdetector
MasterPattern
Generator
SLCControlSystem Event
Generator360 Hz Triggers8.4 ns±10 ps
128-bit wordbeam codes
119 MHz
360 Hz fiducials phase locked to low level RF
Patrick Krejcik
LCLS FAC [email protected]
April 29, 2004
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 RF0.05 S-band (50 fs) phase stability
Timing measurement of the pump-probe laser w.r.t. electron beam in the undulator10 fs resolution
Patrick Krejcik
LCLS FAC [email protected]
April 29, 2004
Controls Issues for Power Supplies
16 types out of a total of 55 power suppliesTightest 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
Patrick Krejcik
LCLS FAC [email protected]
April 29, 2004
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.
Single Bunch Beam Dumper (SBBD) is a 120 Hz pulsed magnet supply
Fast orbit feedback requires power supplies and corrector magnets to respond in <8 ms (120 Hz).
Patrick Krejcik
LCLS FAC [email protected]
April 29, 2004
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 allowsSingle 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 LTUMax. 10 Hz to tune-up dump
Stopper out will arm MPS for stopping beam with the SBBD
Patrick Krejcik
LCLS FAC [email protected]
April 29, 2004
MPS - Beam Rate Limiting
Conditions that will stop the beam at the SBBDTune-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 undulatorVacuum
Magnet movers
BPMs
Energy error in the LTU
PIC’s at the collimators
Launch orbit feedback failing
Magnet power supplies for some key elements
Patrick Krejcik
LCLS FAC [email protected]
April 29, 2004
Jitter determination from Electro Optic sampling
Er
Principal oftemporal-spatial correlation
Line image camera
polarizer
analyzer
EO xtal
seconds, 300 pulses: z = 530 fs ± 56 fs rms t = 300 fs rmsseconds, 300 pulses: z = 530 fs ± 56 fs rms t = 300 fs rms
single pulse
A. Cavalieri
centroidwidth
