Transcript Physics Requirements Overview

Breakout Session: Controls
Physics Requirements Overview
P. Krejcik
April 29, 2004
LCLS FAC
Patrick Krejcik
[email protected]
Key accelerator physics factors driving
controls design
Precision beams
low emittance, short bunch lengths
Stringent stability requirements
Feedback control of
orbit, charge energy and bunch length
Single pass beams
unlike storage ring, every pulse potentially different
Precision timing requirements
April 29, 2004
LCLS FAC
Patrick Krejcik
[email protected]
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
April 29, 2004
LCLS FAC
Patrick Krejcik
[email protected]
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
April 29, 2004
LCLS FAC
Patrick Krejcik
[email protected]
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
April 29, 2004
LCLS FAC
Patrick Krejcik
[email protected]
Bunch length diagnostic comparison
Device Type
Invasive
Single shot
measurement measurement
Abs. or rel.
Timing
Detect
measurement measurement m bunching
Yes: Steal 3
pulses
No: 3 pulses
Absolute
No
No
No for CSR
Yes for CTR
Yes
Relative
No
Yes
Coherent
No for CSR
Radiation
Yes for CTR
Autocorrelation
No
Absolute
No
No
Electro Optic
Sampling
No
Yes
Absolute
Yes
No
Energy
Wake-loss
Yes
No
Relative
No
No
RF Transverse
Deflecting
Cavity
Coherent
Radiation
Spectral power
April 29, 2004
LCLS FAC
(2nd moment
only)
Patrick Krejcik
[email protected]
Feedback global requirements
Description of feedback types and locations
Orbit
charge
energy
bunch length
Control system response time
120 Hz single pulse data transfer, zero latency
April 29, 2004
LCLS FAC
Patrick Krejcik
[email protected]
Energy and Bunch Length Feedback Loops
E
Vrf(L1)
Φrf(L2)
E
Φrf(L3)
E
DL1
Vrf(L0)
L0
Φrf(L1) sz
E
DL1
Spectr
.
L1
April 29, 2004
LCLS FAC
Φrf(L2)
sz
BC2
BC1
L2
L3
BSY
50B1
DL2
Patrick Krejcik
[email protected]
Closed Loop Response of Orbit Feedback
Antidamp
Damp
Gain bandwidth
for different loop
delays
- L. Hendrickson
April 29, 2004
LCLS FAC
Patrick Krejcik
[email protected]
Beam Position Monitoring requirements
April 29, 2004
LCLS FAC
Patrick Krejcik
[email protected]
Beam Position Monitoring requirements
April 29, 2004
LCLS FAC
Patrick Krejcik
[email protected]
Linac type stripline BPMs
Resolution achievable with
existing processor
New BPM processor design
challenges:
• large dynamic range
• Low noise, high gain
• 20 ps timing jitter limit
LCLS
range
April 29, 2004
LCLS FAC
Patrick Krejcik
[email protected]
Cavity beam position monitors in the undulator and LTU
R&D at SLAC – S. Smith
• Raw digitizer records from
beam measurements at ATF
Coordinate measuring
machine verification of cavity
interior
• X-band cavity
shown
• Dipole-mode
couplers
April 29, 2004
LCLS FAC
Patrick Krejcik
[email protected]
Assembled X-band cavity BPM
Mechanical center of
RF BPM well
correlated to electrical
center – more
accurately than for
stripline BPMS
April 29, 2004
LCLS FAC
Patrick Krejcik
[email protected]
Preliminary beam calibration data from a C-band
cavity tested at ATF
R&D at SLAC – S. Smith
200 nm
25 mm
• cavity BPM signal versus predicted position
• bunch charge 1.6 nC
April 29, 2004
LCLS FAC
• plot of residual deviation from linear
response
• << 1 mm LCLS resolution requirement
Patrick Krejcik
[email protected]
Bunch Length Measurements with the RF Transverse Deflecting Cavity
2.4 m
30 MW
Bunch length reconstruction
s y Measure streak at 3 different phases
X10
Y = A * (X - B)**2 + C
A =
1.6696E-02
STD DEV =
1.3536E-03
B =
28.23
STD DEV =
3.084
C =
1328.
STD DEV =
8.235
RMS FIT ERROR
=
23.63
(Streak size)2
1.7
*
sz = 90 mm
Cavity on
1.6
*
*
*
Cavity on
- 180°
1.5
Cavity off
*
*
*
*
*
E
*
*
1.4
*
*
E
*
*
1.3
-80
MANUAL STEPPING.
-40
0
40
SBST LI29 1 PDES (S-29-1)
STEPS =
80
30
1-APR-03 20:21:16
0
April 29, 2004
LCLS FAC
180
Asymmetric parabola indicates
incoming tilt to beam
Patrick Krejcik
[email protected]
Calibration scan for RF transverse deflecting cavity
•
Beam
centroid
[pixels]
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
Cavity phase [deg. S-Band]
April 29, 2004
LCLS FAC
Patrick Krejcik
[email protected]
OTR Profile Monitor in combination with
RF 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.
April 29, 2004
LCLS FAC
Patrick Krejcik
[email protected]
BC1 Bunch Length Monitor
400 GHz
1.2 mm
CSR Power spectral density
signal for bunch length feedback
April 29, 2004
LCLS FAC
Spectral lines accompanying
micro-bunching instability
– Z. Huang.
Patrick Krejcik
[email protected]
BC2 Bunch length monitor spectrum
BC2 bunch length feedback
requires THz CSR detector
4 THz
April 29, 2004
LCLS FAC
Demonstrated with CTR at
SPPS
Patrick Krejcik
[email protected]
Dither feedback control of bunch length
minimization - L. Hendrickson
Bunch length monitor
response
Feedback correction
signal
“ping”
optimum
Dither time steps of 10
seconds
April 29, 2004
LCLS FAC
Linac phase
Jitter in bunch length signal
over 10 seconds ~10% rms
Patrick Krejcik
[email protected]
Timing system requirements
Synchronization of fiducials in low-level RF
with distribution of triggers in the control
system
Linac 476 MHz
Main Drive Line
April 29, 2004
LCLS FAC
Sector feed
Fiducial
detector
119 MHz
Event
Generator
SLC
Control
System
Master
Pattern
Generator
1/360 s
360 Hz fiducials phase
locked to low level RF
360 Hz Triggers
8.4 ns±10 ps
128-bit word
beam codes
Patrick Krejcik
[email protected]
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
0.05 S-band (50 fs) phase stability
Timing measurement of the pump-probe
laser w.r.t. electron beam in the undulator
10 fs resolution
April 29, 2004
LCLS FAC
Patrick Krejcik
[email protected]
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
April 29, 2004
LCLS FAC
Patrick Krejcik
[email protected]
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).
April 29, 2004
LCLS FAC
Patrick Krejcik
[email protected]
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
April 29, 2004
LCLS FAC
Patrick Krejcik
[email protected]
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
April 29, 2004
LCLS FAC
Patrick Krejcik
[email protected]
end
April 29, 2004
LCLS FAC
Patrick Krejcik
[email protected]
Jitter determination from Electro Optic sampling
A. Cavalieri
Principal of
temporal-spatial correlation
single pulse
Line image
camera
EO xtal
analyzer
polarizer
Er
30 seconds, 300 pulses:
April 29, 2004
LCLS FAC
width
centroid
sz = 530 fs ± 56 fs rms
Dt = 300 fs rms
Patrick Krejcik
[email protected]