Breakout Session: Controls

1
Breakout Session Controls

• Physics Requirements
• and Technology Choices for
• LCLS Instrumentation Controls

2
Outline

• Beam position monitors
• Issues for the undulator cavity BPMs
• Issues for signal processing
• Power supplies and controllers
• Pulsed operation of DL1 for diagnostics
• Low level RF
• Source and synchronization issues
• Feedback and x-band regulation
• Bunch length monitors

3
Cavity Beam Position Monitors

• Frequency choice
• Cavity Iris should be masked from SR
• Vacuum chamber dimensions for the undulator are
  now chosen
• 12 mm aperture
• is close to X-band cutoff
• Evaluating two frequency choices (Z. Li)
• Issues
• BPM location with respect to quadrupoles
• Resolution in combination with beam-based
  alignment with EM quads
• Signal processing

5 mm 10 mm
4
Undulator Cavity BPM locations with respect to
quadrupoles

• Quadrupole and BPM mounted adjacent on the
  undulator support cradle to ensure 1 um beam
  based alignment resolution
• Also need to keep the distance between the
  electron beam and the undulator segment axis to
  less than 70 microns rms
• Considering beam position measurement options at
  downstream end as well

Quad BPM assemblies
Optional wire monitors,
Train-linked undulator sections see H.-D. Nuhn
presentation
5
Cavity BPM Signal Processing

• X and Y cavity at each undulator plus 1 phase
  reference cavity per girder
• High-frequency x-band signal is attenuated in a
  short distance
• Incorporate a local mixer to IF at the cavity
• Only a simple passive device in the tunnel
• Temperature stable
• Relatively low radiation loss environment
• Distribution of reference x-band oscillator
  signal in the tunnel
• Choose intermediate frequency to match into the
  RF front end used for stripline

6
Digital BPM Signal Processing

• Use same RF front end for stripline BPMs and
  output from first mixer for cavity BPMs
• Initial desire to use a commercially produced BPM
  processing module (Libera)
• We obtained a try out Libera module
• Integration into the control system not
  proceeding fast enough, e.g. could not access raw
  data in the module.
• Present design solution
• Commercial VME 8 channel digitizer
• RF front end from discrete, commercial components

7
Power supplies and controllers

• Requirements
• Stability of 1E-5 for bunch compressors
• fast response for feedback correctors
• Integrate with epics controls
• reliability
• Design solution
• digital controller/regulator
• developed at PSI and further developed at Diamond
• commercially supplied power modules

8
Power supplies and controllers

• Status
• Test power supply delivered from PSI
• controlled from an epics IOC
• long term current stability tests into resistive
  load are underway

9
PSI Power Supply 12 hour Test
lt2.5E-5
10
Pulsed operation of DL1 for diagnostics

• Propose to allow option of pulsing DL1 bends
• allow pulse stealing at 1 Hz into the
  spectrometer line
• monitor beam profile and energy spread
• Potentially combine with pulsing of the
  transverse cavity

• Laminated magnet
• Experience at SLAC with damping ring DRIP magnets
• Keep two dipoles in series
• Need to maintain 1E-4 stability

• Laminate magnets now
• Develop pulsed supply later

11
Pulsed operation of DL1 for diagnostics

• 1 Hz pulsed into the spectrometer line

• monitor beam profile

• Investigate further if transverse cavity can be
  optimized for slice measurements in the
  spectrometer line

• monitor energy spread

12
Low Level RF

• Feedback and x-band regulation
• Question that arose last time was how to
  distinguish drift in the X-band system from
  errors in the S-band system
• Solution is to keep X-band regulation fixed, and
  compensate errors with the S-band system only
• See next slide
• Source and synchronization issues
• noise and stability issues in oscillator and
  distribution

13
Demonstration of L1 S-band adjustment to
compensate Lx errors courtesey Juhao Wu
X-band phase error of 5o, fixed with L1 S-band
adjustment phase 2.1, voltage - 2.1
X-band amplitude error of 5, fixed with L1
S-band adjustment phase 0.61, voltage 0.18
14
Low Level RF Source and synchronization

• Present design concept
• Microwave crystal oscillator phase locked to SLAC
  MDL low noise in the low frequency band
• Gun laser oscillator mode locked to crystal
  oscillator low noise in the high frequency band
• Under evaluation
• Derive the LLRF 2856 MHz from crystal oscillator
  or from laser optical output
• Distribute LLRF over copper
• or optional optical fiber

15
RF/Laser distribution proposed by Ilday et al,
MIT at the SLAC Timing workshop
Optical-laser synchronization module
Upgrade path Fiber distribution system
Master laser oscillator
RF-optical synchronization module
Low noise crystal microwave oscillator
Baseline Cu Coax distribution
LLRF to klystron
Linac MDL
16
RF stabilization Ilday et al, MIT
17
Derivation of LLRF from laser F. Omer Ilday, MIT
18
Synchronizing Gun and User Lasers F. Omer
Ilday, MIT
19
BC1, BC2 Single-shot Bunch Length Detectors

• Non-intercepting detector for off-axis
  synchrotron radiation
• Reflected through a port to
• Spectral Power detector
• Single shot Autocorrelator

THz power detector
THz autocorrelator
B4 Bend
CSR
Bunch Compressor Chicane
Vacuum port with reflecting foil
20
Bunch Length Monitor Issues

• The CSR we now understand is dominated by
  Coherent Edge Radiation
• Same spectral and angular distribution
  characteristics as transition radiation
• Need to account for interference effects from
  adjacent magnets
• Experimental investigation at SPPS planned
• Can also learn from UCLA expt at BNL-ATF

21
Bunch Length Monitor Issues

• Need practical experience in evaluating
• window materials
• Detectors (pyrometers, Golay cells, bolometers)
• Autocorrelator designs (mirrors, splitters,
  detectors)
• New development of single-shot autocorrelators

22
End of Presentation

• Backup slides

23
Power supply controller system layout
EPICS
I O C
8 ch VME card
ADCCard
Power Supply DSP Controller
5MHz Optical fiber
PWM signal
Monitor signals
DCCT
load
PWM AC Converter
AC line
24
PSI Digital Power Supplies
Master
Fast Optical Link (5 MHz)
ADC/DAC Card
DSP Controller
Optical Trigger
0..6 Slaves
PWM Signal
I
DIO
U1..4
DCCT
Magnet
Power Converter
Courtesy A. Luedeke, PSI
25
Stripline versus Cavity BPM Signals

• noise (resolution) minimized by removing analog
  devices in front of ADC that cause attenuation
• drift minimized by removing active devices in
  front of ADC

26
SPPS Laser Phase Noise Measurements R. Akre
476 MHz M.O.
fiber 1 km
MDL 3 km
TiSa laser osc
EO
VCO
diode
2856 MHz
x6
Phase detector
2856 MHz to linac
scope
27
Courtesy F. Jenni, PSI
28
Energy and Bunch Length Feedback Loops

• Beam based feedback will stabilize RF F,A
• Against drift and jitter up to 10 Hz
• But no diagnostic to distinguish drift of X-band
• Linearization, higher-harmonic RF has the
  tightest tolerance
• No unique beam measurement