01/04/2009 1st ditanet school on diagnostics 1 beam diagnostics at diamond light source guenther...
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01/04/2009 1st DITANET school on Diagnostics 1
Beam DiagnosticsBeam Diagnosticsat Diamond Light Sourceat Diamond Light Source
Guenther RehmGuenther RehmHead of Diagnostics GroupHead of Diagnostics Group
11stst DITANET school on Diagnostics DITANET school on Diagnostics1 April 20091 April 2009
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Outline
• What is a Light Source?
• Diagnostics Requirements for a Light Source
• Diagnostics in the Injector
• Diagnostics in the Storage Ring
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A Light Source?
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How Is Synchrotron Light Produced?
Synchrotron Light (or Radiation) is electromagnetic radiation emitted when a high energy beam of charged particles (electrons) is deflected by a magnetic field
a single bending magnet produces a wide fan of
radiation
multiple bends in an "undulator" or "wiggler"
magnet give higher intensity and more directed radiation
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A Brief History of Synchrotron Light Sources :
• Discovery: 1947, General Electric 70 MeV synchrotron
• First use for experiments: 1956, Cornell 300 MeV synchrotron
• 1st generation: machines built for other purposes, mainly High Energy Physics
• 2nd generation: purpose-built storage rings for production of synchrotron light
• 3rd generation: higher brightness synchrotron light sources, using mainly ‘insertion devices’ (undulators and wigglers) as the X-ray sources
• 4th generation: LINAC followed by ‘Free Electron Laser’, i.e. a series of undulators producing coherent synchrotron light of even higher peak brightness and shorter duration
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SR and the Electromagnetic Spectrum
Electromagneticwaves
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Layout of a 3G Light Source A beam of electrons is accelerated in
a LINAC, further accelerated in a booster synchrotron, then
accumulated in a storage ring.
The circulating electrons emit intense beams of synchrotron light that are
sent along beamlines to the experimental stations.
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235 m
100 MeV Linac
3 GeV BoosterC = 158.4 m
3 GeV Storage RingC = 562.6 m
Experimental Hall and Beamlines
235 m
office building
peripheral labs. and
offices
future long beamlines
technical plant
Layout of Diamond
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Key Parameters of Diamond
Electron Beam Energy 3 GeV
Storage ring circumference 561.6 m
Available space for Insertion Devices 4x8m, 18x5m
Beam current 300 mA
Emittance (hor., vert.) (nm rad) 2.7, 0.03
Minimum ID gap 5 mm
Electron beam sizes (hor., vert) (m) 123, 6
Electron beam divergences (hor., vert) 24, 4 rad
Peak brightness* 2*1020
Peak brightness* (1Å) 1019
* photons/s/mrad2/mm2/0.1%bw
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Diagnostics Requirements• Track charge trough Injector
– Integrating Current Transformers, Faraday Cups and Wall Current Monitors
– Stripline BPMs in transfer paths, buttons in booster– Screens / Cameras / Synchrotron Light Monitors
• Keep stored beam stable– Fast Global Orbit Feedback: Monitor beam position and correct
orbit 10000 per second to sub-um– Transverse Bunch by Bunch Feedback: Monitor bunch motion
and correct after each turn to damp coupled bunch instabilities– Measure betatron tunes without visibly disturbing beam– Monitor beam size, calculate emittance, coupling and energy
spread– Measure stored current and bunch by bunch charge
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230 BLM
5 Faraday-C
7 ICT
2 DCCT
5 SLM
2 Tune Excite
204 BPMs
2 Pinholes
17 Screens
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Faraday Cups, WCMs, ICTs
LTB FC
LINACFC
WCM for LINAC,LTB,BTS
ICT and electronics
ICT shield
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The first bunches on WCM and ICT
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Bunch Charge and Train Structure
from LINAC from booster
WCMs intransferpaths
Buttonin SR
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Booster Current on DCCT
First measurement
Later with extraction after 100ms
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Strip Line BPM Pickups in Transfer Paths
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Screens and Optics
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IEEE1394 Cameras
Camera Repeater
PP
C I
OC
1
Diagnostics VME crate
PP
C I
OC
2
IEE
E1
39
4 P
MC
Eve
nt
Rx
24 V PSU
Repeater
Controls NetworkEvent Network
CameraTrigger
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EDM Camera Display
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Precisely Triggered Acquisition
edge of screen
beam in booster during ramp
kicked beam before main septum
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Image Analysis
1D fits2Dfit
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Orbit Stability Requirements in 3rd Generation Light Sources
mmx 3.121231.0 radradx 4.2241.0' mmy 6.04.61.0
xx 1.0 '1.0' xx
yy 1.0 '1.0' yy
Beam stability should be better than 10% of the beam size
For Diamond nominal optics (at short straight sections)
radrady 4.041.0'
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Motivation and Challenges
• Sources of beam motion:– Insertion devices not fully compensated, ID motion
leads to orbit displacement– Ground vibrations amplified through girders– Magnet power supply drift– Vibrations from water cooling
• Sources of errors in EBPM measurement:– Mechanical / electrical offsets– Noise– Beam current dependence– Pickup thermal motion
Correct as Correct as fast as possiblefast as possible
Minimise or removeMinimise or removefrom correctionfrom correction
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7 BPMs each in 24 cells
Standard BPM
Primary BPM
-50 -40 -30 -20 -10 0 10 20 30 40
-20
-10
0
10
20
-40 -30 -20 -10 0 10 20 30 40
-10
-5
0
5
10
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Button Pickup
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Primary BPM with reference pillar
carbon fibrepillar with lowtemperatureexpansioncoefficient
bellows for mechanical isolation
length gauges senseH/V position with 0.5um resolution
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Standard BPM near Quad
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Some BPMs move after beam loss
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Multiplexing in BPM Electronics
• Crossbar switch routes all four inputs through all processing channels in parallel, but permutes routing
• After digitisation, but before further filtering, the permutation is reversed• By averaging over 4 permutations, any differences/drifts between the
channels will be removed (each input will have been routed through each channel during the averaging period)
• By examining the changes in the outputs during permutation, the gains of the individual channels can be retrieved and then digitally equalised to reduce artefacts of switching
A/D
A/D
A/D
A/DCro
ssba
r S
witc
hFPGA
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Pro
cess
or
Controls Network
PS VME crate
eBPM eBPM eBPM eBPM eBPM eBPM eBPM
Cell -m
Cell -n Cell +n
Cell +m
Fast Orbit Feedback
14 Corrector PSUs
PSU 1 PSU 14
PS
U I
F
…
Event Network
FB
Pro
cess
or
PM
C R
ock
et
IO
Pro
cess
or
Diagnostics VME crate
Eve
nt
Rx
PS
U I
F
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FOFB Installation (one of 24 cells)
Power supplyVME crate
Corrector power supplies
Diagnostics rack
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FOFB Performance60mA
Suppressionof beam motion
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Transverse Bunch-by-Bunch Feedback
RFFrontend
Modulatorand
Amplifier
4 AD converters
(slicing)
Digital Signal Processing
DAConverter
History buffer
FPGA based Feedback Processor
Control
System
StriplineKicker
Button
Pickup
4-waySplitter
500 MHz RF clock
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Beam artificially made unstable in both planes:
1) no feedback → horizontally
unstable
2) feedback in horiz. plane only
→ vertically unstable
3) feedback in both planes
→ stable in both planes
Bunch-by-Bunch Feedback in Action
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Tune Measurement:Kick and Fourier Transform
0 500 1000 1500 2000-400
-200
0
200
400horizontal
turns
posi
tion
[um
]
0 20 40 60 80 100-400
-200
0
200
400
turns
posi
tion
[um
]
0 0.1 0.2 0.3 0.4 0.50
10
20
30
40
50
tune
ampl
itude
[um
]0 500 1000 1500 2000
-150
-100
-50
0
50
100
150vertical
turns
posi
tion
[um
]
0 20 40 60 80 100-150
-100
-50
0
50
100
150
turns
posi
tion
[um
]
0 0.1 0.2 0.3 0.4 0.50
2
4
6
8
10
tuneam
plitu
de [
um]
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More Elegant Tune Measurement: Harmonic Excitation and Detection
cos
sin
Exitation
Beam Position Pickup
In phase
Out of phase
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Amplitude and Phase of Beam Response to Swept Sine Excitation
0.2 0.205 0.21 0.215 0.22 0.225 0.23-400
-200
0
200
400
600
800
tune
in phase signal
out of phase signal
0.2 0.205 0.21 0.215 0.22 0.225 0.230
200
400
600
800
tune
mag
nitu
de
0.2 0.205 0.21 0.215 0.22 0.225 0.23-200
-100
0
100
200
phas
e
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Tune Measurement of Individual Bunches
• Only one bunch is excited with swept sine wave
• Tune depends on charge per bunch
• Head-Tail mode leads to asymmetry of Synchrotron sidebands for larger charges
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X-ray Pinhole Cameras
Pinholes
9.6m 3.85m
Sourcepoints
ScreensOptics
Cameras
12.7m
4.5m
d2 d1
Magnification
1
2
d
dm
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Modified Beam Port Absorbers and Pinholes
X/Z translationand rotation
2 stacks of 4 slabs5mm*1mm*30mm
with shims as spacers
Aluminium/Steelexplosion bondedflange as window
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Pinhole Screens and Optics
CdWO4 screen
mirror
50mm macro lensmagnification 1:1
focus and irisremote control
1024x768 camera4.65um pixel
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Pinhole Image Analysis
Skew quads offSkew quads on
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Storage Ring DCCT
First accumulation of stored current at Diamond
Stored current and life time
Decaying beamMachine
development Top-Up mode
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Fill Pattern Measurement by Time Correlated Single Photon Counting
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Acknowledgements
• Diagnostics: Alun Morgan, Cyrille Thomas, Chris Bloomer, Graham Cook
• Controls: Michael Abbott, Isa Uzun,James Rowland, Mark Heron
• Accelerator Physics: Ian Martin, Riccardo Bartolini
• Engineering: Nigel Hammond, Ron Godwin, Darren Simmons
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Thank you for your attention!