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S. De Santis “Measurement of the Beam Longitudinal Profile in a Storage Ring by Non-Linear Laser Mixing” - BIW 2004 May, 5th
Measurement of the Beam Longitudinal Profile in a
Storage Ring by Non-Linear Laser Mixing
Measurement of the Beam Longitudinal Profile in a
Storage Ring by Non-Linear Laser Mixing
J.-F. Beche, J. Byrd, S. De Santis, P. Denes, M. Placidi,W. Turner, M. Zolotorev
Lawrence Berkeley National Laboratory
S. De Santis “Measurement of the Beam Longitudinal Profile in a Storage Ring by Non-Linear Laser Mixing” - BIW 2004 May, 5th
All-in-One Tool for Synchrotron Rings
All-in-One Tool for Synchrotron Rings
• Online measurement of bunch length and shape
• Bunch current – including nominally unfilled RF buckets (“ghost bunches”)
• Synchronous bunch position• Fast: the results shown were
accumulated in seconds/minutes• Very wide dynamic range (104)
S. De Santis “Measurement of the Beam Longitudinal Profile in a Storage Ring by Non-Linear Laser Mixing” - BIW 2004 May, 5th
Summary
Summary
• Longitudinal Density Monitor overview– what it does, how it does it
• The hardware• Experimental runs at the ALS• Applications to LHC and NLC
S. De Santis “Measurement of the Beam Longitudinal Profile in a Storage Ring by Non-Linear Laser Mixing” - BIW 2004 May, 5th
A Brief HistoryA Brief History
• Original concept: femtoslicing experiments at the ALS (R. Schoenlein and M.Zolotorev, 2000)
• Prototype: LHC Accelerator Research Program (2002-03)
• Longitudinal dynamics studies in damping rings (?)
S. De Santis “Measurement of the Beam Longitudinal Profile in a Storage Ring by Non-Linear Laser Mixing” - BIW 2004 May, 5th
An Optical Sampling Scope
An Optical Sampling Scope
BunchSynchrotronPhotons 1
LaserPhotons 2
MixedPhotons 1+2
PMTNon-linearcrystal[BBO]
Filte
r(1+ 2
)laser pulse length << bunch length
1+2 = visible wavelength
S. De Santis “Measurement of the Beam Longitudinal Profile in a Storage Ring by Non-Linear Laser Mixing” - BIW 2004 May, 5th
Scanning the Bunch
Scanning the Bunch
Piezo-ceramicpositioner
LHC: 40 MHzALS: 71 MHz
Laser
L
C/2L = 40 (or 71) MHzAdjust by changingpath length (phasemodulation)
100-200 mW diode-pumped laser
ALS: 10 Hz
ALS: 50 fs, LHC: 50 ps (10 W)
LHC: 22 bins (std. mode)ALS: 32 bins
S. De Santis “Measurement of the Beam Longitudinal Profile in a Storage Ring by Non-Linear Laser Mixing” - BIW 2004 May, 5th
Schematic (timing)
Schematic (timing)
Laser
Synchrotron Light
PMT
PD
ADC
ADC
DAC
BoardTiming
CavityControl
Processing+Interface(USB to PC)
BBO
LaserTiming
Filter
Ring main RF (PLL)
Orbit clock
S. De Santis “Measurement of the Beam Longitudinal Profile in a Storage Ring by Non-Linear Laser Mixing” - BIW 2004 May, 5th
LDM – Electronics Board Layout
LDM – Electronics Board Layout
• Architecture – Different Boards– #1 : Phase modulation Generator
– #2 : Phase Information Digitization
– #3 : PMT pulse digitization
– #4 : Delay generators/timing
– #5 : Digital Backend (Storage and USB)
1 2 3 4
To Laser Phase Offset
From PMT
From Photodiode
PC
5
S. De Santis “Measurement of the Beam Longitudinal Profile in a Storage Ring by Non-Linear Laser Mixing” - BIW 2004 May, 5th
Electronics - I.
Electronics - I.
Mother Board with 71MHz clock
board
USB Control and histogram/averag
e is fully operational
S. De Santis “Measurement of the Beam Longitudinal Profile in a Storage Ring by Non-Linear Laser Mixing” - BIW 2004 May, 5th
Electronics - II.
Electronics - II.
DAC Analog board for laser phase offset
modulation
Track and Hold board with self trigger for PMT pulse detection (only one bit is used in single
photon counting mode)
Actual Laser phase offset digitization
board
S. De Santis “Measurement of the Beam Longitudinal Profile in a Storage Ring by Non-Linear Laser Mixing” - BIW 2004 May, 5th
DAQ PCI6534 National Instruments
DAQ PCI6534 National Instruments
• Standard DAQ Board• Function Library Labview, C/C++ compatible• Quad 8-bit I/O board, DMA transfer rates up
to 20MHz (8, 16 or 32-bit)
S. De Santis “Measurement of the Beam Longitudinal Profile in a Storage Ring by Non-Linear Laser Mixing” - BIW 2004 May, 5th
Tests at the ALS
Tests at the ALS
Bucket spacing 2 ns
Bunch width ~50 ps
“Camshaft” pulse
328 RF buckets276+1 filled
Gap
(LHC parameters)
(2808/35640)
(280-620 ps)
(2.5 ns)
S. De Santis “Measurement of the Beam Longitudinal Profile in a Storage Ring by Non-Linear Laser Mixing” - BIW 2004 May, 5th
wiggler
bendmagnet
mirror
synchrotronradiatione-beam
Laser System
BBO
2 = ~2 eV
1 = 1.55 eV
1+ 2
delay
slit
Optical layout at the ALSOptical layout at the ALS
L= 800 nm, S= 638 nm =355 nm
Conversion efficiency is proportional to the laser power density and is optimized for = S
S. De Santis “Measurement of the Beam Longitudinal Profile in a Storage Ring by Non-Linear Laser Mixing” - BIW 2004 May, 5th
First Experimental Data (Nov. 2002)
First Experimental Data (Nov. 2002)
First data (Peak Height distribution)Electronics Setup
S. De Santis “Measurement of the Beam Longitudinal Profile in a Storage Ring by Non-Linear Laser Mixing” - BIW 2004 May, 5th
ALS Bunch Profile in Time
ALS Bunch Profile in Time
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0 100 200 300 400 500 600
Time [ns]
Counts/Bunch Passage
SET3
S. De Santis “Measurement of the Beam Longitudinal Profile in a Storage Ring by Non-Linear Laser Mixing” - BIW 2004 May, 5th
Zoom in...
Zoom in...
0.00
0.01
0.01
0.02
0.02
0.03
0.03
0.04
0.04
0.05
-2 0 2 4 6 8 10 12
Time [ns]
Counts/Bunch Passage
SET3
S. De Santis “Measurement of the Beam Longitudinal Profile in a Storage Ring by Non-Linear Laser Mixing” - BIW 2004 May, 5th
Compress Scale...
Compress Scale...
0.00
0.01
0.01
0.02
0.02
0.03
0.03
0.04
0.04
0.05
0 1 2 3 4 5 6
Bunch (270 ps)
Counts/Bunch Passage
SET3
S. De Santis “Measurement of the Beam Longitudinal Profile in a Storage Ring by Non-Linear Laser Mixing” - BIW 2004 May, 5th
Large dynamic range
Large dynamic range
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
159 160 161 162 163 164 165 166 167 168 169 170
Bunch (270 ps)
Counts/Bunch Passage
SET3
S. De Santis “Measurement of the Beam Longitudinal Profile in a Storage Ring by Non-Linear Laser Mixing” - BIW 2004 May, 5th
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
159 160 161 162 163 164 165 166 167 168 169 170
Bunch (270 ps)
Counts/Bunch Passage
Details
Details
0.000
0.001
0.002
0.003
329.9 329.95 330 330.05 330.1
Time [ns]
Counts/Bunch Passage
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
327.9 327.95 328 328.05 328.1
Time [ns]
Counts/Bunch Passage
S. De Santis “Measurement of the Beam Longitudinal Profile in a Storage Ring by Non-Linear Laser Mixing” - BIW 2004 May, 5th
Background
Background
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
80 90 100 110 120 130 140 150
Bunch Number
Total Counts/bunch/passage
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
129 130 131 132
Bunch Number
Counts/bunch/turn
Camshaft/Background ~ 103
S. De Santis “Measurement of the Beam Longitudinal Profile in a Storage Ring by Non-Linear Laser Mixing” - BIW 2004 May, 5th
Synchronous Phase Transients
Synchronous Phase Transients
-0.02
-0.01
0.00
0.01
0.02
0 50 100 150 200 250 300
Bunch Number
t0 offset [ns]
SET3
S. De Santis “Measurement of the Beam Longitudinal Profile in a Storage Ring by Non-Linear Laser Mixing” - BIW 2004 May, 5th
Bunch LengthBunch Length
0
5
10
15
20
25
0 50 100 150 200 250 300
Bunch Number
RMS Bunch Width [ps]
SET3
S. De Santis “Measurement of the Beam Longitudinal Profile in a Storage Ring by Non-Linear Laser Mixing” - BIW 2004 May, 5th
A Longitudinal Monitor for LHC
A Longitudinal Monitor for LHC
• 450 GeV - 7 TeV• Untrapped beam fraction• Protons in the abort gap• Longitudinal bunch tails• “Ghost bunch” population• Etc.
S. De Santis “Measurement of the Beam Longitudinal Profile in a Storage Ring by Non-Linear Laser Mixing” - BIW 2004 May, 5th
LHC Applications of LDM
LHC Applications of LDM
• Bunch core measurement (std. mode)
• Tails and “ghost bunches” (HS mode)• 10 W laser @ 1064 nm• Laser pulse period: 25 ns• Laser pulse length: 50 ps• LHC length: 88.9 µs• Photons/bunch/turn: 10’s (102 gain @ 450
nm) at full current
S. De Santis “Measurement of the Beam Longitudinal Profile in a Storage Ring by Non-Linear Laser Mixing” - BIW 2004 May, 5th
Bunch core measurement
Bunch core measurement
• Measure bunch population at ±2 with 1% accuracy in a time short compared to the synchrotron period (~42 ms @ 7 TeV)
• 22 bins required (50 ps x 22 ≈ ±2).• Time required to map the core once: 22 turns ≈ 2 ms• Expected population: 2·108- 2·106 p/ps.• Accuracy: 0.5-5.5%
S. De Santis “Measurement of the Beam Longitudinal Profile in a Storage Ring by Non-Linear Laser Mixing” - BIW 2004 May, 5th
Tails and “ghost bunches” measurement
Tails and “ghost bunches” measurement
• Measure bunch populations as small as 2·104 p/ps all around the ring (causing background in experiments) with ~50% accuracy. • Entire ring is mapped in 50 ps slices. Minimum number
of turns: 500 (3556 slices/turn).• At 7 TeV, (2±0.8)·104 p/ps give 3.2 ±1.8 counts in a 50
ps slice.• 1000 turns (< 100 ms) are required for the 50%
accuracy as per specs.
LDM is the ideal instrument...
S. De Santis “Measurement of the Beam Longitudinal Profile in a Storage Ring by Non-Linear Laser Mixing” - BIW 2004 May, 5th
NLC Damping Rings Parameters
NLC Damping Rings Parameters
• E = 1.9 GeV• C = 300 m• z= 12 ps• ∆tb= 1.4 ns• Nb= 576/714 (3 trains, laser @ 71 MHz can sample 20 bunches x train)• S= 0.0035 (~300 turns)• Long. damping time = 2.6 ms (2600/3 turns)
Longitudinal dynamics in the machine never reaches a steady state + short bunches the LDM can be a valuable tool for understanding/monitoring the damping rings.
S. De Santis “Measurement of the Beam Longitudinal Profile in a Storage Ring by Non-Linear Laser Mixing” - BIW 2004 May, 5th
Conclusions: Pros and Cons of LDM
Conclusions: Pros and Cons of LDM
• Fast sampling rate (laser cavity frequency)
• High dynamic range• High time resolution (laser pulse
length)• Not limited to optical wavelengths• Requires multi-turn sampling• Requires synchrotron light
Especially suited for dynamics studies in damping rings