s. de santis “measurement of the beam longitudinal profile in a storage ring by non-linear laser...

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...

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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...

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0.01

0.01

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0.02

0.03

0.03

0.04

0.04

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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

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0.02

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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

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0.08

0.10

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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