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


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)


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


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 (?)


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


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


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


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


Electronics - I.

Electronics - I.

Mother Board with 71MHz clock

board

USB Control and histogram/averag

e is fully operational


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


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)


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)


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


First Experimental Data (Nov. 2002)

First Experimental Data (Nov. 2002)

First data (Peak Height distribution)Electronics Setup


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


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]


SET3


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)


SET3


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)


SET3


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)


Details

Details

0.000

0.001

0.002

0.003

329.9 329.95 330 330.05 330.1

Time [ns]


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]



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


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


Bunch LengthBunch Length

0

5

10

15

20

25

0 50 100 150 200 250 300

Bunch Number

RMS Bunch Width [ps]

SET3


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.


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


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%


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...


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.


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

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

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