sch: leade lpm+ag 15/12/031 non intercepting diagnostics based on synchrotron light from a bending...

SCH: LEADE LPM+AG 15/12/03 1

Non intercepting diagnostics based on synchrotron light from a bending magnet

(started as “piggy back” on transverse profile system)

• Longitudinal Beam profile (3564 bunches)

• Abort Gap Population

• Bunched/Debunched beam at injection

• Empty RF Buckets (aka “ghost bunches”)

• Longitudinal wings (high resolution)

• Core Measurements: length, distribution, oscil..

Functional Specification: CERN/EDMS Doc. 328145

LHC- Longitudinal Profile Monitor.


Point 4: EchenevexRF accelerating cavities


Specification Requirements

MODE Ultra-high sensitivity

High sensitivity Standard sensitivity

Sensitivity (p/ps) 60 104 106

Sensitivity/Ult. Peak Density 3x10-7 5x10-5 5x10-3

Dynamic range (p/ps) 60 to 6x104 6x104 to 3x108 5x106 to 5x108

Sampling period 100 ns 50 ps 50 psIntegration time 100 ms 10 s 1 ms

Accuracy 30 p/ps 4x103 p/ps 1%

Transmission rate < 1 s 1 min 100 ms

APPLICATIONS

Abort gap monitor X

Tails X

Ghost bunches X

De-bunched beam X

Core parameters X


Longitudinal Profile Monitor: situation Sept. 2003

LPM is a LARP contribution/“collaboration”, not in-house project

LPM is studied by Berkeley lab, (need similar instrument in ALS)

(n.b. same group responsible for LHC Luminosity measurement)

Initial plan:

2002 R&D (APD/ Laser mixing)

2003 Choice of technology + Prototype design

2004 Production electronics and instruments

2005 Install in LHC

(2006 reserved for transverse instruments)


Undulator and D3 magnet at LHC Point 4

Light production at injection energy too low: SC undulator added


Abort gap, 3s

For Ions: spacing 100ns, total 890 bunches, 1:40 RF cycles

(Protons)


LHC Beam profile

3564 bunches+ 32,076 empty buckets,

RMS Bunch length 0.28ns: sample time 50 ps

89s/50ps = 1,780,000 data bins….

Integrate over 40ms…

…50,000,000 data points/second


Fast Photon Detectors: Commercial Avalanche Photodiode modules

PC card for Time-correlated Single Photon Counting: TimeHarp 200

3MHz count rate, <40ps resolution

…but only 4096 time-bins…

http://www.picoquant.com/products/images/timeharp200_1k.jpg


Fast Photon Detectors: Avalanche Photodiodes

100ps, 16 bins

C-SPAD: Cooled Single-Photon Avalanche DiodeWith active quenching circuit: laser range-finding of satellite in flight, T.Otsubo, CRL, Tokyo


Photon Counting: MCP PMT Hammamatsu R3809U

Photon counting has its problems too,For high dynamic range, there must be no systematic false counts


MCP-PMT: Dynamic range

900 ns

102

Self-generated false counts after event: need to gate detector off for 1us after each event: count rate drops to 10’s of kHz.


Proposed Laser Mixing System:

Synch light, 633nm

40 MHz Laser

Ti:Sapphire 800nm

filters

Mixing crystal

8 bitDetector350nm

Very narrow light spectrum is used, ~3nm (1% of available)Laser pulse timing phase-locked to Machine RF, with offsetLaser used to sample with 10ps pulses at 40MHzMax. Data rate at laser frequency, could be 80MHz?


Laser Mixing: LPM High Sensitivity Mode

400MHz Bucket 2.5ns

25ns laser sample interval, 500 sample points/scan

Increment delay by 50 ps / machine rev

If PMT is 1% accurate, still need to integrate over 1000 samples to get spec accuracy: 55s + settling time ( Spec. 10-4 in 10s )


Compress Scale...

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Bunch (270 ps)

Co

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Passag

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SET3


LM Concerns:

• Low wavelength conversion efficiency - single photon counting- needs longer integration time

• Requires exclusive operating modes-std/high resolution modes

• High res. integration time too long:- 10 sec: increase to 1min


• LM system is unlikely to meet specs for integration time, and is not suitable for abort gap protection (too complex)

• If LM system is used, 3 separate instruments will be needed.

• Avalanche Photon counting has its problems too: as the count rate reduces, the number of detectors becomes large.

• No work is being done on the APD method.


Photon Production and the Abort Gap Monitor

Calculated photon production (450-900nm) : 0.0014 photons/proton at the extraction mirror (…& ions?)

At injection energy, abort level is now x700:60p/ps x 700 = 5.88^6 photons/100ns/turn = 6 10^9 photons / 100ms integration

The 7TeV abort level remains at 60p/ps: 840 000 000 photons/integrated over 100ms=0.3nJ signal (n.b.this is corrected from the value given in talk, the D3 bending magnet is more efficient at 7TeV)

From this must be taken transmission losses, detector efficiency(10%), bandwidth(1%), background noise…


Abort Gap monitor is important machine operating instrument; needs simple robust solution. A separate instrument is considered.

2003: LARP priority for LPM reduced, no funding given (no work done)LBNL team concentrates on Luminosity.

2004: LDM priority raised: ¾ FTE available for LPM+AG (no material)

Priorities now set: 1/ Abort Gap monitor2/ Luminosity3/ LPM (R&D tool?)

To increase the reliability/availability and performance of the AG and LPM, separate, warm undulators are considered, cost and initial design for March ‘04


AG Tests at the ALSAG Tests at the ALS

Bunch spacing 2 ns

Bunch width ~50 ps

“Camshaft” pulse

328 RF buckets276+1 filled

~120 ns gap

(LHC parameters)

(2808/35640)

(280-620 ps)

(2.5 ns)

(3.3 µs)


Hamamatsu R5916U-50 Photomultiplier Tube

Gate min. raise time: 1 ns <2.5 ns RF bucket spacing

Gate voltage: 10 VLow voltage switching required

Gain at –3.4 kV: 106

High gain

< 10 dark counts/secLow noise

Max duty cycle: 1%100 ns -> 100 kHz max sampling rate -> 3 ms to measure entire abort gap (w/o integration)


(Pockels cell)

MCP-PMT experimental setup (present)

SROCHamamatsu

Streak Trigger Unit

HP8114A Pulser

MCPPMT

Visible Light

Stanford DG535Delay

1.5 MHz ~100 kHz

10 V Gate

Hamamatsu C3360HV

-3 kV

Tektronix TDS754D


Camshaft

Parasitic bunchRegular bunches

Empty buckets (gap)


Gate signal on

Parasitic bunch

Gate signal on

Parasitic bunches

Gate signal delayed 28 ns


The Situation 12/03:

Tests to establish Sensitivity and Dynamic range of MCP-PMT…answers for Chamonix?

Studies to establish reliable AG design: accessibility, few interventions

AG data needed for warm undulator design.

More effort should be available in 2005/6 for LPM system: technology choice still open but time very short.

sch: leade lpm+ag 15/12/031 non intercepting diagnostics based on synchrotron light from a bending...

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