c. fischer – lhc instrumentation review – 19-20/11/2001 gas monitors for transverse distribution...

C. Fischer – LHC Instrumentation Review – 19-20/11/2001

Gas Monitors for Transverse Distribution Studies

in the LHC

LHC Instrumentation Review Workshop

CERN - 19-20/11/2001


ACKNOWLEDGMENTS

•Luminescence

Review on behalf of colleagues involved in the topics :

The Luminescence Profile Monitor of the CERN SPS

G. Burtin, J. Camas, G. Ferioli, R. Jung, J. Koopman, R. Perret, A. Variola, J.M. Vouillot

• Ionisation of Rest Gas J. Koopman, G. Ferioli, M. Sillanoli + others (SL/OP…)


Table of Contents• Introduction

• Luminescence - spectrum - signal vs pressure - decay time - data

• Rest Gas Ionization

- resolution

- reproducibility - sensitivity in current - turn by turn operation • Future• Conclusion• Proposed location in LHC


Introduction

• Why gas monitors in LHC ?

study of transverse distributions in the range

450 GeV 2 TeV - 650 m 1.25 m ( = 200 m) • LHC Emittance workshop in July 2000

2 directions recommended: - Luminescence

- Gas Ionization


Luminescence Profile Monitor

PRINCIPLE Uses the light emitted by gas molecules when they return to their ground state after having been excited by the beam:

Nitrogen is a good candidate: high cross-section,

low decay time, well pumped emits towards lower end of the visible spectrum

N 2 injection

To signalprocessing

CCD

I [MCP]

Beam

400 l/s 400 l/s


Luminescence

At 7 10-5 Pa (5 10-7 torr), the photon production corresponds to the N2

+

spectrum: ~ 60% of the light is within the bandwidth of a 400nm ± 35nm filter.

0.00.10.20.30.40.50.60.70.80.91.0

300 400 500 600 700

Wavelength [nm]

Lig

ht

sig

na

l [a

rbit

rary

un

its

] 200 keV p

1.E+03

1.E+04

1.E+05

1.E+06

1.E-05 1.E-04 1.E-03

Nitrogen pressure [Pa]

PM

T c

ount

s [H

z]

Full spectrum

400 nm ± 35 nm

• The light production is linear with pressure: single step process with short decay time suitable for profile measurements.• The pressure can be used to increase the dynamic range of the detector. The pressure increase is negligible in the SPS: 5% for 6 10-5 Pa (5 10-7 torr) over 3 m

Signal as a function of N2 pressure

Spectrum


Luminescence

• Measurement with Pb ions shows the bunch structure (131 ns) indicating a decay time compatible with the 60ns quoted in literature for low energy protons.

• This should generate negligible image broadening (~50m FWHM)

1

10

100

1000

10000

0 2 4 6 8 10 12 14 16 18 20 22 24

T [µs]

PM

co

un

ts [

KH

z], B

ea

m [

a.u

]

BeamPM counts no filterPM counts 400nm

Decay time as a function of wavelength

•Decay is faster with the 400nm filter than with whole spectrum: afterglow up to 2-4s.

•The batch structure is visible at 400nm.

•The profile measurements should hence be taken with the 400nm filter in place

0%

20%

40%

60%

80%

100%

0 100 200 300 400 500 600 700 800 900 1000

Time [ns]

No

rma

lise

d P

MT

co

un

ts

Decay time


Luminescence – data 1

Single shot (20ms, i.e. 840 turns) vertical profile measurement at 6 10-5 Pa (5 10-7 torr) for 2 1013 p (140 mA) at 450 GeV

3D image

Side view (2D)



Single shot (840 SPS turns) profiles at 8 10-5 Pa ( 6 10-7 Torr) with 9 108 (540 mA)

Pb ionsSingle shot (840 SPS turns) at 6 10-5 Pa (5 10-7 Torr) for 2 1013 p (140 mA) at 450 GeV

= 670 m = 1070 m



• Single shot (20 ms) and statistically processed (10 cycles) measurements for low light density: =4 700 m at 14 GeV at low pressure: 6 10-6 Pa: same result as

for 10-4 Pa.

0 100 200pixels

Sig

nal

0 100 200

Statistical data processing for Increased Sensitivity at 6 10-6 Pa ( 5 10-8 torr)



• Agreement with Wire Scanner as reference monitor– 17% ± 2% (wire scanner 244 m upstreamuncertainty)

• Integration Time ( beam energy “resolution” )

– 20 ms ( 0.8 GeV )• Normalised Sigma to observe V emittance blow-up

0.0

0.5

1.0

1.5

2.0

2.5

0 100 200 300 400E [GeV]

sig

ma

V [m

m]

luminescence

Wire Scanner

2.0

2.5

3.0

3.5

4.0

0 100 200 300 400 500

E [GeV]

n

orm

alis

ed

[m

m]

Luminescence

Wire Scanner

Normalised Vertical sigma (mm)Comparison with Wire Scanner

SPS Fixed Target Cycle


Rest Gas Ionization Profile Monitor


Data Presentation


Profile evolution during SPS cycle

34 GeV 150 GeV 312 GeV

430 GeV 450 GeV 450 GeV


B field effect at 450 GeV100% = 560 G

B=40%

B=100%B=80%

B=60%

Measured RMS beam size versus B-field

400

420

440

460

480

500

520

540

560

580

600

30 40 50 60 70 80 90 100 110

B-field (%)

RM

S b

eam

siz

e (

um

)

B-Field RMS1 RMS2 RMS3 Av. RMS St. Dev. Rel. error% um um um um um %40 573 574 573 573 0.6 0.150 546 546 526 539 11.5 2.160 510 514 515 513 2.6 0.570 502 502 497 500 2.9 0.680 487 489 490 489 1.5 0.390 483 494 485 487 5.9 1.2100 489 488 490 489 1.0 0.2


Resolution

Reproducibility


Comparison Wire Scanner - Rest Gas Monitor

• Rest gas monitor data multiplied by 1.89 (theoretical optics ratio).

• At low energies discrepancies due to dispersive effects at the wire scanner.

• Then agreement within 3 % to 5% ( error of instruments + machine optics ).

Rest gas monitor discriminates variations < < 1 mm.

0

1000

2000

3000

4000

5000

6000

7000

8000

0 50 100 150 200 250 300 350 400 450

Beam energy (GeV)

H d

istr

ibu

tio

n r

ms

val

ue

(u

m)

Wire Scanner

Rest Gas Monitor


Ultimate Resolution with present monitor

• With LHC type beam, ultimate resolution of

present monitor is between

300 m and 400 m

( B = 560 G )

LHC beam , 48 or 72 bunches, 3.5 1010 p to 4.5 1010 p /bunch, 450 GeV

Wire scanner data IPM monitor data

m

m

m

m

WS /IPM=2

OK

WS /IPM=1 NOT OK


• Gaussian fit on data above 30% of maximum.

• Relative errors << 1% in general for rms values << 1 mm.

• Shrinking at 450 GeV due to beam extraction.

Timing Approx.beam energy

rms from gaussian fit1 2 3

Averagerms <>

Standarddeviation s

Relativeerror s/<>

(ms) (GeV) (m) (m) (m) (%)7622 185 1246 1232 1250 1243 9.5 0.88702 280 1030 1027 1028 1028 1.5 0.19742 330 861 892 897 883 19.5 2.2

10942 400 797 794 793 795 2.1 0.312342 450 729 725 727 727 2.0 0.313902 450 674 663 664 667 6.1 0.914302 450 450 489 515 485 32.7 6.5

Reproducibilitythree consecutive acceleration cycles


• Sensitivity in Current


One bunch - 870 SPS turns (20 ms)per profile

2 1010 protons/bunch = LHC pilot * 4


Ionization Profile Monitor

One bunch of 2. 1010 protons = LHC pilot bunch * 4

High resolution mode (870 SPS turns) - P = 10 -8 Torr

One bunch of 6 10 9 protons = LHC pilot bunch


One bunch - 870 SPS turns (20 ms)per profile

• Limit with present monitor is LHC pilot intensity on 870 turns - vacuum: < 10-8 TH2

• S/N ratio : 3 to 4

• Fixed noise pattern from camera (radiation)

• Possible improvements: new camera : noise /5

nominal: few turns - pilot: 100 turns ? at 10-8 TH2


• TURN by TURN Studies (injection , matching)


Rest Gas Ionization Profile Monitor (3)

Batch of 40 »LHC» bunches of 3.5 1010 p. each - 3 mm /strip on 500 turns after injection into SPS

SPS Turn by turn data (43 KHz)-P = 10 -8 Torr

1 mm

H rms value evolution over 100 turnstime

Turn by turn average H position over 200 turns

5 mm


Rest Gas Ionization Profile Monitor (4)One bunch of 3.5 1010 p. - 3 mm /strip - on 200 turns

after injection into SPS

SPS Turn by turn data

Turn by turn H rms value evolution over 195 turns (screen left IN beam)

5 mm


Ionization Profile Monitor– turn by turn data

One batch (72 bunches) of 3.5 1010 p / bunch

32 strips - 1 mm /strip - on 150 turns after injection into SPS

Injection

not matched

Turn by turn H rms value evolution over 150 turns Turn by turn average H position over 150 turns

#150 #170 #180 #200

#230 #250 #270 #300

2 mm

4 mm


Ionization Profile Monitor– turn by turn dataOne batch (72 bunches) of 3.5 1010 p / bunch

32 strips - 1 mm /strip - on 150 turns after injection into SPS

Matched

injection

Turn by turn H rms value evolution over 150 turns Turn by turn average H position over 150 turns

2 mm

4 mm

#150 #170 #190 #210

#230 #250 #270 #290


Future –New IPM monitor installed in SPS (LSS5) next year

• B field *4 (2500 G)

better resolution

R. Perret, EST/ME


Conclusion

• present monitor in SPS gives good results down to rms values of 500 m ( 3 TeV in LHC with = 200 m)

• Can also be used in turn to turn mode: fully passive way of tuning the injection matching

• Expected improved resolution with new SPS monitor


Proposed location in LHC: LSS4

• One H&V monitor upstream D3 separator dipole

quiet region (radiation), large beam separation > 300 mm (integration)

• Suitable optics:

H,V 250 m, 1.4 mm at 450 GeV

RF system

RF system

Q7 Q6 Q5D4 D3 IP4 D3 D4 Q5 Q6 Q7

H&V gas monitor

beam 1

beam 2

c. fischer – lhc instrumentation review – 19-20/11/2001 gas monitors for transverse distribution...

Documents

e 045350closed1387553005302

luminescence gas ionization

gas molecules

luminescence profile

lhc emittance workshop

introductionwhy gas

pressure increase

light production