Gas jet based fluorescence profile monitor for
low energy electrons and high energy protons
at LHC
Ondrej Sedlacek

On behalf of Beam Gas Curtain collaboration

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Outline◉ Introduction to a Gas Jet Monitor○ Motivation - Hollow Electron Lens
○ Working principle○ Space-charge & gas thickness broadening◉ Gas jet profile measurements◉ Results○ Electron Beam Test Stand○ Large Hadron Collider◉ Summary

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The International Beam Instrumentation Conference, 2023 Saskatoon, Canada2

Hollow Electron Lens◉

Proposed new stage of LHC collimation system◉

10 keV, 5 A hollow electron beam

Courtesy of A.Rossi

LHC Beam core experiences no field

Beam Halo experiences
nonlineartransverse kicks
Shiltsev, et al. ;BEAM06,CERN2007-002 EPAC08

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The International Beam Instrumentation Conference, 2023 Saskatoon, Canada

3Working principle of Gas Jet Monitor◉Particle beam passing through gas -> fluorescence○ Lower cross section than ionisation○ Not affected by EM depending on gas species○ Used in Los Alamos, PSI, GSI, CERN, J-PARC,…
■■◉

D.P. Sandoval et al., BIW'93 p. 273
I. Yamada et al., PRAB 24, 042801 (2021)

Gas Jet monitor - Beam Gas Curtain (BGC)○ Supersonic sheet of gas○ 45° angle -> 2D transverse distribution○ Minimally invasive to particle beam
○ High gas curtain density○ Low background pressureslogoarea

The International Beam Instrumentation Conference, 2023 Saskatoon, Canada

4Creating Gas Curtain
3rd skimmer

Imagining system

2nd skimmer
1st skimmer
Gas curtain
generation section

Interaction
chamber

NozzleInsertable target

4th skimmer

Gas curtain
direction

Alignment laserBeamdirection
Dump chamber◉ Gas curtain formed by skimmers◉ Passing through beam
◉ Fluorescence photons◉ Pumped out in dump chamber◉ Keeping low background pressure

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The International Beam Instrumentation Conference, 2023 Saskatoon, Canada

5Beam gas curtain monitor at Cockcroft InstituteImagining system

Gas curtain
generation section

Interaction
chamber

Insertable target

4th skimmer

Gas curtain
direction

Alignment laser

Beamdirection
Dump chamber

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Optical system
Intensified camera(2-stage MCP)
Optical filter

Apochromatictripletlogo
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Optical system
Intensified camera(2-stage MCP)
Optical filter

Photon counting or Averaging

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Apochromatictriplet

InsertabletargetThe International Beam Instrumentation Conference, 2023 Saskatoon, Canada

8Working gases
Neon

Nitrogen

λ [nm]

585.4

391.4

10 keV e⁻ σ [cm²]1.4e-209.1e-19

6.8 TeV p σ [cm²]4.7e-223.7e-20

electron beam
5 keV, 0.66 mA

Appl. Phys. Lett.. 2022;120(17).
doi:10.1063/5.0085491

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The International Beam Instrumentation Conference, 2023 Saskatoon, Canada

9Space-Charge effect
Neon

Nitrogen

λ [nm]

585.4

391.4

10 keV e⁻ σ [cm²]1.4e-209.1e-19

6.8 TeV p σ [cm²]4.7e-223.7e-20

Transition

NeutralCharged

τ [ns]

1660

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Virtual-IPM Simulations
LHC bunchSpace-charge effectN₂ curtain

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10Gas jet profile

Appl. Phys. Lett.. 2022;120(17).
doi:10.1063/5.0085491◉ Moveable pinhole○Jet pressure sampling

N₂logoarea

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Gas jet profileNe◉ Moveable pinhole○

Jet pressure sampling◉ Ne/N₂ shape - constant◉ Ne/N₂ density ≈ 2.9
N₂logoarea

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12Gas jet profile
N₂, 0.3 x 9 mm

◉ Moveable pinhole○

Jet pressure sampling◉ Ne/N₂ shape - constant◉ Ne/N₂ density ≈ 2.9◉ 3rd skimmer - thickness, density○

Signal amplitude○

Vacuum background○

Thickness broadeninglogo
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N₂, 0.7 x 9 mm

The International Beam Instrumentation Conference, 2023 Saskatoon, Canada

13Thickness broadening◉

Signal vs Broadening tradeoff◉Thickness d = 830(20) μm
Uniform gas curtain
Gaussian beamAppl. Phys. Lett.. 2022;120(17).
doi:10.1063/5.0085491

logoareaThe International Beam Instrumentation Conference, 2023 Saskatoon, Canada

14Electron Beam Test Stand (EBTS)◉◉

Development of Hollow electron beam
Typically: 7 keV, 1.1 A, 25 𝜇𝜇s pulse, 10 Hz
repetition rate
Interaction chamberPressure [mbar]

Gas Jet OFF

4.71e-8

0.7 x 9 mm 3rd skimmer

2.04e-7

0.3 x 9 mm 3rd skimmer

8.63e-8logo
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EBTS: Profile measurements
7 keV, 1.1 A

Background

Beam int. time: 2 sN₂Background gas
interaction

e⁻ beam

Gas curtain
interaction

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Gas curtain
The International Beam Instrumentation Conference, 2023 Saskatoon, Canada

16EBTS: Gas species◉◉◉

Distribution shape - Constant○ Low charge density - negligible
space-charge effect for N₂
Centre of Mass - ConstantN₂ - Best resolution

7 keV, 1.1 A

Beam int. time: 2 sN₂e⁻ beamNeAr

Vertical profiley [mm]logo
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EBTS: OTR comparison◉◉◉◉OTR - Glassy carbon screen
Distribution shape - Compares
Outer radii - Agree within 1%
Inner radii - Agree within 5-10%

Vertical profile

7 keV, 1.1 A

BGC: N₂

Radial profile
Beam int. time: 2 sOTR

y [mm]

r [mm]
Beam int. time:
0.25 us

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Gas jet installation at LHC◉Gas jet monitor successfully installed at LHC in January of 2023!!

◉Huge effort and success for the whole collaboration

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2022

Optical system

Gas jet monitor at LHC
Point 4C5L4.B

Windowflange

Beam 1

Distributed gas
injection

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2023

Interaction chamberPressure [mbar]

Gas Jet OFF

2.0e-10

Gas Jet On

4.00e-8

Gas jet pressure eq.

≈3.30e-6◉ Validated transparent
for standard LHC
beam

Gas curtain
dump

Gas curtain
injection

The International Beam Instrumentation Conference, 2023 Saskatoon, Canada20

Fi r st Gas Jet fluor escencemeasur ement s at LHC at 6.8 TeVParameters
Beam Energy [TeV]Beam intensity [p]Gas jetIntegration time [s]Background

6.8
2.2e14
Ne1659Background gas
interaction

Proton beamGas jet interaction

Gas curtain21

Di ffer ent i nt egr at i on t i mes

Profile measurements

Centroid measurements

10s

1min

5min

SNR ≈ 14.7

SNR ≈ 35.7

SNR ≈ 62.0

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Fi r st Gas Jet fluor escencemeasur ement s at LHC at 450 GeV
Background

Parameters
Beam Energy [GeV]450

Beam intensity [p]3.7e14

Gas jet

NeIntegration time [s]239

Background gas
interaction

Proton beamGas jet interaction

x [mm]

Gas curtain

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Summary◉ Beam Gas Curtain monitor, a 2D profile monitor utilizing fluorescence of supersonic gas jet◉ Gas curtain density profile shows good transverse uniformity for Neon and Nitrogen curtain◉ Varying 3rd skimmer lowers background and resolution significantly◉ BGC monitor measured a hollow electron beam on Electron Beam Test Stand○Beam profile and centroid using N2, Ne, and Ar gas curtain in agreement◉ BGC monitor measured installed and validated at LHC○First gas jet measurements of 6.8 TeV proton beam!

○Further systematic studies will be performed in near future and published accordinglylogoarea24

Thank you for your attention!
ondrej.sedlacek@cern.ch

Work presented on behalf of the BGC collaboration:
O. Sedlacek12, M. Ady2, A. R. Churchman2, P. Forck3, T. Lefevre2, S. Mazzoni2, M. Sameed2, O. Stringer1, A. Rossi2,
G. Schneider2, C. Castro Sequeiro2, K. Sidorowski2, S. Udrea3, R. Veness2, A. Webber-Date, C. P. Welsch1, H. D. Zhang1,1 Cockcroft Institute and University of LIverpool, UK 2 CERN, Geneva, Switzerland

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3 GSI, Darmstadt, Germany