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Beam-plug and shielding studies

related to HCAL and M2

Robert Paluch, Burkhard SchmidtNovember 25, 2014

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Outline• M2 beam plug:

– Modifications to the beam-plug around M2– Impact on performance– Reminder: Low energy background not considered in these studies,

done with nominal thresholds.

• HCAL beam plug:– Clearance towards the beam pipe around the HCAL beam plug.– Impact on performance on suggested modifications.

• Overall performance of modified or additional shielding.

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Simulation results• Simulation parameters and configuration:

– Gauss version v42r2– detector description dddb-20120831– detector condition sim-20121025-vc-md100– beam configuration file Beam3500GeV-md100-MC11-nu2-50ns.py– beam energy 7 TeV– luminosity per coll. bunch 2.47 x 1029/cm2/s– total luminosity 3.13 1032/cm2/s

Still problems in using the official beam configuration file for 7 TeV, and 25ns bunch spacing and a ν-value of 7.6

• The average track multiplicities/cm2/s refer always to particles leaving up to 4 hits in a chamber, depending on their angle (no double counting of hits coming from the same track).

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Track multiplicities with the layout we had in Run I for the M2 beam-plug

6752 11984 13237 5392

15099 15163

18848 16677

5525 9504 8395 5493

• The track multiplicities vary by a factor three, depending on the chamber position. (The uncertainty on the values given is about 2%.)

• The chambers left and right from the beam-plug have the highest rates (effect of the magnet), as expected: – Left/right: < 16447 > top/bottom: < 10780 > corners: < 5791 >

• The chamber closer to HCAL have a 20% higher rate:– Front row chambers: < 12148 > back row chambers: < 9863 >

A-side C-side

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Effect of adding a plate of 2cm iron in front of M2 R1/R2

-3% 6% -3% 7%

6% 13%

-7% -4%

-11% -7% -15% -2%

• The changes in track multiplicities are larger than expected. • However, the overall reduction is small (~1%).• The rate goes down in the front row chambers, as expected :

Front row chambers: < 11915 > -2% ; back row chamber: < 9898 > +0% The variations in the back row chambers are very large, from +13% to -15%.

This is not understood! The idea has not been followed up.

A-side C-side

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Piece cut out

Small Openings

~12cm

~3cm

~9cm

M2 beam plug

Description of beam-plug and beam-pipe in the simulation

Besides the outer dimension of the plug (which is important!), we are basically back for Run II where the MC description has been for Run I. We learned about the measures necessary to take in order to modify an irradiated piece of iron. To be kept in mind for the future. 7

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Effect of filling the openings in the M2 beam-plug

1.5% -4.6% 8.1% -4.1%

-1.7% 0.8%

-1.7% -3.5%

-3.6% -2.0% 9.4% -0.2%

• The changes in track multiplicities are small, as expected. Overall reduction < 1%.

• The chamber by chamber variations are however larger than expected.• The reason is not really understood. We might need to run with higher statistics

(for time being 4000 events).

Anyhow, the hardware change made to the beam-plug should be beneficial.

A-side C-side

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Studies on the HCAL beam-plug

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HCAL beam plug with beam-pipewhen the calorimeters are closed

• Large clearance between beam-pipe beam plug for both the HCAL and ECAL beam-plugs.

• The reason is mainly that space had been foreseen for the bake-out instrumentation, which is however not permanently installed.

• The beam-plug under M2 goes much closer to the bake-out instrumentation and the beam-pipe.

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HCAL beam plug with beam-pipewhen the calorimeters are closed

• Clearance of 25mm - 45mm between beam-pipe beam plug for both the HCAL and ECAL beam-plugs.

• The HCAL beam-plug has three parts (although it has been molded in one piece). The part close to M2 would need to be modified (in material and in radius).

30mm

~85 mm

45 mm

1. 2. 3.

Summary of simulation results of Oct. 9

• Focus has been recently on last part of the plug in front of M2.

• The 2nd Muon station is not sufficiently protected from background hits– insufficient thickness (λi) of HCAL – showers in the material close to the beam-pipe

• Changes under consideration to reduce the occupancy in M2R1:– Change of material from steel (or lead) to tungsten for HCAL and M2 beam-plug– Additional shielding behind HCAL (replace PMT and CW bases by shielding)

– Max. possible reduction: -55%

-22% (M2 plug)

-25% -43%

HCAL plug: - 15-20%

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Geometry of HCAL beam plug

bellows of the beam-pipe bake out instrumentation

Beam pipe flange M2 plug

• Bake out instrumentation (in orange) clearly visible.• For time being the possibility to reduce the radius of

the last part of the HCAL beam-plug (light blue) is therefore limited

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Simulation results

Effect on M2R1:• Comparison of realistic tungsten shielding

behind HCAL, with no add. shielding – Overall reduction: < -59% >

• Top/bottom: < -53% > ; Left/right: < -65% >Corners: < -48% >

• Front rows: < -60% > ; Back rows: < -56%>

Huge gain in the left/right chambers with the highest rate

-54.5% -54.5% -52.1% -46.0%

-62.6% -59.8%

-69.4% -65.5%

-46.3% -56.8% -48.4% -44.5%

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Conclusions• Effect of openings in M2 beam-plug is minor compared to the

right outer dimensions of the plug. Still, the openings have been closed for Run II with steel plates.

• A reduction of close to 60% can be obtained with a tungsten plug under M2 and part of HCAL, and additional realistic W-shielding behind HCAL.

• The effect of a modified HCAL beam plug with reduced inner radius is large also on the other region (this was not the case previously.

• We will finalize the study in the coming weeks.

Region M2 plug tungsten

M2+add.shield tungsten

M2+HCAL plug + add.shield (W)

M2R1 -22% -43% -59%M2R2 -6% -12% -25%M3R1 -4% -5% -23%M3R2 -1% -6% -14%

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Backup

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HCAL layout

20cm

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HCAL layout• The last 16cm of HCAL (along z), where the PMTs and the CWs

are housed, are easily accessible and can easily be equipped with additional shielding.

• The 20cm (along z) where the wavelength- shifting fibres are bundled, are rather difficult to access, due to the end plate.

• It should be possible to enlarge the area of shielding along x to two HCAL cells (26cm), hence covering all of M2R1 along x.

• In y no changes are envisaged.

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Shielding behind HCAL

PID TDR version Realistic version