1) Introduction 2) GEANT simulations 3) NEW DESIGN 06.06.08: Technology and Assembly

1) Introduction 2) GEANT simulations 3) NEW DESIGN 06.06.08: Technology and Assembly 4) Conclusions

Report by G.Feofilov proposed for the CBM meetings in Dubna -19-22 May 2009 and in Karelia -01-03June 2009

• We present the results of the GEANT model simulations and the technical design of the He-beam pipe for the NA61 installation at CERN proposed to minimize the delta-electrons production in the sensitive volume.

• These results[1,2] could be interesting for the future CBM@FAIR experiment.

[1] G.Feofilov, S.Igolkin, V.Kondratiev,” Beam pipe for NA49-future VTPCs”, report by G.Feofilov at the NA49-future meeting 24.03.07, CERN

[2] G.Feofilov, S.Igolkin, V.Kondratiev,” Beam pipe for NA61 VTPCs: Secondaries and optimization of design”, reported by G.Feofilov at the NA61 meetings 28.10.08, CERN

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1) Disassembly or change of position of VTPCs must be avoided in order to preserve the currently well know alignment of chambers. Thus only the in-site work with VTPCs on the beam-pipe installation is possible.

2) Thin large area mylar windows of VTPCs could not be replaced in the in-site conditions, so the existing films should be preserved.

3) “Clean-room” conditions are to be met in all possible beam pipe assembly operations keeping the inner volume of the VTPCs in safety.

4) Beam pipe materials and performance should not have any influence on the VTPC gas quality

5) Minimum mass requirement is a general VTPC design request: in case of the beam pipe it claims the limitation on the radiation length of all new structures to be below the radiation length of the working gas.

6) Separate N2 gas feeding system for the beam pipe protective layer7) Double sided fixation on the mylar windows8) 8) Non-conductive materials in the VTPS volume9) Minimal influence on VTPC performance due to the interaction of secondaries with material

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Delta-electrons produced in the beam-gas interactions between split field cage area inside the VTPCs could easily “leak” to the active area, piling up and forming

an unnecessary permanent background

(see more details in the reports by S.Igolkin,V.Kondratiev, G.Feofilov at the NA49-future meetings 24.08.06, CERN; 24.03.07, CERN; and NA61 meetings 30.10.07, CERN; 26.01.08, EVO-CERN)

Question: are there any other factors besides this beam-gas interactions ?

Fig.1. GEANT simulation of delta-electrons in VTPCs produced by Pb ions of 158 AGeV for the usual NA49 layout (100 events).

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1) Vacuum thin wall glass fiber (kevlar) beam pipe

2) Helium filled thin wall pipe3) The final – the 3rd solution

[1]: report by G.Feofilov at the NA49-future meeting 24.03.07, CERN

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Initially two main technically feasible options of the self-supported beam pipe were considered to be placed between split field cage area inside the VTPC. 2 mylar (beam input and output) windows are used. Both options are similar in the design and in the mounting procedure and are using the same interface to the VTPC gas envelope:

(i) vacuum thin wall rigid glass fiber (kevlar) rigid beam pipe and

(ii) helium filled thin wall (mylar) beam pipe.

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Benefits: Rather poor vacuum is sufficient. GEANT simulation results show considerable decrease in

delta-electrons produced by beam particles even under 0.1 bar pressure inside the tube.

Insulated glass fiber tube has no influence on the VTPC performance (no distortions of the drift filed, no contamination of the VTPC gas).

Problems: However, the mechanical stability of the beam pipe

requires (even for the poor vacuum) a certain thickness of the beam pipe wall: the last one depends on the pipe diameter. It could be about 2mm for the beam pipe of 70mm in diameter. Thus the amount of material is certainly more if compared to the next option proposed: Helium filled thin wall pipe.

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Benefits: normal pressure It is really a low mass design (125

mkm mylar wall thickness)

Problems: helium leaking to the VTPC gas volume

?…so, the 3rd solution was proposed for

the analysis…

-> “And the winner is: …………………“

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Technical design. The general design of the main beam-pipe/gas-envelope

interface unit and the double-wall 125 mkm mylar He-filled beam-pipe with protective N2 gas layer is presented on the Fig.3.

The main inner beam pipe is formed by the ultrasonic welding of 125 mkm mylar sheet and then the ends of the pipe are glued to the low mass glass fiber short cylinders with mylar windows. These input/output windows for the beam particles provide also the hermetic volume for helium.

The beam-pipe/gas-envelope interface unit (Fig.3.) is the multifunctional module that provides a number of important functions: low-mass support and beam pipe fixation, separation of gases, hermetic sealing.

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Fig.3. General view of the main beam-pipe/gas-envelope interface unit and the double-wall 125mkm mylar He-filled beam-pipe.

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Extremely lightweight Technically feasible Satisfies all demands Installation procedure is well understood

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The VTPCs are filled with the usual working gas mixture (Ne+CO2) and are separated by the air-gap or by the He-bag.

Both VTPCs are placed in the box-shaped magnetic field of 1.5 and 1.1T (for 160 AGeV In beam and 16 times lower in case of 10 AGeV beam).

Different gases were used for the gas volumes inside the beam pipe and in the gap.

Tracks and spectra of delta-electron tracks produced by the In ion beam particles in their interactions with the gas inside the VTPCs volumes and in the gap between 2 chambers were obtained (see some samples below on the Fig..

Summary of the results for major cases are presented in the Table.1.

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.

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Fig.5 (In115, 160 AGeV, He in the beam pipe, Air – between VTPCs

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Fig.6(10 AGeV, He -in the beam pipe, Air – between VTPCs

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E=160A GeV

E=160A GeV

E=160A GeV

E=40A GeV

E=40A GeV

E=40A GeV

Type of gas in VTPC volumes

Beam pipe

VTPC1 VTPC2 Beam pipe

VTPC1 VTPC2

NeCO2+Air

133 8 10 125 41 59

He+Air 51 5 7 12 16 49

NeCO2+He

95 3 4 90 33 40

He+He 16 1 1 15 5 6

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Geant simulations show considerable (8 to 10 fold) reduction of number of delta-electron tracks produced by In ion beam particles in their interactions with the gas inside the VTPSs volume in case of a simple He-based solution for the beam pipe in combination with N2 protective gas layer.

The technical feasibility of the given proposal is presented and discussed in detales below.

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[2] G.Feofilov, S.Igolkin, V.Kondratiev,” Beam pipe for NA61 VTPCs: Secondaries and optimization of design”, reported by G.Feofilov at the NA61 meetings 28.10.08, CERN

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HISTORY: General view of the main beam-pipe/gas-envelope interface unit and the double-wall 125mkm mylar He-filled beam-pipe. Non-conductive plastic is applied (DESIGN 20.01.08)

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HISTORY: 3D view of support unit (DESIGN 20.01.08)

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One central Pb-Pb collision(HIJING): E = 158A GeV, impact parameter - 2.1 fm, number of all particles in a given event – 2698.GEANT: Support unit ,Ls=6cm, material – Al (COMMENT: this Al ring of 4.5 cm in diameter, 1 cm thick, L=6cm, is used for a start in order to get a proper initial reference)

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One central Pb-Pb collision(HIJING): E = 158A GeV, impact parameter - 2.1 fm, number of all particles in a given event – 2698.GEANT: Support unit, Ls=2cm, material – CH2,

ParticlesNumber of particles entering

TPC1-only working

volume! -without a

ring

Number of particles entering TPC1

with Al ring including extras due to

interaction of all secondaries with TPC material (gas, walls.

Etc.)

Number of

particles entering TPC1

with CH2 ring

w=6cm

Number of particles entering TPC1 with CH2 ring

w=2cm

e+ 9 51 25 12e– 7 78 26 16π0 2 2 5 2π+ 328 334 332 332π– 364 383 363 364K+ 35 35 35 33K– 21 18 17 19n 88 103 97 89p 109 114 109 109

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Summary of GEANT SIMULATIONS Al ring, 6cm vs CH2 ring, 2cmOne central Pb-Pb collision: E = 158A GeV, impact parameter - 2.1 fm, total number of all particles in given event – 2698.Support ring: r1=3.5cm, r2=4.5cm, w=6cm ,(Al) vs.Support ring: r1=3.5cm, r2=4.5cm, w=2cm (CH2 )Some electron spectra were shown above

New materials : AIREX+thin CH2layerRadiation length of AIREX: Xo=1380 cm (see the table on the next slide)

New design: the lightest support structureNew Technology

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General view of the main beam-pipe/gas-envelope interface unit (AIREX+CH2) and the double-wall 125mkm mylar He-filled beam-pipe. (DESIGN 06.06.08)

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ParticleNumber of particles entering

TPC1 without a pipeNumber of particles

entering TPC1 with CH2 pipe and CH2

support ring w=2cm(density =1.4 g/cm3

Xo=28.7cm)

Number of particles entering TPC1

with CH2 pipe and

AIREX support ring

(density =0.03 g/cm3 Xo=1380cm)

e+ 9 12 Still to be done/ although the influence

is expected to be negligible

e– 7 12 -π0 2 2 -π+ 328 335 -π– 364 374 -K+ 35 36 -K– 21 16 -n 88 94 -p 109 109 -

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Geant simulations show considerable (8 to 10 fold) reduction of number of delta-electron tracks produced by In ion beam particles in their interactions with the gas inside the VTPSs volume in case of a simple He-based solution for the beam pipe in combination with N2 protective gas layer.

The technical feasibility of the given proposal is presented. New material (AIREX) is proposed in order to minimize the contribution to the production

of electrons by secondaries interacting with the material of the NA61 VTPC He-beam pipe and support units

New technology provides the lightest support of the He-filled double-walled 125mkm mylar structure that meets all 9 NA61 Constraints

(see Slide No.3).

4) CONCLUSIONS

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