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

Delta-electrons suppression and he-Beam pipe for the NA61 VTPC s G.Feofilov , S.Igolkin , V.KONDRATIEV St.Petersburg State University Laboratory of Ultra-High Energy Physics (for NA61 collaboration). 1) Introduction 2) GEANT simulations 3) NEW DESIGN 06.06.08: Technology and Assembly

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

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  1. Delta-electrons suppressionand he-Beam pipe for the NA61 VTPCsG.Feofilov, S.Igolkin, V.KONDRATIEVSt.Petersburg State UniversityLaboratory of Ultra-High Energy Physics(for NA61 collaboration) 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

  2. Abstract • 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

  3. nA61 Collaboration

  4. Constraints on the beam pipe design for VTPCs for NA61 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 layer • Double sided fixation on the mylar windows • 8) Non-conductive materials in the VTPS volume • Minimal influence on VTPC performance due to the interaction of secondaries with material

  5. 1) Introduction • 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 AGeVfor the usual NA49 layout (100 events).

  6. 1.1. Options considered (see [1]): • Vacuum thin wall glass fiber (kevlar) beam pipe • Helium filled thin wall pipe • The final – the 3rd solution [1]: report by G.Feofilov at the NA49-future meeting 24.03.07, CERN

  7. 1.2. Concept considerations. 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.

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

  9. Fig.2. Trajectories of delta-electrons in VTPC-1and 2 for two vacuum beam pipes (at 0.1 pressure)

  10. (ii) helium filled thin wall (mylar) beam pipe. 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: …………………“

  11. 1.3. Technical design: Double wall mylar beam pipe filled with He and containing additional N2 gas protective layer. 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.

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

  13. Features: • Extremely lightweight • Technically feasible • Satisfies all demands • Installation procedure is well understood

  14. 2) Geant simulations: • 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.

  15. Fig.4. In115 beam, 160 AGeV,NeCO2 in the beam volume + air gap .

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

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

  18. Fig.7 (10 AGeV, He -in the beam pipe, +He bag)

  19. Table 1. GEANT-simulations (100 events in each case, two values of the beam energy) of the average number of delta-electrons in the different parts of the VTPCs setup generated by one In115 nucleus along the beam line.

  20. Conclusions for geant simulations • 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.

  21. Upgrade [2] of the initial design of 24.03.07 [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

  22. 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)

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

  24. What isthe contribution to the total Electron production from Secondaries interacting with material - for a given designof 20.01.08 ?

  25. GEANT SIMULATIONS(for the design of 20.01.08) Spectrum of electrons emerging due to the interactions with RING 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)

  26. GEANT SIMULATIONS (for design of 20.01.08) Spectrum of electrons emerging due to the interactions with RING 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,

  27. Summary of GEANT SIMULATIONS Al ring, 6cm vs CH2 ring, 2cm One 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

  28. New materials : AIREX+thin CH2layer Radiation length of AIREX: Xo=1380 cm (see the table on the next slide) New design: the lightest support structure New Technology 3) NEW DESIGN 06.06.08 that meets the requirement to minimize the contribution from the secondaries

  29. 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)

  30. 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

  31. THANK YOU!

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