1.  1) Introduction  2) GEANT simulations  3) NEW DESIGN 06.06.08: Technology and Assembly  4) Conclusions Reported by G.Feofilov, CBM meetings, Dubna -19-22 May 2009 and Karelia -01-03June 2009

2. 10.06.2016 2

3. 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 10.06.2016 3

4. 4

5. 5

6.  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). 10.06.2016 6

7. 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 mylar 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 7) Double sided fixation on the mylar windows 8) 8) Non-conductive materials in the VTPS volume 9) Minimal influence on VTPC performance due to the interaction of secondaries with material 10.06.2016 7

8. 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. 10.06.2016 8

9. 9

10. 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 introduced into the sensitive volume is not negligible. 10.06.2016 10

11. Benefits:  normal pressure  It is really a low mass design (125 mcm mylar wall thickness) Problems:  helium leaking to the VTPC gas volume ? …so, the 3 rd solution was proposed for the analysis… -> “And the winner is: …………………“ 10.06.2016 11

12. Technical design.  The general design of the main beam-pipe/gas-envelope interface unit and the double-wall 125 mcm 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 mcm 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. 10.06.2016 12

13. 10.06.2016 13 Fig.3. General view of the main beam-pipe/gas-envelope interface unit and the double-wall 125mcm mylar He-filled beam-pipe.

14.  Extremely lightweight  Technically feasible  Satisfies all demands  Installation procedure is well understood 10.06.2016 14

15.  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. 10.06.2016 15

16. 10.06.2016 16.

17. 10.06.2016 17 Fig.5 (In115, 160 AGeV, He in the beam pipe, Air – between VTPCs

18. 10.06.2016 18 Fig.6 (10 AGeV, He -in the beam pipe, Air – between VTPCs

19. 10.06.2016 19

20. 10.06.2016 20 =160A GeV E=160A GeV E=40A GeV Type of gas in VTPC volumes Beam pipe VTPC1VTPC2Beam pipe VTPC1VTPC2 NeCO2+ Air 1338101254159 He+Air5157121649 NeCO2+ He 9534903340 He+He16111556

21.  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. 10.06.2016 21

22. 10.06.2016 22 [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

23. 10.06.2016 23 HISTORY: General view of the main beam-pipe/gas-envelope interface unit and the double-wall 125mcm mylar He-filled beam-pipe. Non-conductive plastic is applied (DESIGN 20.01.08)

24. 10.06.2016 24 HISTORY: 3D view of support unit (DESIGN 20.01.08)

25. 10.06.2016 25

26. 10.06.2016 26 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)

27. 10.06.2016 27 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,

28. Particles Number 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+e+ 9512512 e–e– 7782616 π0π0 2252 π+π+ 328334332 π–π– 364383363364 K+K+ 35 33 K–K– 21181719 n881039789 p109114109 10.06.2016 28 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

29. 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 10.06.2016 29

30. 10.06.2016 30

31. 10.06.2016 31 General view of the main beam-pipe/gas-envelope interface unit (AIREX+CH2) and the double-wall 125mcm mylar He-filled beam-pipe. (DESIGN 06.06.08)

32. 10.06.2016 32

33. 10.06.2016 33 Particle Number of particles entering TPC1 without a pipe Number 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+e+ 912 10 e–e– 712 11 π0π0 22 8 π+π+ 328335 329 π–π– 364374 349 K+K+ 3536 27 K–K– 2116 26 n8894 105 p109 93

34. 10.06.2016 34  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 125mcm mylar structure that meets all 9 NA61 Constraints (see Slide No.3). 4) CONCLUSIONS

35. 10.06.2016 35