Radiation study of the TPC electronics

1. Radiation study of the TPC electronics Georgios Tsiledakis, GSI

2. Topics • Radiation transport code (FLUKA) • Geometry description • Definition of the suitable scoring region • Calculation of the number of the particles and their energy distributions defining the left end-plate of the TPC made of 1cm and 10cm Al respectively • Estimation of the particle fluences • Summary

3. Simulation code (FLUKA) • Hadron-hadron and hadron-nucleus elastic and inelastic interactions 0-20 TeV • Electromagnetic and muon interactions 0-100 TeV (pair production and bremsstrahlung, multiple coulomb scattering and magnetic field transport, delta ray production) • Particle transport: all stable hadrons, electrons, positrons, muons, photons • Neutron multigroup transport and interactions 0-20 MeV • Neutron capture reactions with explicit photon emission • Accurate and detailed ionization energy loss • Efficient model for multiple scattering for all charged particles For this study, the transport cut for charged hadrons is set to 10 keV. The energy thresholds for electrons and photons that are used in central detectors are 50 keV and 30 keV respectively.

4. Geometry description FLUKA uses the Combinatorial Geometry. About 3200 volumes and 1500 regions are needed to describe the full ALICE experimental area, including the cavern, tunnels, vertical shafts, rooms, shielding, inner triplet and separation dipoles, the surrounding hall, beam elements, detectors and racks. Particle backscattering from concrete walls of caverns and shafts is taken into account by approximating the walls by a 30 cm layer of concrete. Regions behind this layer are treated as black-holes.

5. TPC gas volume: 79.25<r<278 cm and |z|<275 cm TPC gas: (90% Ne + 10% CO2) Wgttot=0.9MNe+0.1*(MC+2MO) There is a correspondence between FLUKA materials and low-energy neutron cross-sections. FLUKA low-energy neutron library doesn’t include Neon. Therefore, Fluorine has been chosen instead.

6. 4 radial segments of 1cm width for scoring (-297<z<-296) Scoring region 278.17 227.2 177.2 127.2 77.2 Air Al TPC gas 4 3 2 1 • 10cm of Al • (-285<z<-275) • or • 1cm of Al • (-276<z<-275) -296 -285 -275 -77.2 -127.2 -177.2 -227.2 -278.17 Al Air TPC gas 1 2 3 4 [cm]

7. 4 scored layers of air

8. 1 FLUKA event: 80000 pions and kaons (HIJING) are propagated in the ALICE geometry at |eta|<5 In this study 5 fluka runs have taken place for 16000 primaries each run and after merging we had one central event in total, with 1cm and 10cm of Al respectively. Estimation of particle numbers • The radiation is strongly correlated • to the total number of produced • particles. • Use of a “current” estimator for • counting particles from a boundary • crossing scoring on each of the 4 • layers apart that form the scoring • region. [cm] Scoring region [cm]

9. Energy spectra 1cm Al Thermal neutrons ~0.025 eV

10. Energy spectra 98.5 % p 99.9 % p+/-,k+/- E>10MeV 99 % m+/- 4.1 % n 72 % e+/- with E>0.5 MeV 1cm Al 98.7 % p 99.9 % p+/-,k+/- E>10MeV 98.5 % m+/- 6.5 % n 93.9 % e+/- with E>0.5 MeV 10cm Al

11. Number of particles per central event 1cm Al10cm Al Multiply with 4*1010to get the number of particles traversing a layer in 10 ALICE years of Pb+Pb. [(8000 Hz)*(10 years)*(2.5 *106 sec/year)/(5 :to get from central to min bias multiplicity)]

12. Number of particles per 10 ALICE years 1cm Al

13. Number of particles per 10 ALICE years 1cm Al

14. Number of particles per 10 ALICE years 10cm Al

15. Number of particles per 10 ALICE years 10cm Al

16. Z distribution of protons origin in the scoring region Counts 1cm Al 10cm Al Zv (cm) Most of the primary protons are stopped in the 10cm Al end-plate and a significant slow proton production start

17. Particle fluxes and fluences "Flux" counts the rate of arrivals per unit area indepedent of particle direction and its real physical meaning is that of path density, whereas "current" counts the rate crossing through a given plane, referred to area elements in the surface of the plane. In FLUKA, flux is defined as the track-length of a particle per unit of volume and its unit can be expressed as (cm-2 s-1) and fluence is the time integral of flux expressed in units of (cm-2). The results of the FLUKA tracklength estimator are always given as differential distributions of fluence in energy (cm-2 GeV –1 ) per primary. The following plots are designed to allow visual integration of fluence having the areas under the curves proportional to the fluence (lethargy spectrums).

18. 1 cm Aluminum dΦ/dE * E Particles/cm2/primary layer 1 Cumul. Fluence (Particles/cm2/primary) per central event total:1.134e-05 +/- 2 % thermal:1.687e-06 layer 1 Energy (GeV)

19. 1 cm Aluminum dΦ/dE * E dΦ/dE * E Particles/cm2/primary Particles/cm2/primary layer 1 layer 3 Energy (GeV) Energy (GeV) layer 3 Cumul. Fluence (Particles/cm2/primary) per central event total:1.22E-06 +/- 7 % layer 1 Cumul. Fluence (Particles/cm2/primary) per central event total:8.91E-06 +/- 45 %

20. 1cm Al dΦ/dE * E 10cm Al dΦ/dE * E Particles/cm2/primary Particles/cm2/primary layer 1 layer 1 Energy (GeV) Energy (GeV) Cumul. Fluence (Particles/cm2/primary) per central event 1.66E-7 +/- 6 % 1.87E-7 +/- 9 %

21. Cumul. Fluences (Particles/cm2/primary) per central event 1cm Al Multiply with 3.2*1015 to get the cumulative fluences for each layer in 10 ALICE years of Pb+Pb. [(80000 primaries) *(4*1010)=3.2*1015]

22. Cumul. Fluences (Particles/cm2/primary) per central event 10cm Al Multiply with 3.2*1015 to get the cumulative fluences for each layer in 10 ALICE years of Pb+Pb. [(80000 primaries) *(4*1010)=3.2*1015]

23. Cumul. Fluences (Particles/cm2) per 10 ALICE years 1cm Al

24. Cumul. Fluences (Particles/cm2) per 10 ALICE years 1cm Al

25. Cumul. Fluences (Particles/cm2) per 10 ALICE years 10cm Al

26. Cumul. Fluences (Particles/cm2) per 10 ALICE years 10cm Al

27. Total and EM energy deposition in these 1cm thick layers of air per one central event To obtain doses (in Gy) these results must be multiplied by (109*e/rho) , where rho is the material density in g/cm3 and e the electron charge in Cb (rhoair=1.2E-3)

28. Summary The cumulative fluence of neutrons as well as of charged particles is expected to be of the order of 1010 particles/cm2 per 10 ALICE years The results of this simulation concerning the particle rates, fluences and energy distributions should be taken into account for checking the radiation tolerance of the electronics

29. FLUKA calculation of the slow proton production in the TPC with the standard gas and after the addition of 5% Methane

30. Calculation of the slow proton production in the TPC • Use of a “current” estimator for counting particles. • Take into account only the first “hit” position in the TPC. • Include all the “unique” protons that are crossing or are • created in the TPC region. Counts Radial distribution of protons origin in the TPC TPC gas volume: 79.25<r<278 cm and |z|<275 cm TPC gas: (90% Ne + 10% CO2) Wgttot=0.9MNe+0.1*(MC+2MO) New TPC gas: (85% Ne + 10% CO2 + 5% CH4) Rv (cm) Proton energy spectra Proton time spectra Counts Counts TPC gas with 5% CH4 TPC gas Log10(Age) (sec) Log10(Ekin) (GeV)

31. Conclusions • Prompt neutrons can scatter on H(due to the presence of 5% CH4 in the TPC gas) and produce a knockout proton background. • Each slow proton deposit on average ~ 1.1 MeV having ~2 cm tracklength • The additional energy deposition in the TPC due to them should be less than ~3.5% • Slow protons/mip~270