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TLEP3 How radiation issues could be studied through FLUKA simulations.

TLEP3 How radiation issues could be studied through FLUKA simulations. Possible approaches/mitigation schemes. Alberto Fassò. Compared with present (and future !) times, computing resources for shielding design of LEP 1 and 2 were poor . But radiation studies were successful .

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TLEP3 How radiation issues could be studied through FLUKA simulations.

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  1. TLEP3 How radiation issues could be studied through FLUKA simulations. Possible approaches/mitigation schemes Alberto Fassò

  2. Comparedwithpresent (and future!) times, computingresources for shielding design of LEP 1 and 2 werepoor. • But radiation studiesweresuccessful. • I will show: • what the most important radiation problemswere 30 yearsago • how theyweresolved • which issues willbecome more important at TLEP3 • which of thesewillneedimprovements, not alwayseasy to figure out yet

  3. Three main classes of problems: Protection of the machine (includingelectronics)  the mostcritical! Protection of people  easy, not worsethan for anyother large accelerator Protection of the environment technically not toodifficult to calculatewith modern tools.Very important politically and in order to avoidtoo conservative and costly solutions Mitigation of 1. isproblematic. Mitigation easy for 2., provideddeep underground Mitigation of 3. needsdedicatedstudies

  4. Synchrotron Radiation Criticalenergy: Halfpower belowit, halfabove Proportionalto E3/ r (E=electronenergy, r = bending radius) SR power: proportional to E4 /r

  5. The same SR spectra in lethargyunits Criticalenergy: 51.5 GeV: 97.8 keV 86 GeV: 455.2 keV 100 GeV: 715.7 keV 120 GeV: 1400. keV 1400 716 455 98

  6. Calculations for LEP 1 and 2 SR doses to coils, cables in ring damage SR doses to electronics in alcovesdamage (wouldwenowneedalso hadron fluence for SEU?) SR streaming throughducts and mazes  dose to people O3, NOxproduction  damage, impact on environment Dose rate effects (transients) on pick-ups, sparking in high-tension cables (108 Gy/s!)  damage Calculations2., 3. and 4.were made with MORSE Calculations 1. and 5.with MORSE and EGS3 All couldbedonenowwith FLUKA, withmuch better accuracy

  7. Photon streaming • SR streaming in waveguideducts, in long straight sections to the klystron galleries(ducts: 8m long, 80 cm diameter) • Superconductingcavityradiation streaming in waveguideducts (high-energyphotons) • Thesecalculationswere made with MORSE. • FLUKA of course can do it much better

  8. Example of SR streaming calculatedwith MORSE

  9. An educational report explaining the ozone impact on environment, used in the discussions with local populations Production scalingwithtotal escapingpower

  10. Ozone in the environment: calculated values muchsmallerthanmeasured background, but fierce opposition by some local communes

  11. Beamlossesat LEP 1 and 2 • Injection losses: assumed 1.55×1010 e±/s •  720 mSv/h at 4 m (canbemuchhigher in top-off • mode) • Storedbeamlosses: assumed 1.1×1013e±/s (2×10 mA) lostlocally •  99mSvintegrated dose •  in experiments, 1.20 m concreteequivalent • (280 g/cm2) required in all directions fromloss point • Experiments:assumed to beself-shielded (needs active collaboration between RP and experiment designers) • ShieldinghighenergylosseswascalculatedusingSwanson’s book (noweverythingcouldbedonewith FLUKA)

  12. SWANSON’s BOOK

  13. Calculations for LEP 1 and 2 Neutron production from SR and beamlosses (from SR minimal at LEP, willincreasewithhighercriticalenergies)  dose to people nearductsand mazes Neutron shielding in experimental areas (due to beamlosses)  dose to people Muons in experimentalareas (due to beamlosses)  dose to people Thesecalculationsweredoneanalytically by hand, usingverycrudeassumptions. For calculation8., a muon transport code TOMCATwasalsoused. All could be done now with FLUKA, with much better accuracy

  14. MORSE as used for LEP SR: Multigroup photon transport: 21 g-ray energy groups (max. energy 14 MeV) P3 Legendre angular expansion  only 2 scattering angles ateach collision ) No electron transport (pair production accounted for as scattering to 511 keV group!) Specialscoring and biasingpreparedat CERN (laterbrought to FLUKA…) FLUKA as canbeused for LEP3 SR and beamlosses: Continuous transport of g and electrons up to PeVenergies. Explicit effects: photoelectric, Compton, pair prod., e+ annihilation Photon polarization (important for SR!) Photonuclearreactionsat all photon energies. Photomuon production.

  15. Inducedactivity Lowat LEP 1 and 2 (although important on dumps), but required a big effort atdecommissioning time: M. Silari and L. Ulrici, Investigation of inducedradioactivity in the CERN Large Electron Positron collider for itsdecommissioning NIM A 526, 510-536 (2004) Frombeamlosses, calculated first usingSwanson’s book, with FLUKA later. From SR, negligibleat LEP 1 and 2, will not besoat LEP3. Photonuclearreactions in FLUKA are OK, but cross-sections nearthresholdwillbecritical, and are not all wellknownyet. Photofission possible in Pb.

  16. Alsoinducedactivity

  17. Pb thickness 3 or 8 mm, attenuates power by 98 to 99% Wouldbevery ineffective athigher SR energies!!! How to mitigate? Don’t know: needs new ideas

  18. Photon cross sections Photoelectric dominated Compton dominated Pair dominated Compton dominated Pair dominated Photoelectric dominated p.e.=photoelectric cross section; incoh=Compton cross section; coherent=Rayleigh cross section; nuc=photonuclear cross section; N=pair production cross section, nuclear field; e=pair production cross section, electron field

  19. Radiation Damage Assumedcriterion for acceptability of materials: must survive after 200 Ah at 86 GeV Coilinsulation: glass-fiberreinforcedepoxyresins  Survive at < 108 Gy Cableinsulation: no PVC or otherthatcanproduce corrosive gases (EPR: ethylene-propylenerubber, polyethylene)  survive < 106 Gy

  20. Measured!

  21. Too good to betrue!

  22. Effects on environmentwere minimal, but werecalculated in a verycrudeway (e.g. inducedactivitiescalculated as integrated values over all soilthicknesses). But politically VERY important!!! Veryaccurate and detailedcalculations are now possible with FLUKA, and needed due to the constrainingevolution of legallimits and the excessive cost of a too conservative approach

  23. The RAWOG (RAdiationWOrkingGroup) The LEP radiation studieswereorganized by the RAWOG, in a waythatprovedverysuccessful. Members of RAWOG were radiation physicists, LEP engineers and physicists, and experts fromvariousEuropeanelectronaccelerators (DESY, Frascati, Orsay…) The working group met once everymonth to present and discuss one or two radiation issues. During the comingmonth, radiation physicists made relevant calculationswhoseresultswerepresented and discussed in the nextmonthly meeting. Examples: mazes, klystron galleries, alcoves, vacuum chambershielding…

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