1 / 17

Backgrounds in heavy-ion operation of the LHC (reminders …)

Backgrounds in heavy-ion operation of the LHC (reminders …). John Jowett With thanks for contributions from: Giulia Bellodi, Roderik Bruce. Present status. Little discussion of backgrounds in HI modes so far, but related subjects treated … we lack “resources”. Can say a few things based on:

newton
Télécharger la présentation

Backgrounds in heavy-ion operation of the LHC (reminders …)

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Backgrounds in heavy-ion operation of the LHC(reminders …) John Jowett With thanks for contributions from: Giulia Bellodi, Roderik Bruce

  2. Present status • Little discussion of backgrounds in HI modes so far, but related subjects treated … we lack “resources”. • Can say a few things based on: • Collision “debris” • Pb-Pb collisions create secondary beams, somewhat different from p-p • Studies of Pb ion collimation • More complicated interactions than p-p, more nuclides • Beam-gas cross-sections

  3. Possible sources (accelerator view) • Collision “debris” • Pb-Pb collisions create secondary beams, somewhat different from p-p • Collimation • Analogous to p-p but more complicated interactions, more nuclides • Beam-gas • Analogous to p-p but more complicated interactions, more nuclides

  4. (some) Ultraperipheral reactions in nuclear collisions Fragments within momentum acceptance of arcs can propagate, may be picked up by momentum collimation.

  5. Nuclides that can circulate in LHC Red shows isotopes that might propagate around inside ring aperture.

  6. Phys. Rev. ST Accel. Beams 12, 071002 (2009)

  7. Main and secondary beams from IP2 Optimal position for one cryo-collimator?

  8. Ion Collimation in LHC • Collimation system essential to protect machine from particles that would be lost, causing magnet quenches or damage • Ions undergo nuclear fragmentation or electromagnetic dissociation in primary collimator before scattering enough • Machine acts as spectrometer: isotopes lost in other locations, including SC magnets • Different simulation technique from protons, ICOSIM program, less statistics • Some losses expected on tertiary collimators, have not seen much on beam pipe near IP so far • ICOSIM does not track light fragments • If the solution of new “cryo”-collimators in dispersion suppressors is adopted, situation will improve a lot.

  9. Physics interactions in collimators Large variety of daughter nuclei, Monte Carlo calculated specific x-sections Mainly loss of 1 neutron (59%) or 2 (11%)  207Pb, 206Pb

  10. Example of 206Pbcreated by 2-neutron EMD • Green rays are ions that almost reach collimator • Blue rays are 206Pb rays with rigidity change

  11. Beam1, betatron collimation E=3.5TeV/A, b* =3.5m, 12min lifetime • aperture hits/S collimator hits= h= 0.033 • losses < 0.5 W/m Max load on TCP.B6L7.B1=122W Some losses before DS ICOSIM results from G. Bellodi

  12. only TCPs at 5.7s Beam1, betatron collimation E=3.5TeV/A, b* =3.5m, 12min lifetime • aperture hits/S collimator hits= h= 0.205 Max load on TCP.B6L7.B1=122.5W ICOSIM results from G. Bellodi

  13. Beam1, momentum collimation E=3.5TeV/A, b* =3.5m, 12min lifetime Max load on TCP.6L3.B1=250W • aperture hits/S collimator hits= h= 0.025 ICOSIM results from G. Bellodi

  14. Possible path for simulations • Use ICOSIM to provide collimation loss patterns at interface plane by analogy with protons • Depends also on collimator settings, energy, b* etc. Need to clarify conditions. • May need longer runs than done up to now to get statistics. • MARS/FLUKA/GEANT/BDSIM simulations • Few input species: 207Pb, … ?

  15. Interaction of Pb ions with residual gas • Losses due to nuclear scattering on residual gases • Atoms in residual gases (6 usual suspects in Design Report for protons) have Z≤8. • For simplicity, discuss only the dominant inelastic nuclear scattering (leave out elastic and electromagnetic contributions, EMD, ECPP which are smaller). Somewhat optimistic! • Dominant beam-gas lifetime:is independent of intensity • Multiple Coulomb scattering on residual gas also causes emittance growth (similar to protons, not treated here). • Lost ions are a heat load:

  16. Pb, Barashenkov Pb, Hard-sphere pA, Hard-sphere pA, Barashenkov Inelastic nuclear cross sections • Cross-sections of proton-nucleus and nucleus-nucleus inelastic interactions at ~10 GeV/n, assumed similar at 2.75 TeV/n (as is the case for protons) • Simple formula, V.S. Barashenkov, 1993 Comparison with earlier Hard-sphere overlap model (Bradt & Peters 1950)

  17. Protons with lifetime 100h Lead ions with lifetime 100h Required gas pressures Lead ions with pressure that gave proton lifetime 100h Implies higher fractional losses from Pb beam than p beam – but intensities are > 1000 times less.

More Related