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Asynchronous Beam Dump Studies C.Bracco, B.Goddard

Asynchronous Beam Dump Studies C.Bracco, B.Goddard. Worst-case for 1 bunch with TCDQ position OK. Initial distribution: one bunch of 32’000 particles centered at 7.5 mm on TCDQ.

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Asynchronous Beam Dump Studies C.Bracco, B.Goddard

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  1. Asynchronous Beam Dump StudiesC.Bracco, B.Goddard

  2. Worst-case for 1 bunch with TCDQ position OK Initial distribution: one bunch of 32’000 particles centered at 7.5 mm on TCDQ Beam 2 tracked from TCDQ to TCTs in IP5, that is the most critical region for losses in case of asynchronous beam dump.

  3. Worst-case: particles absorbed at collimators All the particles reaching the TCTH and TCTV have been scattered by the TCSG or grazed by the TCDQ (< 1%) no primary protons 626 seeds for scattering routine  ~ 11E6 p+ TCDQ TCTH TCSG TCSG TCTH TCTV p+ Absorbed at: * TCTV TCTV p+ Absorbed at: * TCTH * TCSG * TCDQ Collimators set at the physical aperture (in mm) defined during beam based alignment

  4. Density of Particles at the TCTH Density [p/sigma] Density [p/sigma] x [sigma] y [sigma] Density [p/sigma] y [sigma] • All losses come from p+ scattered through TCSG which fill acceptance with scattered primaries • Total p+ on TCTH is 0.3% of single bunch (8% impacting TCSG in this simulation) or 3.3108 p+ • Peak p+ density is about 0.016% of single bunch (equivalent to 2.5106 p+ with nominal ex,y) • Consistent with expectations - full bunch on TCSG would be attenuated by 10, and have 180 emittance increase x [sigma]

  5. Loss Map for Beam 2, 3.5 TeV, 2m b* in IP5 From SixTrack simulations: Ds = 10 cm @ magnets Ds = 1 m @ collimators (jaw length) Totabs = 8’463’489 # particles lost in Ds Local cleaning inefficiency: h = Ds × Totabs Collimators Cold Magnets Warm Magnets 1 bunch case TCDQ +TCSG Beam2 120 TCTH+TCTV Statistical error = 1/√N  max = 0.03 Nominal bunch (1.1E11 p+): 3.3E8 p+ on TCT (3e-3 ratio) Only primary protons losses.

  6. 3.5 TeV, 2m b*, 2mm (=1σ)offset IR6 saturated IR7 15Gy/s TCTH.4R5.B2 0.6 Gy/s  2E7 p+ Leakage from TCDQ ~2E-2 from BLMs (but saturated). Measured ~4e9 p+ with abort gap monitor (AGM) at moment of dump Using abort gap population and, according to our assumptions, the leakage from TCDQ is ~2E-3 BSRA

  7. Possible worst-case scenarios... • During setup with beam at 3.5 TeV: • Single bunch hitting metal collimator • Requires asynchronous dump/kicker pretrigger, PLUS ‘unlucky’ timing, PLUS collimator at correct phase to be exposed • Any way for single bunch to hit triplet aperture?? • Seems unlikely (TCDQ/TCSG should protect TCT, and this is inside triplet) • Should check carefully through details of setup procedure and see what asynch dump would give at each stage • During normal operation: • Multiple bunches hitting metal collimator • Requires another ‘non standard’ error somewhere (orbit at TCDQ, or TCDQ/TCT position, ...) • Studied by T.Kramer in PhD thesis • Detailed results obtained for different TCDQ retractions (same as orbit error)

  8. Impacts on metal collimators from asynch dump 7 TeV prefire dump case with0.5 m * and all LHC errors.

  9. Work needed to give FLUKA input... • Define machine parameters for study (b*, optical errors, orbit, setup errors, ...) • Already some issues here – make many runs with many different machines, to find average and worst case, or take a typical case (but what is ‘typical’?) • Choose failure case to give more ‘realistic’ input for FLUKA • For setup, need to choose “worst” time in procedure to have asynch dump • Check with tracking the impact parameters and distribution • For operational scenarios, more difficult • Need some assumption on the “concurrent” failure at time of asynch dump – orbit, setup errors, ... • Not to forget the “multiple pre-trigger” cases which are still possible until 2013 • Also need not to forget the basic case with the transmission of particles through 1 stage cleaning • Should not have damage during “normal” asynch dump at 0.55 m b*

  10. Conclusions • Asynchronous beam dump simulations for a single bunch at 3.5 TeV (2m b* in point 5) have been performed with SixTrack for beam 2 – all movable elements at nominal positions • Simulations show that losses at the TCT come from particles scattered at the TCSG (less than 1% from particles grazing the TCDQ), no losses of primary protons are observed • Simulations allow to visualize the distribution of particles absorbed at the TCT: peak density is equivalent of 0.016% of full bunch with nominal emittance • An asynchronous beam dump, performed for the same case (3.5 TeV, 2m b* in point 5), and losses (from PM) have been analyzed. • Measurements agreed well with simulations • For worst-case situations, need to carefully choose conditions AND methodology • easier for setup scenarios • beam experience for the operational scenarios? • detailed input from both LBDS and COLL teams needed – then simple 1 turn tracking

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