1 / 30

Update on Beam Gas and Simulations for ALICE

Update on Beam Gas and Simulations for ALICE. A. Alici , A. Di Mauro , A . Lechner A. Morsch , N.V. Shetty. Overview of beam gas simulations. Machine Induced Background in ALICE Gas pressure calculation in the IR2 by G. Bregliozzi (LHC Vacuum group)

anakin
Download Presentation

Update on Beam Gas and Simulations for ALICE

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. Update on Beam Gas and Simulations for ALICE A. Alici, A. Di Mauro, A. Lechner A. Morsch, N.V. Shetty

  2. Overview of beam gas simulations • Machine Induced Background in ALICE • Gas pressure calculation in the IR2 by G. Bregliozzi (LHC Vacuum group) • LSS2 FLUKA modeling and beam-gas interactions by A. Lechner (CERN FLUKA team) and E. Leogrande. Results of simulation presented @ LBS #43 • Propagation through ALICE with Geant3 and FLUKA (FLUKA VMC interface) • MKI erratic 28/07/2011, 16h30 (injected beam impacting on the TDI) • TDI impact distributions (Sixtrack) by J. Uythoven and C. Bracco • Propagation through LSS2 with FLUKA by A. Lechner and N.V. Shetty • Propagation through ALICE with FLUKA • MKI erratic 28/07/2011, 18h00 (injected beam grazing on the TDI) • TDI impact distributions (Sixtrack) by J. Uythoven and C. Bracco • Propagation through LSS2 with FLUKA by A. Lechner and N.V. Shetty • Propagation through ALICE with FLUKA LBS meeting #51, 27/01/2014

  3. Simulated gas pressure profile in IR2 left TDI TCDD ID800 • LSS2 pressure profile for the reference fill 2736 (16/06/2012) • 50ns_1374_1368_0_1262filling scheme • bunch intensity = 1.53E11 p/b • total current = 2.1E14 proton (278 mA) IP2 pressure in the TDI in Oct 2012 Values of gas pressure used in the simulation represent a typical 2012 scenario (it is not a worst case scenario). LBS meeting #51, 27/01/2014

  4. Position sampling of beam-gas interactions Position along the z axis of the primary beam-gas collisions in the LSS2. z vertex of all the background particles entering the ALICE hall. • all particles at the interface plane machine/experimental hall • all particles at the interface plane within the beam pipe ID800 chamber + TDI D1 + inner triplet Q1Q2Q3 TCDD results from 500k beam-gas interaction in the LSS2 left side of ALICE. LBS meeting #51, 27/01/2014

  5. Cumulative distribution functions • beam-gas interactions • all particles at the scoring plane • all particles at the scoring plane within the beam pipe 40% of particles from TCDD+D1+Q1Q2Q3 80% of primary in ID800+TDI The CDF for particles at the scoring plane within the beam pipe is consistent with the observed proportionality between background rate in ALICE and the product of the beam intensity times the average of the vacuum pressure in the last part of LSS2 (measured by the gauges in the ID800, TDI and TCDD). 60% of particles from ID800+TDI LBS meeting #51, 27/01/2014

  6. Beam-Gas rate in ALICE • The probability that a proton traversing IR2 (left side) has an inelastic nuclear interaction with a residual gas nucleus, given the vacuum pressure profile as simulated by G. Bregliozzi, is 1.09E-12 (A. Lechner). • The rate of beam-gas collision in the LSS2 should be = 1.09E-12x frevx Ibeam1= 2.56 MHz • (frev = 11245 Hz andIbeam1= 2.1E14 protons) • The expected beam-gas rate (from left side) measured in ALICE • by the V0 detector is ~ 350 kHz (higher V0 efficiency in the MC) t = -11.3 ns t = 3 ns IP V0A rin=8 cm rout=100 cm snapshot with online measurements at beginning of fill 2736 V0C rin=8 cm rout= 76 cm 340 cm 90 cm LBS meeting #51, 27/01/2014

  7. Comparison Geant3-FLUKA • Geant3-FLUKA comparison by considering hits (no digits, no reconstruction). V0A detector η = [2.8,5.1] r(cm) = [4,44] hit radial distribution hit multiplicity hit multiplicity ITS detector η =[-0.9,0.9] r(cm) = [4,44] hit multiplicity TOF detector η = [-0.9,0.9] r(cm) = [370,390] longitudinal distribution LBS meeting #51, 27/01/2014

  8. Comparison Simulation-Data • Geant3-data comparison by considering reconstructed quantities (normalized to the same number of Beam-Gas triggers). zoom zoom LBS meeting #51, 27/01/2014

  9. Charged particles fluence in ALICE with FLUKA VMC TRD MIB TPC Solenoid doors Muon spectrometer front absorber RB24 shielding (1.2 m concrete + 0.8 m cast iron) LBS meeting #51, 27/01/2014

  10. Charged particles fluence in ALICE with FLUKA VMC TPC solenoid doors compensator magnet on the mini-frame ITS • Presence of massivecomponents on beam pipe close to IP2 (valve, gauge, ion pump and bellows) •  refurbishment of vacuum equipment after RUN2 under discussion with VSC people. LBS meeting #51, 27/01/2014

  11. Distribution of secondary vertices in ALICE • Distribution of secondary vertices from interactions with material inside the ALICE Hall. TPC ITS compensator magnet on the mini-frame RB24 shielding LBS meeting #51, 27/01/2014

  12. Distribution of secondary vertices in ALICE • Rough estimation of background sources contribution inside ALICE by counting the hits in the TPC (and ITS) associated to a secondary interaction in a given region • only ~ 2% of TPC hits (~ 0.01% of ITS hits) are caused by particles that entered the ALICE cavern outside the beam pipe ; • ~ 30% of TPC hits (~ 25% of ITS hits) are caused by particles originated in the forward vacuum equipment. primary particles with R>3cm vacuum equipment Vacuum equipment in AliRoot geometry Ion pump Gauge Bellows Manual valve LBS meeting #51, 27/01/2014

  13. Scoring with FLUKA VMC interface • TID: Total Ionising Dose (the dose dE/dmis the mean energy imparted to matter of mass m) • 1 MeV neq: hadron fluence quoted in 1 MeV neutron equivalents • this numbers determine the long term radiation damages • >20 MeV hadrons: fluence of hadrons with a kinetic energy in excess of 20 MeV • this number determines the rate of single event upsets in the microelectronics circuitry • charged particles: fluence of all charged particles • this number determines the detector load values per beam-gas interaction in the LSS2 (100k events considered) LBS meeting #51, 27/01/2014

  14. Scoring with FLUKA VMC • To give this numbers in a more meaningful way we compared: • the dose and the 1 MeV neutron equivalents integrated during fill 2736 (17h 40min) with values integrated in 2012 due to genuine pp collisions; • the fluence rate of high energetic hadrons and of charged particles at the beginning of fill 2736 with expected fluencesfor PbPb 5.5 TeV/nn @ 50 kHz. values integrated for fill 2736 wrt. 9.88 pb-1 (ALICE pp 2012) values at the beginning of fill 2736 wrt. PbPb 5.5TeV/nn @ 50kHz 100k events considered LBS meeting #51, 27/01/2014

  15. Beam-Gas forecast in ALICE 2011 and 2012 fits based on data. 2015 and HL-LHC extrapolations considering linear scaling with beam intensity. A vacuum better than 5 10-9 mbar is advisable. LBS meeting #51, 27/01/2014

  16. MKI erratic on 28/07/2011 • 16:30 erratic turn-on of MKI2 MS3. The interlock system detected the problem and discharged the MKI. No circulating beams. • A batch of 144 bunches was injected but not kicked, hence impacting on the TDI upper jaw (~3 cm impact parameter) • 18:00 again erratic turn-on of MKI2 MS3. This time the interlock system did not detect it and kicker C was powered for 9 ms. • 176 circulating bunches impacted on the TDI; out of these bunches, ~162 were kicked with 12.5% of the nominal MKI strength, hence grazing on the lower TDI jaw. • In both cases the beam was dumped by ALICE BCM system (station A): • 16:30 RS1 80 times larger than threshold • 18:00RS32-Sum 3559 times larger than threshold LBS meeting #51, 27/01/2014

  17. Injection scheme Miss-kicked Injected batch TDI grazing MKI grazing CirculatingLHC beam - Kicked Circ. beam - Over-kicked inj. batch Injected batch full impact grazing impact LBS meeting #51, 27/01/2014

  18. Injection failures 28/07/2011 LBS meeting #51, 27/01/2014

  19. Injection failures 28/07/2011 • Fluences of all charged particles at the interface plane: • full impact • grazing impact 1M events considered LBS meeting #51, 27/01/2014

  20. Injection failures 28/07/2011 • Fluences of all charged particles inside experimental hall: • full impact • grazing impact 200k events considered LBS meeting #51, 27/01/2014

  21. ALICE BCM system BCM-A 8 sensors z= + 4.8 m, r= 13-14 cm • Beam Conditions Monitor are protections against circulating beam failures • Based on pCVD diamond sensors (1 cm2 x 500 μm) • Typical sensitivity: 1 nA RS2 (80 ms integration) => ~100 p/cm2 LBS meeting #51, 27/01/2014

  22. Comparison with BCM measurements • BCM response: 1 MIP produces 5000 e-, 100 part/cm2 ~ RS2: 1 nA • MKI failure, dump of 144 bunches • fluence at BCM-A (from FLUKA): 5.6 10-8 cm-2 per impacting proton • total intensity 1.73 1013 ~ 106 part/cm2 • RS2 current of 0.01 mA (vs 0.02 mA observed) • MKI failure, grazing of 162 bunches • fluence at BCM-A (from FLUKA): 2.010-5 cm-2 per grazing proton • total intensity 1.95 1013 ~ 3.9 108 part/cm2 • RS2 current of 3.9 mA (vs 0.84 mA observed) LBS meeting #51, 27/01/2014

  23. Injection failure – full TDI impact event at 16:30 wrt. 9.88 pb-1 (ALICE pp 2012) event at 16:30 wrt. PbPb 5.5TeV/nn @ 50kHz 200k events considered LBS meeting #51, 27/01/2014

  24. Injection failure – TDI grazing event at 18:00 wrt. 9.88 pb-1 (ALICE pp 2012) event at 18:00 wrt. PbPb 5.5TeV/nn @ 50kHz 200k events considered LBS meeting #51, 27/01/2014

  25. Conclusions • Several beam related simulations have been performed; predictions (rates and topology) are in a reasonable agreement with observations. • We can used them to: • find solutions to reduce the background level in ALICE; • define the ALICE requirements in terms of vacuum in the machine for the future running scenarios; • define thresholds in the protection systems (like BCM). LBS meeting #51, 27/01/2014

  26. backup LBS meeting #51, 27/01/2014

  27. Distributions @ scoring plane Time delay of particles crossing the scoring plane (t=0: bunch crosses scoring plane); 99% of particles with t<25ns (98.2% of charged hadrons and 99.4% of muons). particles/ns/primary interaction Radial distribution @ 19m left of IP2; 20% of particles with r < 3cm. Transverse distribution for all particles @ 19.9m left of IP2 with lower energy cut of 20 MeV. This vertically elongated shape is due to the vertical opening in the warm MBXWT dipole just upstream of the scoring plane (it has a vertical opening of ± 25.5 cm and a horizontal of only ± 3.5 cm). Consolidation Task Force Meeting - A. Alici

  28. Scoring with FLUKA • Reference fill 2736: • beam intensity: 1.53E11 p/b × 1380 = 2.1E14 proton (378 mA) @ 8 TeV • total SB time = 17h 40min (63600s) • Y0 = I × <vacuum>LSS2 = 2.1E14 × (3+2+2)E-8 /3 = 6.4E6 proton × mbar <Y> = Y0 × 0.55 at the beginning of fill 2736 values integrated for fill 2736 100k events considered LBS meeting #51, 27/01/2014

  29. MKI2 MS3 Erratic on 28/7/2011 @ 16:30hrs • At 16:30:43hrs, on 28/7/2011, an erratic turn-on of MKI2 MS3 (Melton) at full PFN voltage; • Interlocks detected an MS erratic and correctly triggered MS’s and DS’s of system (within 2µs), emptying PFN via both ends. Hence all 4 kicker magnets pulsed for up to 4.5µs, emptying PFNs of energy. • Circulating beam was not in IP2 and therefore not disturbed. • Batchwas extracted from SPS but saw no kick at MKI2 and went straight into the TDI. • Note: this MS, Melton, was put in place during the last TS (July 2011) and has since made 5 erratics (only last 2 effected beam). Charging current & PFN voltage Current in kicker magnet MS3 erratic MS3 erratic, after resonant charging 4.5µs 2µs

  30. MKI2 MS3 Erratic on 28/7/2011 @ 18:03hrs PFNs 1 & 2 at normal voltage (~50kV) • At 18:03:09hrs , on 28/7/2011 , an erratic turn-on of MKI2 MS3 (Melton) occurred during resonant charging – sending current to 1 of the 4 kickers (Note: it is unusual to have an erratic at such low voltage); • Interlocks did NOT detect erratic of MS3 (at 33kV): hence no immediate action was taken to turn-on other thyratrons. Therefore the full 9µs of PFN pulse length sent, via MS3, to kicker C. • Other 3 PFNs correctly discharged via the DS after 4ms (no further kicker magnet current); • The erratic occurred ~500µs into the charging process, and the extraction from the SPS was inhibited; • Circulating beam was swept over the aperture and protection elements (~17% of normal kick) for ~9µs. PFNs 4 at low voltage (~33kV) because of MS3 erratic Erratic (untriggered) turn-on of MKI2 MS3 ~9µs circulating beam not dumped J. Wenninger M.J. Barnes

More Related