1. ALICE sensitivity to background and injection failures with the smaller aperture A. Di Mauro TREX meeting, 31/07/2014

2. A Large Ion Collider Experiment Introduction 1.In RUN1, after beam intensity ramp-up, ALICE suffered from high beam-gas background due to bad vacuum (up to ~10 -7 mbar) in LSS2 (ID800 ZDC recombination chambers, TDI). This prevented running many detectors for several hours from the beginning of the fill. 2.Vacuum issues never affected UX25, typically 2-3 orders of magnitude lower than in the LSS2 and observed only during pp runs (in Pb-Pb or p-Pb much lower beam intensity). 3.Two misinjected beam incidents occurred on July 28 th, 2011:  Beam impact on TDI jaw.  Beam grazing the TDI jaw  permanent damage to SDD detector electronics (it was “READY” even during injection).  Q.: with the central beampipe aperture reduction from 6 cm to 3.8cm (OD) will ALICE become more sensitive to 1) machine induced background and 2) injection failures?  Try to get a preliminary answer from background simulations with existing beam pipe… 31/07/14TREX meeting - A. Di Mauro2

3. A Large Ion Collider Experiment Overview of background simulations  Machine Induced Background in ALICE  Gas pressure profile calculation in the IR2 fro FILL 2736 by G. Bregliozzi (TE-VSC)  LSS2 FLUKA modeling and beam-gas interactions by A. Lechner (EN-STI)and E. Leogrande (ALICE) up to 20 m scoring plane (first results of simulation presented @ LBS #43).  Propagation through ALICE from scoring plane using Geant3 and FLUKA (FLUKA VMC interface) by A. Alici (Results of simulation presented @ LBS #46 and #51)  MKI erratics on 28/07/2011, @ 16h30 (injected beam impacting on the TDI) and @ 18h00 (injected beam grazing on the TDI)  TDI impact distributions (Sixtrack) by J. Uythoven and C. Bracco  Propagation through LSS2 up to 20 m scoring plane using FLUKA by A. Lechner and N.V. Shetty  Propagation through ALICE from scoring plane using FLUKA by A. Alici (Results of simulation presented @ LBS #51) TREX meeting - A. Di Mauro31/07/143

4. A Large Ion Collider Experiment 31/07/14TREX meeting - A. Di Mauro4 Simulation of beam-gas interactions in LSS2 LSS2 pressure profile for fill 2736 50ns_1374_1368_0_1262 filling scheme bunch intensity = 1.53E11 p/b total current = 2.1E14 proton (278 mA) ID800 TDI TCDD Cumulative distribution functions  beam-gas interactions  all particles at the scoring plane  all particles at the scoring plane within the beam pipe ~ 80% of primaries in ID800+TDI ~ 60% of particles from ID800+TDI 40% of particles from TCDD+D1+Q1Q2Q3 ID800 chamber + TDI TCDD z-position of primary beam-gas interactions

5. A Large Ion Collider Experiment Particle’s kinematics at the scoring plane 31/07/14TREX meeting - A. Di Mauro5 Extrapolated trajectory of beam-gas background particles in empty space. The majority of particles are contained inside the beam pipe with a strong forward peak. Reducing the beam-pipe diameter will not significantly change this scenario, the number of particles will depend only on vacuum conditions.

6. A Large Ion Collider Experiment Distribution of secondary vertices in ALICE 31/07/14TREX meeting - A. Di Mauro6

7. A Large Ion Collider Experiment 31/07/14TREX meeting - A. Di Mauro7 Distribution of secondary vertices in ALICE primary particles with R>3cm Vacuum equipment in AliRoot geometry Ion pump Manual valve GaugeBellows 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. vacuum equipment

8. A Large Ion Collider Experiment Beam-pipe contribution to background 31/07/14TREX meeting - A. Di Mauro8 distribution of secondary vertices inside ALICE cavern (beam-gas) beam-gas distribution of secondary vertices for particles originated by interaction with the central Be pipe beam-gas ITS: 1% TPC: 5%

9. A Large Ion Collider Experiment Beam-pipe contribution to background In conclusion: only 1% of the background inside the ITS and 5% in the TPC is due to beam-gas interactions with the beam-pipe! Most of the background is indeed generated by the vacuum equipment on the A-side (30%) and by the compensator magnet (30%). There is a plan to remove the gauge and make the ion pump in Al for LS2. 31/07/14TREX meeting - A. Di Mauro9

10. A Large Ion Collider Experiment MKI erratics 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  s.  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  18:00 RS32-Sum 3559 times larger than threshold TREX meeting - A. Di Mauro31/07/1410 Miss-kicked Injected batch - Kicked Circ. beam - Over-kicked inj. batch grazing Injected batch Circulating LHC beam MKI TDI

11. A Large Ion Collider Experiment 28/07/11 injection failures impact on ALICE DetectorEvent 16:30Event 18:00 SDD (silicon drift detector) injectors to calibrate drift velocity: 50% of them on the layer closer to the beam pipe are not working (permanent damage) TPCField Cage tripped, 1 readout chamber tripped Field Cage tripped, 12 readout chambers tripped TRDall HV (anode) channels trippedmany HV (almost all anode) channels tripped EMCALHV and LV errors in 3 SMs PHOSHV and LV errors in 2 sectorsHV and LV errors in 1 sector FMDsome detector errors HMPID1 chamber trippedall 48 HV channels tripped MCHHV tripsHV and LV trips MTR~30% tripped TREX meeting - A. Di Mauro31/07/1411

12. A Large Ion Collider Experiment 28/07/11 injection failures simulation  Fluence of all charged particles at the scoring plane:  full impact  grazing impact 1M events considered TREX meeting - A. Di Mauro31/07/1412

13. A Large Ion Collider Experiment 31/07/14TREX meeting - A. Di Mauro13 28/07/11 injection failures simulation  full impact  grazing impact  Energy fluence per event at the scoring plane ( from IPAC14 paper “FLUKA SIMULATION OF PARTICLE FLUENCES TO ALICE DUE TO LHC INJECTION KICKER FAILURES”, N. V. Shetty et al. )

14. A Large Ion Collider Experiment 28/07/11 injection failures simulation  Fluence of all charged particles inside experimental hall:  full impact  grazing impact 200k events considered TREX meeting - A. Di Mauro31/07/1414 No effect of beam pipe in case of full impact; for grazing impact, particle and energy fluence inside ALICE would not change significantly for a smaller pipe diameter (TBC by dedicated study and simulation with new beam-pipe).

15. A Large Ion Collider Experiment Conclusions Contribution of beam-pipe to beam-gas background seen by detectors is ~ 5% in simulation with existing beam-pipe; a smaller radii should not change drastically this figure. The load on detectors from injection failures is related mainly to secondaries produced in the TDI: – in dump events, one can expect no or negligible impact of smaller beam-pipe due to the low fluence at small radii – in grazing events, the distribution at the scoring plane is peaked like beam-gas background and one can expect a similar contribution from the beam pipe A detailed simulation is being performed using the smaller beam pipe to confirm its negligible impact on background and injection failures. 31/07/14TREX meeting - A. Di Mauro15

16. A Large Ion Collider Experiment 31/07/14TREX meeting - A. Di Mauro16 Back-up slides

17. A Large Ion Collider Experiment 31/07/14TREX meeting - A. Di Mauro17 Charged particle fluence in beam-gas simulation TPC RB24 shielding (1.2 m concrete + 0.8 m cast iron) Solenoid doors front absorber Muon spectrometer TRD MIB