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MKI UFO Knowledge and Future Plans: a Brief Update

MKI UFO Knowledge and Future Plans: a Brief Update. M.J. Barnes.

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MKI UFO Knowledge and Future Plans: a Brief Update

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  1. MKI UFO Knowledge and Future Plans: a Brief Update M.J. Barnes Acknowledgements: T. Baer, W. Bartmann, C. Bracco, F. Cerutti, B. Dehning, L. Ducimetière, A. Ferrari,N. Fuster Martinez, N. Garrel, A. Gerardin, B. Goddard, E.B. Holzer, S. Jackson, M. Jimenez, V. Kain, A. Lechner,V. Mertens, M. Misiowiec, R. MorónBallester, E. Nebot del Busto, L. Norderhaug Drosdal, A. Nordt, S. Redaelli, J. Uythoven, B. Velghe, V. Vlachoudis, J. Wenninger, C. Zamantzas, F. Zimmermann, … M.J. Barnes: LHC UFO meeting

  2. Overview of Presentation • Layout of MKI region; • Brief review of state of knowledge concerning MKI UFOs; • Screen conductors configuration and relationship to MKI UFOs; • MDs Proposed; • Conclusions. M.J. Barnes: LHC UFO meeting

  3. Layout of MKI8 Region Screen conductors capacitively coupled to “ground” (metallization on ceramic tube) Q5 Q4 TMR connection • Four MKI tanks per beam, between Q4 and Q5, pulsed at about 50 kV; • Vacuum valves at tank ends, plus sector valves: 10 in total per beam; • Each ferrite yoke is 2.65 m long, with a ~3.0 m Al2O3 tube presently with 15 nickel-chrome screen conductors installed. ferrite yoke ground plate HV plate ground plate capacitor HV plate Kicked Beam TMR connection entrance box connection 5 April 2012 M.J. Barnes: LHC UFO meeting 3

  4. Knowledge re MKI UFOs • MKI UFOs can be produced by pulsing the MKIs [1]; • At point 2, most UFO events occur around MKI2-D [5]: FLUKA simulations of the UFOs at the MKIs in point 2 show that the UFO location must be in, or nearby upstream, of MKI2-D [2]; • At point 8, the distribution of UFOs is more equal [5]; • Measurements in the lab show that pulsing the MKIs at 50 kV leads to mechanical vibrations and displacements of ~10 nm [3, 4], which might cause UFOs; • The temporal distribution of UFOs is from a few up to several hundred ms after a pulse [5]; • UFOs occurring before ~60 ms after a pulse cannot be explained by gravitational effects, but could be due to negatively charged particles accelerated by the electric field of the MKIs [6]; • An MKI, removed from LHC in winter TS 2010/11, was opened and inspected for macro particles [7]: • Energy-dispersive X-ray spectroscopy of the particles showed that they mainly consist of Al and O, leading to the conclusion that the macro particles originate from the Al2O3 ceramic tube. • clean room air: 100 particles on filter; new ceramic tube: 10‘000 particles on filter; sample from ceramic tube from removed MKI: 5,000,000 particles on filter. • UFOs were not produced by pulsing the MKQs [5]; • Energy dependence means that UFOs could limit LHC performance after LS1 [8]; • There is a positive correlation between vacuum pressure and UFO rate [9]; • No correlation identified between UFO signal magnitude and time after the MKI pulse [5]. M.J. Barnes: LHC UFO meeting

  5. Screen Conductors – Configuration and Voltage [10] Note: plot for 60kV PFN • Notes: • Screen conductors are hard-coupled to “ground” at beam-exit, and capacitively coupled to “ground” at beam entrance; • Screen conductors at beam-entrance: • transiently jump to +ve HV during field rise (total capacitive current to ground of +60 A & -40 A predicted); • 0V during flattop of field pulse; • transiently jump to −ve HV during field fall. Originally, for beam coupling impedance reasons, 24 screen conductors were to be installed; In general 15 screen conductors are presently installed to minimize risk of electrical breakdown. Note: plot for 50kV PFN. M.J. Barnes: LHC UFO meeting

  6. Comparison of 15 & 24 Screen Conductors: Flattop Field (Efield: kV/m) [10] 15 screen conductors 24 screen conductors UFOs occurring before ~60 ms after a pulse cannot be explained by gravitational effects, but could be due to negatively charged particles accelerated by the electric field of the MKIs [6] (with 15 screen conductors installed). • 24 screen conductors are expected to give ~one-third of beam induced heating in comparison with 15 screen conductors; • In addition, flattop electric field is significantly lower with 24 screen conductors than 15 – hence installing 24 may reduce incidence of UFOs; M.J. Barnes: LHC UFO meeting

  7. 24 Screen Conductors: Without Electrical Breakdown ….. Two approaches are being followed to potentially allow the use of 24 screen conductors without electrical breakdown: • Screen conductors are beneath the surface of the ceramic, thus preventing breakdown between adjacent conductors; • Inserting screen conductors will not dislodge Al2O3 macro particles into ceramic tube aperture; • Beam impedance issues are being studied by Hugo Day; • BUT the ~3 m long ceramic, with closed slots, is very difficult to manufacture. • “Spheres” on the end of each/most screen conductors reduce the electrical field strength at the capacitively coupled end, thus decreasing the risk of electrical breakdown; • Slots of end of tube are machined (not shown above): the first tube is capable of having 19 screen conductors with spheres and 5 without; • Next generation tube will have increased OD, at the end to permit 3 mm wall thickness. M.J. Barnes: LHC UFO meeting

  8. Metallization of Ceramic Chamber…. • UFOs were not produced by pulsing the MKQs [5]: the MKQs have a metalized ceramic chamber. • Simulations have been carried out to assess the effect of metalizing the MKI ceramic chamber: M.J. Barnes: LHC UFO meeting

  9. Improved and Standardized Cleaning of Ceramic Chamber…. • Current generation of ceramic tubes are cleaned with high pressure water (> 100 bar), at “dirty” factory, then baked out at ~800˚C. • Ceramic particles are probably dislodged when inserting screen conductors into grooves, but could also be dislodged during moving of MKIs, during pulsing and during bake-out of the kicker magnet. • Procedure for an initial standard procedure for cleaning the generation 2b ceramic tubes (open grooves with “spheres”). To be applied to the new tube for MKI 5: • Clean chamber with nitrogen at 15 bar; • Dust Sampling • Insert (a few?) screen conductors in chamber • Dust sampling • Insert more screen conductors in chamber / Dust sampling • Clean chamber with nitrogen at 15 bar; • Dust sampling (repeat flushing chamber at 15 bar and dust sampling until little improvement is noted) • Thermal bake-out of magnet • Dust sampling (when mounting valves) • Other cleaning methods, such as snow cleaning, are being investigated. M.J. Barnes: LHC UFO meeting

  10. MDs Proposed [5] • Effect of reduced length of MKI pulse upon UFO production (to confirm whether or not the UFO production is mainly dependent upon the rising/falling edges of the pulse or the flattop; • Production mechanism and asymmetry between MKIs by pulsing individual MKIs. • Study of the UFO dynamics by using the BLM study buffer with 80 µsresolution. The increased resolution should allow resolving the temporal structure of single UFO events. • Study influence of vacuum activity by switching off the e-cloud solenoids around the MKIs. • Unlike in 2011, the studies are preferred to be done with 25 ns spacing and higher beam intensities, which gives important input to the dynamics model and for the extrapolations to nominal parameters. M.J. Barnes: LHC UFO meeting

  11. Conclusions • The macro particles originating from the Al2O3 ceramic tube are likely responsible for the MKI UFOs. • The most promising means of reducing the MKI UFOs is by greatly reducing the number of the Al2O3 macro particles, e.g. by: • Burying screen conductors beneath the surface of the ceramic – long timescale due to difficulty of manufacturing ceramic tube; • Installing 24 screen conductors to reduce electric field – to be tested on next MKI; • Improved cleaning procedure – to be tested on next MKI. • Metallization of the MKI ceramic chamber is not considered feasible. • There is a proposal to install an MKI during the August TS (with 24 screen conductors, 19 of which will have “spheres”): • Pre-scrubbing of this MKI, to reduce Ecloud in the copper bypass tube is being actively considered (together with: F. Caspers, M. Holz, P. Costa Pinto, M. Taborelli) M.J. Barnes: LHC UFO meeting

  12. References [1] T. Baer et al., “MKI UFOs at Injection", CERN-ATS-Note-2011-065 MD, Aug. 2011. [2] A. Lechner, “FLUKA Studies of UFO-induced Beam Losses in the LHC”, CERN Accelerator School Poster Session, Sept. 2011. [3] R. MorónBallester et al., “Vibration analysis on an LHC kicker prototype for UFOs investigation”, CERN EDMS Document No. 1153686, Aug. 2011. [4] J. Uythoven et al., “Synthesis and status of MKI vibration studies”, LHC UFO meeting, 15/09/2011. [5] T. Baer et al., “MD on UFOs at MKIs and MKQs”, CERN-ATS-Note-2012-018 MD, 22/02/2012. [6] F. Zimmermann, “Update on Dynamics Modeling - Effect of Kicker Field", 66th LHC Injection and Beam Dump Meeting, Nov. 2011. [7] A. Gerardin et al., “EDS analyses of filters used for UFO sampling”, CERN EDMS Document No. 1162034, Sept. 2011. [8] T. Baer et al., “UFOs: Observations, Studies and Extrapolations”, proc. of Evian 2011, https://indico.cern.ch/getFile.py/access?contribId=27&sessionId=5&resId=1&materialId=paper&confId=155520. [9] T. Baer et al., “UFOs Will they take over?”, Chamonix Workshop 2012, 09/02/2012. [10] M.J. Barnes, “Characterization of a Thin Coating for Shielding", 66th LHC Injection and Beam Dump Meeting, Nov. 2011. [11] M.J. Barnes et al., “MKI Strategy Discussion. Developments: prospects for improvements, time-lines, ….”, 19/01/2012. M.J. Barnes: LHC UFO meeting

  13. Spare Slides M.J. Barnes: LHC UFO meeting

  14. Installed MKI Magnets M.J. Barnes: LHC UFO meeting

  15. Distribution of UFOs at Point 8 and Point 2 courtesy of T. Baer, Chamonix 2012. Distribution of the most upstream BLM at which the UFO is observable. The BLM dedicated to a MKI is located directly downstream of the corresponding MKI tank. At Pt. 2 most UFO events occur around the MKI2.D, whereas the distribution is more equal for the UFOs at Pt. 8. M.J. Barnes: LHC UFO meeting

  16. 15 Screen Conductors (Efield: kV/m) Flattop (~7.8µs): Falling edge (~1µs): Start of flattop (~680ns): Highest electric fields, inside ceramic chamber, occur during field flattop (longest duration too), especially in bottom half of ceramic chamber. M.J. Barnes: LHC UFO meeting

  17. 24 Screen Conductors (Efield: kV/m) Flattop (~7.8µs): Falling edge (~1µs): Start of flattop (~680ns): Highest electric fields, inside ceramic chamber, occur during field during field rise and fall. M.J. Barnes: LHC UFO meeting

  18. MKI UFOs courtesy of T. Baer, Chamonix 2012. • 11 dumps due to MKI UFOs in 2011. 8 dumps at 3.5 TeV, 2 dumps during stable beams. • In total 2340 UFOs around MKIs 847 in Pt.2 and 1493 in Pt.8. • Temporal distribution:Mainly within 30 min after last injection. • Many events within a few hundred ms after MKI pulse. • Positive correlation between MKI UFO rateand local pressure at 450 GeV. 1236 UFOs around MKIs for fills lasting at least 3 hours after last injection. 3.5σ statistical significance. 101 MKI UFOs in Pt. 8 between last injection of beam 2 and beginning of ramp for 102 fills with 1380 bunches. 5 April 2012 M.J. Barnes: LHC UFO meeting 18

  19. Number of MKI UFOs courtesy of T. Baer, Chamonix 2012. • No general conditioning effect obvious for MKI UFOs. On average: 8.9 MKI UFOs per fill.(3.4 at MKIs in Pt. 2 and 5.5 at MKIs in Pt. 8) MKI UFO storms (Pt. 2) 1664 UFOs around injection kicker magnets between 14.04. and 31.10.2011 in Pt. 2 and Pt.8 for fills reaching stable beams with >100 bunches. MKI Flashover (Pt. 8) 5 April 2012 M.J. Barnes: LHC UFO meeting 19

  20. MKI UFO Studies • FLUKA: UFO location must be in MKIs (or nearby upstream). (A. Lechner, 3rd LHC UFO Study Group Meeting) • Minimum particle radius of 40µm needed to explain large UFO event on 16.07.2011.(T. Baer et al., Evian Workshop 2011) • Vibration measurements using accelerometers and lasers: Mechanical vibrations of tank (≈10nm) during MKI pulse. (R. MorónBallester et al., EDMS: 1153686) Mechanical vibrations of ceramic tube (≈??nm) during MKI pulse. courtesy of A. Lechner and the FLUKA team. Accelerometer 5 April 2012 M.J. Barnes: LHC UFO meeting 20

  21. Macro Particles in MKIs • MKI.C5L2 (removed from LHC in winter TS 2010/11) was opened and inspected for macro particles. Energy-dispersive X-ray spectroscopy of the particles showed that they mainly consist of Al and O, leading to the conclusion that the macro particles originate from the Al2O3 ceramic tube. • Reference measurements:clean room air: 100 particles on filter new ceramic tube: 10‘000 particles on filter • 5‘000‘000 particles on filter found during inspection of removed MKI. • Typical macro particle diameter: 1-100µm. 100µm 10µm Al courtesy of A. Gerardin, N. Garrel • EDMS: 1162034 O 5 April 2012 M.J. Barnes: LHC UFO meeting 21

  22. Temporal Distribution of Observed UFOs after MKI Pulse courtesy of T. Baer, Chamonix 2012. • There are several events within a few 10 ms after the MKI pulse and the tails extending to a few hundred ms. The first clear UFO event occurred 10.2 ms after the MKI pulse. • Assuming that a particle is released from the top of the aperture at the moment of the kicker pulse and accelerated only by gravitational force towards the beam, the expected delay is more than 60 ms. • Thus gravitational force does not explain many of the relatively short times between pulsing an MKI and the UFO occurring (T. Baer et al., CERN-ATS-Note-2012-018 MD; F. Zimmermann, 66th LIBD Meeting). 1 eventat 1330 ms 5 April 2012 M.J. Barnes: LHC UFO meeting 22

  23. Lead MKI UFOs courtesy of T. Baer, Chamonix 2012. • MKI UFO at MKI.D5R8. • 10 % of threshold at MQML.10L8.Losses are not as localized as for protons. • Highest loss is in the dispersion suppressor downstream of the IR (due to ion fragmentation). IP8 MQML.10L8 (highestloss) MKI (UFO location) TCTH Horizontal dispersion 5 April 2012 M.J. Barnes: LHC UFO meeting 23

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