1. status report from ad-hoc study group* on experimental UFO study programme Frank Zimmermann LMC meeting #109, 5 October 2011 *this study group established as an ACTION from LMC#95 (8 June 2011)

2. UFO study meeting organization UFO study-group meetings – Meetings ~every 6 weeks with minutes, ~16 presentations so far – web site https://cern.ch/lhc-ufohttps://cern.ch/lhc-ufo – organized by Frank Zimmermann MKI UFO meetings – MKI UFO status reported at LMC #105 – organized by Brennan Goddard – web site https://proj-lti.web.cern.ch/proj- lti/LTIcoordination/RelatedMeetings/LIBD/LIBD.htmhttps://proj-lti.web.cern.ch/proj- lti/LTIcoordination/RelatedMeetings/LIBD/LIBD.htm MKI dust meetings – organized by Volker Mertens – web site https://espace.cern.ch/te-dep- abt/tc/Lists/MKI%20dust%20meetings/AllItems.aspxhttps://espace.cern.ch/te-dep- abt/tc/Lists/MKI%20dust%20meetings/AllItems.aspx UFO study meeting organization

3. participants in study-group meetings Tobias Baer, Eduardo Del Busto, Mike Barnes, Francesco Cerutti, Bernd Dehning, Riccardo De Maria, Alfredo Ferrari, Nuria Fuster, Eva Barbara Holzer, Massimiliano Ferro-Luzzi, Miguel Jimenez, Anton Lechner, Eduardo Nebot del Busto, Kazuhito Ohmi (KEK), Marc Ross (FNAL), Yasunori Tanimoto (KEK), Jan Uythoven, Bob Velghe, Vasilis Vlachoudis, Jörg Wenninger, Frank Zimmermann addt’l input Ralph Assmann, Swapan Chattopadhyay (CI), Brennan Goddard, Volker Mertens, Lenny Rivkin (PSI), John Seeman (SLAC), Uli Wienands (SLAC), … study-group participants additional input

4. survey “dust” studies at other accelerators (KEK PF-AR, CESR, SLAC PEP-II, ISR, LEP) LHC observations UFO dynamics studies FLUKA simulations MDs (so far only for MKI UFOs) hardware studies - vibrations, dust etc (MKI) future MDs, mitigation measures lines of attack

5. UFO & dust distributions measured UFO strength distribution 3670 arc UFOs (>cell 12) at 3.5 TeV with signal RS01 > 1∙10 -3 Gy/s. dust contamination measured in SMI2 most of the dust consists of silica; deviations at large dust sizes are due to human interventions and could be steel, silver, Ti, etc size 3 (  m 3 ) number T. Baer M. Jimenez measured dust distribution consistent with observed UFO strength distribution

6. model trajectories for falling objects trajectories for different beam intensities & two initial x positions    =0.3 mm, x 0 =0.3 mm    =0.3 mm, x 0 =1.0 mm    =0.3 mm, x 0 =0.1 mm N. Fuster repulsion after charging up – macroparticles do not reach the beam center; possibility of multiple loss events with ~80 ms separation

7. predictions vs observations – loss shape macroparticle mass (proton mass units) N p,tot =1.4×10 14, σ = 0.3 mm temporal loss profile of UFO on 23.08.2010 predicted temporal loss shapes observed loss shape predicted & observed loss durations comparable; asymmetry in loss profile contains information on macroparticle mass N. Fuster T. Baer 1 ms

8. predictions vs observations – loss duration σ = 0.3 mm predicted loss duration versus intensity N p =10 12 N p =10 13 N p =10 14 N p =10 13 observed loss duration versus intensity N. Fuster E. Nebot UFO duration gets shorter with higher beam intensity

9. size of UFO particles FLUKA simulations with MKI BLMs ~10 9 nuclear interactions / UFO A. Lechner A=10 17 A=10 15 N p = 10 14 model prediction for total # of lost protons  N p =10 6  N p =10 4 mm-size UFOs at MKI? N. Fuster ~10 4 -10 6 interactions for UFOs with radius 1 - 25  m 10 13

10. predicted beam-size dependence design intensity, N tot =3.2×10 14 total # of lost protons N. Fuster → 7 TeV might be worse; could this dependence also explain why MKI- D sees more UFOs?

11. model predictions still to be tested proton loss is maximum for N p,tot= 10 13 and decreases with further increasing beam intensity (slide 9) loss duration increases with larger beam size non-monotonic dependencies: proton loss versus transverse beam size (slide 10); peak loss rate versus beam current particle temperature stays below melting point N tot =3.2×10 13 loss duration versus beam size log (peak loss rate [1/s]) peak loss rate versus A and N tot data analysis/MDs to test these addt’l predictions N. Fuster

12. desired model extensions refinements to the model charging rate e.g. position dependent potential (metal vs dielectric) & energy loss of delta electrons inside the macroparticle corrections for finite UFO size e.g. UFO particles larger than the beam size other UFO shapes not only spherical object, but e.g. needles, foils,… further model improvements are planned – resources?

13. still mounted on the HER collimator; Uli Wienand’s finger is on the leads of the solenoid; the black pin sticking up is the rod that gets moved by the solenoid PEP-II dust thumper

14. dust injectors TRISTAN AR,H. Saeki, early 1990’sTRISTAN AR, S. Kato, mid 1990’s PF-AR, Y. Tanimoto, late 2000’s Y. Tanimoto XFEL future, J. Hajdu need controlled dust injector (L. Rivkin)

15. cleaning techniques Dry Ice nozzle – Reschke /DESY Jets of single-cell HPR system efficient dust-removal techniques in SRF & SC communities water pressure variation on TESLA cavity Particle removal in semiconductor industry: 1.High Pressure Jet Cleaning 2.Snow Cleaning 3.Ice Scrubber Cleaning 4.Ultraviolet - Ozone Cleaning 5.Megasonic Cleaning 6.Isopropyl Alcohol Vapor Displacement 7.Aerosol Jet Cleaning (supersonic aerosol jet) 8.Laser Steam Cleaning (Kneisel and Lewis) in-situ cleaning? M. Ross

16. proposed 3-step strategy 1.“hammer” to induce UFOs - SLAC thumper will arrive mid November (U. Wienands) - proposal to install it in IR7 (many BLMs, but no beam dump) during Xmas break ; MDs in 2012 - later hammer at warm-cold transition? 2.dust injector (in IR7) - use modified (spare) BGI to inject dust - or build dedicated micro/nano-technology injector - learn/borrow from SASE FELs (nano-cluster injector guns) 3.cleaning - turbulent He flow through beam screen to shake chamber? - procedure as for RF cavities – dry-ice nozzle on robot? - send “hairy ball” through arc chamber (L. Rivkin’s proposal) each step to be decided and approved