status report from ad-hocstudy group* on experimental

UFO study programme

Frank ZimmermannLMC meeting #109, 5 October 2011

*this study group established as an ACTION from LMC#95 (8 June 2011)

UFO study meeting organization• UFO study-group meetings

– Meetings ~every 6 weeks with minutes, ~16 presentations so far– web site https://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.htm

• MKI dust meetings – organized by Volker Mertens – web site

https://espace.cern.ch/te-dep-abt/tc/Lists/MKI%20dust%20meetings/AllItems.aspx

UFO study meeting organization

participants in study-group meetingsTobias 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

• 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

UFO & dust distributions

measured UFO strength distribution

3670 arc UFOs (>cell 12) at 3.5 TeV with signal RS01 > 1∙10-3 Gy/s.

∝ 𝒙−𝟎.𝟗𝟐

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 size3 (mm3)

number

T. Baer

M. Jimenez

measured dust distribution consistent with observedUFO strength distribution

∝ 𝒙−𝟎.𝟖𝟗

model trajectories for falling objectstrajectories for different beam

intensities & two initial x positions

A=1015, s=0.3 mm,x0=0.3 mm

A=1015, s=0.3 mm,x0=1.0 mm

A=1014, s=0.3 mm,x0=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

predictions vs observations – loss shape

macroparticle mass (proton mass units)

Np,tot=1.4×1014, 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

1 ms

predictions vs observations – loss duration

σ = 0.3 mmpredicted loss duration versus intensity

Np=1012

Np=1013

Np=1014

Np=1014Np=1013

observed loss duration versus intensity

N. Fuster

E. Nebot

UFO duration gets shorter with higher

beam intensity

size of UFO particles

FLUKA simulations with MKI BLMs

~109 nuclear interactions / UFO

A. Lechner

A=1017A=1015

Np=1014

model prediction fortotal # of lost protons

DNp

=106DNp

=104

mm-size UFOs at MKI?

N. Fuster

~104 -106 interactions for UFOs with radius 1 - 25 mm

1013

predicted beam-size dependence

design intensity, Ntot=3.2×1014

total # of lost protons N. Fuster

→ 7 TeV might be worse; could this dependence also explain why MKI-D sees more UFOs?

model predictions still to be tested

• proton loss is maximum for Np,tot=1013 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

Ntot=3.2×1013

loss duration versus beam size

log(peakloss rate[1/s])

peak loss rate versus A and Ntot

data analysis/MDs to test these addt’l predictions

N. Fuster

desired model extensions

• refinements to the model charging ratee.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?

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

dust injectorsTRISTAN AR,H. Saeki, early 1990’s TRISTAN AR, S. Kato, mid 1990’s

PF-AR, Y. Tanimoto, late 2000’s

Y. Tanimoto

XFELfuture, J. Hajdu

need controlled dust injector(L. Rivkin)

cleaning techniques

Dry Ice nozzle – Reschke/DESY

Jets of single-cell HPR system

efficient dust-removal techniques in SRF & SC communities

waterpressurevariationon TESLAcavity

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

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