1. Status-Quo and Future Direction
UFO Studies
Status-Quo and Future Direction
Presentation at the 37th BLM Thresholds Working Group Meeting
L. Grob, B. Auchmann, J. Blomberg Ghini, R. Schmidt

2. The different approaches to the UFO problem
UFO event tracking & database
Statistical analysis
Theoretical modelling
Experimental studies

3. The different approaches to the UFO problem
UFO event tracking & database
Statistical analysis
Theoretical modelling
Experimental studies

4. UFO detection and foot prints
Measured UFO signal
Courtesy of T. Baer
UFO characteristics:
Localized beam losses
Assymetric Gaussian
Duration around 640 µs
UFO Buster (2011)

5. UFO Buster working principle
Software developed in Python (T. Bär, )
Based on BLM integration times (RS1 40 µs, RS2 80 µs, RS µs, RS µs…)
accessable via CCM → LHCOP → LHC control → Fixed Displays → BLM → UFO Buster (use only I/O tab)
Algorithm based on the following assumption:
Min. 2 BLMs within 40 m distance detect the beam loss signal
Losses in RS 4 > 1∙10-4 Gy/s (noise level about 2∙10-5 Gy/s)
Additional noise filters:
RS2/RS1 > 0.55
RS3/RS1 > 0.30*
*For MKI studies and 2011 data: RS1 > 1∙10-2 Gy/s
RESULT: searchable UFO database

6. UFO Buster 2.0 (?)
UFO Buster algorithm seems to register a lot of UFO-like losses, which always occur in the same components
Q: How can we easily make sure, it‘s really UFOs?
A: Look at elastic proton losses!

7. UFO losses in IP 7 to verify UFO event
Idea: After UFO event the elastic scattered protons travel around the LHC
At collimators (e.g. in IP 7) they are absorbed and seen as beam losses
Proof of principle done for some UFOs with high RS4 losses:
RS4IP7 BLM/RS4triggering BLM= 0.42
RS4IP7 BLM/RS4triggering BLM= 0.55
0.01
Gy/s
0.005
tUFO

8. Open questions regarding UFO detection
Lowest detection limit for UFO event in IP7
Signal height in IP7, IP6 and IP3 wrt to triggering BLM
Dependency on beta function
Potential tool to simulate elastic losses and IP7 UFO signal
Additional dBLM data with ns time resolution (the plot shows that the bunch structure can be fully resolved)

9. The different approaches to the UFO problem
UFO event tracking & database
Statistical analysis
Theoretical modelling
Experimental studies

10. UFO rate plots to quantify impact
UFO Buster database can be analyzed via scripts (e.g. Mathematica or Python)
Standardized plots of UFOs/hour (see above)
UFO distribution along the ring wrt B1/B2 (see below, left), UFO events in standardized Arc FODO cell (see below, right)
Beam 1 UFO rate along LHC
courtesy of J. Ghini
Beam 2 UFO rate along LHC
courtesy of J. Ghini
courtesy of J. Ghini

11. Current status & outlook
G. Papotti looks into UFO rate comparison
J. Blomberg Ghini, B. Auchmann and L. Grob use Mathematica-based scripts to produce the before-mentioned plots
Hope: find new correlations (e.g. different UFO rates/severity in B1/B2, in different sectors or magnets)
Idea:
Migration to Python (faster, same language as UFO Buster)
Development of analysis scripts, which can automatically produce some standard plots
Regular creation frequency of those plots
Maybe small software tool, which adds up to the UFO Buster (?)

12. The different approaches to the UFO problem
UFO event tracking & database
Statistical analysis
Theoretical modelling
Experimental studies

13. UFO Model simulates underlying physics
Initiated by F. Zimmermann, revised and optimized by B. Auchmann and S. Rowan
Analytical simulation of UFO event in Mathematica based on:
UFO Buster UFO criteria, new BLM layout
Physics input: beam parameters (σ, β, τ), transverse electrostatic E/B fields, mirror charges UFO differential equation (gravity, el. force), UFO
Model output: reproduces UFO-shape charge and ionization rate
Limitations: only based on gravity!
Monte Carlo simulation of UFOs in Arc cells:
UFO generator with: UFO location = [0, 2L], UFO path = ½ dbeam screen ,UFO radius = µm
Model output: 4 TeV simulations provided UFO size distribution for 6.5 TeV extrapolation, calculation of BLM responses and energy deposition (quench prediction)
courtesy of B. Auchmann
courtesy of S. Rowan (part of his upcoming thesis)

14. The different approaches to the UFO problem
UFO event tracking & database
Statistical analysis
Theoretical modelling
Experimental studies

15. UFO Busting anlysis of real LHC contaminants
Course of action:
Develop dust extraction procedure and tool
Tests on stored beam screen parts, collection of reference samples from tunnel and assembly hall
Extract dust from spare LHC magnets
Analysis:
Microscopic analysis (optical & SEM)
Energy-dispersive X-ray diffraction (XEDS) or similar technique to reveal chemical composition
Goal: Knowledge of UFO size distribution & material composition
better understanding of release mechanism, UFO dynamics and hopefully removal

16. THANK YOU VERY MUCH FOR YOUR ATTENTION!
I would like to thank the following people for their greatly appreciated support on that project:
B. Auchmann, M. Barnes, P. Chiggiato, P. Cruikshank, A. T. Perez Fontenla, J. Blomberg Ghini, H. Kos, G. Iadarola, A. Lechner, S. Le Naour, G. Papotti, S. Rowan, N. Pietralla, R. Schmidt and the other co-workers of the technical department
Selected literature:
T. Bär, Very Fast Losses of the Circulating LHC Beam, their Mitigation and Machine Protection, CERN-THESIS
B. Auchmann, „How to survive a UFO attack“ in 6th Evian workshop proceedings 2015
G. Papotti, „MACROPARTICLE-INDUCED LOSSES DURING 6.5 TEV LHC OPERATION “ in IPAC2016 proceedings
S. Rowan, „INTERACTIONS BETWEEN MACROPARTICLES AND HIGH-ENERGY PROTON BEAMS“ in IPAC2015 proceedings
This work is sponsored by the Wolfgang-Gentner-Scholarship of the BMBF

19. Software-based approach
Optimization of existing UFO model: include know-how gained from dust samples (size distribution and material composition) to include adhesion
Modification of UFO Buster software: implementation of a new algorithm respecting IP7 losses (elastic scattering products) to filter „fake“ UFO events
Statistical analysis of UFO Buster data: comparison of run 1 and run 2, searching for correlations in special fills to understand physics behind release mechanism and dynamics in e-mag fields
Co-Analyse dBLM data: if available the dBLMs provide bunch by bunch resolution of UFO events
Investigate connection between UFO rate and SEY conditioning

20. Experimental approach
UFO collection:
extract original contamination from LHC beam screen (spare magnets)
analyze it for chemical composition and size distribution to get hint on: origin, adhesive behavior, release mechanism, dynamics, removal
Beam pipe mock-up:
develop a vacuum setup which simulates the electric field inside the beam pipe and study particle behavior with laser to further understand dynamics
insert this mock-up into a magnet and see how the dynamics change in B field
Systematic UFO removal:
investigate strategies to clean the LHC beam pipe from the contaminants
Study of UFO adhesion force:
vibration study: vacuum chamber with dusty beam screen and hammer with tunable force, laser particle counter to detect released UFOs

21. BLMTI.06L7.B1E10_TCP.C6L7.B1
3.99 E-2 in RS4

22. Loss signal/Threshold: 7.13 E-2
BLMQI.18L6.B1E10_MQ
UFO timestamp , 09:06:35
Loss signal/Threshold: 7.13 E-2
Losses in RS 4: 9.42 E-2

23. Loss signal/Threshold: 1.92E-2
BLMBI.26L5.B0T20_MBA-MBB_26L5
UFO timestamp :22:30.0
Loss signal/Threshold: 1.92E-2
Losses in RS 4: 8.57E-3

24. TIMBER data for BLMBI.26L5.B0T20_MBA-MBB_26L5
LDB
MDB