M Väänänen B Lindström D Wollmann P Belanger CERN Technical meeting 25 April 2019 UFO observations in the LHC LHC first proton accelerator to suffer from their impact Still many unknowns impact expected to increase in future higher beam energy higher beam intensity ID: 791739
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Slide1
UFO type 1 dynamics studies using diamond beam loss monitors and blown-up bunches
M Väänänen, B Lindström, D Wollmann, P. BelangerCERN
Technical meeting – 25 April 2019
Slide2UFO observations in the LHC
LHC first proton accelerator to suffer from their impact
Still many unknowns, impact expected to increase in future (higher beam energy, higher beam intensity...)
Mika Väänänen
2
Understanding their dynamics important
clue for employing countermeasures
Courtesy
A.
Lechner
Slide3Beam-macroparticle interaction
Dust particle falls into beam (on assumption by gravity)Intense beam losses, duration ~1 msPremature beam dumps and superconducting magnet quenches-> up to 12 hours downtime!
Mika Väänänen
3
beam
UFO
e
-
e
-
+
beam losses
beam loss monitor (BLM)
+
Slide4Beam Loss Monitors (BLM)
Mika Väänänen4
Collimator
beam
UFO
dBLM
ICBLM
Collimator
scattered protons
particle showers
Slide5Mika Väänänen
5
Collimator
beam
UFO
dBLM
ICBLM
Collimator
scattered protons
particle showers
ICBLM:
Main beam loss monitoring system of LHC
40
m
s time resolution (half LHC turn)
dBLM
:
ns resolution (bunch-by-bunch, 25 ns)
Beam Loss Monitors (BLM)
Slide6ICBLM:
Main beam loss monitoring system of LHC40 ms time resolution (half LHC turn)
dBLM:ns resolution, bunch-by-bunch
Beam Loss Monitors (BLM)
Mika Väänänen
6
Collimator
beam
UFO
dBLM
ICBLM
Collimator
scattered protons
particle showers
1 cm
2
Slide7Wire-scanner: Thin carbon wire,
~30 µm, similar dimension and speed to UFOBeam losses detected by fast diamond BLM
UFO simulated using a Wire
7
Mika Väänänen
wire
beam
Slide8Wire-scanner: Thin carbon wire,
~30 µm, similar dimension to UFOBeam losses detected by fast diamond BLM
8
Can study movement of matter intercepting the beam
Detected 7 turns earlier
Consecutive LHC turns
Mika Väänänen
wire
bunches
Using
blown-up
bunches
to
detect
plane
of
movement
Slide9Mika Väänänen
9
Trigger
algorithm
for
new
readout
electronics
Recorded
12
events
with
the
trigger
Slide10UFOs at end of run
2 proton physicsSpecial beam
configuration during ~3
weeks
of
normal
physics operationsIn non-colliding 12b train, two blown-up
bunches: one
horizontally, one vertically per
beamNumber of events during this
time
: 14
Confirmed
by existing UFO Buster: 7dBLMs only at IR7, UFO Buster triggers on spatial distribution -> differences in triggering3 at top energy, all
others at ramp 1096-4522 GeVMika Väänänen10
Slide11Bunch-by-bunch
losses (30 Sep 2018)
Mika Väänänen
11
Slide12Insight
into UFO dynamics
Mika Väänänen
12
Losses
proportional
to proton
density -> proton density depends
on location -> We can derive
location
of UFO!
Losses
BLM
Slide13Location estimate based
on bunch by bunch losses
Mika Väänänen
13
Slide14UFO simulation model
Physical model of beam-macroparticle interaction to study UFOsPartially validated against UFO type 1 events (temporal loss pattern, # inelastic collisions; assuming ~20-30 µm particles, Cu, C)
14
Mika Väänänen
Simulate
possible
trajectories
based
on
starting
position and
initial
chargeCompare ratio
of bunch losses to measurement
Slide15Example simulation: charged
UFO with horizontal offset
Mika Väänänen
15
50 µm
carbon
particle
;
starting at (x0, y0) = (5.178, 5.333) mm; initial
charge
-2e-11 C
Slide16Comparison of simulations and measurements
50 µm
carbon particle; starting
at (x0, y0) = (5.178, 5.333) mm;
initial
charge -2e-11 CBest correspondence between simulation and measurement
Mika Väänänen
16
Slide17Integral ratio deviation
from measurement (WIP)
Mika Väänänen
17
Slide18Conclusions
Successfully studied UFOs
with blown-up
bunches
,
during
normal physics operationNew triggering system allows detecting UFOs
with diamond BLMs
14 events were
recorded with blown-up bunchesStrong indication
of
partial
horizontal
movement in one eventUFO needs to be negatively pre-charged -> movement can’t be explained by gravity alone
Furthers our understanding of the release mechanism-> Work ongoing
Mika Väänänen
18
Slide19Thank you!
Mika VäänänenMany thanks
to OP, J. Kral, D. Valuch
for
making
this study possible!19
Slide20UFO types
Mika Väänänen
20
A.
Lechner
~ 1
ms
second phase ~3 to 100’s
ms
Type 1
Type 2
p+
solid nitrogen
nitrogen gas
beam
very fast beam instability develops
Slide21UFO types
Type 1Traditional type, present since high-intensity operationsShort loss spike (~1 ms)SporadicAlong the entire length of the LHC
Type 2Present at specific magnet interconnect (16L2)
Hypothesis: caused by frozen nitrogen
macroparticle
Contamination of beam vacuum by air at 16L2 confirmed
Fastest observed beam instability in the LHCMika Väänänen
21
Slide22Peak count trigger
Mika Väänänen 05/09/2018
22
5ms
5ms
Slide23Trigger algorithm development
Developed in iterations
1. 3ms + 3ms, 9000 units, 10 peaks
9000 too high a threshold
2. 5ms + 5ms, 8500 units, 5 peaks
~200 triggers/day (~80GB of data); too sensitive
3. 5ms + 5ms, 8200 units, 100 peaks
~10 triggers/day; noticeably better efficiency
Mika Väänänen 05/09/2018
23
Slide24icBLM
vs dBLM correlation (30
Sep 2018)
Mika Väänänen
24
ICBLMs
are
a trusted
systemDBLM signal integrated in 80 us
bins
correlates
well
with ICBLM data
Slide25Turn
by turn, bunch
by bunch losses
(30
Sep
2018)
Mika Väänänen25
Elevated
losses in horizontally blown-up bunch
High
amplitude
, long
event
Best signal we had
Slide26Turn
by turn, bunch
by bunch losses (17
Oct
2018)
Mika Väänänen
26
Elevated
losses in vertically blown-up bunch
Losses
in
other
bunches
very lowAt the limit of what we can observe
Slide27Bunch
intensities
Mika Väänänen
27
Slide28Possible locations in both
planesLocation based on losses
from horizontally blown-up
bunch
Location
based on
losses from vertically
blown-up bunch
Mika Väänänen
28
Slide29Possible locations in both
planes
Mika Väänänen
29
Intersections
are
possible
UFO
locations