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. Morón Ballester, E. Nebot del Busto, L. Norderhaug Drosdal, A. Nordt, S. Redaelli, J. Uythoven, B. Velghe, V. Vlachoudis , J. Wenninger, C. Zamantzas, F. Zimmermann, …
5 April 2012 M.J. Barnes: LHC UFO meeting 1
Layout of MKI region;
Brief review of state of knowledge concerning MKI UFOs;
Screen conductors configuration and relationship to MKI UFOs;
MDs Proposed;
Conclusions.
Overview of Presentation
5 April 2012 M.J. Barnes: LHC UFO meeting 2
Layout of MKI8 Region
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.
Q4 Q5
TMR connection
Screen conductors capacitively coupled to “ground”
(metallization on ceramic tube)
5 April 2012 M.J. Barnes: LHC UFO meeting 3
ground plate
Kicked Beam
TMR connection entrance box
connection
capacitor
ferrite yoke
ground plate
HV plateHV plate
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].
Knowledge re MKI UFOs
5 April 2012 M.J. Barnes: LHC UFO meeting 4
Screen Conductors – Configuration and Voltage [10]
-14-12-10-8-6-4-202468
101214161820222426
0.0E+00
1.0E-06
2.0E-06
3.0E-06
4.0E-06
5.0E-06
6.0E-06
7.0E-06
8.0E-06
9.0E-06
1.0E-05
1.1E-05
1.2E-05
Volta
ge (k
V)
Time (s)
V(MagIn)V(Stripe3_In)V(Stripe6_In)V(Stripe9_In)V(Stripe12_In)
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.Note: plot for 50kV PFN.
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.
05
1015202530354045
1 2 3 4 5 6 7 8 9 10 11 12 13
Conductor Number
Max
.-Min
. Con
duct
or .
Vol
tage
(kV
)
00.511.522.533.544.5
Max
.-Min
. Int
er-C
ondu
ctor
.. V
olta
ge (
kV)
(HV) (GND)
Note: plot for 60kV PFN
5 April 2012 M.J. Barnes: LHC UFO meeting 5
Comparison of 15 & 24 Screen Conductors: Flattop Field (Efield: kV/m) [10]24 screen conductors
17k
0k
23k
-0.1k
-21mm: -398k-20mm: -59k
2.7k
-19.3k
12k
393k
1k
-10.9k
30k
26k
139k
3k
1k
151k
-150k
0k
31k
0k
17k
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;
459k
0k
134k
-0.5k
542k
1.7k
231k
415k
774k
80k
-107k
306k
121k
240k
632k
165.5k
644k
1117k
0k
287k
0k
678k
15 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).
5 April 2012 M.J. Barnes: LHC UFO meeting 6
24 Screen Conductors: Without Electrical Breakdown …..Two approaches are being followed to potentially allow the use of 24 screen conductors without electrical breakdown:
5 April 2012 M.J. Barnes: LHC UFO meeting 7
“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.
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.
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:
-505
101520253035404550556065707580859095
100105
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Nor
mal
ized
Fiel
d (%
)
Time (µs)
24 Screen Conductors, Cap coupled.0.5um homogeous Ti. Hard coupled1um homogeous Ti. Hard coupled0.5um homogeous Ti. Cap coupled1um homogeous Ti. Cap coupled
Configuration: Rise-time [ns] (0.5% to 99.5%)24 Screen Conductors, Cap coupled 8050.5µm homogeous Ti. Hard coupled -1µm homogeous Ti. Hard coupled -0.5µm homogeous Ti. Cap coupled 29601µm homogeous Ti. Cap coupled 4540
5 April 2012 M.J. Barnes: LHC UFO meeting 8
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.
Improved and Standardized Cleaning of Ceramic Chamber….
5 April 2012 M.J. Barnes: LHC UFO meeting 9
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 µs resolution. 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.
5 April 2012 M.J. Barnes: LHC UFO meeting 10
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)
5 April 2012 M.J. Barnes: LHC UFO meeting 11
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. Morón Ballester 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 LHCInjection 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.
5 April 2012 M.J. Barnes: LHC UFO meeting 12
Spare Slides
5 April 2012 M.J. Barnes: LHC UFO meeting 13
Installed MKI Magnets
Status des aimants MKI Date: 12/10/2010
Installés P2 (sens d'injection)
No aimants Diam. Tube
céramiqueNbr stripes
Nbr.dampingresistor
Nbr. essais Labo
Nbr. Pls Cond. Labo
Nbr. Pls Cond.
LHC
Nbr. Pls Opération
Nbr. Totalde pulses
Nbr. Cls Cond. Labo
Nbr. Cls Cond.
LHC
Nbr. Cls Opération
Dissipationen
W/mRemarques
9 53 15 2 6 537503 537503 40 89 (4) D MKI44. graded conductors4 53 15 2 3 207052 15617 222669 0 0 76 (2) C MKI43. graded conductors
10 53 15 2 97 (5) B mki46a. Graded conductors8 53 15 2 2 150954 15617 166571 0 0 60 A MKI37. Staggered conductors
Installés P8 (sens d'injection)
No aimants Diam. Tube
céramiqueNbr stripes
Nbr.dampingresistor
Nbr. essais Labo
Nbr. Pls Cond. Labo
Nbr. Pls Cond.
LHC
Nbr. Pls Opération
Nbr. Totalde pulses
Nbr. Cls Cond. Labo
Nbr. Cls Cond.
LHC
Nbr. Cls Opération
Dissipationen
W/mRemarques
6 51 15 1(masse) 1 164294 114240 278534 6 0 D2 51 15 1(masse) 2 223244 114240 337484 6 0 C3 51 15 2 3 105820 114240 220060 1 1 B1 51 24 (9 raccourcis) 2 4 488689 114240 602929 3 0 88 A
Réserve
No aimants Diam. Tube
céramiqueNbr stripes
Nbr.dampingresistor
Nbr. essais Labo
Nbr. Pls Cond. Labo
Nbr. Pls Cond.
LHC
Nbr. Pls Opération
Nbr. Totalde pulses
Nbr. Cls Cond. Labo
Nbr. Cls Cond.
LHC
Nbr. Cls Opération
Dissipationen
W/mRemarques
7
Remarques(1) Surtension PFN (1er cl à 59,6 KV) Analyse de gaz douteuse, deux claquages en opération (un durant softstart, l'autre avec faisceau)(2) Mauvais contact mini dégazage à chaque pulse, (3) Claquage en opération, suite à radiations dues à l'ouverture faisceau en amont (vanne vide trop haute de 5 mm)(4) No PT100's(5) #10 as from Dec 10, 2010 (was #05)
BEAM
BEAM
5 April 2012 M.J. Barnes: LHC UFO meeting 14
MKI
.D
MKI
.C
MKI
.B
MKI
.A
0
2
4
6
8
10
12
14
16
18
20MKI.05R8MKI.05L2
BLM name
num
ber o
f UFO
eve
nts
Distribution of UFOs at Point 8 and Point 2courtesy of T. Baer,
Chamonix 2012.
Distribution of the most upstream BLM at which the UFO is observable. TheBLM 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.
5 April 2012 M.J. Barnes: LHC UFO meeting 15
15 Screen Conductors (Efield: kV/m)Start of flattop (~680ns): Flattop (~7.8µs): Falling edge (~1µs):
-116k
0k
321k
-0.6k
-560k
2.3k
-287k
-134k
-353k
339k
-161.7k
66k
-243k
358k
-321k
-83k
356k
-518k
0k
116k
0.1k
-259k
232k
0k
-48k
0k
365k
1.1k
204k
195k
590k
-116k
98k96k
141k
140k
384k
146k
494k
790k
0k
75k
0k
425k
459k
0k
134k
-0.5k
542k
1.7k
231k
415k
774k
80k
-107k
306k
121k
240k
632k
165.5k
644k
1117k
0k
287k
0k
678k
Highest electric fields, inside ceramic chamber, occur during field flattop (longest duration too), especially in bottom half of ceramic chamber.
5 April 2012 M.J. Barnes: LHC UFO meeting 16
24 Screen Conductors (Efield: kV/m)Start of flattop (~680ns): Flattop (~7.8µs): Falling edge (~1µs):
-242k
0k
-303k
0.5k
-21mm: -720k-20mm: -361k
2.7k
-12k
-241k
324k
-298k
1k
-233k105k
-150k
-250k
-1k
81k
-391k
0k
-245k
0k
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401k
0k
480k
-1.1k
455k
0.5k
-11k
387k
182k
449k
-19.1k
406k
-126k
467k
391k
11k
158.5k
352k
0k424k
0k
413k
17k
0k
23k
-0.1k
-21mm: -398k-20mm: -59k
2.7k
-19.3k
12k
393k
1k
-10.9k
30k
26k
139k
3k
1k
151k
-150k
0k
31k
0k
17k
Highest electric fields, inside ceramic chamber, occur during field during field rise and fall.5 April 2012 M.J. Barnes: LHC UFO meeting 17
• 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 rate and local pressure at 450 GeV.
MKI UFOs
1236 UFOs around MKIs for fills lasting at least 3 hours after last injection.
101 MKI UFOs in Pt. 8 between last injection of beam 2 and beginning of ramp for 102 fills with 1380 bunches.
3.5σ statistical significance.
courtesy of T. Baer, Chamonix 2012.
5 April 2012 M.J. Barnes: LHC UFO meeting 18
• 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)
Number of MKI UFOs
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)
MKI UFO storms (Pt. 2)
courtesy of T. Baer, Chamonix 2012.
5 April 2012 M.J. Barnes: LHC UFO meeting
19
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. Morón Ballester 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
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 filternew 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.
courtesy of A. Gerardin, N. Garrel
EDMS: 1162034
100µm
10µm
0 2 4 6 8 10Energy (keV)
0
20
40
60
cps
C
O
Al
AuAu
Al
O
5 April 2012 M.J. Barnes: LHC UFO meeting 21
Temporal Distribution of Observed UFOs after MKI Pulse
• 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).
(0,2
5](2
5,50
](5
0,75
](7
5,10
0](1
00,1
25]
(125
,150
](1
50,1
75]
(175
,200
](2
00,2
25]
(225
,250
](2
50,2
75]
(275
,300
](3
00,3
25]
(325
,350
](3
50,3
75]
(375
,400
](4
00,4
25]
(425
,450
](4
50,4
75]
(475
,500
]0
2
4
6
8
10
12MKI.05R8MKI.05L2
time after MKI pulse [ms]
num
ber o
f UFO
eve
nts
1 event at 1330 ms
5 April 2012 M.J. Barnes: LHC UFO meeting 22
courtesy of T. Baer, Chamonix 2012.
Lead MKI UFOs
• 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).
• Horizontal dispersion
MKI (UFO location)
MQML.10L8 (highest loss)
IP8
TCTH
5 April 2012 M.J. Barnes: LHC UFO meeting 23
courtesy of T. Baer, Chamonix 2012.