mki ufo knowledge and future plans: a brief update

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


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)


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


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


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).


24 Screen Conductors: Without Electrical Breakdown …..Two approaches are being followed to potentially allow the use of 24 screen conductors without electrical breakdown:


“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


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….


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.


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)


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.


Spare Slides


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)



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



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


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.


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.


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

-244k

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.


• 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)


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


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


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



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



mki ufo knowledge and future plans: a brief update

Documents

mki ufo knowledge

mki pulse

mki ufos mds

mki tanks

mki ufos5

ufo rate

ufo events

ufo location