with contributions by: Etienne CARLIER, Volker MERTENS

LHC Beam Dump SystemLHC Beam Dump System Kicker maintenance and Kicker maintenance and

sparesspares Laurent DUCIMETIERE

References to talk by V. MERTENS, LHC Technical Committee (LTC) held on 24th October 2007 http://ab-div.web.cern.ch/ab-div/Meetings/ltc/2007/ltc_2007-16d.pdf

LHC Beam Dumping System (LSS6L/R, schematic)

MKD(15x)MKD(15x)

MSD(3x5)

MSDA MSDC

MSD(3x5)

MSDA MSDC

TDETDE

MKB

MKBH(4x)

MKBV(6x)

MKB

MKBH(4x)

MKBV(6x)

MKBH(4x)

MKBV(6x)

Q5R

Q4R

Q4L

Q5L

TCDS

TCDQ

Beam 2

Beam 1

V-defl, 2.4 mrad

H-defl, 0.3 mrad

MKD

Not to scale !

MKD pulse generators

FHCT stack with trigger transformer

1 complete spare generator in place per 15 operational; replacement itself quick, but must be followed by fine-adjustment of parameters and in-

depth revalidation of the dump system.

Extraction kickers MKD

total (15 magnets) horizontal deflection 0.28 mrad

Granularity and “one-off redundancy”(7 TeV extraction still clean if 1 of 15 MKD fails during dump action)but failing unit must be repaired before dump system can be re-qualified for use.

Lots of I/XPOC (internal/external post-operational checks, at each dump action) to detect slow degradation. E.g. :

- loss of capacity (self-healing capacitors)

- broken FHCT in stack

- erosion of high-current contacts

Analysis must be thorough, and results must be taken serious;

Failures (magnets, as the rest of the system, thoroughly tested; normally no “early faults” expected):

- vacuum leak on ceramic vacuum chamber

- HV flash-over at HV coil

- HV coaxial cable breakdown

MKD kickers – intervention related aspects, spares

Spares:

- 2 complete generators for 30 operational units

- 2 complete magnets for 30 operational units

- 5 ceramic chambers (long lead time items) for 30 operational units

- 1 spare cable already in place per magnet (per bundle of 8 cables)

Replacement of a magnet/chamber involves (everything x 5 (vacuum sub-sectoring)):

- dismantling of the opposite chamber

- bake-out of the ceramic chamber

- remounting of the new magnet and testing

- remounting of the opposite chambers and bake-out of those

MKD kickers– intervention related aspects, spares

time estimate: 2-3 weeks

MKD spares

This list (like all others) is for the complete units and those components which can be fitted in situ.

Besides those there are further spare components for repair of broken units in the laboratory

(notably long-lead time items involving many fabrication steps like cores, HV coils, …).

*) replacement itself fairly quick, but every repair affecting the impedance of the HV circuit must be followed by fine-adjustment of parameters (and in-depth re-validation of the dump system).

Dilution kickers MKBH, MKBV

Each tank houses 2 magnets

circulating beams

extracted beam

MKB spares

Will have a lot of spares in 2008 …

(until the staged equipment

will be installed and operational).

Very similar basic components as MKD

(cores, coils, …) … but in a vacuum tank.

Failures similar as well …

MKBH during insertion

Electronics & controls

Have at least 1 spare for each electronics module used (≈ 150 different types, incl. PLCs).

Typical spare level 10 %.

Crates, CPUs, timing modules, … managed by AB/CO (not discussed here).

About MTBF:

assembly errors sorted out, first “burn-in” made initial wave of faults mainly over

failures over lifetime: new type of equipment, statistics not well known

Low power electronics not expected to fail frequently (if not over-rated …), also PLC (2 mods br.)

More wear for power and high-voltage equipment (trigger modules, charging power supplies).

Should consider to purchase a few further charging supplies to bridge the time when a broken one is sent away for repair, and still keeping the test stands in 867 operational.

Have to see how electronics ages in the tunnel (dust, humidity, contact corrosion, …)

CERN wide central storage for common equipment would be useful

e.g. all SIEMENS PLC stuff in a place in 874, as already initiated

possible rotation of equipment with manufacturer can avoid a number of problems

Summary

Main choices on number of spares were made in the mid 90 (similar to the SPS policy).

In some cases (e.g. MKB) more parts where “added on the fly” allowing to complete a full spare magnet tank (less downtime because repair can be done off-line).

Number of full spare units seems generally correct: “canonical value” ≈ 10 %

In reality 5 – 15 % (more if the devices are difficult or time-consuming to repair (and vice versa))

No “full spares of spares” for everything …

… but typically a reasonable number of additional sub-components to repair failing units.

Early numbers based on SPS experience – to be confirmed during LHC operation.

Failure risk to be re-assessed, and strategy to be adapted as needed.

Regular “spares reviews” to be made.

Various things to be organised (responsibilities, storage, re-testing frequency, re-plenishing, …).

Certain items could profit from a more central management (e.g. PLC accessories in CCC).

Would a more centrally organised spares mgmt also be useful for other hardware elements ?

Issues to be addressed

Hardware aspects :

Certain sub-assemblies to be pre-fabricated for faster intervention.

Kicker HV circuitry: erosion of high-current contacts is a recurring risk – watch out.

Organisational aspects :

Where to store spares: centrally in lab, or distributed in the galleries ?

Centrally less effort to manage and keep hardware alive

less costly as well (less duplication, e.g. electronics partly in common with PS/SPS)

… but downtime is usually longer.

Transport team needed (for heavy stuff).

Spares “stewardship” ?

test the equipment regularly to make sure it still works; apply changes on oper. eqpt.

Who is responsible for “spares management” ?

prevent loss of knowledge from turn-over / departure of personnel …

Clear identification of components

bar code system (discussed since long …) ?

MTF should be helpful to trace history of (re-)used components …

Regular review of spare situation and strategy in the group (at least).