geneva, 23-01-2001 m. ferro-luzzi, cern/ep status report on the introduction/reminder improved...

Geneva, 23-01-2001 M. Ferro-Luzzi, CERN/EP

Status Report on the

• Introduction/Reminder

• Improved mechanical design

• Wake fields

• Vacuum system design

• Cooling system for Si detectors

• Summary and outlook

• Introduction/Reminder

• Improved mechanical design

• Wake fields

• Vacuum system design

• Cooling system for Si detectors

• Summary and outlook

Geneva, 23-2-2001 Massimiliano Ferro-Luzzi, CERN/EP

Vertex


LHCb VD - LHC machine integration issues

The LHCb Vertex Detector system should not hamper LHC operation

Address:• vacuum issues

static and dynamic vacuum see Adriana Rossi’s presentation calculations and test measurements

• radio-frequency issues high frequency modes, coupling impedance Z|| / n calculations and test measurements

• safety issues define level of acceptability perform risk analysis


Side flange withfeedthroughs

Bending hinges

Support frame

Si detector

Detector support and cooling

Bellows (22000signal wires)

moves by 30 mmonly two positions:open or closed !!

“TP” Designpresented at LEMIC

February 2000

Si encapsulation and center frame are not shown !see LHCb note 99-042/VELO


Difficulties with TP designDifficulties with TP design• FEA displacement studies led to a rather bulky center frame

poor sideways accessibility for (a) wake field suppressors (b) Ti evaporator insertion

• System was not bakeable (the reverse was under study) base primary vacuum pressure p1 ~ 10-8 mbar aging of NEGs due to gas flow from VDS (?) dynamic vacuum: struggle to get Icrit > 3.4 A

• Communicating 1ary and 2ary volumes NEGs must be regenerated after every access to Si detectors limited to ~10 cycles (?)


TP designcenter frame

Desired situation

Side wake field suppressors Ti evaporator

No room onthe sides !

Si detectorbox


Optimized SystemOptimized System

• Decouple access to Si detectors from access to 1ary vacuum

• Use ultrapure neon venting

• NEGs need not be baked after access to Si detector

• Baking up to 150 oC is possible

• Mount two detector halves independently

• use of non-standard, large-size, rectangular bellows

M. Doets, NIKHEF

airair

2ary vacuum2ary vacuum

1ary vacuum1ary vacuum


bellowschain/belt

cooling/bake out

gearbox1:40

ball spindle 16x2

10 mm

linearbearing 2x

30 mm

motor

• Detectors halves opened/closed in steps (remote-controlled)

vert. = 10 mm, horiz. = 2x30 mm

• Microswitches at out position

• LVDTs

• Steel frame

• Alignment:– 2 planes

– 3 points each

– define IP

• All motors, bearings, gearboxes, etc., are outside vacuum

Support and motion mechanicsSupport and motion mechanics

30 mm


Support systemSupport system

• Alignment pins for reproducible coupling

• Reproducible positioning

• Outer switch positions aligned to nominal beam axis


Vessel installationVessel installation

• Move bellows and couplings to “closed” position

• Install vessel from top

• Align vessel to beam line

• Fix vessel to frame

• Attach bellows


Install detector housingsInstall detector housings• Remove upstream

flange (need 2 m access)

• Rectangular bellows– 60 mm stroke

– normal 30 mm

– lateral 6 mm

– need not withstand atmospheric differential pressure

• Fabrication– difficult and costly!

– Palatine, Bird, Calorstat, MB, VAT, ...

= 2ary vacuum vessel

• Install wake field suppressors and close upstream spherical flange


Complete installation of 2ary vacuum system

Complete installation of 2ary vacuum system

• Detector system separated from vacuum system functionality

• Connect inner system (detector housing) to motion drives via side flanges

• Install– pump-out, valves

– turbo pumps, damping

• Seals: – 1ary / air: all metal

– 1ary / 2ary: viton & metal

– 2ary / air: viton & metal


Detector installationDetector installation

• Install detector halves from sides

• Decouple detectors from flange box

• Tooling needed

• Detector half can be replaced by a dummy flange box

Detectors

Flange box


VELO assemblyVELO assembly


• Install wake field suppressors after mounting 2ary vacuum container

• Mount through top flanges

– seal with view ports ?

• Upstream is easier: mounted with large flange off

WF screens

420

910

IP

Wake field suppressorsWake field suppressors


Current design:

• Up/downstream suppressors are identical

• Material: CuBe

• Length: 179 mm

• Thickness: 100 m

• 16 segments

• Mounting to detector box is non-trivial




…continued:

• Segments deform differently during movement

• Coating needed on suppressors (?)

• Press-fit to beam pipe structure

• Anneal CuBe, deform, harden at 400o C


Wake field simulationsWake field simulationsPerformed MAFIA simulations:• full tank model and smaller models• detector halves in position open and closed• compared various detector encapsulations with different corrugation shape and depth• complex non-symmetric structures!

LHCb-99-041 “A first study of wake fields in the LHCb VD” LHCb-99-043 “W. f. in the LHCb VD: strip shielding”LHCb-99-044 “W. f. in the LHCb VD: alternative designs for the w. f. suppr.”Conclusions:

• Frequency domain: no problematic resonant effects for corrugated encapsulation with corrugation depth < 20 mm • Time domain: losses are acceptable

Under study: • low frequency slope of Im(Z||) Time-consuming and CPU intensive (ABCI & MAFIA)

N. van BakelVU Amsterdam

Thanks to:O. BrüningD. BrandtL. Vos


RF tests at NIKHEFRF tests at NIKHEF

First 3 measured eigenmodes of empty tank: 220, 270, 320 MHzCompare to simulation with MAFIA

Study:• Eigenmodes, short range effects, Z||

• Effect of WF screens, open/close halves• RF fields inside secondary vacuum (pick-up)

Use:• Wire method• Multiple (rotatable) loop antennas• Reference LHC pipe

F. Kroes, NIKHEF


Vacuum system layoutVacuum system layoutMain changes since last LEMIC (february 2000):

• removed conductance between 1ary and 2ary volumes conductance: 1 l/s 10-5 l/s reduced contamination of 1ary vacuum and NEGs

• development of gravity-controlled safety valves used in addition to pressure-switch electrically activated valves intrinsically safe solution

• decoupled air exposure of 1ary and 2ary volumes (see mech. design) use of ultrapure neon venting procedure to preserve NEGs

bakeable system (T 150 oC) reduces effect of several (static & dynamic) vacuum phenomena!


…continued

Unchanged since last LEMIC (february 2000):

• thin separation foil between 1ary and 2ary vacuums which does not withstand atmospheric pressure

performed extensive MC physics simulations (assess effect of material) investigated feasibility of Beryllium option (Brush Wellman) performed extensive FEA calculations for Al and Be developed a gravity-controlled safety valve to protect against differential pressure increase

• mixed-phase CO2 cooling system for Si detectors in 2ary vacuum

Vacuum system layoutVacuum system layout


Beryllium (1 mm thick):

• FEA: max p 500 mbar*

• ~500 kUS$ per container

if at all feasible!

• safety issues

Aluminum (0.25 mm thick):

• FEA: max p 15 mbar*

• NIKHEF: successfully welded

100 m on 300 m

• press-shaping being developed at NIKHEF

• “cheap & readily” available (compared to Be)

* means: irreversible deformation, no safety factor included

Thin vacuum foilThin vacuum foil


FEA for Al foil 0.25 mm FEA for Al foil 0.25 mm

Assumed annealed Alyield strength of 40 MPa(typical Al ~ 40…250 MPa)

Max p 15 mbar (irreversible deformation no safety factor included)

By Marco Kraan, NIKHEFmany more results at http://www.nikhef.nl/pub/departments/mt/projects/lhcb-vertex/

Displacement [mm]


FEA for Be foil 1.0 mm FEA for Be foil 1.0 mm

Assumed S-200F hot pressed block with a yield strength of 270 MPa (SR-200 cross rolled sheet: yield strength = 340 Mpa)

Max p 500 mbar (irreversible deformation no safety factor included)

By Marco Kraan, NIKHEFmany more results at http://www.nikhef.nl/pub/departments/mt/projects/lhcb-vertex/

Displacement [mm]


Multiple scatteringMain Problem: trigger decision based on tracks displaced from

primary vertex no momentum information at this trigger stage low-momentum particles undergo more multiple

scattering fake signatures of a displaced secondary vertex

performed extensive Monte Carlo simulation and analysis

Result: Increasing thickness of Al foil (100250mm) reduces vertex trigger efficiency by factor ~1.2 (20% loss of good events)

Other Problems: increased background rates increased occupancies

0.08

00 0.4 Signal efficiency

Min

imum

bia

s re

tent

ion

0.2

0.04

III, 250 m foilII , 250 m foilTP, 250 m foil

III, 100 m foilII , 100 m foilTP, 100 m foil


• Labour intensive:– manufacture moulds

– make foils: ~12 press/anneal cycles, etc.

• Extensive prototyping program

Chiel Bron

CP?!



• Increase radius (10 20 mm) to avoid folding• Crystal structure seems affected• Development tests:

– Employ Al alloy with Mg

– Deform at higher

temperature: 150 - 200 oC

• Later, vacuum tests:– microscopic holes ? (leaks)

– mechanical properties:

deformation pressure,

rupture pressure, etc.



Mixed-phase CO2 Cooling system

Advantages:• Radiation hard (used in nuclear power plants)• Non toxic (conc. < 5%), non flammable• Low pressure drop in microchannel tubes• Good thermodynamic properties• Widely available at low cost• No need to recover or recycle

Principle of operation:• CO2 is used in a two-phase cooling system. • The coolant is supplied as a liquid, the heat is taken away by evaporation. • LHCb VD: in total, ~ 54 40 W of heat, each cooled by a pipe of OD=1.1mm/ID=0.9 mm.

Tested at NIKHEF: See LHCb 99-046/VELO• capacity of cooling pipe > 50 W• heat transfer coefficient between pipe and coolant > 2 W cm-2 K-1

Phase diagram CO2

1

10

100

-80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50

Temperature [°C]

Pre

ssu

re [

ba

r]

vapor

liquidsolidgas

critical point

triple point


CO2 Cooling system layoutCO2 Cooling system layout

Standardrefrigerator unit

Behind shielding wallHall area2ary vacuum

Storage vessel

Liquid CO2 pump

Heat exchanger

Restriction (0.85*40 mm)

Needle valve(sets total flow)

Pressure regul. valve (70 bar)

Shutter valve

Cooling tubes(0.9/1.1 mm)

Gas return (12mm)

~ 60 m

Liquid supply (6mm)

H. Boer Rookhuizen, NIKHEF


CO2 Cooling TubesCO2 Cooling Tubes

• Total amount of CO2 in the system

6 of liquid 3 m3 of gas at STP• In the 2ary vacuum volume:

100 m 100 g of liquid

30 of gas at STP

50 mbar in 600 at Troom

• Total amount of CO2 in the system

6 of liquid 3 m3 of gas at STP• In the 2ary vacuum volume:

100 m 100 g of liquid

30 of gas at STP

50 mbar in 600 at Troom

• ID = 1.1 mm, OD = 0.9 mm• vacuum brazed (no flux, no fittings)• can sustain p > 300 bar (CO2: pequilib = 72 bar at 30 oC)

• ID = 1.1 mm, OD = 0.9 mm• vacuum brazed (no flux, no fittings)• can sustain p > 300 bar (CO2: pequilib = 72 bar at 30 oC)

Flow restrictionsFlow restrictions


Vacuum System ControlsVacuum System Controls• By NIKHEF group (from former NIKHEF

accelerator) in close collaboration with LHC-VAC group.

• Meeting in Amsterdam on 11+12 Jan. 2001

• Towards a detailed description of the vertex detector system:– detailed layout of vacuum system – monitoring and safety equipment– control system (PLC based)– describe static and transient modes– etc.

• Risk assessment

L. Jansen, J. Kuyt NIKHEF


Gravity-controlled valveGravity-controlled valve• weight ~ few grams, area ~ few cm2

• reacts to differential pressure ~ few mbar

• no electrical power

• no pressurized air

• intrinsically safe solution

to 1ary vacuum

to 2ary vacuum

to auxiliary pump

Use tandem valve to protect against both possible signs of differential pressure


• Spurious conductance in normal operation, i.e. molecular flow regime

• Dynamic response to sudden pressure change

• System behaviour during pump down

Tests of gravity-controlled valveTests of gravity-controlled valve

Sander Klous, NIKHEF


Test setup


First Measurement ResultsFirst Measurement Results

• Conductance (for H2O in range 10-3…7 mbar):

– 110-3 liter/sec without auxiliary pump 10-7 mbar liter/sec

– 110-5 liter/sec with auxiliary pump 10-9 mbar liter/sec

Expected leak rate for nominal

2ary vacuum pressure (10-4 mbar)

• Reaction to abrupt leak: p maintained < 6 mbar

• Pump-down time through a restriction: preliminary, – 3 hours for p < 1 mbar

approximate– 3 hrs more for p < 10-5 mbar results


Risk AnalysisRisk Analysis

Purpose: To provide an objective basis for a constructive and methodical evaluation of the VDS design.

• comprehensive overview of all (major) risks involvedwhat risk scenarios, what consequences, what probabilities to occur ?

• requirements/recommendations for a given design choicewhat tests should be performed and what results obtained to make the chosen option acceptable ?

• basis for a later, more detailed risk analysis f.i. risk of “injuries to personnel” are not assessed in details, but believed to be downtime and equipment loss risks


Framework of Risk AnalysisFramework of Risk Analysis

Use same model as for CERN Safety Alarms Monitoring System (CSAMS)

(1) Identify undesired event (UE)(2) Determine the consequence category of UE(3) Use predefined table to fix maximum allowable frequency (MAF)(4) Determine required frequency by reducing MAF by factor 100


Framework: frequency categoriesFramework: frequency categories

Indicative frequency Category Description level (per year)

Frequent Events which are very likely to occur > 1 in the facility during its life time

Probable Events which are likely to occur 10-1 - 1in the facility during its life time

Occasional Events which are possible and expected 10-2 - 10-1

to occur in the facility during its life timeRemote Events which are possible but not expected 10-3 - 10-2

to occur in the facility during its life timeImprobable Events which are unlikely to occur in the 10-4 - 10-3

facility during its life timeNegligible Events which are extremely unlikely to < 10-4

occur in the facility during its life time


Framework: consequence categories

EquipmentCategory Injury to personnel loss in CHF Downtime

(indicative) (indicative) (indicative)

Catastrophic Events capable of resulting > 108 > 3 monthsin multiple fatalities

Major Events capable of resulting 106 - 108 1 week to 3 monthsin a fatality

Severe Events which may lead 104 - 106 4 hours to 1 weekto serious, but not fatal injury

Minor Events which may lead 0 - 104 < 4 hoursto minor injuries

Turns out to be the dominant criterium


Frequency Consequence categorycategory Catastrophic Major Severe Minor

Frequent I I I II

Probable I I II III

Occasional I II III III

Remote II III III IV

Improbable III III IV IV

Negligible IV IV IV IV

Framework: risk classification tableFramework: risk classification table

max allowable frequency

required frequency

Legend: I = intolerable riskII = undesirable but tolerable if risk reduction is out of proportion III = tolerable if risk reduction “exceeds” improvement gainedIV = negligible risk


Functional AnalysisFunctional Analysis

Within context of risk analysis, consider 3 STATIC modes of operation:

Normalring valves open full aperture of VD < 54 mmnormal running mode for LHCb physics

Standbyring valves open full aperture of VD > 54 mme.g. beam filling/tuning, scheduled dump

(in some cases LHCb might take data)

Isolatedring valves closed full aperture of VD is anye.g. hall access, remote-controlled or in-situ maintenance


TRANSIENT states:

NEG-preserving vent procedure and subsequent pump-down• use ultrapure Ar/Ne• 1ary and 2ary volumes are separated • monitor |p1-p2| and |p1-pair| , control p1 (pump/inject)

NEG-saturating vent procedure and subsequent pump-down• use clean gas• 1ary and 2ary volumes are communicating• followed by a bake-out of VDS and LHCb pipe

Functional AnalysisFunctional Analysis


Assumptions

• If the NEGs are exposed to ambient air (even if via a leak)

baking is needed after the subsequent pump-down !

if beam-induced desorption properties of a saturated (but not “air-vented”) NEG are good enough, this constraint could be relaxed

• If primary vacuum system vented with ultrapure Ar/Ne baking is not needed

standard procedure used at CERN (EST/SM, LHC/VAC, ...)


Downtime estimationsDowntime estimationsNeeded to assess gravity of a given undesired event!Tasks:• obtain access to VD restricted area 1 shift ? • bring VDS to 1 atm (and Troom) 1 shift • prepare LHCb beam pipe for bake-out of NEGs 2 days• remove or install a detector half 1/2 shift• remove or install detector encapsulations 1 day ?• replacement of LHCb beam pipe section 2 weeks ?• pump down to p1,2 < pcrit (5 mbar) 1 shift • bake out VDS and pump down to p < pactivateNEG 1 day• bake out NEGs 1 day• pump down to p < pbeamfilling (assuming active NEGs) 1 day ?• reverse of “prepare … for bake-out of NEGs” 2 days• evacuation and closing of experimental zone 1 hour ?

(some tasks can proceed in parallel !) 1 day = 3 shifts = 24 hours

10-4…5 mbar

10-7…8 mbar ?


Undesired EventsUndesired Events

UE-1: Damaged feedthrough pin on secondary vacuum a) p remains < pcrit : safety valves remain closed b) p exceeds pcrit : safety valves work properly c) p exceeds pcrit : all safety valves fail

UE-2: Loss of electrical power UE-3: CO2 cooling system goes downUE-4: Leak of CO2 cooling pipeUE-5: Uncontrolled beam displacementUE-6: Ion-getter pump goes downUE-7: Turbomolecular pump station goes downUE-8: Bellow between 1ary & 2ary vacuums breaksUE-9: Jamming of detector halves motion mechanicsUE-10: Bellow between air & primary vacuum breaks . . .


Sample Undesired EventUE-1a: Damaged feedthrough pin on secondary vacuumAssumptions: • due to human action mode Isolated (ring valves closed)• leak rate into 2ary vacuum small enough that safety valves stay closed• leak rate to 1ary vacuum small enough that NEGs are negligibly affected NEG-preserving venting procedure with Ar/Ne (1 shift)Estimated damage:• 1ary vacuum not exposed to air baking-out NEGs not needed• replace feedthrough flange (1/2) and pump down (7) LHC downtime < 3 days category: SevereRequirements/remarks:• required frequency: Remote (see experience with LEP/SPS/... ?)• demonstrate that breaking of feedthrough pin will in most cases:

(a) not cause a p increase which triggers safety valves to open(b) negligibly affect the NEGs

• precautions: countersink flange connectors, tighten cable connectors, tighten cables, mount protective cage around feedthroughs, ...


Sample Undesired Event (continued)

UE-1b: as UE-1a but differential pressure triggers safety valves to openAssumptions: • as in UE-1a except that leak rate into 2ary vacuum is such that safety valves open• leak rate to 1ary vacuum substantial fraction of leak rate to 2ary vacuum vent procedure with clean gas or Ar/Ne (1 shift)Estimated damage: (compare to UE-1a)• 1ary vacuum was exposed to air NEG bake-out needed

1. replace detector half with flange (1/2) 2. prepare beam pipe for baking (6) 3. pump down to p1,2 < pcrit (1) 4. bake VDS + pump down to p < pactivateNEG (3) 5. bake out NEGs (3) 6. pump down to p < pbeamfilling (3)

• service/inspect pumps, … (3 more shifts) LHC downtime 1 week category: Severe (but downtime is longer for LHCb !)Requirements/remarks:• required frequency: Remote this is automatically fulfilled if actual frequency of UE-1a is Remote


Sample Undesired Event (continued)

UE-1c: as UE-1b but all safety devices fail to protect the thin-walled boxAssumptions: • as in UE-1b except that electrically activated valves and gravity-controlled safety valves fail to protect the thin-walled box vent procedure with clean gas or Ar/Ne (1 shift)Estimated damage: (compare to UE-1b)• as in UE-1b, but the thin-walled box (and perhaps some Si modules ?) must be replaced • replace thin boxes, debris (if any) must be collected, replace detector• LHCb beam pipe must be checked (and replaced ?) (2 weeks ?) If agreed by other parties: after bake out, install (new) vertex detector and move in all other LHCb detectors (additional 1 week) If not agreed: LHCb waits for next opportunity, but LHC is up ! LHC downtime = 1 ... 4 weeks category: MajorRequirements/remarks:• required frequency: Improbable • demonstrate that probability for coincidental failure is < 0.1, if actual frequency of UE-1b is Remote


• Design of LHCb VD is based on 2ary vacuum system– use thin separation foil protected by gravity-controlled and

electrically controlled safety valves

– First tests of gravity-controlled safety valves are positive

– use 2-phase CO2 cooling system in 2ary vacuum

– started risk analysis

– needs formal agreement from LHC/VAC for TDR and further developments

– allows baking up to T 150 oC

– decouples access to Si detectors from access to 1ary vacuum system

– employs venting with ultrapure Ar/Ne

• Wake field effects under study

• Perform required tests before installation into LHC

• Full vacuum setup with wake field suppressors in LHC during single beam operation

Summary and OutlookSummary and Outlook

geneva, 23-01-2001 m. ferro-luzzi, cern/ep status report on the introduction/reminder improved...

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