Status Report on the

1
Status Report on the

• Introduction/Reminder
• Improved mechanical design
• Wake fields
• Vacuum system design
• Cooling system for Si detectors
• Summary and outlook

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

3
Support frame
TP Design presented at LEMIC February 2000
Bellows (22000 signal wires)
Si detector
Bending hinges
Detector support and cooling
Side flange with feedthroughs
moves by 30 mm only two positions open or closed
!!
Si encapsulation and center frame are not shown !
see LHCb note 99-042/VELO
4
Difficulties 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 gt 3.4 A
• Communicating 1ary and 2ary volumes
• NEGs must be regenerated after every access to
  Si detectors
• limited to 10 cycles (?)

5
TP design
Desired situation
center frame
Si detector box
No room on the sides !
Side wake field suppressors
Ti evaporator
6
Optimized System
M. Doets, NIKHEF
air

• 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

1ary vacuum
2ary vacuum
7
Support and motion mechanics
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

bellows
chain/belt
30 mm
cooling/bake out
30 mm
gearbox 140
10 mm
ball spindle 16x2
linear bearing 2x
8
Support system

• Alignment pins for reproducible coupling
• Reproducible positioning
• Outer switch positions aligned to nominal beam
  axis

9
Vessel installation

• Move bellows and couplings to closed position
• Install vessel from top
• Align vessel to beam line
• Fix vessel to frame
• Attach bellows

10
Install detector housings
2ary vacuum vessel

• 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, ...

• Install wake field suppressors and close
  upstream spherical flange

11
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

12
Detector 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
13
VELO assembly
14
Wake field suppressors

• 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

15
Wake 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

16
Wake field suppressors

• continued
• Segments deform differently during movement
• Coating needed on suppressors (?)
• Press-fit to beam pipe structure
• Anneal CuBe, deform, harden at 400o C

17
Wake field simulations
N. van Bakel VU Amsterdam

• Performed 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 lt 20 mm
• Time domain losses are acceptable
• Under study
• low frequency slope of Im(Z)
• Time-consuming and CPU intensive (ABCI
  MAFIA)

Thanks to O. Brüning D. Brandt L. Vos
18
RF tests at NIKHEF
F. Kroes, NIKHEF

• 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

First 3 measured eigenmodes of empty tank 220,
270, 320 MHz Compare to simulation with MAFIA
19
Vacuum system layout

• Main 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!

20
Vacuum system layout
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

21
Thin vacuum foil

• 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

22
FEA for Al foil 0.25 mm
Displacement mm
Assumed annealed Al yield strength of 40
MPa (typical Al 40250 MPa) Max ?p ? 15 mbar
(irreversible deformation no safety factor
included)
By Marco Kraan, NIKHEF many more results at
http//www.nikhef.nl/pub/departments/mt/projects/l
hcb-vertex/
23
FEA for Be foil 1.0 mm
Displacement 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, NIKHEF many more results at
http//www.nikhef.nl/pub/departments/mt/projects/l
hcb-vertex/
24
Multiple scattering

• Main 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 (100?250mm)
• reduces vertex trigger efficiency by factor
  1.2
• (20 loss of good events)
• Other Problems
• increased background rates
• increased occupancies

III, 250 ?m foil II , 250 ?m foil TP, 250 ?m
foil III, 100 ?m foil II , 100 ?m foil TP, 100
?m foil
Minimum bias retention
0.08
0.04
0
0
0.4
0.2
Signal efficiency
25
Thin vacuum foil

• Labour intensive
• manufacture moulds
• make foils 12 press/anneal cycles, etc.
• Extensive prototyping program

CP?!
Chiel Bron
26
Thin vacuum foil

• 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.

27
Mixed-phase CO2 Cooling system
Phase diagram CO2

• Advantages
• Radiation hard (used in nuclear power plants)
• Non toxic (conc. lt 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 OD1.1mm/ID0.9 mm.
• Tested at NIKHEF See LHCb 99-046/VELO
• capacity of cooling pipe gt 50 W
• heat transfer coefficient between pipe and
  coolant gt 2 W cm-2 K-1

critical point
100
liquid
solid
gas
Pressure bar
10
vapor
triple point
1
-80
-70
-60
-50
-40
-30
-20
-10
0
10
20
30
40
50
Temperature C
28
CO2 Cooling system layout
H. Boer Rookhuizen, NIKHEF
Behind shielding wall
Hall area
2ary vacuum
Storage vessel
Gas return (?12mm)
Standard refrigerator unit
60 m
Liquid supply (?6mm)
Liquid CO2 pump
Heat exchanger Restriction (?0.8540 mm) Needle
valve(sets total flow) Pressure regul. valve (70
bar) Shutter valve
Cooling tubes (?0.9/1.1 mm)
29
CO2 Cooling Tubes

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

• Total amount of CO2 in the system
• ? 6 l of liquid ? 3 m3 of gas at STP
• In the 2ary vacuum volume
• ? 100 ml ? 100 g of liquid
• ? 30 l of gas at STP
• ? 50 mbar in 600 l at Troom

Flow restrictions
30
Vacuum System Controls

• By NIKHEF group (from former NIKHEF accelerator)
  in close collaboration with LHC-VAC group.
• Meeting in Amsterdam on 1112 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
31
Gravity-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 auxiliary pump
Use tandem valve to protect against both
possible signs of differential pressure
to 2ary vacuum
32
Tests of gravity-controlled valve
Sander Klous, NIKHEF

• Spurious conductance in normal operation, i.e.
  molecular flow regime
• Dynamic response to sudden pressure change
• System behaviour during pump down

33
Test setup
34
First Measurement Results

• Conductance (for H2O in range 10-37 mbar)
• 1?10-3 liter/sec without auxiliary pump ? 10-7
  mbar liter/sec
• 1?10-5 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 lt 6 mbar
• Pump-down time through a restriction
  preliminary,
• 3 hours for p lt 1 mbar approximate
• 3 hrs more for p lt 10-5 mbar results

35
Risk Analysis

• Purpose To provide an objective basis for a
  constructive and methodical evaluation of the VDS
  design.
• comprehensive overview of all (major) risks
  involved
• what risk scenarios, what consequences, what
  probabilities to occur ?
• requirements/recommendations for a given design
  choice
• what 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

36
Framework 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
37
Framework frequency categories
Indicative frequency Category Description
level (per year) Frequent Events which
are very likely to occur gt 1 in the
facility during its life time Probable Events
which are likely to occur 10-1 - 1 in 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
time Remote Events which are possible but not
expected 10-3 - 10-2 to occur in the facility
during its life time Improbable Events which are
unlikely to occur in the 10-4 - 10-3 facility
during its life time Negligible Events which are
extremely unlikely to lt 10-4 occur in the
facility during its life time
38
Framework consequence categories
Turns out to be the dominant criterium
Equipment Category Injury to
personnel loss in CHF Downtime (indicative) (
indicative) (indicative) Catastrophic Events
capable of resulting gt 108 gt 3 months in
multiple fatalities Major Events capable of
resulting 106 - 108 1 week to 3 months in a
fatality Severe Events which may lead 104 -
106 4 hours to 1 week to serious, but not
fatal injury Minor Events which may lead 0
- 104 lt 4 hours to minor injuries
39
Framework risk classification table
max allowable frequency
Frequency Consequence category category
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
required frequency
Legend I intolerable risk II undesirable
but tolerable if risk reduction is out of
proportion III tolerable if risk reduction
exceeds improvement gained IV negligible risk
40
Functional Analysis
Within context of risk analysis, consider 3
STATIC modes of operation Normal ring valves
open full aperture of VD lt 54 mm normal running
mode for LHCb physics Standby ring valves open
full aperture of VD gt 54 mm e.g. beam
filling/tuning, scheduled dump (in some cases
LHCb might take data) Isolated ring valves
closed full aperture of VD is any e.g. hall
access, remote-controlled or in-situ maintenance
41
Functional Analysis

• 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

42
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, ...)

43
Downtime estimations

• Needed 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 lt pcrit (?5 mbar) 1 shift
• bake out VDS and pump down to p lt
  pactivateNEG 1 day
• bake out NEGs 1 day
• pump down to p lt 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

10-45 mbar
10-78 mbar ?
44
Undesired Events

• UE-1 Damaged feedthrough pin on secondary
  vacuum
• a) ?p remains lt ?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 down
• UE-4 Leak of CO2 cooling pipe
• UE-5 Uncontrolled beam displacement
• UE-6 Ion-getter pump goes down
• UE-7 Turbomolecular pump station goes down
• UE-8 Bellow between 1ary 2ary vacuums breaks
• UE-9 Jamming of detector halves motion
  mechanics
• UE-10 Bellow between air primary vacuum breaks
• .
• .
• .

45
Sample Undesired Event

• UE-1a Damaged feedthrough pin on secondary
  vacuum
• Assumptions
• 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 lt 3 days ? category Severe
• Requirements/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, ...

46
Sample Undesired Event (continued)

• UE-1b as UE-1a but differential pressure
  triggers safety valves to open
• Assumptions
• 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 lt pcrit (1) 4. bake VDS
  pump down to p lt pactivateNEG (3)
• 5. bake out NEGs (3) 6. pump down to p lt
  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

47
Sample Undesired Event (continued)

• UE-1c as UE-1b but all safety devices fail to
  protect the thin-walled box
• Assumptions
• 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
  Major
• Requirements/remarks
• required frequency Improbable
• demonstrate that probability for coincidental
  failure is lt 0.1, if actual frequency of
• UE-1b is Remote

48
Summary and Outlook

• 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

49
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