1. LHCb and its VErtex LOcator integration into the LHC
Overview of LHCb
Current VELO design:
Mechanics
Cooling system for Si detectors
Vacuum issues
RF issues
Road map
Summary and outlook

2. Typical event for LHCb B0  - D*+  D0 + B0  +- Generated polar
angles of b and
b hadrons
(with PYTHIA)
B0  - D*+ 
D0 +
Primary vertex
B0  +-
10 mm
LHCb: identify B-mesons and their age at decay
Crucial information: particle ID, 1ary and 2ary vertices
vertex detector used in trigger level-1
offline decay distance resolution  120 m
(proper decay time resolution  0.04 ps)

3. LHCb Detector Acceptance: q=10...300 mrad Bakeable NEG-coated
beam pipe
Subsystems can
be retracted from
conical beam pipe
Warm dipole:
-  B dz  4 Tm
- correction scheme
- ramp with LHC
- reverse polarity
displaced IP8
“original” IP8

4. LHCb Si Vertex Locator Modules
etc.
r|f
f|r
-20 80
[cm]
towards
spectrometer Z
r|f mm r f
300 mm thick Si single-side n-on-n
Design work ongoing for front-end chip
(DMILL and subm technologies)
total of 220 k channels, analogue, S/N=15
one module: r and f measuring planes
with stereo angle
small overlap between opposite halves
for alignment and acceptance
cool down: -25 < Toperate < +10 oC
come as close as possible to LHC beams
minimise material between vertex and
first hit on Si  put detectors in vacuum
large outgas rates of detector components
 separate detectors from LHC vacuum
retract by
 3 cm
during beam
filling/tuning
detector prototype

5. VELO mechanical design
Decouple access to silicon detectors
from access to primary vacuum
Baking up to 150 oC is possible
Use ultrapure neon venting
VELO and NEGs need not be rebaked
after access to Si detector
Openings for feedthrough flanges
(25’000 pins)
Vertex
detector half
120 cm
25 cm
RF/Vacuum
thin shield
Exit window
1.5-2 mm
thick Al
Cooled Si sensors in secondary vacuum

6. 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 VELO: in total, ~ 54  40 W of heat, each cooled by a pipe of OD=1.1/ID=0.9 mm.
Tested at NIKHEF: See LHCb /VELO
capacity of cooling pipe > 50 W
heat transfer coefficient between pipe and coolant > 2 W cm-2 K-1
Phase diagram CO2
critical point
100
solid
liquid
gas
Pressure [bar] 10
vapor
triple point 1
-80
-70
-60
-50
-40
-30
-20
-10 10 20 30 40 50
Temperature [°C]

7. Wake field suppressors
Aim:
Provide a continuous conducting wall throughout the VELO to guide the mirror charge
Install wake field suppressors after mounting 2ary vacuum container
Upstream is “easy”: mounted with large flange off
Downstream is more delicate: mount through top flanges

8. Wake field suppressors
Current design:
Up/downstream suppressors
are identical
Material: CuBe (anneal,
form, harden at 400o C)
16 segments (which deform
differently during movement)
Coat suppressors (?)
Press-fit to beam pipe
Mounting to detector box is
non-trivial
Thickness: 100 m
194mm

9. LHCb VELO - LHC machine integration issues
The LHCb vertex detector system should not hamper LHC operation
Address:
vacuum issues
static and dynamic vacuum (ions, electrons and photons)
calculations and test measurements
radio-frequency issues
high frequency modes, losses, coupling impedance
safety issues
define level of acceptability
perform risk analysis

10. Wake field simulations
N. van Bakel
VU Amsterdam
Aim:
acceptable heat dissipation in the VELO
minimize coupling impedance
Performed MAFIA simulations (frequency domain):
full tank model and smaller models
detector halves in position open and closed
compared various detector encapsulations with
different corrugation shape and depth
deal with complex non-symmetric structure!
time-consuming and CPU intensive
LHCb “A first study of wake fields in the LHCb VD”
LHCb “W. f. in the LHCb VD: strip shielding”
LHCb “W. f. in the LHCb VD: alternative designs for the w. f. suppr.”

11. Wake field simulations (continued)
106
104
102
Wake field simulations (continued)
d=160mm d
Beam axis
Si sensors
Al shield
~35mm
104
103
102
d=20mm
Shunt resistance ()
Conclusion:
no problematic resonant effects for
corrugated encapsulation with
corrugation depth d < 20 mm
Under study:
time domain (ABCI & MAFIA)
low frequency slope of Im(Z//)
loss factor k//
103
102
d=5mm
100 W limit
Frequency (MHz)

12. RF tests at NIKHEF Study: Eigenmodes, impedance 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
222 MHz
272 MHz
320 MHz
Use network analyser and coupling loops to measure the reflection for different frequencies.
First 3 measured eigenmodes
of empty tank: 220, 270, 320 MHz
Compare to simulation with MAFIA

13. Vacuum constraints for stable pressure in VELO: a first glance
LHC beam-gas life time limit   24 h requires LHC integrated density
tmax  1  1016 H2/cm2 .
H2 pressure of 10-7 mbar  2 m (300K) corresponds to  0.005% of tmax.
 rather “loose” constraint for stable pressure in VELO.
10-7 mbar  1.2 m (H2 300K)  1.5 % of LHCb nominal luminosity
More serious: pumping life time of NEGs in LHCb beam pipe.
Estimate: pCO  10-8 mbar  6 m of pipe saturated in ~3 months (?)

14. Dynamic Vacuum Dynamic vacuum phenomena must be taken into account
in the design of the LHCb vacuum system (including VELO):
Ion-, electron- and photon-induced desorption
Electron multipacting
 stringent constraints on geometry and surface desorption properties,
e.g. for ion-induced desorption: local pumping speed and
surface materials must be chosen such that the critical current
Icrit > 2  2  0.85 A = 3.4 A
Safety factor two beams

15. Dynamic pressure profile
Unbaked VELO tank
hi as for unbaked metal
LHCb beam pipe
(NEG saturated, i.e. not pumping)
hi as for baked surface
ion desorption yield
(incident ion energy Eion ~ 300 eV)
p (torr)
Comments:
new VELO design is bakeable
 less outgassing and beam-induced desorption
 NEGs not saturated
most of COx desorption in this calculation is photon-induced
 if needed: reduce locally the photon flux
A. Rossi, LHC-VAC
No electron-induced desorption in the model

16. VELO vacuum system Differential pumping system:
No valves between VELO 1ary vacuum and LHCb NEG-coated beam pipe
VELO 1ary vacuum base pressure (no beam) ~10-9 mbar
Detectors in 2ary vacuum ~10-4 mbar
Separation 1ary/2ary vacuum by thin Al foil
Developing gravity-controlled safety valve to protect the foil against
differential pressure
Coat foil with NEG or titanium if needed (see dyn. vac. phenomena)
Access to Si detectors decoupled from access to primary vacuum
In-situ baking of primary vacuum surfaces up to 150 oC
Use ultrapure neon venting so that VELO and NEGs need not be rebaked
after access to Si detector
Working on a detailed description of the VELO vacuum system:
components (pumps, ducts, ...)
monitoring and safety equipment
control system (PLC based)
describe static and transient modes

17. Vacuum System

18. Thin vacuum foil Beryllium (1 mm thick):
Max p  500 mbar*
Beryllium (1 mm thick):
very expensive… if at all feasible!
safety issues
Aluminium (250 m thick):
“cheap & readily available” (compared to Beryllium)
NIKHEF: extensive prototyping program, welded 100 m on 300 m
Labour intensive: manufacture moulds, make foils, ~12 press/anneal cycles, etc.
Max p  15 mbar*
* Means irreversible deformation, no safety factor included.
Values are approximate as mechanical properties can deviate
substantially for the actual foil (hence, tests on prototypes are needed).

19. Thin vacuum foil (0.25 mm Al)

20. 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

21. Risk Analysis
Purpose: To provide an objective basis for a constructive and methodical evaluation of the VELO design.
comprehensive overview of all 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

22. 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

23. Road map Feb 15 1st VELO presentation to LEMIC 2000 Jan 23
2nd VELO presentation to LEMIC
Fabricate prototype 250 m Al shield
Test mechanical properties of shield
Test vacuum safety devices (crash scenarios)
Measure Z//()
Build and test full scale CO2 cooling system
Manufacture vacuum tank
Full system test:
baking demonstration
pump-down procedure
venting with ultrapure neon
motion mechanics
etc.
(Milestones to be agreed upon in
1st VELO review, Apr 3&4, 2001)
Apr 3
1st VELO review with LHC
2001
May 28
Submit TDR to LHCC
Jul 4
Presentation of TDR to LHCC
Nov 5
Approval of TDR by RB
Feb xx
2nd VELO review with LHC
2002
Feb yy
3rd VELO review with LHC
(production readiness review)
2003

24. Road map (continued) Apr 1 LHC octant test 2004 Sep 30
Last dipole delivered
Mar 31
Installation of VELO at IP8
2005
Ring closed and cold
Dec 31
Full machine commissioning
Single beam
First collisions (pilot run)
Shutdown
Jan 31
Mar 31
Apr 30
Jul 31
VELO commissioning, EMC tests, first tracks
LHCb commissioning
2006
Physics run
Feb 28
LHCb: run after...
2007

25. Summary
After numerous LHC/LHCb meetings, including two LEMICs, the design of the VELO has matured to a system with
silicon detectors located in a 2ary vacuum system
thin separation foil (for RF and vacuum) protected by gravity-controlled and electrically controlled safety valves
a 2-phase CO2 cooling system in 2ary vacuum
decoupled access to Si detectors from access to 1ary vacuum system by using ultrapure inert gas venting
possibility to bake out up to T  150 oC
smooth conducting wall throughout setup for mirror charge (study wake field effects by simulations and tests with full scale model)
Major integration issues being addressed: dynamic vacuum, electron multipacting, impedance, RF losses, safety
Design has now clear support from LHC/VAC
(see LEMIC jan/2001 and LHC-TC feb/2001)
 “door open” for TDR

26. Outlook LHCb/VELO: continue extensive prototyping and testing
Mechanism for supervision by LHC was set up:
at least 3 reviews before installation at LHC
risk analysis to assess acceptability (not only LHC-VAC...)
perform all required tests before installation into LHC
Further interaction with LHC groups is essential:
vacuum: “sector” valves, more data and simulations needed on dyn. vac. effects, e.g. hi of saturated NEGs, photon flux at IP8, e-multipacting, etc.
choice and configuration of equipment: vacuum pumps, valves, diagnostics equipment, controls (PLCs), etc. (radiation environment)
beam failure scenarios and IP8, radiation monitors, etc.
Aim: full system setup with Si detector modules in LHC during single beam operation in feb+mar 2006