1. Commissioning of the Beam Conditions Monitor of the LHCb Experiment at CERN Ch. Ilgner, October 23, 2008 on behalf of the LHCb BCM group at TU Dortmund: M. Domke, S. Köstner (CERN), M. Lieng, M. Nedos, J. Sauerbrey, S. Schleich, B. Spaan, K. Warda
Beam conditions monitoring
motivation: protecting sensitive detectors
in HEP experiments
readout concept and integration into LHCb
The LHCb BCM project at TU Dortmund is supported by:
Ch. Ilgner (TU Dortmund), NSS-MIC 2008, Oct. 23, 2008

2. Implementation in LHCb
Sensitive devices, such as the
Vertex Locator („VeLo“), need
protection from adverse beam
conditions.
BCM-U BCM-D
The VeLo,
Courtesy of LHCb VeLo group
-2131mm mm
Ch. Ilgner (TU Dortmund), NSS-MIC 2008, Oct. 23, 2008

3. Accident Scenarios – Time Scales
Name
Operation mode
Loss type
Loss location
ΔT/turns
D1 warm
collision
local
triplet/collimator 5
damper
injection
arc/triplet 6
warm quadrupoles
any
distributed
collimator 18
dump septum
diluter kicker/septum 35
warm orbit corrector
aollision 55
RF (?)
arc/triplet/septum
arg/triplet/collimators
120
D1 Cold
220
arc/triplet/collimator
250
MB quench
280
D1 magnet failure:
fastest generic beam-loss scenario, timescale: 5 turns ~ 500 μs
→ defines the response time scale (beam dump becomes effective after 270 μs (max., depending on the position of the abort gap)
(anything faster than that could help in LHC commissioning)
after V. Kain, R. Schmidt, R. Assmann, EPAC 2002
Ch. Ilgner (TU Dortmund), NSS-MIC 2008, Oct. 23, 2008

4. Radiation Levels in the Vertex Locator and the BCM
What VeLo sees (in last Si plane) if it gets hit by one 7 TeV proton:
What BCM-D sees (energy deposition (sum over all 8 diamond sensors) if VeLo gets hit by one 7 TeV proton:
X-check:
VeLo signal
BCM-D signal
Ch. Ilgner (TU Dortmund), NSS-MIC 2008, Oct. 23, 2008

5. Simulated Energy Deposition in the Vertex Locator
Energy deposition of 40μs of minimum-bias events
in the Vertex Locator (VeLo):
Normal LHC running
conditions over 107s
(15MHz event rate):
13.3 kGy for
„upstream“ BCM
sensors
3.4 kGy for
„downstream“ BCM
Sensors
10.6 kGy for VeLo
Si paddles
(Simulations: M. Lieng)
Failure scenario: MCBX.1L8 magnet with reversed field at full strength.
BCM-D signals as multiples of nominal signal
Energy deposition of 40μs of minimum-bias
events in the Vertex Locator (VeLo):
Ch. Ilgner (TU Dortmund), NSS-MIC 2008, Oct. 23, 2008

6. BCM-D Station tested at ELBE Facility (FZD)
Exposure to 71fA to 225pA electron beam current (20MeV) in order to calibrate diamond sensors and analogue frontend electronics.
Beam currents through sensors: 5.62 pA, 39.6 pA, 805 pA, 2.59 nA, 17.8 nA.
Sensor currents: 1nA-3 μA.
The support by FZD staff (P. Michel, U. Lehnert et al.) is greatly appreciated.
Ch. Ilgner (TU Dortmund), NSS-MIC 2008, Oct. 23, 2008

7. LHC-Experiments Data Exchange
General Machine Timing (GMT)
Beam Dump System
VeLo Interlocks
Beam Conditions Monitor
LHC Injection
BCM ok
Safe Beam Flags,
Post-Mortem Trigger
Injection Inhibit
Beam Dump
(BIS)
LHCb
Experiment
Control
System
(ECS)
Injection Inhibit, Status & Flags
Courtesy of
R. Jacobsson
Ch. Ilgner (TU Dortmund), NSS-MIC 2008, Oct. 23, 2008

8. (effective after <270ms)
Beam-Abort Logics 1 2
32 (1280 μs)
FPGA features three parallel algorithms to trigger an LHC beam dump
Sampling period: 40 μs
Fast abort:
80 μs
3 adjacent sensors consecutively over threshold
Slow abort: 1280 μs discarding min. and 2 max. values, summing over the other values
Single bunch mode:
3 adjacent sensors in one CFC frame OR
Beam abort
(effective after <270ms)
Only during
injection
Coincidence conditions provide protection against
erratic dark currents (commonly known for pCVD diamond detectors)‏
Ch. Ilgner (TU Dortmund), NSS-MIC 2008, Oct. 23, 2008

9. First LHC beams as seen by the BCM
Threshold excesses during exposure of TDI at small particle fluxes:
threshold
, 20:36h:
Max(BCM-D): 500nA
(20% of threshold)‏
Max(BCM-U): 50nA
(0.5% of threshold)
 Dump logics have been successfully tested.
Ch. Ilgner (TU Dortmund), NSS-MIC 2008, Oct. 23, 2008

10. Conclustion
LHCb BCM measures ...
... CCC operator confirms three turns.
The LHCb Beam Conditions Monitor has been successfully calibrated, integrated into the LHCb control structure and proven to monitor reliably the particle flux at startup of CERN‘s Large Hadron Collider. A careful but realistic test has shown that the dump logics work reliably.
Ch. Ilgner (TU Dortmund), NSS-MIC 2008, Oct. 23, 2008