1. Why do BLMs need to know the Quench Levels?
Measurement principle
BLM design consideration
Loss locations
Response time, dynamic range (quench level vs loss duration or vs energy)
Detector locations
Particle shower development
Why do BLMs need to know the Quench Levels, B.Dehning

2. Measurement Principle
Detection of shower particles outside the cryostat to determine the coil temperature increase due to particle losses => comparison with thresholds => beam dump if exceeded
Relation between loss rate and temperature increase quench levels: (J.B. Jeanneret et al., LHC Project Report 44)
Relation between loss rate and particle flux outside the cryostat fluence: (A. Arauzo Garzia et al., LHC Project Note 238, see:
Why do BLMs need to know the Quench Levels, B.Dehning

3. Loss Levels and Required Accuracy
Relative loss levels
450 GeV
7 TeV
Damage to components
320/5
tran./slow
1000/25 tran./slow
Quench level 1
Beam dump threshold for quench prevention
0.3
0.3/0.4 tran./slow
Warning
0.1
0.1/0.25
Specification:
Absolute precision (calibration)
< factor 2
initially:
< factor 5
Relative precision for quench prevention
< 25%
Accurately known quench levels will increase operational efficiency
Why do BLMs need to know the Quench Levels, B.Dehning

4. Simulation Results on Longitudinal Proton Loss Distribution
Tracking of tertiary halo particles, E.B. Holzer and V. Kain (end of 2003), complete aperture model (DS and arc right of IR7), (halo particles simulated by R. Assmann), ideal alignment.
Longitudinal losses strongly peaked at the beginning of the quadrupoles, bin width = 1 m (dipoles not shown).
Why do BLMs need to know the Quench Levels, B.Dehning

5. Location of Proton Losses along the LHC
Q11 Q8 Q7
p lost / p on primary collimator
Dispersion suppressor and beginning of arc right of IR7, z [m]
Why do BLMs need to know the Quench Levels, B.Dehning

6. Change of Aperture at Quadrupoles
Tertiary halo tracking => proton loss location (talk G. Robert-Demolaize) => location of highest energy density in coil
Why do BLMs need to know the Quench Levels, B.Dehning

7. LHC Bending Magnet Quench Levels, LHC Project Report 44
38 mJ/cm3 = 5 mJ/g
5 mW/cm3 = 0.6 mW/g
0.8 mJ/cm3 = 0.09 mJ/g, (RHIC=2 mJ/g, Tevatron=0.5mJ/g)
(RHIC = 8 mW/g, Tevatron = 8mW/g)
Why do BLMs need to know the Quench Levels, B.Dehning

8. Approximation of Quench Levels
Dump level tables are loaded in a non volatile RAM
Any curve approximation possible
Loss durations
Energy dependence
Relative error kept
< 20 %
Why do BLMs need to know the Quench Levels, B.Dehning

9. Quench Levels and Energy Dependence
Fast decrease of quench levels between 0.45 to 2 TeV
Why do BLMs need to know the Quench Levels, B.Dehning

10. Operational Range of BLMs
Quench level and observation range
450 GeV
7 TeV
Damage levels
Arc
2.5 ms
Ionisation chamber
1 turn
SEM
Dynamic
Arc: 108
BLMS*: 3.2E13 protonen (nominal SPS injection) lost in about 10E-5 seconds.
Why do BLMs need to know the Quench Levels, B.Dehning

11. BLM locations in the arcs – longitudinal
3 loss locations simulated: shower development in the cryostat, GEANT 3.
The positions of the BLMs are chosen to:
minimize crosstalk
reduce difference between inside and outside loss
difference with and without MDCO.
BLM position
Loss location
Why do BLMs need to know the Quench Levels, B.Dehning

12. Shower Development in Dispersion Suppressor Magnets
Shower maximum: 1m after impact location
Shower width: FWHM  0.5m
Why do BLMs need to know the Quench Levels, B.Dehning

13. Beam and Magnetic Field Directions
4 combinations of beam directions and magnetic fields.
3 loss locations: inside and outside of beam screen and top of beam screen (bottom is about the same as top).
Why do BLMs need to know the Quench Levels, B.Dehning

14. Shower Development in Dispersion Suppressor Magnets
Angles theta (angle to the x-axis) and phi of charged particles at detector location: mostly in horizontal plane and with an angle of 45 degrees to the x-axis.
Why do BLMs need to know the Quench Levels, B.Dehning

15. Shower Development in Arc Magnets
BLM position
Loss location
Different corrector magnet layouts simplified to two cases (with and without MDCO in front of the dipole magnet).
Dependence on energy studied: Factor of 10 to 25 in signal for a 7 TeV proton compared to a 450 GeV proton.
10-4 MIPs/ p cm2
Why do BLMs need to know the Quench Levels, B.Dehning

16. Why do BLMs need to know the Quench Levels, B.Dehning
Location of Detectors
Installation with a small support and straps or cables on the cryostats
Chamber (89 mm) + fixation (8 mm) just fits between the cryostat and the transport space (2 mm space left).
Why do BLMs need to know the Quench Levels, B.Dehning

17. Why do BLMs need to know the Quench Levels, B.Dehning
Detector Signal Chain
Threshold Comparator: Losses integrated in 12 time intervals to approximate quench level curve.
Why do BLMs need to know the Quench Levels, B.Dehning

18. Why do BLMs need to know the Quench Levels, B.Dehning
Subjects to be Studied?
3700 monitors need threshold values (11 time slots and 30 energy slots)
Loss locations and their variations
Quench levels as function of time and energy for the different magnet types
Transient loss values
Quench levels between few ms to 10 s (heat flow in magnet)
Steady state values (heat flow)
Identification of error margins
Why do BLMs need to know the Quench Levels, B.Dehning

19. Why do BLMs need to know the Quench Levels, B.Dehning
Beam Loss Display
Why do BLMs need to know the Quench Levels, B.Dehning