1. LHC Beam Instrumentation Detectors and Acquisition Systems
LECC 2002
Colmar - 9th-13th September 2002
Rhodri Jones (CERN)

2. Outline Introduction LHC Beam Instrumentation Selection
What do we mean by “Beam Instrumentation”
What instruments are involved
LHC Beam Instrumentation Selection
Beam Position Measurement
Beam Loss Measurement
Beam Intensity Measurement
Luminosity Measurement
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

3. Introduction What do we mean by beam instrumentation?
The “eyes” of the machine operators
i.e the instruments that observe beam behaviour
What beam parameters do we measure?
Beam Position
Horizontal and vertical all around the ring
Corrected using orbit corrector magnets (dipoles)
Beam Loss all around the ring
Especially important for superconducting machines
Beam Intensity (& lifetime measurement for a collider)
Circulating current and bunch-by-bunch charge
Beam size
Transverse and longitudinal distribution
Collision rate / Luminosity (for colliders)
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

4. More “Exotic” Measurements
Machine Tune QF QD SF SD
Characteristic Frequency
of the Magnet Lattice
Controlled by Quadrupole magnets
Machine Chromaticity
Optics Analogy:
Spread in the Machine Tune
due to Particle Energy Spread
Controlled by Sextupole magnets
Achromatic incident light
Lens
Focal length is
energy dependent
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

5. The Typical Instruments
Beam Position
electrostatic or electromagnetic pick-ups
Beam Loss
ionisation chambers or pin diodes
Beam Intensity
beam current transformers
Beam Size (transverse)
synchrotron light
wire scanners
secondary emission or optical transition radiation screens
Beam Size (longitudinal)
RF pick-ups or synchrotron light
Luminosity
ionisation chambers or semiconductors
Machine Tune and Chromacitity
resonant beam position monitors combined with a PLL system
ordinary beam position monitors with data processing
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

6. LHC BPM System - General Layout
~ 24 Special BPMs for Transverse Damper,
Tune & Chromaticity Measurements
24 Directional Couplers
& 44 Enlarged Button
BPMs for the
Interaction Regions
44 Warm BPMs -
24mm Button Electrodes
100 Warm, Button Electrode BPMs
Buttons Recuperated from LEP
922 Button Electrode BPMs (24mm)
for the
Main Arcs & Dispersion Suppressors
Total of 1158 BPMs for the LHC
and its Transfer Lines
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

7. The Arc BPM - SSS Layout LECC2002 - Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

8. LHC Arc Type BPM (String 2)
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

9. Arc BPM - Button Feedthrough
Beam Screen
49mm aperture
Liquid Helium
Cooling Capillary
24mm button
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

10. Interaction Region BPMs
Liquid Helium
Capillaries
Stripline
Electrode
Q2 Coupler
Directional stripline couplers
Outputs signals only from the upstream port
Can distinguish between counter-rotating beams
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

11. The Front-End Electronics
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

12. The Wide Band Time Normaliser
Beam
A + (B + 1.5ns) A B
B + 1.5ns
1.5ns
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

13. The Wide Band Time Normaliser
A + (B + 1.5ns) A B
Dt depends on position
A + 1.5ns A
1.5ns
B + (A + 1.5ns) B
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

14. The Wide Band Time Normaliser
A+(B+1.5ns)
B+(A+1.5ns)+10ns
Interval = 10  1.5ns
System output
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

15. The Wide Band Time Normaliser
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

16. LHC Beam Position System Layout
Acquisition
Chassis
 4
Acquisition
Chassis
 4
TTC Timing
Ethernet
Real-Time Network
Acquisition
Chassis
 4
Acquisition
Chassis
 4
Surface Point (1 of 8)
1/16th of
LHC
Tunnel
SSS
containing
2 BPMs
F.E.
Electronics
SSS
containing
2 BPMs
F.E.
Electronics
SSS
containing
2 BPMs
F.E.
Electronics
Up to 28
Quadrupoles
31 Drop-offs
max.
31.25kbit WorldFIP fieldbus for slow control
Fibre-optic Link using “blown” fibres
7 Drop-offs
max.
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

17. WBTN - Linearity v Intensity
For LHC Arc BPMs 1% ~ 130mm
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

18. WBTN - Linearity v Position
For LHC Arc BPMs 1% ~ 130mm
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

19. WBTN - Radiation Issues
The Front-end Electronics for the Arc BPMs will be located under the main quadrupoles
can expect to see a dose of some 12Gy/year
Tests in the SPS-TCC2 area during 2000 showed that use of DIGITAL components in the tunnel should be avoided
Most memories and FPGA’s too easily corrupted
Qualification of components long & difficult
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

20. WBTN - Radiation Issues
In 2001 : Fibre-Optic Link added to LHC BPM system
only the minimum of analogue electronics kept in tunnel
all sensitive digital electronics located on the surface
allows easy access to most of the acquisition system
Cost of large scale fibre-optic installation compensated by
elimination of 13km of expensive low loss coaxial cable
reduction in number of acquisition crates
no bunch synchronous timing required in the tunnel
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

21. WBTN - Radiation Test Results
2001 Test results of the
very front-end WBTN card
with Fibre-Optic Link
Initial performance
After 650Gy no significant
deterioration in the performance
is visible
6.5ps rms
jitter
6ps rms jitter
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

22. The LHC BPM Acquisition System
Very Front-End WBTN Card
70MHz Low Pass Filters
Supplied by TRIUMF (Canada)
Single-Mode Fibre-Optic Link
1310nm Diode Laser Transmitter
Tunnel
Surface
VME based
Digital Acquisition Board
TRIUMF (Canada)
(2 x 12bit 40MHz Acq)
WBTN Mezzanine Card
(10bit digitisation at 40MHz)
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

23. Operational Prototype Results in 2001
System extensively used in SPS for electron cloud & instability studies.
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

24. The Typical Instruments
Beam Position
electrostatic or electromagnetic pick-ups
Beam Loss
ionisation chambers or pin diodes
Beam Intensity
beam current transformers
Beam Size (transverse)
synchrotron light
wire scanners
secondary emission or optical transition radiation screens
Beam Size (longitudinal)
RF pick-ups or synchrotron light
Luminosity
ionisation chambers or semiconductors
Machine Tune and Chromacitity
resonant beam position monitors combined with a PLL system
ordinary beam position monitors with data processing
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

25. The LHC Beam Loss System
Role of the BLM system:
Protect the LHC from damage
Dump the beam to avoid magnet quenches
Diagnostic tool to improve the performance of the LHC
Acquisition requirements:
Calculation of quench level equivalent chamber signal
Electric currents from 600 pA to 300 A
A dump should be requested at 50% of the quench level
i.e. from 300 pA to 150 A
Extend dynamic range for sufficient sensitivity at low losses
Measuring current from 60 pA to 300 A
Arc BLM acquisition rate not faster than one turn (89 s)
Fastest total loss is ~ 6 turns & will be detected by special BLMs.
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

26. Structure of the BLM Readout Chain
transforms particle losses into an electric current
6 per quadrupole (3 for each LHC ring)  ~3000 monitors
Analogue Front-End
measures current and transmits data from Tunnel  Surface
Dump Controller
processes data and interfaces to the beam interlock system
Ionisation Chamber
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

27. Quench Level Equivalent Chamber Current
600 pA
One turn
60 pA
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

28. Charge-Balanced Converter
iin(t) + Iref
iin(t)
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

29. Current-Frequency Characteristics
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

30. Front-End Frequency Evaluation
8-bit asynchronous counting of the reset pulses
each pulse represents a constant charge
every ~40 s the count from each of the 6 channels are multiplexed
serial data stream is Manchester encoded
FAW
Ch 1
Ch 2
...
Ch 6
Tunnel to surface transmission
Two choices
Cable transmission (tested for 2Mbit up to 1.8km)
Differential signal transmission provides noise immunity
High speed driver / receiver pair
Fibre-optic transmission
Final decision will depend on cable distance and transmission rate
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

31. The Typical Instruments
Beam Position
electrostatic or electromagnetic pick-ups
Beam Loss
ionisation chambers or pin diodes
Beam Intensity
beam current transformers
Beam Size (transverse)
synchrotron light
wire scanners
secondary emission or optical transition radiation screens
Beam Size (longitudinal)
RF pick-ups or synchrotron light
Luminosity
ionisation chambers or semiconductors
Machine Tune and Chromacitity
resonant beam position monitors combined with a PLL system
ordinary beam position monitors with data processing
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

32. Fast Beam Current Transformer
Installed in the SPS and LHC transfer lines
LHC fast BCT will be a scaled version
Capable of 40MHz bunch by bunch measurement
Dynamic range to cover 5109 to 1.7  1011 cpb
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

33. Fast Beam Current Transformer
Image
Current
1:40 Passive
Transformer
Ceramic Gap
80nm Ti Coating
20W to damp any
cavity resonances
BEAM
Calibration winding
500MHz Bandwidth
Low droop (< 0.2%/ms)
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

34. Acquisition Electronics
Designed by the Laboratoire de Physique Corpusculaire, Clermont-Ferrand for use in the LHCb Preshower Detector.
[see Session B53]
Uses interleaved, 20MHz integrators and sample & hold circuitry to give 40MHz data.
Digital Acquisition
PMC size Mezzanine card developed by CERN & contains
Fast integrator chip
12bit, 40MHz ADC
Timing provided by the TTCbi module, part of the Timing, Trigger & Control system developed for the LHC experiments [see Session P54 – Bruce Taylor]
Mezzanine sits on the same VME 40MHz Data Acquisition Board developed for the LHC Beam Position System (TRIUMF, Canada)
Analogue Acquisition based on a fast integrator chip
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

35. Acquisition Electronics
To VME
Digital
Acquisition
Board
Fast Integrator Chip
Track
& Hold
MUX
Differential
Input from
Fast BCT
12-bit
ADC
40MHz TTC Input from TTCbi
20MHz Clock Creation
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

36. Acquisition Electronics
Integrator Output
25ns
FBCT Signal after 200m of Cable
Data taken on LHC type beams at the CERN-SPS (2002)
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

37. Results from the CERN-SPS (2002)
Bad RF Capture of a single SPS LHC Batch (72 bunches)
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

38. The Typical Instruments
Beam Position
electrostatic or electromagnetic pick-ups
Beam Loss
ionisation chambers or pin diodes
Beam Intensity
beam current transformers
Beam Size (transverse)
synchrotron light
wire scanners
secondary emission or optical transition radiation screens
Beam Size (longitudinal)
RF pick-ups or synchrotron light
Luminosity
ionisation chambers or semiconductors
Machine Tune and Chromacitity
resonant beam position monitors combined with a PLL system
ordinary beam position monitors with data processing
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

39. LHC Luminosity Measurement
Requirements:
Capable of 40MHz acquisition
Has to withstand high radiation dose: ~108 Gy/year
estimated 1018 Neutrons/cm2 over its lifetime (20yrs LHC operation)
estimated 1016 Protons/cm2 over its lifetime (20yrs LHC operation)
No maintenance
Candidates:
Ionisation Chambers
developed by LBL
Good radiation hardness
Difficult to get working at 40MHz
CdTe detectors
developed by CERN in collaboration with LETI (Grenoble)
Fulfills 40MHz requirement
Not yet proven for the highest levels of radiation
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

40. Polycrystalline CdTe Detectors
Experience at CERN with CdTe X-RAY detector
running in LEP for beam emittance measurement
was used up to the end with total dose 1014 Gray
Advantages
large number of e- created per MIP (~5  Diamond)
very fast response time
simple construction
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

41. CdTe Detectors – Test Set-up
Sr90
Source
Amplifier Output
Averaged
Output Histogram
~10ns
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

42. Polycrystalline CdTe Detectors
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

43. Irradiation Test Results
CERN-SPS (2001)
Irradiation test up to 1015 neutrons/cm2
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

44. Irradiation Test Results
Triga type reactor (Ljubljana,Slovenia )
Irradiation steps
1013 neutrons/cm2
1015 neutrons/cm2
1016 neutrons/cm2 activation of all set-up
next step 1018 neutrons/cm2 (2003)
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation

45. Summary LHC is a superconducting machine
tight tolerances on all beam parameters
instruments have to measure to better than tolerances
Increasing demands for all instruments
40MHz bunch-by-bunch resolution
large dynamic range
Provides a challenging field of development
all the main instruments have been defined
Installation of some systems begin next year (transfer lines)
Final choices for most instruments foreseen by 2004
LECC Rhodri Jones (CERN - SL/BI)
LHC Beam Instrumentation