LHC Beam Instrumentation Detectors and Acquisition Systems LECC
LHC Beam Instrumentation Detectors and Acquisition Systems LECC 2002 Colmar - 9 th-13 th September 2002 Rhodri Jones (CERN)
Outline • Introduction ® 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 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
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 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
More “Exotic” Measurements • Machine Tune QF SF QF QD SF SD QD SD QF SF Characteristic Frequency of the Magnet Lattice Controlled by Quadrupole magnets • Machine Chromaticity Spread in the Machine Tune due to Particle Energy Spread Optics Analogy: Achromatic incident light Controlled by Sextupole magnets Lens Focal length is energy dependent LECC 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
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 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
LHC BPM System - General Layout 24 Directional Couplers & 44 Enlarged Button 44 Warm BPMs for the. BPMs ~ 922 24 for Transverse Damper, 100 Special Warm, Button Electrode BPMs Total of 1158 BPMs for the (24 mm) LHC Interaction Regions 24 mm Button Electrodes Tune & Chromaticity Buttons Recuperated Measurements from LEP for the Lines and its Transfer Main Arcs & Dispersion Suppressors LECC 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
The Arc BPM - SSS Layout LECC 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
LHC Arc Type BPM (String 2) LECC 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
Arc BPM - Button Feedthrough Beam Screen Liquid Helium Cooling Capillary 49 mm aperture 24 mm button LECC 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
Interaction Region BPMs Liquid Helium Capillaries Q 2 Coupler Stripline Electrode • Directional stripline couplers ® Outputs signals only from the upstream port ® Can distinguish between counter-rotating beams LECC 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
The Front-End Electronics LECC 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
The Wide Band Time Normaliser A + (B + 1. 5 ns) A B Beam A B B + 1. 5 ns LECC 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
The Wide Band Time Normaliser A + (B + 1. 5 ns) A B A A + 1. 5 ns B B + (A + 1. 5 ns) Dt depends on position LECC 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
The Wide Band Time Normaliser A B A+(B+1. 5 ns) B+(A+1. 5 ns)+10 ns System output Interval = 10 1. 5 ns LECC 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
The Wide Band Time Normaliser LECC 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
LHC Beam Position System Layout Acquisition Chassis 44 Chassis 4 Real-Time Network Ethernet TTC Timing Surface Point (1 of 8) 1/16 th of LHC Tunnel Up to 28 Quadrupoles 7 Drop-offs max. 31 Drop-offs max. SSS containing 2 BPMs F. E. Electronics 4 SSS containing 2 BPMs F. E. Electronics Fibre-optic Link using “blown” fibres 31. 25 kbit World. FIP fieldbus for slow control LECC 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
WBTN - Linearity v Intensity For LHC Arc BPMs 1% ~ 130 m LECC 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
WBTN - Linearity v Position For LHC Arc BPMs 1% ~ 130 m LECC 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
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 12 Gy/year • Tests in the SPS-TCC 2 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 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
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 13 km of expensive low loss coaxial cable ® reduction in number of acquisition crates ® no bunch synchronous timing required in the tunnel LECC 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
WBTN - Radiation Test Results 2001 Test results of the very front-end WBTN card with Fibre-Optic Link Initial performance 6 ps rms jitter 6. 5 ps rms jitter After 650 Gy no significant deterioration in the performance is visible LECC 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
The LHC BPM Acquisition System Very Front-End WBTN Card 70 MHz Low Pass Filters Supplied by TRIUMF (Canada) 1310 nm Diode Laser Transmitter Tunnel Single-Mode Fibre-Optic Link Surface VME based Digital Acquisition Board TRIUMF (Canada) (2 x 12 bit 40 MHz Acq) WBTN Mezzanine Card (10 bit digitisation at 40 MHz) LECC 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
Operational Prototype Results in 2001 System extensively used in SPS for electron cloud & instability studies. LECC 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
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 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
The LHC Beam Loss System Role of the BLM system: 1. Protect the LHC from damage 2. Dump the beam to avoid magnet quenches 3. Diagnostic tool to improve the performance of the LHC • Acquisition requirements: ® Calculation of quench level equivalent chamber signal – Electric currents from 600 p. A to 300 A ® A dump should be requested at 50% of the quench level – i. e. from 300 p. A to 150 A ® Extend dynamic range for sufficient sensitivity at low losses – Measuring current from 60 p. A 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 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
Structure of the BLM Readout Chain • Ionisation Chamber ® 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 LECC 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
Quench Level Equivalent Chamber Current 300 A 600 p. A One turn 60 p. A LECC 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
Charge-Balanced Converter iin(t) + Iref LECC 2002 - Rhodri Jones (CERN - SL/BI) iin(t) LHC Beam Instrumentation
Current-Frequency Characteristics LECC 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
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. . . Ch 6 FAW Ch 1 Ch 2 . . . Ch 6 FAW Ch 1 . . . • Tunnel to surface transmission ® Two choices • Cable transmission (tested for 2 Mbit up to 1. 8 km) – 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 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
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 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
Fast Beam Current Transformer • Installed in the SPS and LHC transfer lines • LHC fast BCT will be a scaled version • Capable of 40 MHz bunch by bunch measurement • Dynamic range to cover 5 109 to 1. 7 1011 cpb LECC 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
Fast Beam Current Transformer 1: 40 Passive Transformer Image Current Ceramic Gap BEAM Calibration winding 80 nm Ti Coating 20 W to damp any cavity resonances • 500 MHz Bandwidth • Low droop (< 0. 2%/ s) LECC 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
Acquisition Electronics • Analogue Acquisition based on a fast integrator chip ® Designed by the Laboratoire de Physique Corpusculaire, Clermont. Ferrand for use in the LHCb Preshower Detector. • [see Session B 53] ® Uses interleaved, 20 MHz integrators and sample & hold circuitry to give 40 MHz data. • Digital Acquisition ® PMC size Mezzanine card developed by CERN & contains • Fast integrator chip • 12 bit, 40 MHz ADC • Timing provided by the TTCbi module, part of the Timing, Trigger & Control system developed for the LHC experiments [see Session P 54 – Bruce Taylor] ® Mezzanine sits on the same VME 40 MHz Data Acquisition Board developed for the LHC Beam Position System (TRIUMF, Canada) LECC 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
Acquisition Electronics Fast Integrator Chip Track & Hold Differential Input from Fast BCT MUX To VME Digital Acquisition Board 12 -bit ADC Track & Hold 20 MHz Clock Creation 40 MHz TTC Input from TTCbi LECC 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
Acquisition Electronics Integrator Output 25 ns FBCT Signal after 200 m of Cable Data taken on LHC type beams at the CERN-SPS (2002) LECC 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
Results from the CERN-SPS (2002) Bad RF Capture of a single SPS LHC Batch (72 bunches) LECC 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
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 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
LHC Luminosity Measurement Requirements: • Capable of 40 MHz acquisition • Has to withstand high radiation dose: ~108 Gy/year ® estimated 1018 Neutrons/cm 2 over its lifetime (20 yrs LHC operation) ® estimated 1016 Protons/cm 2 over its lifetime (20 yrs LHC operation) • No maintenance Candidates: • Ionisation Chambers ® developed by LBL – Good radiation hardness – Difficult to get working at 40 MHz • Cd. Te detectors ® developed by CERN in collaboration with LETI (Grenoble) – Fulfills 40 MHz requirement – Not yet proven for the highest levels of radiation LECC 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
Polycrystalline Cd. Te Detectors • Experience at CERN with Cd. Te 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 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
Cd. Te Detectors – Test Set-up Sr 90 Source Amplifier Output ~10 ns Averaged Amplifier Output Histogram LECC 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
Polycrystalline Cd. Te Detectors LECC 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
Irradiation Test Results • CERN-SPS (2001) ® Irradiation test up to 1015 neutrons/cm 2 LECC 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
Irradiation Test Results • Triga type reactor (Ljubljana, Slovenia - 2002) ® Irradiation steps • 1013 neutrons/cm 2 • 1015 neutrons/cm 2 • 1016 neutrons/cm 2 activation of all set-up – next step 1018 neutrons/cm 2 (2003) LECC 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
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 ® 40 MHz 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 2002 - Rhodri Jones (CERN - SL/BI) LHC Beam Instrumentation
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