1. Magnetic measurement equipment in the LHC era L Bottura, M Buzio, J Garcia Perez (AT/MTM)
Contents
Future requirements for magnetic measurements
Today’s instruments
Baseline scenario
Further developments
FAME
ADC/DSP Integrators
Fixed coils
NMR
SSW
Universal mole

2. I) Machine Operation & Magnet Maintenance
1. Future requirements for magnetic measurements
I) Machine Operation & Magnet Maintenance
Qualify spares/faulty/repaired magnets to be installed in the machine (e.g. inner triplets to be replaced due to irradiation, quenching magnets, etc…), with the same methods/criteria as used today for acceptance. Experience from other superconducting accelerators: up to 0.1 % of magnets to be re-measured each year.
Characterize off-line in full detail selected representative LHC magnets to support commissioning and improve operation quality (see Jean-Pierre’s talk):
Refine existing dynamic effect models (FIDEL), by widening exploration of the relevant parameter space
Measure history-dependent harmonic effects due to untested variations of machine cycle or new operation modes
Carry out special investigations deemed of “2nd order” and left out during series tests, e.g.: change of shape due to thermal contractions or Lorentz forces, long-term electrical, power and magnetic stability, non-linear cross-talk between adjacent magnets, fringe field effects, magnetic effects of cryostat and other materials, etc…
Answer any unforeseen question raised during commissioning
Improve the characterization of resistive magnets of the injector chain (hysteresis effects, fringe fields, etc …) (see Gianluigi’s and Juan’s talks)

3. II) Additional objectives
1. Future requirements for magnetic measurements
II) Additional objectives
Characterize and qualify models, prototype and series magnets for foreseeable LHC upgrades and future accelerators:
fast pulsed SC magnets for PS/SPS upgrades (up to 6T/s)
IR quads for luminosity upgrade (large aperture, high field)
Nb3Sn dipoles and quadrupoles for LHC energy upgrade
narrow-aperture magnets for linear colliders (?)
All foreseeable future activities involve high magnetic field/superconductivity  establish CERN-wide reference infrastructure to measure magnets & materials avoid duplication and merge efforts with other communities involved with magnetic measurements at CERN: experiments, special magnets, SC cables …
Maintain collaboration with other projects (e.g. GSI, CARE, LARP, CNAO etc)
the capability to carry out magnetic measurements with today’s instruments, at a reduced rate, is vital for the commissioning and long-term maintenance of LHC additional improvements are needed to survive in the long term with staff cuts, to adapt to future demands and to keep CERN at the forefront of magnet technology

4. Today’s Instruments for LHC Magnets
Units
Harmonics
Field Integral
Magnetic Axis
Field Direction
Notes
15 m dipole coil shafts + Twin Rotation Unit
2×6
warm cold no
longitudinal field profiles + integral
9 m quad coil shafts + Twin Rotation Unit
2×2
arc + short MS/DS SSS only
Chaconsa scanner 2
detailed longitudinal profiles + integral Time-consuming
Single Stretched Wire 3
reference for BdL, GdL, F.D.
Only instrument for cols magnetic axis so far
B3/B5 Hall Sensor Probe 1
cold
follow locally the fast snapback transient
Warm AC Mole 8 ?
warm
series SSS measurements
Cold AC Mole
just finalized and commissioned
DIMM 24
dipole industry measurements
QIMM 12
quadrupole industry measurements
Warm IPT Mole
set aside in 2004 due to lack of resources for the necessary HW/SW finalization
Cold IPT Mole
Polarity Checker 5
order, type and polarity of main harmonic only
LEICA™ Laser Tracker
Support to SSW, AC Moles, mechanical alignment of magnets and benches
Metrolab™ NMR 6
Used for reference dipoles in SM18 and I8
Metrolab™ 3D Teslameter
Used for special checks (fringe fields, polarity inside beam screen, etc…)

5. Baseline “minimum” scenario: short-term maintenance of LHC magnets
Instrument
Objective
Notes
15 m dipole coil shafts + Twin Rotation Unit
Harmonics, BdL in MB
fragile, all spares needed
9 m quad coil shafts + Twin Rotation Unit
Harmonics, GdL in SSS
fragile, all spares needed extra prolongations needed for MS/DS SSS to replace Chaconsa
Chaconsa scanner
Too complex to operate and maintain
Mechanical alignment & control system expertise soon to be lost
Single Stretched Wire
Field Direction BdL/GdL cross-calibration Cold magnetic axis
Measurement of short corrector magnets not possible
B3/B5 Hall Sensor Probe
Snapback transient
Local measurement must be extrapolated to whole magnet
Warm AC Mole
Magnetic & mechanical axis
Cold AC Mole
Magnetic axis
May replace Chaconsa & SSW for cold axis measurements (low field, AC excitation only)
DIMM
Not needed any longer for cryostated magnets, since warm harmonics can be measured with long shafts; however, may still be needed for collared coils and cold masses in the Magnet Rescue Factory
QIMM
Warm IPT mole
Cold IPT Mole
Might be resurrected if magnetic axis measurements of correctors at high field are needed
Polarity Checker
Order, type and polarity of main harmonic
LEICA™ Laser Tracker
Support
Metrolab™ NMR
Cross-calibration
Metrolab™ 3D Teslameter
Special tests

6. Rationale for the following proposals:
Further developments
the “minimum” scenario cannot guarantee to fulfill all needs in the medium- and long-term
Rationale for the following proposals:
Improve long-term reliability and maintainability of essential instruments, despite the inevitable obsolescence of HW&SW + loss of support personnel
Enhance measurement capabilities (accuracy, speed) of LHC-related measurements
Adapt to advanced requirements for next-generation magnets
General guidelines: - standardization of hardware and software wherever possible
simplification via elimination of redundant systems
exploit synergies between overlapping requirements

7. FAME (FAst MEasurement system)
New integrated system for fast off-line measurement of strength and harmonics of main dipoles and quadrupoles - aimed at precise determination of ramp and dynamic effects - use different instruments in parallel to cover optimally different needs at different times during an LHC cycle - future integration into real-time LHC control system (?)
long rotating coil shafts integral of all harmonics, one aperture
fixed coils local B1/B2 during ramps (to be extrapolated)
NMR probe (B1 calibration at the center of the magnet, to be extrapolated)
Hall probe local B3/B5 during snapback (to be extrapolated)

8. VFC-based integrators on a VME bus (design adapted later by Metrolab)
FAME: Integrators
Harmonic-coil magnetic measurements at CERN and in the industries (Long shaft systems in SM18, Bloc4 systems, DIMM, QIMM, IPT Moles, PDI for field advance) use today a common 15 years old HW and SW infrastructure which is limited in acquisition speed and accuracy:
VFC-based integrators on a VME bus (design adapted later by Metrolab)
MMP software by AB/CO
The FAME system, being developed in collaboration with Universities of Florida and of Sannio (IT), will include:
Continuously rotating coils with signals passed through slip-rings
State-of-the-art DSP integrators on a PXI bus, based on a 18-bit, 800 kHz ADC, expected to improve resolution by two orders of magnitude at short integration times (theoretical limit: 1 2 s)
Advanced analysis algorithms for fast harmonic measurements in changing field
The new integrators will replace the DAQ in all the above systems + form the basis of all new developments for rotating and fixed coil systems. The adoption of more modern HW and SW shall guarantee continuity and maintainability throughout the LHC lifespan.
status: 2nd prototype card being tested, firmware being finalized. First measurement tests in a dedicated bench foreseen in June. Final prototype with DSP expected this summer.
(see Juan’s seminar on 19 April)

9. FAME: fixed–coil system
Fixed coils guarantee the best precision of B1 and B2 measurements in a changing field
System initially focused on LHC ramp measurements (up to T/s), should be dimensioned to be compatible in future with measurements of pulsed superconducting magnets up to 4-6 T/s. (possible additional synergy with kicker magnet community ?)
Possible integration of the new acquisition electronics with existing fixed-coil system used for warm magnets.
Status: pending, waiting for integrator.

10. quadrupole and sextupole compensation coil systems
FAME: NMR probes
NMR sensors are the only way to obtain ppm accuracy on B1 during steady-state phases at injection and flat-top
Additional R&D is required to use commercial systems in the not-so-uniform field of LHC dipoles, including e.g.:
quadrupole and sextupole compensation coil systems
methods and algorithms to lock in the resonance signal (non-uniformities cause the spectrum to spread)
very small-volume probes
The result of NMR measurement can be used to cross-calibrate on-line measurements obtained with other sensors
Possible integration in a real-time B-train like system
status: basic R&D to be carried out to judge feasibility, topic well adapted to external collaboration.

11. Other desirable improvements :
SSW
The system, which is our reference for BdL, GdL, magnetic axis and field direction, works well today but support from FERMILAB (i.e. Joe Di Marco) is essential to work reliably (e.g. understand fully the nature of system errors, repair or circumvent faults and bugs, upgrade to new operating systems or network protocols, etc…)
Support is provided on a more or less voluntary basis and is not guaranteed at all, we need to assimilate the system if we don’t want to lose it.
Essential action: take control of the software, e.g. port or rewrite existing operation and analysis code under a CERN supported platform.
Other desirable improvements :
User-friendly software interface, with on-line system and measurement validation
Hardware improvements: easier wire fixation system, optical readout of wire position to avoid calibration problems
New working modes: vibrating and pulsed wire technique (high accuracy axis finding)
Possible SW/HW integration with existing Single and Double Stretched Wire Systems used for warm magnets
status: best suitable new HW and SW platforms must be investigated

12. Hardware may be based on:
Universal Mole
Eliminate the zoo of different moles in use today - maintenance and repair will become impossible in the long term as staff members and expertise are lost
Incorporate extensive operation experience gained with IPT, AC moles, DIMM, QIMM and Polarity Checker to synthesize “universal” instrument for warm & cold field strength, polarity, harmonics, axis and direction.
Hardware may be based on:
Piezoelectric ultrasonic stepping motor compatible with high fields, provides quasi-continuous or stepwise coil rotation
Continuously rotating coils + slip ring to avoid cable-related problems and allow high rotation speeds
FAME integrator for high speed harmonic measurement
Synchronous detection for high-sensitivity AC measurement (useful at room temperature, or at cryogenic temperature when high current cannot be injected through main leads)
Optical encoder to provide angular reference during harmonic measurement and closed-loop precise positioning during AC measurements.
Wyler tilt sensor for horizon reference (tested to be compatible with high fields, off-line calibration correction may be necessary at high fields)
Retro-reflector target for LEICA tracking
On-board Hall sensor to cross-check strength and polarity of coil signal.
status: just an idea for now …