Active compensation of field errors within ±2ppm in superconducting magnets

Abstract

A system for the active compensation of magnetic field errors within ±2 ppm relative to the main field in superconducting magnets is proposed. A high-performance rotating coils system is exploited in order to combine high time resolution and integral field measurements. The compensation is based on an enhanced characterization of the corrector magnets and the measured field: this allows the system to be used as off-line reference in accelerator facilities. As an experimental case study, the measurement system and the procedure for compensating field errors of dipole magnets of the Large Hadron Collider at the European Organization for Nuclear Research (CERN) are illustrated. Published in Nuclear Instruments and Methods in Physics Research A 2011Geneva, Switzerland CERN-ATS 2011-009

Performance of a fast digital integrator in on-field magnetic measurements for particle accelerators

“…The time variation of the "decay" and "snapback" of the sextupole component is measured with unprecedented precision, allowing a correction in the order of few ppm. 32 Furthermore, owing to the on-board integration algorithm, besides the higher accuracy, the size of the transferred and stored flux data is reduced by a factor in the order of 500. For small-aperture magnets, the FDI allows the target of ±0.02% of field uncertainty to be reached owing to its negligible noise contribution with respect to PDI.…”

A rotating coil transducer for magnetic field mapping

“…In this case, according to recent developments on printed circuits [11], the coil can actually be made very compact without significant quality loss. Considering the systems presented in [18,19], the 1-σ relative repeatability (relative standard deviation over several revolutions) of dipole magnetic measurements is less than ±10 −4 . Moreover, the rotation and mechanical instability effects must be considered and related to the measurement results of field quality.…”

“…Wire-based systems [17] are used only for straight geometries and are not generally suited for local magnetic field measurements. The main coil-based systems are the Dipole or Quadrupole Industry Magnetic Measurement (DIMM and QIMM) [18] and the Fast Measurement Equipment (FAME) [19]. The QIMM system exploits a traveling rotating shaft ("mole") [20], carrying from 3 to 5 sensing coils.…”

“…In this paper, a compact rotating coil transducer for local and integral field measurement is proposed. This transducer can be fully immersed in a strong magnetic field and, thanks to its low weight and short coil length (30 < l coil < 80 mm) with respect to other rotating coil transducer [18,19,21], can be made to follow arbitrary paths throughout magnets with gaps between 40 and 200 mm, and curvature radii between 1 and 12 m. The main idea is to have a high-accuracy transducer and a fine longitudinal discretization of the magnetic field, useful to nonlinear magnetic fields investigation and space charge effects forecast. In the following sections, the requirements, the architecture, and the first prototype of the proposed transducer are described in detail.…”

“…The manufacturing precision is fundamental to have low dimensional tolerances. As described in [26,27], high rotation speeds could increase mechanical instability in traditional rotating systems [18,19]. Specifically, speed variations must be analyzed experimentally in order to check the rotation stability and the related measurement errors on the harmonic analysis.…”