Rotating Coil Magnetometer Research Articles

Single Stretch Wire and vibrating wire measurement system for characterization of multipole accelerator magnets

A stretch wire magnetometer is a versatile instrument and can be treated as the primary standard of magnetic qualification of accelerator magnets. Bhabha Atomic Research Centre has developed a Stretch wire magnetic measurement system to cater to the requirements of magnetic measurements on accelerator magnets. This bench also includes a vibrating wire system. The scheme used in this instrument for measurements of magnetic flux ensures drift compensations after each scan. This feature along with post-signal processing gives an accuracy of homogeneity measurements comparable to that of a rotating coil magnetometer. Unlike conventional stretch wire systems, wire moves in the r-z plane (along r-axis) at different azimuthal angles. This provides the opportunity for drift compensation at each scan. This has immensely enhanced the measurement accuracy of non-homogeneity of integral fields to less than 3 units. The same is cross-verified with a rotating coil system. The comparison between rotating coil and stretch wire is presented. The Paper gives the step-wise procedure for the measurement of key performance indicators of an accelerator magnet. This paper brings out salient features of the system along with design and calibration results.

Metrological characterisation of rotating-coil magnetometer systems

Rotating-coil magnetometers are among the most common and most accurate transducers for measuring the integral magnetic-field harmonics in accelerator magnets. The measurement uncertainty depends on the mechanical properties of the shafts, bearings, drive systems, and supports. Therefore, rotating coils require a careful analysis of the mechanical phenomena (static and dynamic) affecting the measurements, both in the design and in operation phases. The design phase involves the estimation of worst-case scenarios in terms of mechanical disturbances, while the operation phase reveals the actual mechanical characteristics of the system. In previous publications, we focused on modelling the rotating-coil mechanics for the design of novel devices. In this paper, we characterise a complete system in operation. First, the mechanical model is employed for estimating the forces arising during shaft rotation. Then, the effect of the estimated disturbances is evaluated in a simulated measurement. This measurement is then performed in the laboratory and the two results are compared. In order to characterise the robustness of the system against mechanical vibrations, different revolution speeds are evaluated. This work thus presents a complete procedure for characterising a rotating-coil magnetometer system.

A magneto-mechanical model for rotating-coil magnetometers

Rotating-coil magnetometers are among the most common transducers for measuring local and integral magnetic fields of accelerator magnets. The measurement uncertainty strongly depends on the mechanical properties of the shafts, bearings, drive systems, and supports. This paper proposes an analytical mechanical model for rotating-coil magnetometers, which allows a sensitivity analysis of mechanical phenomena affecting magnetic measurements. Both static and dynamic effects are considered. The model is validated numerically with a finite element model, and experimentally on an operational device.

A Rotating-Coil Scanner for the Precise Magnetic Characterization of Superconducting Accelerator Magnets at Ambient Temperature

This article presents a versatile scanning system for the magnetic measurements of the accelerator magnets. This system, based on a rotating-coil magnetometer, has been developed to meet the accuracy requirements imposed by the inner-triplet quadrupoles for the High Luminosity Large Hadron Collider (HL-LHC) project at CERN. The main field strength of the magnet must be measured with an accuracy of 100 ppm, and the required accuracy for the angle and the axis are 0.1 mrad and 0.1 mm, respectively. All these parameters must be measured both locally and integrated over the entire magnet length at various stages of production. In this way, it is possible to intercept the manufacturing errors at an early stage of production. Moreover, these measurements are used for the alignment of the magnet assembly in its cryostat. The measurements are performed at an ambient temperature, with low excitation currents. The presented system provides a full set of data for the characterization of the magnet in a single measurement run, including the field quality (multipole field errors) and the magnetic axis location at several longitudinal positions in the magnet bore. The system is able to achieve the required accuracy by using induction coils based on the printed circuit board (PCB) technology, a high-resolution encoder, and retro-reflectors for the laser tracker positioned directly on the PCB. The system is also equipped with a motor unit that allows a high degree of automation in the measurements.

Development of a rotating-coil scanner for superconducting accelerator magnets

Abstract. The High-Luminosity upgrade project for the Large Hadron Collider (HL-LHC) at CERN (Conseil Européen pour la Recherche Nucléaire) will require new superconducting magnets for the insertion regions. Among these magnets, the new triplet quadrupoles, based on Nb3Sn technology, require magnetic-field measurements of a high precision in the field angle and multipole field errors. In this paper, we present a scanning system based on a rotating-coil magnetometer and its transport system, including the design of the mechanical structure and the induction coils based on printed-circuit-board (PCB) technology. The system and its components are cross-calibrated with other field transducers, such as stretched-wire systems, and their measurement precision is established in a measurement campaign of 2 m long reference quadrupoles.

Challenges in extracting pseudo-multipoles from magnetic measurements

Extracting the coefficients of Fourier–Bessel series, known as pseudo-multipoles or generalized gradients, from magnetic measurements of accelerator magnets involves technical and mathematical challenges. First, a novel design of a short, rotating-coil magnetometer is required that does not intercept any axial field component of the magnet. Moreover, displacing short magnetometers, step-by-step along the magnet axis, yields a convolution of the local multipole field errors and the sensitivity (test function) of the induction coil. The deconvolution must then contend with the limited signal-to-noise ratio of the measured quantities, which are integrated voltages corresponding to spatial flux distributions. Finally, the compensation schemes, as implemented on long coils and based on scaling laws derived for the integrated field harmonics, cannot be applied to short magnetometers intercepting only a local field distribution. All this requires careful design of experiment to derive the optimal length of the induction coil, the step-size of the scan, and the highest order of pseudo-multipoles in the field reconstruction. This paper presents the theory of the measurement method, the data acquisition and deconvolution, and the design and production of a saddle-shaped, rotating-coil magnetometer.

A Rotating-Coil Magnetometer for Scanning Transversal Field Harmonics in Accelerator Magnets

This paper presents a rotating-coil magnetometer that was designed and validated for scanning local transversal field harmonics, required for extracting so-called pseudo-multipoles in accelerator magnets. The magnetometer consists of four layers of flexible printed circuits with a track thickness of 40 μm. The design aimed at maximizing the sensitivity factors for field harmonics up to order 13 and at a compensation ratio for the main component in the same range of what is achievable with standard rotating coils. Key innovative features of the induction coil are the shape for minimizing the sensitivity to the longitudinal field component and the manufacturing technology. The design, the uncertainty analysis of the manufacturing tolerances, as well as preliminary application results are presented.

Boundary element method reconstruction of two‐dimensional magnetic‐field maps from measured boundary data in accelerator magnets

Rotating-coil magnetometers are standard devices for measuring integrated magnetic fields of accelerator magnets. The coil intercepts the magnetic flux at a radius given by the dimensions of the measurement shaft that comprises a set of induction coils. For magnets of a rectangular aperture with a large aspect ratio (larger than 3:1) the cylindrical domain will cover only a portion of the magnet aperture. We, therefore, explore an alternative sampling technique using boundary data acquired from a displaced stretched-wire or from a translating fluxmeter. The method presented in this study concerns the reconstruction of the two-dimensional map of the integrated magnetic field distribution in the entire magnet aperture using the measured boundary data.

A rotating-coil magnetometer for the scanning of transversal field harmonics in particle accelerator magnets

The conceptual design of a rotating-coil magnetometer for magnetic field measurements in accelerator magnets is discussed. The magnetometer is designed for a high signal-to-noise ratio and the ablity to measure the transveral harmonics in the fringe-field region of the magnet. The paper focuses on the coil design and production technology.

Rotating- and translating-coil magnetometers for extracting pseudo-multipoles in accelerator magnets

PurposeThe purpose of this paper is to establish the mathematical foundations of magnetic measurement methods based on translating-coil and rotating-coil magnetometers for accelerator magnets and solenoids. These field transducers allow a longitudinal scanning of the field distribution, but require a sophisticated post-processing step to extract the coefficients of the Fourier–Bessel series (known as pseudo-multipoles or generalized gradients) as well as a novel design of the rotating coil magnetometers.Design/methodology/approachCalculating the transversal field harmonics as a function of the longitudinal position in the magnet, or measuring these harmonics with a very short, rotating induction-coil scanner, allows the extraction of the coefficients of a Fourier–Bessel series, which can then be used in the thin lens approximation of the end regions of accelerator magnets.FindingsThe extraction of the leading term in the Fourier–Bessel series requires the solution of a differential equation by means of a Fourier transform. This yields a natural way to de-convolute the measured distribution of the multipole content. The author has shown that the measurement technique requires iso-parametric coils to avoid interception of the longitudinal field component. The compensation of the main signal cannot be done with the classical arrangement of search coils at different radii, because no easy scaling law exists. A new design of an iso-perimetric induction coil has been found.Research limitations/implicationsIn the literature, it is stated that the pseudo-multipoles can be extracted from field computations or measurements. While this is true for computations, the author shows that the measurement of the field harmonics must be done with iso-parametric coils because otherwise the leading term in the Fourier–Bessel series cannot be extracted.Practical implicationsThe author has now established the theory behind a number of field transducers, such as the moving fluxmeter, the rotational coil scanner and the solenoidal field transducer.Originality/valueThis paper brought together the known theory of the orthogonal expansion method with the methods and tools for magnetic field measurements to establish a field description in accelerator magnets.

A tool for simulating rotating coil magnetometers

When investigating the quality of a magnetic measurement system, one observes difficulties to identify the trouble maker of such a system as different effects can yield similar influences on the measurement results. We describe a tool in this paper that allows to investigate numerically the effects produced by different imperfections of components of such a system, including, but not limited to: vibration and movements of the rotating coil, influence of electrical noise on the system, angular encoder imperfections. This system can simulate the deterministic and stochastic parts of those imperfections. We outline the physical models used that are generally based on experience or first principles. Comparisons to analytical results are shown. The modular structure of the general design of this tool permits to include new modules for new devices and effects.

The theory of the measurement of magnetic multipole fields with rotating coil magnetometers

The theory of the measurement of multipole fields with rotating coil devices is developed particular emphasis on the analysis of the sources of error in these measurements. The theory is developed in cylindrical coordinates for the full three-dimensional magnetic field. The presentation is quite detailed so that the reader can easily follow the development and, more importantly, adapt the results presented to his or her own requirements.

On the errors of rotating coil magnetometers

The errors caused by the eccentricity or vibration of the rotating coil magnetometer are discussed in this paper. The relations between the errors and eccentricity or vibration are also given.

Palaeomagnetism, palaeogeography and the multicomponent analysis of middle and upper Cambrian rocks of the Barrandian in the Bohemian Massif

With a view to the importance of the Barrandian in the Bohemian Massif for global palaeogeographic reconstructions, considerable attention has been devoted to palaeomagnetic stability tests and multicomponent analysis of rocks of the pre-Variscan formations, using substantially improved laboratory techniques. This study is devoted to samples of Upper Cambrian andesite and Middle Cambrian sediments. Alternating and thermal fields were used for magnetic cleaning. A thermal demagnetizer fitted with a newly developed inductor of high sensitivity, the ROCOMA (rotating coil magnetometer), with a sensitivity of 0.1 to 0.2 nT, was used. The whole newly built and fully tested MAVACS system (magnetic vacuum control system) guaranteed a high degree of compensation of the magnetic field in a volume of 5 1, to a value not exceeding 2 nT. As numerous laboratory experiments have shown, the high magnetic vacuum was necessary to derive the palaeomagnetic directions of rocks of the older formations affected significantly by the Variscan orogenic phase. The position of the Upper Cambrian pole (28.6°S, 131.2°E) should be considered tentative because it was derived using samples from only three andesite outcrops. Two other andesite outcrops preserved Carboniferous or Permo-Carboniferous palaeomagnetic directions. The position of the Middle Cambrian pole (11.3°S, 154.0°E) was determined using samples of sediments (mainly greywackes and shales) from ten outcrops, some of which represent extensive rock cross-sections. By combining multicomponent analysis with fold tests, the mean direction of the pre-Variscan magnetization could be derived. The very low values of the moduli of the natural remanent magnetization of the Middle Cambrian sediments, and the considerable amount of magnetically soft components, required special care to be taken in the laboratory procedures. The palaeozoogeographic zones of the Barrandian are related to palaeogeographic latitudes of about 40°S, derived from palaeomagnetic data. Cold water is characteristic for the Bohemian fauna, but arctic conditions can be ruled out due to the amount of primary red sediments, mostly of continental origin.

On the techniques of analysing the multi-component magnetization of rocks using the Rocoma magnetometer

The study is devoted to the interpretation procedures and laboratory techniques used in the palaeomagnetic laboratory of Geofyzika, N. C., Brno, Prague Division, in Průhonice near Prague. The newly developed demagnetization system, equipped with a sensitive ROCOMA magnetometer (Rotating Coil Magnetometer), guarantees a magnetic vacuum. Improved laboratory procedures provide for a more accurate analysis of the multi-component magnetization of rocks, qualitatively and quantitatively. The gyromagnetization effect, generated in rocks of particular physical properties when rotated in spinner magnetometers is pointed out, and the suppression of this undesirable effect is discussed. The procedures described were used to determine the palaeomagnetization in rocks which were affected by a number of phases of orogenic activity.

A Turbine Driven Rotating Coil Magnetometer

A rotating coil magnetometer which utilizes an air turbine to turn the coil has been developed. Since the turbine rotor forms the mount for the coil, there are no shafts or gears. Thus, this magnetometer may be used to measure fields in locations inaccessible to more conventional rotating coil devices. The precision of the suspension of the turbine and the lack of mechanical vibration make it possible to measure transverse field components of the order of one milligauss in a field of one kilogauss. The sensitivity of the magnetometer is made independent of the rotational speed of the coil through the use of an electronic integrator. The coil and integrator circuit is used in conjunction with another system which allows the determination of the direction of the magnetic field being measured relative to a predetermined direction.

Rotating Coil Magnetometer for the Measurement of the Earth's Magnetic Field

Rotating Coil Magnetometer for the Measurement of the Earth's Magnetic Field

Magnetic measurements on the cornell alternate gradient synchrotron

A brief description of the synchrotron magnet is followed by a summary of the factors leading to a choice of field gradient, and a description of the pole tip design. Measurements of the synchrotron field gradients at low, medium and high fields are described. The medium and high field gradients are measured using a rotating coil magnetometer. The gradients at injection time have been determined by two independent methods: (1) using the electron beam itself to find the radial and vertical focal points; and (2) using peaking strips to make zero time measurements. The results of these measurements and also the determination of the magnetic lens boundaries are summarized.

A sensitive rotating-coil magnetometer

This paper describes a sensitive rotating-coil magnetometer in which the flux due to the earth's field or to a magnet is neutralized by that due to a current passing through a fixed concentric compensating coil which forms with the rotating coil a variable mutual inductance. It shows how the first-order correcting term due to the length of the magnet may be made to vanish if the angle of contact be suitably chosen, and that the second-order correction may be eliminated by a correct choice of the dimensions of the coil. Many experiments bearing on the theory and uses of the magnetometer are described. In particular, the ohm may be measured very simply, in terms of a mutual inductance and a period, by Weber's method of damping.