Rotating Coil Probe Research Articles

Magnetic Measurements on the Twin Aperture Orbit Correctors for HL-LHC at IMP

The Large Hadron Collider (LHC) upgrade, namely, High Luminosity LHC (HL-LHC) is planned for the next decade. A set of twin aperture beam orbit correctors positioned on the approaches to the ATLAS & CMS experiments will be developed. Two Chinese Academy of Sciences institutes, i.e., IHEP (Institute of High Energy Physics) and IMP (Institute of Modern Physics), and one company in China will work on the magnet R&D and series production. IMP is in charge of the performance test both at ambient and cryogenic temperatures, and the first China-built model (MCBRDP2) has been tested recently. In this paper, the test setup for magnetic measurements, the room temperature bore, and the rotating coil probe being system used at IMP are presented. The quench record and the measurement results, such as integral field, multipoles, cross-talk, are given and discussed.

Magnetic Field Measurements of First Pre-series Full-Length 4.2 m Quadrupole MQXFA03 Using PCB Rotating Coils for the Hi-Lumi LHC Project

The U.S. Hi-Lumi LHC Accelerator Upgrade Project (AUP) and CERN have joined efforts to develop high field quadrupoles for the Hi-Lumi LHC upgrade. The US national laboratories in the AUP project will deliver 10 magnets and each cryostat has two 4.2 m high gradient quadrupoles in it. These magnets are made of Nb3Sn conductors, with large aperture (150 mm) and integrated gradient of 556.9 T. This paper reports on magnetic measurements performed during the vertical test at Brookhaven National Laboratory (BNL) in 2019-2020. A warm measurement Z-Scan (+/-15 A) with 42 Z-positions before cool-down was performed at BNL. The results were directly compared to field data measured at LBNL during magnet assembly. Measured harmonics and magnetic center offsets (ΔX and ΔY) have provided timely and informative diagnostics on the magnet structure's shape at both warm and cold temperatures. A new centering fixture was designed and added to better center the warm bore tube which contains the rotating coil probe. After the quench training to 16.47 kA was achieved, a complete set of cold measurements (Z-Scan at 16.47 kA and I-Scan from 960 A to 16.47 kA and back to 960 A) was made. Periodic axial variation of allowed and nonallowed harmonics was observed which is related to the coil radial and/or mid-plane variations along the magnet axis. Overall, the average harmonics in the straight section are within the required field boundaries.

Magnetic Field Measurement of 2-m-Long Model of Beam Separation Dipole for the HL-LHC Upgrade

KEK has been developing a beam separation dipole magnet for the high luminosity large hadron collider upgrade. The magnet has a coil aperture of 150 mm and uses NbTi superconducting cable. A dipole magnetic field of 5.6 T is generated at 12 kA at 1.9 K to provide a field integral of 35 T·m. KEK has started the development of the first 2-m-long model magnet to evaluate the design and performance of the beam separation dipole magnet. The excitation test at 1.9 K of the first 2-m-long model magnet was performed from April to June 2016 at KEK. This paper presents the results of the magnetic field measurements of the first 2-m-long model magnet by a rotating coil probe.

SIS100 Dipole Magnet Optimization and Local Toroidal Multipoles

SIS100 is the world's second fast ramped synchrotron using superconducting magnets. The foreseen high current operation requires a sound understanding of the field homogeneity next to a field parametrization which allows investigating if the existing inhomogeneity introduces transverse oscillations on the particle beam. The SIS100 dipole magnets are curved so local toroidal multipoles were developed as these follow the orbit of the ion beam. The end of the magnet creates the main field deterioration due to the coil end shape which has to be compensated by a 3D end shim. In this paper we present the Local Toroidal Multipoles next to formulae to derive these from rotating coil probe measurements. Further we outline the possible geometrical options for meeting the field quality target.

Rotating coil field measurement of superconducting magnet for BEPCII interaction region

Two multifunction superconducting magnets in the interaction region (IR) for Beijing electron positron collider upgrade project (BEPCII) have been measured in BESIII detector hall in 2007. Each superconducting magnet package contains multiple concentric layers with several function magnets called as a vertical focusing quadrupole (SCQ), a horizontal corrector (HDC/SCB), a vertical corrector (VDC), a skew quadrupole (SKQ) and three anti-solenoids (AS1, AS2 and AS3) to compensate the experimental detector solenoid field. All these function magnets SCQs, SCB/HDCs, VDCs and SKQs have been measured using two rotating coils. Their integral fields, their high order harmonics contents and the local fields along the beam line are obtained in detail with the rotating coil probe system. Comparing the results to the stretched wire, the differences for the integral fields are less than 0.2%. As a result, the method presented in this paper can be used as an absolute field measurement in our lab.

Mole for Measuring SIS100 Magnets Commissioning and First Test Results

The SIS100 synchrotron utilizes fast ramped superconducting magnets operated with a frequency of 1 Hz. The beam pipe is of elliptic aperture and the dipole magnets are curved. Therefore, elliptic and toroidal multipoles were developed which allow describing the field concisely within the whole aperture. A mole (i.e., a measurement system based on a rotating coil probe with all auxiliary components operating within the magnet's field) was developed able to sustain ramp rates of up to 4 T/s. It was tested in the field of a conventional magnet and in the first SIS100 superconducting prototype magnet. We recall general design issues of the mole and describe their advantages. We present the first measurements of the mole on the SIS100 prototype and compare them to the results obtained with an independent system. We outline how the rotating coil probe measurements have to be interpreted in the curved magnet using toroidal multipoles, and possible further improvements of the system.

A Fast Continuous Magnetic Field Measurement System Based on Digital Signal Processors

In order to study dynamic effects in accelerator magnets, such as the decay of the magnetic field during the dwell at injection and the rapid so-called "snapback" during the first few seconds of the resumption of the energy ramp, a fast continuous harmonics measurement system was required. A new magnetic field measurement system, based on the use of digital signal processors (DSP) and Analog to Digital (A/D) converters, was developed and prototyped at Fermilab. This system uses Pentek 6102 16 bit A/D converters and the Pentek 4288 DSP board with the SHARC ADSP-2106 family digital signal processor. It was designed to acquire multiple channels of data with a wide dynamic range of input signals, which are typically generated by a rotating coil probe. Data acquisition is performed under a RTOS, whereas processing and visualization are performed under a host computer. Firmware code was developed for the DSP to perform fast continuous readout of the A/D FIFO memory and integration over specified intervals, synchronized to the probe's rotation in the magnetic field. C, C++ and Java code was written to control the data acquisition devices and to process a continuous stream of data. The paper summarizes the characteristics of the system and presents the results of initial tests and measurements

A mole for warm magnetic and optical measurements of LHC dipoles

A new rotating coil probe (a mole) has been developed for the simultaneous measurement of the magnetic field and magnetic axis of warm superconducting LHC dipoles and associated corrector windings. The mole houses a radial rotating coil and travels inside the magnet aperture by means of an externally driven two-way traction belt. The coil is rotated by an on-board piezo motor, being tested in view of future devices for cold measurements as the only type of motor compatible with strong magnetic fields. A virtual light spot is generated in the coil center by a LED source. The position of this light spot is measured from the outside by a system including a telescope, a CCD camera and a DSP. Jigs on reference granite tables are used to transfer the optical measurements to the magnet fiducials. We describe here the main characteristics and performance of the mole.

A rotating coil probe for the magnetic field measurement on a long pulsed tokamak

In order to determine the magnitude and the position of the plasma current in a long pulsed tokamak such as the International Thermonuclear Experimental Reactor (ITER), it is urged to establish a reliable method which is free from the zero-level drift of the integrator as well as the radiation damage for the steady-state magnetic field measurement. For this purpose, we have developed a hybrid system, a combination of a conventional magnetic probe for the measurement of fast varying magnetic field and a rotating coil magnetic probe for that of slowly varying field. The rotating coil is energized by an air turbine to avoid electromagnetic interference and the induce signal with a constant rotation frequency is picked up through a transformer to eliminate mechanical contacts. An automatic gain control circuit is also designed for the compensation of rotation speed fluctuation. The system is proved to achieve a flat frequency response with a proper choice of cross over frequency for high- and low-frequency systems. The rotating coil probe is tested for over 170 h without any trouble. The probe was applied to the poloidal magnetic field measurement on the TRIAM-1M long pulsed tokamak, and proved to work satisfactorily.

A Programmable Magnetic Field Mass Spectrometer with On-Line Data Processing

A single focusing, 30.48 cm radius, 60° sector magnet mass spectrometer was constructed with symmetric conjugate foci calculated from fringe field data and corresponding to a beam deflection of 68°. Experimental and calculated optical characteristics agree well. A rotating coil probe and a rate coil are employed as field sensors for a nulling device and for field scanning. The magnetic field can be set to 27 values corresponding to the center of spectral lines and zero lines on both sides of each peak. The automatic scanning consists of: (1) rapid field change between adjacent field values (∼500 G/sec); (2) locking in at the preset field values (∼0.3 sec); (3) remaining in a channel for a preset time during which the ion beam current is integrated and the data digitized. Repeated arbitrary excursions between channels do not cause effective field variations of more than |ΔB/B| = 2×10−5. For 0.2 mm source and 0.64 mm collector slit settings, a typical peak at mass 88 is flat for 2.7 G to 0.01% at a 14 kV accelerating potential. Data consist of channel intensity, scale factors, and internally provided clock time; data signals drive a typewriter and tape punch. A cyclic scan of five isotopes including background requires 35 sec. A segment of data (∼10 cycles) is processed by the computer and the results returned to the operator.