Magnetization in superconducting corrector magnets and impact on luminosity-calibration scans in the Large Hadron Collider (original) (raw)

Dynamic magnetic measurements of superconducting magnets for the LHC

IEEE Transactions on Appiled Superconductivity, 1995

Dynamic Magnetic Mé'surements of Superconducting Magnets for the LHC M we 3 S 93 LHC Note 294 CERN AT/94-2.9 g (MA) / CERN'AT'94'39 llllllllllllllllllllllllllllllllllllll CERN LIBRARIES, GENEVA EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH constant rate. the shaft rotation rate is constant and the same OCR Output revolution and averaged. The current changes with a By + iBx = Blzfbn + ia,_)(z/r0)" measurements are performed with both directions of eliminate to first order these disturbances. The B1 of the magnet at x = ro: Two characteristics of the measuring device are used to The field B(B,,B,) is expanded relative to the main field errors on the harmonics, mainly the lowest ones. measured as a function of the angle, non-linearity's seen as H. DEFNITION OFFHDERRORS coils assemblies introduces, in the integrated voltage during the several seconds needed for a revolution of the wider superconducting cable used. sweeps brings another complication. The change of the field

Performance of the superconducting corrector magnet circuits during the commissioning of the LHC

2008

The LHC is a complex machine requiring more than 7400 superconducting corrector magnets distributed along a circumference of 26.7 km. These magnets are powered in 1446 different electrical circuits at currents ranging from 60 A up to 600 A. Among the corrector circuits the 600 A corrector magnets form the most diverse and differentiated group. All together, about 60000 high current connections had to be made. A fault in a circuit or one of the superconducting connections would have severe consequences for the accelerator operation. All magnets are wound from various types of Nb-Ti superconducting strands, and many contain parallel protection resistors to by-pass the current still flowing in the other magnets of the same circuit when they quench. In this paper the performance of these magnet circuits is presented, focussing on the quench behaviour of the magnets. Quench detection and the performance of the electrical interconnects will be dealt with. The results as measured on the entire circuits are compared to the test results obtained at the reception of the individual magnets.

Fast Cycled Magnet Demonstrator Program at CERN: Instrumentation and Measurement Campaign

IEEE Transactions on Applied Superconductivity, 2014

In an effort to develop economical magnets for an upgrade of the LHC injector complex, CERN started an R&D program on superconducting Fast Cycled Magnets (FCM) in 2009. One of the challenges in this program was to develop a test station, which started working in summer 2012 when the FCM dipole demonstrator was tested. The magnet contains several important features, like forced-flow cooling of supercritical He and it has a protection scheme based direct voltage measurement with co-wound voltage tap wires. In this paper we report on the cryogenic and powering requirements and operation, the quench protection system, the temperature and mechanical measurements. The functioning of the test station and instrumentation are evaluated and we will discuss the measurements on a detailed level.

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

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2011

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.

Advanced measurement systems based on digital processing techniques for superconducting LHC magnets

The Large Hadron Collider (LHC), a particle accelerator aimed at exploring deeper into matter than ever before, is currently being constructed at CERN. Beam optics of the LHC, requires stringent control of the field quality of about 8400 superconducting magnets, including 1232 main dipoles and 360 main quadrupoles to assure the correct machine operation. The measurement challenges are various: accuracy on the field strength measurement up to 50 ppm, harmonics in the ppm range, measurement equipment robustness, low measurement times to characterize fast field phenomena.

A Vector Hysteresis Model for Superconducting Filament Magnetization in Accelerator Magnets

IEEE Transactions on Magnetics, 2004

Magnetic field changes in the coils of superconducting magnets are shielded from the filaments' core by so-called persistent currents which can be modeled by means of the critical state model. This paper presents a semi-analytical 2-dimensional model of the filament magnetization due to persistent currents for changes of the magnitude of the magnetic induction and its direction while taking the field dependence of the critical current density into account. The model is combined with numerical field computation for the calculation of field errors in superconducting magnets. The filament magnetization and the field errors in a nested orbit corrector magnet for the LHC project at CERN have been calculated as an example.

Magnetization measurements on LHC superconducting strands

IEEE Transactions on Appiled Superconductivity, 1999

Abstra-When using superconducting magnets in particle accelerators like the LHC, persistent currents in the superconductor. often determine the field quality at injection, where the magnetic field is low. This paper describes magnetization measurements made on LHC cable strands at the Technical University of Vienna and the Institute of Physics of the Polish Academy of Sciences in collaboration with CERN. Measurements were performed at T=2K and T=4.2K on more than 50 strands of 7 different manufacturers with NbTi filament diameter between 5 and 7 micrometer. Two different measurement set-ups were used: vibrating sample magnetometer, with a sample length of about 8mm, and an integrating coil magnetometer, with sample length of about lm. The two methods were compared by measuring the same sample. Low field evidence of proximity effect is discussed. Statistics like ratio of the width of the magnetization loop at 4.2K and 2K, and the initial slope dM/dB after cooldown are presented. Decrease of the magnetization with time, of the order of 2% per hour, was observed in some samples.

Statistical Analysis of Conductor Motion in LHC Superconducting Dipole Magnets

IEEE Transactions on Appiled Superconductivity, 2004

Premature training quenches are usually caused by the transient energy release within the magnet coil as it is energized. The dominant disturbances originate in cable motion and produce observable rapid variation in voltage signals called spikes. The experimental set up and the raw data treatment to detect these phenomena are briefly recalled. The statistical properties of different features of spikes are presented like for instance the maximal amplitude, the energy, the duration and the time correlation between events. The parameterization of the mechanical activity of magnets is addressed. The mechanical activity of full-scale prototype and first preseries LHC dipole magnets is analyzed and correlations with magnet manufacturing procedures and quench performance are established. The predictability of the quench occurrence is discussed and examples presented.

Characterization of a Measurement System for Dynamic Effects in Large-Aperture SC Quadrupole Magnets

A new measurement system, based on a large-diameter search-coil rotating in the superfluid helium, a fast digital integrator, a motor drive unit with slip rings, and a flexible software environment was developed at CERN for the measurement of dynamic effects in superconducting magnets. This system has made it possible the measure, with a resolution of up to 1 Hz, the multipole field errors due to superconductor magnetization and interstrand coupling currents. In this paper we present the development and calibration of the measurement system, its installation in the vertical cryostat of CERN’s recently refurbished test station, and its application to the US-LARP built, 120-mm aperture Nb3Sn quadrupole magnet (HQ01e) for the upgrade of the LHC insertion regions.

Quench-back Management for Fast Decaying Currents in SHMS Superconducting Magnets at Jefferson Lab

IEEE Transactions on Applied Superconductivity, 2019

The Super High Momentum Spectrometer (SHMS) of Hall C, part of the 12 GeV Upgrade at Jefferson Lab, was successfully commissioned in 2017. Early operation shows that fast dumps of the SHMS Q2/Q3 and Dipole superconducting magnets triggered quenches, causing some level of operational difficulty. Tests and detailed analyses indicate that a fast discharge produces a fast current decay, which results in substantial AC loss in the conductor and subsequently triggers a quench-back effect. The OPERA/ELECTRA software package was used to calculate the amount of heat deposited in the copper stabilizer from a fast current decay. The magnets' external protection dump resistor values were lowered to slow the fast dumping of the magnet's current, which therefore reduces or eliminates the quench-back effects. A worst-case adiabatic quench scenario was analyzed, assuming no external dump resistor and no liquid helium surrounding the coil, to ensure the safety of the magnets. The stress levels in the coil imposed by winding, collaring preload, Lorentz force, and temperature gradient during a quench, were also examined. The Tsai-Wu material failure criterion was used to determine the acceptable combined stress level. Linear orthotropic analysis of the coil indicates that the magnets can be operated safely with appropriately sized dump resistors. Fast dump tests with the modified dump resistors have been planned to verify the performance and suitability.  Index Terms-Magnet, fast discharge, superconducting, AC loss, quench-back, dump resistor, Tsai-Wu criterion I. INTRODUCTION Jefferson Lab's 11 GeV Super High Momentum Spectrometer (SHMS), consisting of Horizontal Bend (HB), Q1, Q2, Q3, and Dipole magnets has been commissioned successfully [1]-[5] with all magnets achieving the required 11 GeV specifications. Fig. 1 indicates the layout of all five superconducting magnets in experimental Hall C [5]. Table 1 summarizes the key design parameters for the magnets. The magnet design employs 36-strand NbTi-Rutherford cable, originally manufactured for the dipoles of the now abandoned Superconducting Super Collider (SSC) [5]. The HB and Q1 used bare SSC cable while the Q2, Q3, and the Cos θ Dipole used copper stabilized SSC cable. During pre-commissioning, the HB experienced a series of training quenches, starting at 2640 A, before reaching 4000 A (3900 A is required for 11 The Manuscript received XXXXXX.