Olaf Dunkel

Twin rotating coils for cold magnetic measurements of 15 m long LHC dipoles

We describe here a new harmonic coil system for the field measurement of the superconducting, twin aperture LHC dipoles and the associated corrector magnets. Besides field measurements the system can be used as an antenna to localize the quench origin. The main component is a 16 m long rotating shaft, made up of 13 ceramic segments, each carrying two tangential coils plus a central radial coil, all working in parallel. The segments are connected with flexible Ti-alloy bellows, allowing the piecewise straight shaft to follow the curvature of the dipole while maintaining high torsional rigidity. At each interconnection the structure is supported by rollers and ball bearings, necessary for the axial movement for installation and for the rotation of the coil during measurement. Two such shafts are simultaneously driven by a twin-rotating unit, thus measuring both apertures of a dipole at the same time. This arrangement allows very short measurement times (typically 10 s) and is essential to perform cold magnetic measurements of all dipoles. The coil surface and direction are calibrated using a reference dipole. In this paper we describe the twin rotating coil system and its calibration facility, and we give the typical resolution and accuracy achieved with the first commissioned unit.

Cold Test Results of the LARP HQ

The high gradient quadrupole magnet is a 120-mm-aperture, 1-m-long Nb3Sn quadrupole developed by the LHC Accelerator Research Program collaboration in support of the High-Luminosity LHC project. Several tests were performed at Lawrence Berkeley National Laboratory in 2010-2011 achieving a maximum gradient of 170 T/m at 4.4 K. As a next step in the program, the latest model (HQ01e) was sent to CERN for testing at 1.9 K. As part of this test campaign, the magnet training has been done up to a maximum current of 16.2 kA corresponding to 85% of the short sample limit. The ramp rate dependence of the quench current is also identified. The efficiency of the quench heaters is then studied at 4.2 K and at 1.9 K. The analyses of the magnet resistance evolution during fast current discharge showed evidence of quench whereas high energy quenches have been successfully achieved and sustained with no dump resistor.

\hbox{Nb}_{3} \hbox{Sn}

The high-luminosity upgrade for the LHC (HL-LHC) envisages the replacement of some 15-m-long NbTi dipoles in the dispersion suppressor area by shorter Nb3Sn magnets with a nominal field of 11 T. The new magnets must be compatible with the lattice and other main systems of the LHC. The shorter length of new units will allow the installation of collimators. The successful use of the Nb3Sn technology requires an intense R&D program, and therefore, a CERN-Fermilab joint development program was established. This paper describes the magnetic measurement procedure and presents the analysis of the magnetic measurements on the first 2-m-long single-aperture demonstrators built and tested at CERN. The geometrical field multipoles, the iron saturation effects, and the effects of persistent currents are presented. The experimental data are compared with the magnetic calculations using the CERN field computation program ROXIE and are discussed in view of the requirements for machine operation.

Quadrupole Magnet at 1.9 K

More than 400 twin aperture lattice quadrupoles are needed for the Large Hadron Collider (LHC) which is under construction at CERN. The main quadrupole is assembled with correction magnets in a common cryostat called the Short Straight Section (SSS). We plan to measure all SSSs in cold conditions with an unprecedented accuracy: integrated gradient of the field within 150 ppm, harmonics in a range of 1 to 5 ppm, magnetic axis of all elements within 0.1 mm and their field direction within 0.2 mrad. In this paper we describe the automatic measurement system that we have designed, built, and calibrated. Based on the results obtained on the two first prototypes of the SSSs (SSS3 and SSS4) we show that this system meets all above requirements.

Magnetic Measurements and Analysis of the First 11-T Nb 3 Sn Dipole Models Developed at CERN for HL-LHC

The Facility for Antiproton and Ion Research (FAIR) is currently being constructed at GSI Darmstadt. Around 500 superconducting magnets are being procured for the heavy ion synchrotron SIS100, and around 180 are being procured for the Super Fragment Separator (Super-FRS). All these magnets have to be tested at cryogenic temperature in order to verify and guarantee their performances before they are installed in the tunnel. Test stations, measurement equipment, and the required infrastructure are being built up at the host laboratory and, due to the large number of magnets and testing requirements, at CERN and JINR. We report on the plans, testing strategy, developments, and, particularly, the status of preparations for testing of the SIS100 dipoles at GSI.

A system for series magnetic measurements of the LHC main quadrupoles

Current installation of the large hadron collider (LHC) particle accelerator at CERN has required the use of a harmonic coil magnetic measurement system to quantify the magnetic field harmonic quality of the superconducting, twin aperture LHC dipoles. Current and future needs for measuring fast changing magnetic fields necessitates the use of a rotating unit (RU) and associated electronics to drive this long shaft with increased speed and measurement bandwidth. Therefore, the fast magnetic measurement equipment (FAME) project has been launched to deliver such a system. A primary obstacle to achieving the goals of the FAME project is the possibility of amplifying mechanical vibrations due to increased speeds. This paper presents the methodology and results of an experimental investigation conducted to estimate mechanical vibrations of the long shaft within a cold-bore mounted anti-cryostat at various rotational speeds using magnetic measurements.

Testing of the Superconducting Magnets for the FAIR Project

All LHC twin aperture magnets will be tested under operating conditions to verify their performance. The field measurement equipment works at ambient temperature and pressure. Each magnet is therefore equipped with two warm bore anticryostats. As a consequence a total of nearly 80 anticryostats of different lengths have to be assembled, handled and serviced during the test period. Two main constraints determine the frame for the design of these anticryostats: inside a given beam pipe aperture of 50 mm kept at 1.9 K, a warm bore aperture of 40 mm must provide the highest possible mechanical stability and robustness for numerous mounting cycles as well as the lowest possible heat losses towards the cryogenic system. In addition, compatibility with high magnetic fields and an insulation vacuum of about 10−7 mbar have to be maintained. This paper describes how a satisfactory mechanical stability as well as heat losses in the order of 0.8 W/m are achieved with a design based on very careful space and material ...

Estimation of Mechanical Vibrations of the LHC Fast Magnetic Measurement System

A new magnetic measurement system for validating and characterizing permanent and fast-pulsed iron-dominated magnets is presented. This system is going to be used on the magnet series tests of the new linear particle accelerator Linac 4 of the Large Handron Collider at the European Organization for Nuclear Research (CERN) to perform a complete field analysis of the entire acceleration line. Measurement results will be useful to tune better the beam brightness during the first acceleration step. In this paper, the requirements, the architecture, and the most critical parts of the design are highlighted. Then, the preliminary experimental results obtained over the first Linac 4 magnet prototypes are discussed.

A Warm Bore Anticryostat for Series Magnetic Measurements of LHC Superconducting Dipole and Short-Straight-Section Magnets

The high-luminosity upgrade of the large hadron collider (HL-LHC) requires new high-field and large-aperture quadrupole magnets for the low-beta inner triplets (MQXF). CERN and LARP are currently collaborating to develop a 150-mm-aperture quadrupole based on Nb

A measurement system for fast-pulsed magnets: a case study on Linac4 at CERN

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