V. I. Datskov

Accelerator-Quality HTS Dipole Magnet Demonstrator Designs for the EuCARD-2 5-T 40-mm Clear Aperture Magnet

Future high-energy accelerators will need very high magnetic fields in the range of 20 T. The Enhanced European Coordination for Accelerator Research and Development (EuCARD-2) Work Package 10 is a collaborative push to take high-temperature superconductor (HTS) materials into an accelerator-quality demonstrator magnet. The demonstrator will produce 5 T stand alone and between 17 and 20 T when inserted into the 100-mm aperture of a Fresca-2 high-field outsert magnet. The HTS magnet will demonstrate the field strength and the field quality that can be achieved. An effective quench detection and protection system will have to be developed to operate with the HTS superconducting materials. This paper presents a ReBCO magnet design using a multistrand Roebel cable that develops a stand-alone field of 5 T in a 40-mm clear aperture and discusses the challenges associated with a good field quality using this type of material. A selection of magnet designs is presented as the result of the first phase of development.

New, Coupling Loss Induced, Quench Protection System for Superconducting Accelerator Magnets

A new and promising method for the protection of superconducting high-field magnets is developed and tested on the so-called MQXC quadrupole magnet at the CERN magnet test facility. The method relies on a capacitive discharge system inducing, during a few periods, an oscillation of the transport current in the superconducting cable of the coil. The corresponding fast change of the local magnetic field introduces a high coupling-current loss, which, in turn, causes a fast quench of a large fraction of the coil due to enhanced temperature. Results of measured discharges at various levels of transport current are presented and compared to discharges by quenching the coils using conventional quench heaters and an energy extraction system. The hot-spot temperature in the quenching coil is deduced from the coil voltage and current. The results are compared to simulations carried out using a lumped-element dynamic electro-thermal model of the so-called MQXC magnet developed with Cadence PSpice. The calculated voltages and currents are in good agreement with the measured data. Simulation and test results show that this new protection system, called coupling-loss induced quench, is a feasible method to reduce the hot-spot temperature in high-field superconducting magnets, even more when used in combination with conventional quench heaters.

A new hybrid protection system for high-field superconducting magnets

The new generation of high-field superconducting accelerator magnets poses a challenge concerning the protection of the magnet coil in the case of a quench. The very high stored energy per unit volume requires a fast and efficient quench heating system in order to avoid damage due to overheating. A new protection system for superconducting magnets is presented, comprising a combination of a novel coupling-loss induced quench (CLIQ) system and conventional quench heaters. CLIQ can provoke a very fast transition to the normal state in coil windings by introducing coupling loss and thus heat in the coils conductor. The advantage of the hybrid protection system is a global transition, resulting in a much faster current decay, a significantly lower hot-spot temperature, and a more homogeneous temperature distribution in the magnets coil.

Protecting a full-scale Nb3Sn magnet with CLIQ, the new coupling-loss-induced quench system

A new protection system for superconducting magnets called coupling-loss induced quench system (CLIQ) has been recently developed at CERN. Recent tests on Nb-Ti coils have shown that CLIQ is a valid, efficient, and promising method for the protection of high-magnetic-field superconducting magnets. However, the protection of new-generation Nb3Sn accelerator magnets is even more challenging due to the much higher stored energy per unit volume and to the significantly larger enthalpy needed to initiate and propagate a normal zone in such coils. Now, the CLIQ system is tested for the first time on a Nb3Sn magnet in the CERN magnet test facility in order to investigate its performance in practice, thereby validating the method for this type of superconducting magnets as well. Furthermore, we successfully reproduced the electrothermal transients during a CLIQ discharge. Finally, the implementation of various CLIQ-based protection schemes for the full-scale Nb3Sn quadrupole magnet for the LHC high luminosity upgrade is discussed. The impact of key system parameters on CLIQ performance and the advantages and drawbacks of using multiple CLIQ units on a single magnet are discussed.

First Implementation of the CLIQ Quench Protection System on a 14-m-Long Full-Scale LHC Dipole Magnet

The coupling-loss-induced quench (CLIQ) is an innovative system for the protection of superconducting magnets. Its energy-deposition mechanism, based on coupling loss generated directly in the superconductor, is fundamentally faster than heat diffusion, upon which traditional quench-heater-based systems rely. CLIQ electrical design relies on simple and robust components, i.e., easy to install and be replaced in case of damage. After being successfully tested on model magnets of different geometries and types of superconductor, CLIQ is now applied for the first time for the protection of a full-scale dipole magnet. For this purpose, a 14-m-long LHC twin-aperture dipole magnet is equipped with CLIQ terminals and two 80-mF 500-V CLIQ units are connected to its windings. Experimental results obtained under various operating conditions convincingly show that a CLIQ-based quench protection system can effectively protect large-scale magnets by quickly and homogeneously transferring to the normal-state voluminous regions of the winding packs. A developed dedicated simulation code correctly reproduces the complex electrothermal transient occurring during a CLIQ discharge. The successful test completes the development program of CLIQ quench protection systems, which has convincingly demonstrated the maturity and readiness of the system for application in large-scale magnet systems.

First Implementation of the CLIQ Quench Protection System on a Full-Scale Accelerator Quadrupole Magnet

The coupling-loss induced quench system (CLIQ) is an innovative method for the protection of high-field superconducting magnets. With respect to the conventional method based on quench heaters, it offers significant advantages in terms of electrical robustness and energy-deposition velocity. Its effective intrawire heating mechanism targets a fast and homogeneous transition to the normal state of the winding pack, hence assuring a quick magnet discharge and avoiding overheating of the coils hot spot. Furthermore, it is possible to implement CLIQ as a time- and cost-effective repair solution for the protection of existing magnets with broken quench heaters. After being successfully tested on model magnets of different geometries and made of different types of superconductor, CLIQ is now applied for the first time for the protection of a full-scale quadrupole magnet at the CERN magnet test facility. One aperture of a 3.4-m-long LHC matching quadrupole magnet is equipped with dedicated terminals to allow the connection of a CLIQ system. Experimental results convincingly show that CLIQ can protect this coil over the entire range of operating conditions. The complex electrothermal transients during a CLIQ discharge are successfully reproduced by means of a 2-D model. The test is part of the R&D program of CLIQ quench protection systems, which has convincingly demonstrated the maturity of this technology and its effectiveness also for large-scale magnet systems. The proposed CLIQ-based solution for the quench protection of the LHC matching quadrupole magnet is now ready to be implemented in the LHC machine if needed.

LHC IR Upgrade Nb–Ti, 120-mm Aperture Model Quadrupole Test Results at 1.8 K

Over the last five years, the model MQXC quadruple, a 120-mm aperture, 120 T/m, 1.8 m long, Nb-Ti version of the LHC insertion upgrade (due in 2021), has been developed at CERN. The magnet incorporates several novel concepts to extract high levels of heat flux and provide high quality field harmonics throughout the full operating current range. Existing LHC-dipole cable with new, open cable and ground insulation was used. Two, nominally identical 1.8-m-long magnets were built and tested at 1.8 K at the CERN SM18 test facility. This paper compares in detail the two magnet tests and presents: quench performance, internal stresses, heat extraction simulating radiation loading in the superconducting coils, and quench protection measurements. The first set of tests highlighted the conflict between high magnet cooling capability and quench protection. The second magnet had additional instrumentation to investigate further this phenomenon. Finally, we present test results from a new type of superconducting magnet protection system.

Superconducting Magnets for Astroparticle Shielding in Interplanetary Manned Missions

The space radiation environment represents a serious problem for long duration interplanetary manned missions. During the last four decades, active magnetic shields have been considered to protect the astronauts against the ionizing radiations of galactic cosmic rays. The previous studies indicate that up to a factor of 10 reduction in the dose could be achieved with a magnetic screen composed of large volume superconducting magnets, which would surround a habitat module of about 300 cubic meters. A screen of this dimension operating in space represents a formidable technological challenge. The choice of a high-temperature superconductor or MgB2, would avoid the complications of helium cryogenics. The results of preliminary studies to identify the critical aspects and the feasibility of the magnet shield to provide a solution in the near future are reported.

submitter : Quench Protection of a 16-T Block-Coil Dipole Magnet for a 100-TeV Hadron Collider Using CLIQ

Protection against the effects of a quench is a crucial challenge for 16-T-class superconducting dipole magnets for a future 100-TeV Hadron collider. To avoid damage due to overheating of the coils hot spot, heat generated during the quench has to be homogeneously distributed in the winding pack by quickly and uniformly transferring to the normal-state voluminous coil sections. Conventional protection systems rely on quench heaters placed on the outer surfaces of the coils. However, this technique has to confront significant challenges in order to achieve the fast transitions required by high magnetic field magnets. The recently developed coupling-loss-induced quench (CLIQ) utilizes interfilament coupling loss as an effective intrawire heat deposition mechanism, which, in principle, is faster than thermal diffusion. Furthermore, the CLIQ technology is based on simple and robust electrical components in contact with the coil only in a limited number of easily accessible and well-insulated points. Hence, expected occurrence of failure and electrical breakdown is significantly reduced. As a case study, the design of a CLIQ-based protection system for a 14-m-long 16-T Nb 3Sn block-coil dipole magnet is demonstrated here. Various magnet design features can be adjusted to improve CLIQ performance and optimize its integration in the magnet system. CLIQ provides future magnet designers with a solution for a very effective, yet electrically robust, quench protection system, resulting in better magnet performance and lower cost than would be possible with a traditional approach to magnet protection.

Advanced Quench Protection for the Nb 3 Sn Quadrupoles for the High Luminosity LHC

The goal of the High Luminosity LHC project is upgrading the LHC in order to increase its luminosity by a factor of five. To achieve this, 24 150-mm-aperture 12-T Nb3Sn quadrupole magnets are to be installed close to the two interaction regions at ATLAS and CMS. This new generation of high-field magnets poses a significant challenge concerning the protection of the coils in the case of a quench. The very high stored energy per unit volume requires a fast and effective quench heating system in order to limit the hot-spot temperature and hence avoid damage due to overheating. Conventional protection systems based on quench heaters have a limited response time due to the thermal insulation between the heater and the coil. An advanced solution for the protection of high-field magnets is the coupling-loss induced quench (CLIQ) system, recently developed at CERN. Due to its fast intrawire energy-deposition mechanism, CLIQ is a very effective, yet electrically robust, quench protection system. Various protection scenarios, including quench heaters, CLIQ, or combinations of the two methods, are analyzed and discussed, with the aim of minimizing the coils hot-spot temperature and thermal gradients during the discharge. The proposed design assures a fully redundant system.