Critical Current and Stability of High-${\rm J}_{\rm c}$${\rm Nb}_{3}{\rm Sn}$ Rutherford Cables for Accelerator Magnets

et al. 2013

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In the frame of the planned luminosity upgrade of the Large Hadron Collider, new quadrupole and dipole magnets are being designed and tested. Cabled conductors have been tested in the FRESCA test station to aid this effort. Part of this work is to characterize the thermal stability of the Nb 3 Sn conductors, because this is difficult to measure in a real magnet. When measured at nominal operating current at 1.9 and 4.3 K, the minimum quench energy (MQE) diminishes when the system is cooled. When the temperature is decreased but the nominal current is increased to profit from the increased I c , the temperature margin across the entire magnet cross-section decreases. Unlike Nb-Ti, Nb 3 Sn conductors are not aided by the super-fluidity of the helium in the magnet because they are impregnated. It is argued here that given the material properties and effects, the MQE decreases with decreasing temperature. This conclusion is validated experimentally and is used to determine the MQE in a Large Hadron Collider quadrupole upgrade magnet.

Section: Point Heaters and Sample Poweringmentioning

confidence: 99%

“…Two cables from this program are available at CERN for validation of a new sample holder [2]. After the performance test they were equipped with point heaters to study the thermal stability.…”

Section: Introductionmentioning

confidence: 99%

Thermal Stability at 1.9 K and 4.3 K of $\hbox{Nb}_{3} \hbox{Sn}$ Cables for Quadrupole Magnets for the LHC Upgrade

Rapper

Dhallé

et al. 2013

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“…The problem persists even when the effective filament size is reduced, which can cure a strand suffering from another type of instability, magnetization instability [3]. The magneto-thermal instability has been observed also in Nb 3 Sn superconducting cables and magnets [4], [5]. From now on in this document, "the instability" refers particularly to the magneto-thermal instability.…”

Section: Introductionmentioning

confidence: 94%

An Experimental Setup to Measure the Minimum Trigger Energy for Magnetothermal Instability in $\hbox{Nb}_{3}\hbox{Sn}$ Strands

Takala

Bremer

et al. 2012

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Magneto-thermal instability may affect high critical current density Nb3Sn superconducting strands that can quench even though the transport current is low compared to the critical current with important implications in the design of next generation superconducting magnets. The instability is initiated by a small perturbation energy which is considerably lower than the Minimum Quench Energy (MQE). At CERN, a new experimental setup was developed to measure the smallest perturbation energy (Minimum Trigger Energy, MTE) which is able to trigger the magneto-thermal instability in superconducting Nb 3 Sn-strands. The setup is based on Q-switched laser technology which is able to provide a localized perturbation in nano-second time scale. Using this technique the energy deposition into the strand is well defined and reliable. The laser is located outside the cryostat at room temperature. The beam is guided from room temperature on to the superconducting strand by using a UV-enhanced fused silica fibre. The strand is mounted on a VAMAS barrel. A part of the beam's energy is absorbed into the strand acting as the trigger energy for the magneto-thermal instability. In this paper the experimental setup and the calibration of the absorbed energy is presented.Presented at the 22nd International Conference on Magnet Technology 12-16 September 2011, Marseille, France Geneva, Switzerland CERN-ATS-2012-032February 2012 Abstract-Magneto-thermal instability may affect high critical current density Nb3Sn superconducting strands that can quench even though the transport current is low compared to the critical current with important implications in the design of next generation superconducting magnets. The instability is initiated by a small perturbation energy which is considerably lower than the Minimum Quench Energy (MQE). At CERN, a new experimental setup was developed to measure the smallest perturbation energy (Minimum Trigger Energy, MTE) which is able to trigger the magneto-thermal instability in superconducting Nb3Sn-strands. The setup is based on Q-switched laser technology which is able to provide a localized perturbation in nano-second time scale. Using this technique the energy deposition into the strand is well defined and reliable. The laser is located outside the cryostat at room temperature. The beam is guided from room temperature on to the superconducting strand by using a UV-enhanced fused silica fibre. The strand is mounted on a VAMAS barrel. A part of the beam's energy is absorbed into the strand acting as the trigger energy for the magneto-thermal instability. In this paper the experimental setup and the calibration of the absorbed energy is presented.

Critical Current in High-J$ _{\rm c}$ Nb$_{3}$Sn Rutherford Cables Affected Substantially by the Direction of the Applied Magnetic Field

Rapper

Naour

et al. 2012

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Recently several Rutherford-type Nb Sn cables for possible use in new magnets for upgrades of the LHC have been measured at CERN. A summary is provided including a comparison of the critical current of various cable types and strand materials versus their respective extracted strand measurements. The conductors were cabled at CERN and Lawrence Berkeley National Laboratory. The summary shows an unsurprising linear relation between the strand and the cable performance. However, assuming that the local peak magnetic field in the conductor is the relevant factor for determining the relation, a discrepancy is found when results from different directions of applied magnetic field on the cable are compared.In this paper it is shown that the critical current as a function of the peak magnetic field in the conductor can change in the range of 7-12% depending on the direction of the applied magnetic field. This effect originates from the superposition of the self field of the conductor and the applied magnetic field. When the direction of the applied magnetic field is changed, the position of the peak magnetic field in the conductor shifts. Mechanical degradation during the cabling process can create a local reduction in the critical current. When the position of the peak magnetic field shifts from a more degraded to a less degraded area, the measured curve of the conductor will change accordingly. The measured effect is in principle present in all cables exhibiting non-uniform cabling degradation but is substantially present in Nb Sn conductors for the reasons mentioned.