The test of the first LARP (LHC Accelerator Research Program) Long Quadrupole is a significant milestone toward the development of Nb 3 Sn quadrupoles for LHC (Large Hadron Collider) Luminosity ...Upgrades. These 3.7-m long magnets, scaled from the 1-m long Technological Quadrupoles, are used to develop our capabilities to fabricate and assemble Nb 3 Sn coils and structures with lengths comparable to accelerator magnet dimensions. The long quadruples have a target gradient of 200 T/m in a 90-mm aperture. Pre-stress and support are provided by an Al-shell-based structure pre-loaded using bladders and keys. The coils were fabricated at BNL and FNAL, the shell-based structure was designed and assembled at LBNL, the test is performed at FNAL. In this paper we present the final steps of the development of the first model (LQS01), several upgrades to the test facility, the test results of witness cables, and the short sample limit.
First Performance Test of Ceramic-insulated Conductors Rochepault, E.; de Rapper, W. M.; Vedrine, P. ...
IEEE transactions on applied superconductivity,
2012-June, 2012-06-00, 20120601, Letnik:
22, Številka:
3
Journal Article
Recenzirano
An innovative ceramic insulation has been developed by CEA Saclay for Nb 3 Sn cables. As the ceramic cures during the heat treatment of the Nb 3 Sn, there is no need for an impregnation afterwards. ...This process eliminates the epoxy-impregnation steps which present the risk to damage the conductor. The porosity of this insulation is expected to increase the capacity of the heat extraction needed by the next magnets generation. However, in high field magnets, the transverse compressive stress on the cables can exceed 150 MPa, due to Lorentz forces. The effects of this high compressive stress on the critical current of Nb 3 Sn conductors has been investigated at CEA Saclay in collaboration with CERN using two experimental setups. This paper reports the first quench data measured on ceramic-insulated cables. The samples are compared to a witness sample in order to compute the degradation. It finally appears that the ceramic insulation gives a weaker mechanical support than epoxy-impregnation, leading to an additional degradation of the conductor. Some solutions are proposed to improve the mechanical strength of the ceramic.
In the framework of future LHC upgrades using Nb 3 Sn magnets, supported in part by the US LHC Accelerator Research Program (LARP) and the European EuCARD program, CERN is intensifying its research ...on Nb 3 Sn Rutherford cables. In the FRESCA cable test facility at CERN, two new Nb 3 Sn cable samples were investigated concerning their quench and critical current as well as stability performance. The two samples are based on RRP type strands with comparable layout. They have 27 strands with 0.7 mm diameter while the strands have 54 or 108 superconducting sub-elements. The cables are 10 mm wide and have a transposition pitch of about 75 mm. The cables are used in magnets built for LARP. Their performance is measured as a function of magnetic field up to 10 T with ramp rates of 10 to 1000 A/s and temperature of 1.9 and 4.3 K. A hall probe array is present to study the current distribution. Point heaters are used to study cable stability and current redistribution.
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 ...(I c ) 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 I c (B) 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 I c (B) 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 3 Sn conductors for the reasons mentioned.
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 hbox Nb 3 hbox 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, hbox Nb 3 hbox 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.
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 Ic , 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.
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 Formula Omitted 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 Formula Omitted, the temperature margin across the entire magnet cross-section decreases. Unlike Nb-Ti, Formula Omitted 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.
An innovative ceramic insulation has been developed by CEA Saclay for rm Nb 3 rm Sn cables. As the ceramic cures during the heat treatment of the rm Nb 3 rm Sn , there is no need for an impregnation ...afterwards. This process eliminates the epoxy-impregnation steps which present the risk to damage the conductor. The porosity of this insulation is expected to increase the capacity of the heat extraction needed by the next magnets generation. However, in high field magnets, the transverse compressive stress on the cables can exceed 150 MPa, due to Lorentz forces. The effects of this high compressive stress on the critical current of rm Nb 3 rm Sn conductors has been investigated at CEA Saclay in collaboration with CERN using two experimental setups. This paper reports the first quench data measured on ceramic-insulated cables. The samples are compared to a witness sample in order to compute the degradation. It finally appears that the ceramic insulation gives a weaker mechanical support than epoxy-impregnation, leading to an additional degradation of the conductor. Some solutions are proposed to improve the mechanical strength of the ceramic.
PDF
