A. Ballarino

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.

Development of MQXF: The Nb 3 Sn Low-

The High Luminosity (HiLumi) Large Hadron Collider (LHC) project has, as the main objective, to increase the LHC peak luminosity by a factor five and the integrated luminosity by a factor ten. This goal will be achieved mainly with a new interaction region layout, which will allow a stronger focusing of the colliding beams. The target will be to reduce the beam size in the interaction points by a factor of two, which requires doubling the aperture of the low-β (or inner triplet) quadrupole magnets. The use of Nb3Sn superconducting material and, as a result, the possibility of operating at magnetic field levels in the windings higher than 11 T will limit the increase in length of these quadrupoles, called MQXF, to acceptable levels. After the initial design phase, where the key parameters were chosen and the magnets conceptual design finalized, the MQXF project, a joint effort between the U.S. LHC Accelerator Research Program and the Conseil Européen pour la Recherche Nucléaire (CERN), has now entered the construction and test phase of the short models. Concurrently, the preparation for the development of the full-length prototypes has been initiated. This paper will provide an overview of the project status, describing and reporting on the performance of the superconducting material, the lessons learnt during the fabrication of superconducting coils and support structure, and the fine tuning of the magnet design in view of the start of the prototyping phase.

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The quadrupole and dipole magnets for the high-luminosity large hadron collider (HL-LHC) upgrade will be based on Nb ₃Sn Rutherford cables that operate at 1.9 K and experience magnetic fields of up to about 12 T. An important step in the design of these magnets is the development of the high-aspect-ratio Nb₃Sn cables to achieve the nominal field with sufficient margin. The strong plastic deformation of unreacted Nb₃Sn strands during the Rutherford cabling process may induce non-negligible <inline-formula><tex-math notation=LaTeX>

Quadrupole for the HiLumi LHC

I_{c}

submitter : Optimization of Nb

</tex-math> </inline-formula> and Residual Resistivity Ratio degradation. In this paper, the cabling degradation is investigated as a function of the cable geometry for both Powder-in-Tube and Restack Rod Process conductors. Based on this analysis, new baseline geometries for both 11 T and quadrupole magnets of HL-LHC are proposed.

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High critical current density Nb3Sn wires (Jc > 2500 A/mm 2 at 4.2 K and 12 T) are the conductors considered for next-generation accelerator magnets. At present, the large magnetization of these strands is a concern within the scientific community because of the impact it might have on the magnet field quality. In order to characterize the magnetic behavior of these wires, an extensive campaign of magnetization measurements was launched at CERN. Powder-in-tube strands by Bruker-EAS and Restacked Rod Process strands by Oxford Superconducting Technology were measured between 0 and 10.5 T at different temperatures (ranging from 1.9 to 14.5 K). The samples, based on strands with different subelements dimensions (35 to 80 μm), were measured with a vibrating sample magnetometer. The experimental data were analyzed to: (1) calculate the effective filament size and the optimal parameters for the pinning force scaling law and (2) define the field-temperature region where there are flux jumps. It was found that the flux-jump can limit the maximum magnetization of the Nb3Sn wires and that the maximum magnetization at higher temperatures can be larger than the one at lower temperatures. In this paper, the experimental results and the analysis are reported and discussed.High critical current density Nb3Sn wires (Jc > 2500 A/mm2 at 4.2 K and 12 T) are the conductors considered for next-generation accelerator magnets. At present, the large magnetization of these strands is a concern within the scientific community because of the impact it might have on the magnet field quality. In order to characterize the magnetic behavior of these wires, an extensive campaign of magnetization measurements was launched at CERN. Powder-in-tube strands by Bruker-EAS and Restacked Rod Process strands by Oxford Superconducting Technology were measured between 0 and 10.5 T at different temperatures (ranging from 1.9 to 14.5 K). The samples, based on strands with different subelements dimensions (35 to 80 μm), were measured with a vibrating sample magnetometer. The experimental data were analyzed to: (1) calculate the effective filament size and the optimal parameters for the pinning force scaling law and (2) define the field-temperature region where there are flux jumps. It was found that the flux-jump can limit the maximum magnetization of the Nb3Sn wires and that the maximum magnetization at higher temperatures can be larger than the one at lower temperatures. In this paper, the experimental results and the analysis are reported and discussed.

Sn Rutherford Cables Geometry for the High Luminosity LHC

Roebel-type cables made of a ReBCO conductor are potential candidates for high-field accelerator magnets. The necessity to promote a large effective transverse section in a Roebel cable to avoid local overstress leading to degradation in electrical performance has been recently addressed. In this paper, a new geometry of meander tapes for a Roebel cable that enhances both the transverse effective section and the current margin at crossing segments is discussed. As Roebel cables are bent at the coil ends, the modulation of the bending radius of strands along the cable pitch leads to a shift of the strands with respect to each other. The shift magnitude is analytically investigated in this paper as a function of both cable features and coil geometry. Finally, the minimum transposition pitch of Roebel cables is determined on the basis of coil characteristics.

Magnetization Measurements of High- Strands

The quadrupole magnets for the LHC High Luminosity (Hi-Lumi) upgrade will be based on Nb3Sn Rutherford cables that operate at 1.9 K and experience magnetic fields larger than 12 T. Because of the large stored energy, one of the major issues in the design of these magnets is their protection. To study the quench propagation in Nb3Sn Rutherford cables for the Hi-Lumi Quadrupole magnets, a campaign of measurements was carried out in the FRESCA test station at CERN. In addition to the critical and stability current measurements at 4.3 K and 1.9 K, we performed a series of tests where the quenches were induced by resistive heaters impregnated in the cable. The longitudinal and transversal speeds of the normal zone propagation were investigated at different magnetic fields and operating currents. In this paper, the numerical and experimental results are reported, compared and discussed.

submitter : On Roebel Cable Geometry for Accelerator Magnet

The quadrupole magnets for the LHC High Luminosity (Hi-Lumi) upgrade will be based on Nb3Sn Rutherford cables that operate at 1.9 K and experience magnetic fields larger than 12 T. Because of the large stored energy, one of the major issues in the design of these magnets is their protection. To study the quench propagation in Nb3Sn Rutherford cables for the Hi-Lumi Quadrupole magnets, a campaign of measurements was carried out in the FRESCA test station at CERN. In addition to the critical and stability current measurements at 4.3 K and 1.9 K, we performed a series of tests where the quenches were induced by resistive heaters impregnated in the cable. The longitudinal and transversal speeds of the normal zone propagation were investigated at different magnetic fields and operating currents. In this paper, the numerical and experimental results are reported, compared and discussed.

Quench Propagation in Nb

The quadrupole magnets for the LHC High Luminosity (Hi-Lumi) upgrade will be based on Nb3Sn Rutherford cables that operate at 1.9 K and experience magnetic fields larger than 12 T. Because of the large stored energy, one of the major issues in the design of these magnets is their protection. To study the quench propagation in Nb3Sn Rutherford cables for the Hi-Lumi Quadrupole magnets, a campaign of measurements was carried out in the FRESCA test station at CERN. In addition to the critical and stability current measurements at 4.3 K and 1.9 K, we performed a series of tests where the quenches were induced by resistive heaters impregnated in the cable. The longitudinal and transversal speeds of the normal zone propagation were investigated at different magnetic fields and operating currents. In this paper, the numerical and experimental results are reported, compared and discussed.