Conceptual Design of a New Sample Holder for the FRESCA Cable Test Station

Abstract

Abstract-At present Nb 3 Sn Rutherford Cables seem to be the most suitable conductors for next generation superconducting accelerator magnets. These magnets will have a peak field in the coils larger than 10 T and the large Lorentz forces will impose coil pre-stresses significantly larger than 100 MPa. Since Nb 3 Sn is strongly sensitive to strain it is mandatory to characterize the cable under a transverse pressure comparable to the one experienced in future magnets. As a part of its High Field Magnet program, CERN is developing a sample holder for the FRESCA Facility that allows testing 10 mm wide superconducting Rutherford cables under a transverse pressure up to 200 MPa. The sample holder will be able to house cables up to 20 mm wide. In this paper the conceptual design is presented together with the experimental results of the mechanical test performed on a 40 cm long model. The results show that the structure can apply a transverse pressure larger than 200 MPa on 10 mm wide cables with sufficiently high pressure homogeneity.

Critical Current Measurements of High-<formula formulatype="inline"><tex Notation="TeX">$J_{c}$</tex> </formula> <formula formulatype="inline"><tex Notation="TeX">$\hbox{Nb}_{3}\hbox{Sn}$</tex></formula> Rutherford Cables Under Transverse Compression

“…The new sample holder is based on the conceptual design described in an earlier paper [12]. This design consisted in an external Al 7075 tube that houses two Ti6Al4V pads, a Ti6Al4V 'U-cage', 2 stainless steel keys and a cable sample, see Fig.…”

“…Once the required pressure is reached the keys are inserted; they will maintain a certain pressure when the bladder is depressurized and removed. Additional pressure on the cable stack is applied during the cool down of the sample holder thanks to the differential thermal contraction between the Al 7075 and the Ti6Al4V [12]. For example, a 10-mm-wide Al I 3OrCA-01 bar that substitutes the cable stack and is compressed with 55 MPa at room temperature would experience 200 MPa at 4.2 K [12].…”

“…Additional pressure on the cable stack is applied during the cool down of the sample holder thanks to the differential thermal contraction between the Al 7075 and the Ti6Al4V [12]. For example, a 10-mm-wide Al I 3OrCA-01 bar that substitutes the cable stack and is compressed with 55 MPa at room temperature would experience 200 MPa at 4.2 K [12]. The conceptual design was implemented in the final sample holder by building: a 2-m-long U-cage, two Al 7075 tubes (30 and 40 cm long respectively), two 36-cm-long Ti6Al4V upper pads, two Ti6Al4V lower pads (30 and 40 cm long respectively), a 70-cm-long, 2.5-cm-wide bladder and twelve 316LN 11.65-cm-long keys.…”

Transverse pressure effect on superconducting Nb3Sn Rutherford and ReBCO Roebel cables for accelerator magnets

“…To the best of our knowledge, only four test facilities worldwide are presently capable to measure the critical current of accelerator-type cables under transverse pressure, located at: the National High Magnetic Field Laboratory (NHMFL) in Tallahassee [124,125], the Brookhaven National Laboratory (BNL) [126,127], CERN [128] and the University of Twente [129].…”

“…Figure 2.10 shows the setup used in the FRESCA test station at CERN [103,104,128]. An external aluminum tube houses two pads, a titanium U-cage, two stainless steel keys and cable samples up to 1.8 m long and 20 mm wide.…”