We present a design of superconducting magnets, optimized for application in a gantry for proton therapy. We have introduced a new magnet design concept, called an alternating-gradient canted cosine theta (AG-CCT) concept, which is compatible with an achromatic layout. This layout allows a large momentum acceptance. The 15 cm radius of the bore aperture enables the application of pencil beam scanning in front of the SC-magnet. The optical and dynamic performance of a gantry based on these magnets has been analyzed using the fields derived (via Biot-Savart law) from the actual windings of the AG-CCT combined with the full equations of motion. The results show that with appropriate higher order correction, a large 3D volume can be rapidly scanned with little beam shape distortion. A very big advantage is that all this can be done while keeping the AG-CCT fields fixed. This reduces the need for fast field ramping of the superconducting magnets between the successive beam energies used for the scanning in depth and it is important for medical application since this reduces the technical risk (e.g., a quench) associated with fast field changes in superconducting magnets. For proton gantries the corresponding superconducting magnet system holds promise of dramatic reduction in weight. For heavier ion gantries there may furthermore be a significant reduction in size.

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Canted-Cosine-Theta (CCT) magnet is an accelerator magnet that superposes fields of nested and tilted solenoids that are oppositely canted. The current distribution of any canted layer generates a pure harmonic field as well as a solenoid field that can be cancelled with a similar but oppositely canted layer. The concept places windings within mandrel's ribs and spars that simultaneously intercept and guide Lorentz forces of each turn to prevent stress accumulation. With respect to other designs, the need for pre-stress in this concept is reduced by an order of magnitude making it highly compatible with the use of strain sensitive superconductors such as Nb 3 Sn or HTS. Intercepting large Lorentz forces is of particular interest in magnets with large bores and high field accelerator magnets like the one foreseen in the future high energy upgrade of the LHC. This paper describes the CCT concept and reports on the construction of CCT1 a "proof of principle" dipole.

Although the high-temperature superconducting (HTS) REBa 2 Cu 3 O x (REBCO, RE = rare earth elements) material has a strong potential to enable dipole magnetic fields above 20 T in future circular particle colliders, the magnet and conductor technology needs to be developed. As part of an ongoing development to address this need, here we report on our CORC ® canted cos θ magnet called C2 with a target dipole field of 3 T in a 65 mm aperture. The magnet was wound with 70 m of 3.8 mm diameter CORC ® wire on machined metal mandrels. The wire had 30 commercial REBCO tapes from SuperPower Inc., each 2 mm wide with a 30 µm thick substrate. The magnet generated a peak dipole field of 2.91 T at 6.290 kA, 4.2 K. The magnet could be consistently driven into the flux-flow regime with reproducible voltage rise at an engineering current density between 400 -550 A mm −2 , allowing reliable quench detection and magnet protection. The C2 magnet represents another successful step towards the development of high-field accelerator magnet and CORC ® conductor technologies. The test results highlighted two development needs: continue improving the performance and flexibility of CORC ® wires and develop the capability to identify locations of first onset of flux-flow voltage.

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A novel concept for a superconducting, fixed-field bending section is presented for use in a proton therapy gantry. The large momentum acceptance of this design allows for treatment over the full proton energy range of 70–220 MeV with fixed field in the superconducting magnets, eliminating the technical risks associated with fast-field ramping to match beam energy changes during treatment. A combined study of beam dynamics and magnet design is shown for such a system in which a simple magnet geometry with straight Nb–Ti racetrack coils is used to produce the desired fields. Particle tracking through this design is compared with clinical requirements for beam spot shape and size at isocenter over the full range of proton energy.

Abstract-A four-layer canted-cosine-theta 16-T dipole has been designed as a possible candidate for future hadron colliders. The design maintains part of the future-circular-collider magnet requirements, i.e., a 50 mm clear bore and 16 T operating at 1.9 K. The magnet intercepts Lorentz forces with an internal structure of ribs and spars, minimizes conductor, and reduces the number of layers and magnet size by using wide cables. The role of iron and its impact on field and magnet size is discussed. A three-dimensional magnetic analysis was carried out for 1-in-1 and 2-in-1 designs including a structural analysis for the 1-in-1 case. Thoughts on future improvements during winding are also discussed.

A future circular collider (FCC) with a center-ofmass energy of 100 TeV and a circumference of around 100 km, or an energy upgrade of the LHC (HE-LHC) to 27 TeV require bending magnets providing 16 T in a 50-mm aperture. Several development programs for these magnets, based on Nb 3 Sn technology, are being pursued in Europe and in the U.S. In these programs, cos-theta, block-type, common-coil, and canted-costheta magnets are ex-plored; first model magnets are under manufacture; limits on con-ductor stress levels are studied; and a conductor with enhanced characteristics is developed. This paper summarizes and discusses the status, plans, and preliminary results of these programs.