Conformal REBCO Windings for the Dipoles of an Ultimate-Energy Hadron Collider

REBCO tape has remarkable performance for superconducting technology, but it is extremely expensive and it is a strongly anisotropic superconductor. The design of a 3.5 T collider dipole is presented in which all turns of the body winding are oriented so that all the turns of REBCO tape operate with maximum current density. Each turn within the winding contains a stack of Cu-clad REBCO tapes; all tapes within the turn are compressed to provide low-resistance Cu-Cu contact, but the successive turns are electrically isolated. Each turn is oriented so that the local magnetic field at the tapes is closely parallel to the tape surface. Sextupole is controlled using a current-programmed turn to provide excellent homogeneity over a 20:1 dynamic range. Issues of current re-distribution during ramping, quench stability, AC losses, synchrotron radiation, and cryogenics have been considered. Two examples are evaluated: the 3.5 T dipole for a 500 TeV Collider-in-the-Sea, and a REBCO insert for an 18 T dipole for a 100 TeV FCC collider.