  Development of energy-efficient fast cycling accelerator magnets is critical
for the next generation of proton rapid cycling synchrotrons (RCS) for neutrino
research and booster accelerators of future muon colliders. We see a unique
opportunity for having such magnets to be built on base of High Temperature
Superconductors (HTS). Besides being superconducting at relatively high
temperatures, rare-earth HTS tapes have shown very small AC losses compared to
low-temperature NbTi superconductor cables. Recent tests of the HTS-based 0.5 m
long two-bore superconducting accelerator magnet have shown record high dB/dt
ramping rates of about 300 T/s at 10 Hz repetition rate and 0.5 T B-field span.
No temperature rise in 6 K cooling He was observed within the 0.003 K error
setting the upper limit on the cryogenic power loss in the magnet conductor
coil to be less than 0.2 W/m. Based on this result we outline a possible
upgrade of this test magnet design to 2 T B-field in the 10 mm beam gap with
the dB/dt ramping rates up to 1000 T/s. The power test results of this short
sample magnet will be used to project both cryogenic and electrical power
losses as a function of the magnet B-field and the dB/dt ramping rates. Then
these projections will be scaled to the range of expected accelerator magnet
beam gaps and B-fields for the proton and muon RCS accelerators. We invite
collaborators to join these studies and call for support of the R&D program
aimed at comprehensive demonstration of this approach that includes design,
construction, and power tests of a long prototype of the HTS-based fast-cycling
accelerator magnet by 2028.

Accelerator Physics