This talk gives an overview of the design, fabrication, and test efforts of the development of high-field high-temperature superconducting accelerator magnets in the USA with a focus on efforts of developing the canted-cosine-theta Bi-2212 and REBCO magnets at the Berkeley lab. Several prototype magnets have been built and tested in the standalone configurations and we are planning to test them in a background magnets field provided by Nb₃Sn magnets. Several engineering challenges will be discussed, in particularly the issue of dealing with the effects of electromagnetic coupling and electromechanical interactions between insert and outsert magnets on electrical and mechanical safety and quench protection. Moreover, quench detection of two Bi-2212 standalone accelerator magnets (common coil configuration and canted-cosine-theta) built and tested will be compared and analyzed to shed lights on questions such as what is the limit of the voltage tap based quench detection, and how can it be improved relative to the dogma established for Nb-Ti and Nb₃Sn accelerator magnets. A third topic is the fundamental concept of the margin of safety of the HTS magnets. A revised MIITS (I²t) method that suits for HTS magnets than the prevalent method for Nb-Ti and Nb₃Sn magnets will be introduced for analyzing the hot spot temperature, and illustrate how can the margin of safety be improved with improved quench detection and for the case of the common coil configuration Bi-2212 accelerator magnets by a significant degree.

Acknowledgement: This work at LBNL was supported by the U.S. Department of Energy, Office of Science, Office of High Energy Physics (HEP) through the US Magnet Development Program under contract no. DE-AC02-05CH11231 and additionally by a US-Japan HEP collaboration between KEK, Kyoto University, Brookhaven National Lab, and LBNL. We thank our colleagues within the US Magnet Development Program and at LBNL who contribute to fabrication of the coils and magnets discussed.

Keywords: High temperature superconducting magnets, Superconducting accelerator magnets, Quench protection