A magnetic horn system to be operated at a pulsed current of 320 kA and to survive high-power proton beam operation at 750 kW was developed for the T2K experiment. The first set of T2K magnetic horns was operated for over 12 million pulses during the
four years of operation from 2010 to 2013, under a maximum beam power of 230 kW, and $6.63times10^{20}$ protons were exposed to the production target. No significant damage was observed throughout this period. This successful operation of the T2K magnetic horns led to the discovery of the $ u_{mu}rightarrow u_e$ oscillation phenomenon in 2013 by the T2K experiment. In this paper, details of the design, construction, and operation experience of the T2K magnetic horns are described.
Low-field (6-110 mT) magnetic resonance of bismuth (Bi) donors in silicon has been observed by monitoring the change in photoconductivity induced by spin dependent recombination. The spectra at various resonance frequencies show signal intensity dist
ributions drastically different from that observed in conventional electron paramagnetic resonance, attributed to different recombination rates for the forty possible combinations of spin states of a pair of a Bi donor and a paramagnetic recombination center. An excellent tunability of Bi excitation energy for the future coupling with superconducting flux qubits at low fields has been demonstrated.
