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.
Characterizing the surfaces of rocky exoplanets via the scattered light will be an essential challenge to investigate the existence of life on habitable exoplanets. We present a simple reconstruction method for fractional areas of different surface t
ypes from photometric variations, or colors, of a second Earth. We create mock light curves for Earth without clouds using empirical data. Then these light curves are fitted to the isotropic scattering model consisting of 4 surface types: ocean, soil, snow and vegetation. In an idealized situation where the photometric errors are only photon shot noise, we are able to reproduce the fractional areas of those components fairly well. We may be even able to detect a signature of vegetation from the distinct feature of photosynthesis on the Earth, known as the red edge. In our reconstruction method, Rayleigh scattering due to the atmosphere has an important effect, and for terrestrial exoplanets with atmosphere similar to our Earth, it is possible to estimate the presence of oceans and an atmosphere simultaneously.
