LHC is now delivering proton and heavy ion collisions at the highest energy. Upgrading the LHC beyond its design performance is a long term program that started during the LHC construction, with some fundamental R&D programs. The upgrade program is based on a vigorous superconductor and magnet R&D, aimed at increasing the field in accelerator magnets from 8 T to 12 T for the luminosity upgrade, with the scope of increasing the collider luminosity by a factor 5 to 10 from 2022. The upgrade program might continue with the LHC energy upgrade, which would require magnets producing field in the range of 16-20 T. The results obtained so far and the future challenges are discussed together with the possible plan to reach the goals.
A three-pole hybrid wiggler has been developed at the Saga Light Source synchrotron radiation facility. The development goal was to realize a three-pole wiggler with high operational stability and reliability under conditions of limited human resources and maintenance cost. The wiggler consists of a 4 T superconducting main pole and two 1 T normal-conducting side poles. The main pole can generate hard X-rays in the energy range up to approximately 40 keV. Use of the normalconducting side poles ensures significant margins for stationary and transient heat loads on the cryogenic system. The cryocooler cools the superconducting coils and iron poles via mechanical contact without liquid helium. To suppress the beam displacement due to the second integral of the magnetic field of the main pole, the main pole was designed to have relatively large field clamps at both pole ends. The wiggler was manufactured in FY2009 and was installed at the Saga Light Source storage ring in March 2010. Synchrotron radiation from the wiggler was observed at the beam line BL7 in late June 2010. Official user operation of the wiggler started in November 2010. To date, the wiggler has operated stably.
Cryogenic slush fluids such as slush hydrogen and slush nitrogen are solid-liquid, two-phase fluids containing solid particles in a liquid. As a functional thermal fluid, there are high expectations for use of slush fluids in various applications such as fuels for spacecraft engines, clean-energy fuels to improve the efficiency of transportation and storage, and as refrigerants for high-temperature superconducting equipment. Experimental flow tests were performed using slush nitrogen to elucidate pressure-drop characteristics of converging-diverging (C-D) pipes and corrugated pipes. The results of pressure-drop tests for two different types of C-D pipes, long-throated and short-throated, both with an inner diameter of 15 mm, confirmed a pressure-drop reduction for the short-throated pipe at a flow velocity of 1.5 m/s or greater, and a maximum pressure-drop reduction of 40-50% compared to liquid nitrogen. In the case of two different types of corrugated pipes with an inner diameter of either 12 mm or 15 mm, a pressure-drop reduction was confirmed at a flow velocity of 2 m/s or greater, and reached a maximum value of 37% at 30 wt. % compared to liquid nitrogen. The greater the solid fractions, the smaller the pipe friction factor became, and the pipe friction factor at the same solid fraction showed a constant value regardless of the Reynolds number. From the observation of the solid particles' behavior using a high-speed video camera and the PIV method, the pressure-drop reduction mechanisms for both C-D and corrugated pipes were demonstrated.
Multi-laminated HTS tape conductors wound into double-pancake (DP) coils are planned to be used widely in the production of large superconducting coils. If the HTS tapes are simply laminated to form the conductor, the current distribution in the laminated tape conductor of the coil is not homogeneous because of the different inductances of all the tapes. Non-uniform current distribution should be avoided because it causes increased AC loss and decreased critical current in the conductor. Transposition of these tapes at the innermost or outermost layer of the coil so as to arrange the tapes symmetrically is effective for inducing homogeneous current distribution. However, geometrically, this method does not result in perfect symmetry of the conductor for tapes with more than double-lamination and restricts the coil arrangement. In this paper, we analyze the current distribution in the tape conductor using an electrical circuit model, and then discuss how to obtain homogeneous current distribution in multi-laminated HTS tape conductors wound into DP coils for various coil arrangements. We propose a new method to obtain uniform current distribution by adjusting gaps between HTS tapes in the conductor, and apply this method to tapes laminated four times and wound into solenoid coils and a toroidal coil. In this paper, the solenoid coils are composed of two or three DP coils and the toroidal coil is composed of eight unit coils made of a single DP coil. The homogeneous current distribution in the multi-laminated HTS tapes for the arbitrary solenoid coil and toroidal coil composed of multiple DP coils can be obtained by symmetrical transposition at the middle of the unit coil and insertion of appropriate additional thickness between tapes.