55538978
HIGH GRADIENT BEHAVIORS OF LARGE GRAIN ICHIRO SINGLE CELL CAVITY BY CHEMICAL POLISHING
We have started high gradient R&D with the combination of ICHIRO shape, sliced large grain niobium, and buffered chemical polishing (BCP). We fabricated one large grain ICHIRO single cell cavity that had end cell shape of ICHIRO 9-cell but no end group. We processed this cavity surface by centrifugal barrel polishing (CBP) and BCP. This cavity successfully achieved the high gradient of 42MV/m at the first vertical test. We made series test by repeating BCP on this cavity. The results of the series test will be reported. INTRODUCTION Large grain niobium SRF cavities have been developed in many laboratories, Jlab, DESY, IHEP, KEK, and so on. Our KEK LL group made breakthrough of LG Nb sheet production in 2008 [1]. We have successfully developed the multi-wire slicing method for niobium ingots with 270mm diameter collaborating with KEK, Tokyo Denkai Co. Ltd., TKX Co.Ltd., and Toyo Advanced Technologies Co. Ltd. This technology can reduce the cost of Nb sheet productions. LG cavity also can achieve high gradient of 40MV/m by BCP, not by electro polishing (EP) [2]. In order to make the breakthrough of ILC cavity cost, we are proposing the combination of sliced LG Nb materials + ICHIRO shape + BCP. This could promise the cheap, easy, and high reliable performance cavity production. In this paper, we will describe about our R&D on LG single cell cavity made of sliced Nb sheets.
125432193
State-of-the-art and future prospects in rf superconductivity
137182571
A New Material Evaluation Method on Niobium by Magnetization Measurement
As a new evaluation method for the material defects or surface contamination of niobium, we have tried magnetization measurement using very small niobium samples. We could see the hyst~resis curve varied depending on the sample's history. This method has a high sensitivity. Th~ m.f1uence ?y surface treatments was observed on the hysteresis curve; annealing, chemical p~hshmg, Q-dlsease due to hydrogen etc .. In this paper we will report several study results by this method.
55249742
Activities on Superconducting Cavities at TOSHIBA
Abstructs R&D activities on superconducting cavities at TOSHIBA are presented. Two L-band single-cell niobium cavities and an L-band three-cell structure were fabricated in our company and measured at KEK. The maximum field gradient of Eacc,max>30MV/m in both single-cell cavities and Eacc,max =18MV/m in the three-cell structure were attained respectively. An optimization study on the annealing temperature for the hydrogen Q-disease is reported. R&D of hydroforming to fabricate seamless cavities is also presented.
6846765
HIGHER HARMONICS BEAM LOADING COMPENSATION FOR A BROAD BAND MA-LOADED RF CAVITY
A broad band RF cavity loaded with magnetic alloy cores has been developed for the Japanese Hadron Facility synchrotrons. Its Q-value can be chosen at between 0.5 and 5. To reduce transient beam loading effects, a small Qvalue (< 3) is preferable to shorten the transient period. However, the circulating beam current of up to 7 A will induce a spurious voltage at the accelerating gap, which deforms the gap voltage due to higher harmonics components, if the Q-value is less than 3. The resulting RFbucket distortion may cause the beam loss. Therefore we have designed a beam loading compensation system to suppress the higher harmonics components.
94312812
High Field Studies on L-band Superconducting Cavities at KEK
Several 1.3 GHz single-cell and nine-cell niobium cavities were fabricated to attain a higher maximum accelerating gradient and to understand the phenomena limiting it. Vertical cold tests at {approx}1.8 K for the 4 single-cell cavities prepared by various surface treatments have been conducted 15 times. In eight of the tests, maximum accelerating gradients (E{sub acc}, max) of more than 14 MV/m were obtained with no field emission. Furthermore, E{sub acc}, max values of higher than 20 MV/m with a high Q{sub 0} value of {approx}10{sup 10} were achieved repeatedly after heat treatment at 1400 degrees C. Once quenching was observed at E{sub acc}, max (14 {approx} 20 MV/m), however, a common phenomenon resulting in Q{sub 0}-deterioration occurred in every test. The cavity performances and the phenomenon at high fields are reported in this paper.
10938062
Composite nucleons in scalar and vector mean fields.
We emphasize that the composite structure of the nucleon may play quite an important role in nuclear physics. It is shown that the momentum-dependent repulsive force of second order in the scalar field, which plays an important role in Dirac phenomenology, can be found in the quark-meson coupling (QMC) model, and that the properties of nuclear matter are well described through the quark-scalar density in a nucleon and a self-consistency condition for the scalar field. The difference between theories of pointlike nucleons and composite ones may be seen in the change of the {omega}-meson mass in nuclear matter if the composite nature of the nucleon suppresses contributions from nucleon-antinucleon pair creation.
20024482
European Muon Collaboration effect in deuteron and in three-body nuclei.
We investigate the European Muon Collaboration (EMC) effect in deuteron and three-body nuclei. The binding and the Fermi motion effects of nucleons are studied in detail. They reduce the structure function ratios from unity by less than 5%. Roles of excess pion are also discussed in connection with the momentum sum rule, which is violated by the binding effect.