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.
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.
125432193
State-of-the-art and future prospects in rf superconductivity
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.
107821728
Characteristics of the results of measurement on 1.3 GHz high gradient superconducting cavities
118449579
Scalar and vector meson propagation in asymmetric nuclear matter
Abstract The propagation of the scalar ( σ and δ ) and vector ( ω and ρ ) mesons in an iso-asymmetric nuclear matter is studied in detail, using the Walecka model. We calculate the invariant masses and spectral functions of the mesons, including the effect of meson mixing. At finite density, the mixing effect is quite important in the propagation of the scalar and (longitudinal) vector mesons. In the σ channel, we find a three-peak structure in the spectral function, caused by the mixing effect.
118287869
The challenge of the EMC effect
A number of relatively successful quark model descriptions of nuclear matter have recently been developed, based on a mean-field description of non~overlapping nucleons bound by the self-consistent exchange of (1' and w mesons. By combining one such model with a recently developed method of calculating structure functions for the free nucleon, we are able tc. make a microscopic calculation of the structure functions of finite nuclei (in the local density approximation). As well as providing a semi-quantitative understanding of existing data, the model suggests that the impulse approximation, used in many theoretical treatments of nucleon binding, may be quite unreliable.
17407776
The quark-meson coupling model
We review the quark-meson coupling model, in which the quark degrees of freedom are explicitly involved to describe the properties of not only nuclear matter but also finite nuclei. Then, we present the electric and magnetic form factors for the proton bound in specific orbits for several closed-shell nuclei.
121131573
New Scaling Phenomena in Nuclear Structure Functions
We consider the nuclear mass-number (A) dependence of the nuclear structure functions. We restrict ourselves to a two-component model, in which we assume the existence of an exotic component other than the normal nucleon component in nuclei. We find that there exist scaling phenomena and that the structure function of the exotic component should be independent of A. We also show that the A dependence of the nuclear structure function can be attributed to that of the surface-to-volume ratio which is incorporated in the probability of finding the exotic component in the nucleus.
123091013
Masses of the Multiquark States in the MIT Bag Model with the Pion-Cloud
We study the masses of the low-lying multiquark states, especially the dibaryon states, within the framework of the MIT bag model with the pion-cloud, in which the non-local pion-quark· interaction is taken into account. We find that the pionic effect does not greatly alter the original predictions of the MIT bag model for the dibaryon states with Y = 1 and 2, while it increases the mass of the lowest Y = 0 dibaryon state. The Y = 0 dihyperon predicted by Jaffe may be either unbound or very weakly bound. In this letter we wish to study the low-lying multiquark states in the MIT bag model with the pion-cloud. In the original MIT bag model some authors calculated the masses of the multiquark states and discussed their properties. 1l • 2 ) Recent1y' however, it ~as pointed out that the contribu­ tion of the pion-cloud to the masses of the ordi­ nary hadrons amounts to about 100 MeV and especially the pion-cloud plays an important role in the origin of the N-LJ and the .E-A mass differences. 3 )A) We should, therefore, estimate the effect of the pion-cloud on the masses of the multiquark states. Of special interest is the deep­ ly bound state of the dihyperon UI"=OO+) predicted by Jaffe. 2 ) (This state is 70~80 MeV lower than the A-A threshold in the MIT bag model.) Here we will use the chiral and the cloudy bag models with the non-local interaction between the quark and pion,a) in which the extent of the pion is taken into account. The pionic corrections will be treated as a perturbation to the masses of the multiquark states. In the naive chiral S ) and cloudy 6) bag models there are two difficulties, i.e., the collapse of the bag and the divergence of the quark self-energy, which are due to the pion­ cloud. In the first order of the pionic correction we can, however, avoid these difficult problems by using the non-local description of the quark-pion interaction. In the limit of a static and spherical cavity with the radius R the usual mass formula for the N­ quark state is given by