135200451
Beam loading in JHF 50 GeV proton synchrotron
107821728
Characteristics of the results of measurement on 1.3 GHz high gradient superconducting cavities
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.
55112672
Improvement of cavity performance by electropolishing in the 1.3 GHz Nb superconducting cavities
A steep drop of the cavity quality factor (Q/sub 0/) at high electric field has been observed frequently in chemically-polished and high-pressure-rinsed Saclay cavities, even in the absence of field emission. Three single-cell cavities from Saclay were tested at KEK following electropolishing and high pressure rinsing. This treatment eliminated the steep Q/sub 0/ drop, the quench field increased to an accelerating gradient of more than 30 MV/m with a quality factor above 2/spl times/10/sup 10/. No dependence of the quench field on the niobium RRR was observed between RRR=200 and 320 in electropolished cavities.
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.
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.
119376503
Scalar and vector form factors of the in-medium nucleon
Abstract Using the quark–meson coupling model, we calculate the form factors at σ- and ω-nucleon strong-interaction vertices in nuclear matter. The Peierls–Yoccoz projection technique is used to take account of center of mass and recoil corrections. We also apply the Lorentz contraction to the internal quark wave function. The form factors are reduced by the nuclear medium relative to those in vacuum. At normal nuclear matter density and Q 2 =1 GeV 2 , the reduction rate in the scalar form factor is about 15%, which is almost identical to that in the vector one. We parameterize the ratios of the form factors in symmetric nuclear matter to those in vacuum as a function of nuclear density and momentum transfer.
18878762
Nucleon structure effect on the longitudinal response function
Using the quark-meson coupling model, we study the longitudinal response function for quasielastic electron scattering from nuclear matter within relativistic RPA. In QMC the coupling constant between the scalar meson and the nucleon is expected to decrease with increasing nuclear density. Furthermore, since the electromagnetic form factors of the in-medium nucleon are modified at the same time, the longitudinal response function and the Coulomb sum are reduced by a total of about 20% in comparison with the Hartree contribution.
6356292
A Quark - meson coupling model for nuclear and neutron matter
Abstract An explicit quark model, based on a mean field description of non-overlapping nucleon bags bound by the self-consistent exchange of σ, ω and ϱ mesons, is used to investigate the properties of both nuclear and neutron matter. We establish a clear understanding of the relationship between this model, which incorporates the internal structure of the nucleon, and QHD. Finally, we use the model to study the density dependence of the quark condensate in-medium.
119178074
Fermi matrix element with isospin breaking
Abstract Prompted by the level of accuracy now being achieved in tests of the unitarity of the CKM matrix, we consider the possible modification of the Fermi matrix element for the β -decay of a neutron, including possible in-medium and isospin violating corrections. While the nuclear modifications lead to very small corrections once the Behrends–Sirlin–Ademollo–Gatto theorem is respected, the effect of the u − d mass difference on the conclusion concerning V u d is no longer insignificant. Indeed, we suggest that the correction to the value of | V u d | 2 + | V u s | 2 + | V u b | 2 is at the level of 10 − 4 .