13952308
Meson mixing amplitudes in asymmetric nuclear matter
Abstract Using a purely hadronic model, we study the charge-symmetry-breaking ρ – ω , σ – δ , σ – ρ and δ – ω mixing amplitudes in isospin asymmetric nuclear matter. The basic assumption of the model is that the mixing amplitude is generated by nucleon and antinucleon loops and hence driven entirely by the difference between proton and neutron Fermi momenta and the proton–neutron mass difference. We find that the behavior of the mixing amplitude is very complicated in the spacelike region and quite sensitive to the proton fraction of nuclear medium and nuclear density. In particular, in neutron rich nuclei (like Pb) and/or neutron stars the mixing amplitudes become about 10∼100 times as large as those in typical mirror 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.
119162077
The quark-meson coupling model and chiral symmetry
We extend the quark‐meson coupling (QMC) model to incorporate chiral symmetry. The relationship between the QMC model and chiral perturbation theory is also discussed. The nuclear central potential is modified by the effect of internal structure of the nucleon.
119311709
A new molecular dynamics calculation and its application to the spectra of light and strange baryons
A new approach based on antisymmetrized molecular dynamics is proposed to correctly take account of the many-body correlations. We applied it to the spectra of low-lying, light and strange baryons. The inclusion of the quark–quark correlation is important to predict the precise spectra, and the semi- relativistic kinematics is also vital to correct the level ordering. The baryon spectra calculated by the present method is as precise as the Faddeev calculation.
15022310
A Deformable Bag Model of Hadrons. I
As a generalization of the MIT spherical bag model, we construct the spheroidal bag model of hadron with an arbitrary eccentricity. This generalization is made by slightly modifying the MIT linear boundary condition: The linear boundary condition is examined in detail. Our model always satisfies two necessary requirements of the MIT bag model --i. e., n-j=O, no quark colour flux leaves the bag, and ijq =0, the scalar density of quark should vanish on the bag surface-- and it reduces to the MIT spherical bag model in the limit of zero-eccentricity. Lagrangian formalism of our model is briefly described. The eigenfrequencies of a single massless quark confined in this spheroidal bag are numer­ ically calculated. We obtain the level-splitting of the excited quark orbits, which is just analogous to the well-known Nilsson's splitting of single particle orbits in deformed nuclei. By using the numerical results of the lowest orbit, the effect of the bag-deformation on the mass of low-lying hadrons is estimated. It is found that, although the spherical bag is stable, tbe quark bag is extremely soft against the quadrupole deformation. Brief discussions are added on the mechanisms which make the spherical bag more stable.
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.
97830649
Detailed spatial measurements and Monte Carlo analysis of the transportation phenomena of thermal and epithermal neutrons from the 12-GeV proton transport line to an access maze
Abstract In order to investigate the neutron transportation from a beam-line tunnel to an access maze at a 12-GeV proton accelerator, we measured the spatial distribution of thermal and epithermal neutrons by using the Au activation method in detail. Gold foils were placed at about 70 positions in the maze in the case of the insertion (or extraction) of a copper target of 1 mm thickness into (or from) the beam axis in front of the maze. After the end of accelerator operation, relative activities of the Au foils were simultaneously measured by using an imaging plate technique and the radioactivity of one reference foil was also measured with a HPGe detector to convert to the absolute activities of all foils. It was found that the neutrons reach to the depth of the maze in the case of the insertion of the copper target. This result reflects higher proportion of high-energy particles from the copper target to that from other beam loss points and high-energy particles become the successive source of low-energy neutrons. Furthermore, it was found that several circumstances such as door walls and electric wire cables obviously affect the absorption effect of thermal neutrons. The reaction rates obtained in this study were also used for the benchmark of the Monte Carlo simulation code, MARS15 (version of February 2008). The results of the MARS15 calculations precisely reproduced experimental results and significant effects of the electric wire cables and door walls.
55891691
Beam Loading Experiment with Short Bunched Electron Beams for New Type of Accelerating RF System of High Intensity Proton Synchrotron
Beam loading effects on rf system is one of the most difficult parts of high intensity proton synchrotrons. To investigate the effects, beam loading test experiment using an intense electron beam has been carried out. The wake voltages induced by an actual electron beam have been measured at an accelerating gap of an rf cavity. The electron beam used in the experiments was modulated with the frequency of about 3 MHz and the pulse width can be variable in due consideration of the circulating beam of the JHF synchrotrons. The maximum beam current is about 9 A. The beam loading compensation also has been tried.
33534124
Higher-Order-Mode Damping of L-Band Superconducting Cavity Using A Radial-Line HOM Damper
For the energy recovery linacs, strong damping of higher-order-modes (HOMs) is indispensable to avoid beam breakup instabilities. We studied a new HOM damping scheme using a radial-line HOM damper with a choke structure. Both models of the radial-line damper and the TESLA-type 9-cell cavity were prepared and the HOM characteristics of this scheme were experimentally investigated. Measurement results showed a promising performance of the radial-line HOM damper.
121098853
X-band prebunched FEL amplifier
Abstract We have designed and constructed a prebunched FEL amplifier consisting of a prebuncher and a standard FEL. Microwave power saturation with a short wiggler length has been realized by a prebunched beam. We have also examined microwave phase evolutions. It has been demonstrated the adjustable range of the output microwave phase by changing the input microwave phase is restricted within a narrow band due to spontaneous emission radiated by the prebunched beam.
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.