109094513
Development of a superconducting cavity for high gradient accelerators
A collaboration between KEK and CEBAF is pursuing the development of a superconducting high gradient accelerating structure for application in future accelerator which optimally requires the high field gradient above 25 MV/m. In the first phase of this collaboration three single cell 1300 MHz niobium cavities have been built and tested. In the second phase a full scale 9-cell niobium cavities was manufactured. This paper describes the fabrication and measurement result of the joint 9-cell Nb cavity.
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.
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.
125432193
State-of-the-art and future prospects in rf superconductivity
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.
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.
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.
55610926
EVALUATION OF MAGNETIC ALLOYS FOR JHF RF CAVITY
A new type of rf accelerating cavity using a high permeability magnetic alloy (MA) has been developed for the high intensity JHF proton synchrotrons. Compared with ordinary ferrites, the MA cores are very stable at high rf magnetic field and thus very high accelerating gradient (=accelerating voltage per cavity length) is available. We have measured several magnetic alloys in order to find a proper material for the cavity. In this paper, the test results are summarized and the evaluation of these materials is presented.
135524505
A New type of RF cavity for high intensity proton synchrotron using high permeability magnetic alloy
A new type of rf accelerating cavity using a high-permeability magnetic alloy (MA) core is proposed for a highintensity hadron synchrotron. The prototype of a single-gap high gradient cavity whose total length is only 40cm is under development and a maximum rf voltage of 20kV has been obtained so far.
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.
118292595
Quarks in nuclear medium
Using the quark-meson coupling (QMC) model we study nuclear matter from the point of view of quark degrees of freedom. As the nucleon model we adopt the MIT bag model and the relativistic constituent quark model, where a square well and harmonic oscillator potentials are used to confine the quarks. We introduce the Lorentz-vector type confining potential as well as the Lorentz-scalar type one in order to examine how the vector confining potential contributes to the properties of the nucleon and nuclear matter. Next, we perform a re-definition of the scalar field in matter and transform the QMC model to a QHD-type model with a non-linear scalar potential. The result obtained from QMC is then compared with the potentials which are determined so as to fit various properties of finite nuclei and nuclear matter in relativistic mean-field models. The QMC model provides the parameters $\kappa \sim 20 - 40$ (fm$^{-1}$) and $\lambda \sim 80 - 400$ for the standard, non-linear scalar potential. We discuss a relationship between the QMC and QHD-type models in detail.