121309735
Casimir effect on quark-gluon plasma
We study the Casimir effect on baryon-free quark-gluon plasma confined in a slab region. The energy and entropy densities of confined QGP at the transition temperature are 2∼3 times as large as those of unconfined QGP when the width of the slab is about 1 fm.
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.
119441340
Relationship between the Quark-Meson Coupling Model and Quantum Hadrodynamics
Using the quark-meson coupling (QMC) model, we study nuclear matter from the point of view of quark degrees of freedom. Carrying out a re-definition of the scalar field in matter, we transform the QMC into a QHD-type model with a non-linear scalar potential. The potentials obtained from the QMC are compared with those of relativistic mean-field models. Since at present, rigorous studies of quantum chromodynamics (QCD) are limited to matter systems with high temperature and zero baryon density, it is important to build models that help to bridge the discrepancy between nuclear phenomenology and QCD. We have proposed a relativistic quark model for nuclear matter and finite nuclei that consists of non-overlapping nucleon bags bound by the self-consistent exchange of isoscalar, scalar (σ) and vector (ω) mesons in the mean-field approximation (MFA). This model is called the quark-meson coupling (QMC) model. 1) It has also been found in recent theoretical studies that various properties of finite nuclei can be described very well by relativistic mean-field (RMF) models, i.e., quantum hadrodynamics (QHD). 2) In this Letter, we consider the relationship between the QMC and the QHD and study howthe internal structure of the nucleon plays a role in effective nuclear models. In our previous works, 1) the MIT bag model has been used to describe the quark structure of the nucleon. Because the confined quarks interact with the scalar field σ in matter, the effective nucleon mass M � N in the QMC is given by a function of σ through the quark model of the nucleon. (Although the quarks also interact with the ω meson, it has no effect on the nucleon structure, except for a shift in the nucleon energy. 1) ) The (relativistic) constituent quark model (CQM) is an alternative model for the nucleon. Recently, Shen and Toki 3) have proposed a newversion of the QMC — the quark mean-field (QMF) model, in which the CQM is used to describe the nucleon. In the present study, in addition to the bag model (BM), we use the relativistic CQM with confining potentials V (r) of a square well (SW) and harmonic oscillator (HO) type to see the dependence of the matter properties on the quark model. It is assumed that the light (u or d) quark mass mq is 300 MeV in the CQM and 0 MeV in the BM. Furthermore, we introduce a Lorentz vector-type confining potential that is proportional to γ0, in addition to one of the scalar type, as
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.
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.
20298579
Relativistic hydrodynamics of quark-gluon plasma and stability of scaling solutions.
The scaling solutions of the relativistic hydrodynamics are expected to play an important role in describing the expansion stage of a quark-gluon plasma which may be formed in nucleus-nucleus collisions at high energies. After summarizing some general properties of the scaling solutions, we study in detail their stability against small perturbations. In some typical cases of the two-dimensional scaling solution it is found that (i) the scaling solution is stable if the Reynolds number {ital R} defined in terms of the viscosity coefficients is larger than a critical value {ital R}{sub {ital c}} (=1), (ii) it is also stable for a long-wavelength perturbation if {ital R} is small enough, and (iii) it becomes unstable when {ital R} approaches {ital R}{sub {ital c}} from below. It is also shown that these results are related to the time dependence of the Reynolds number, the entropy density, and the temperature, and the point {ital R}={ital R}{sub {ital c}} corresponds to a critical instant when the heating due to the dissipative processes balances with the cooling due to the expansion of the fluid. The stability of the scaling solution of the quark-gluon plasma is examined for typical ranges of the relevant parameters.
138718634
Improvements of cleaning methods for high Q-SLOPE problem in full end single cell cavity
We are developing LL high gradient SRF cavity for ILC. Recently we have observed a Q-slope problem at higher gradient over 35-40MV/m on the full end single cell cavities, which have a HOM coupler and an input coupler on a beam tube. This problem might be due to poor rinsing in such a complicate structure. We have studied new post EP cleaning methods: inner ultrasonic cleaning, steam cleaning, and so on. In this paper we will report these results. INTRODUCTION KEK WG5 group is developing an ACD high gradient SRF cavity applied low loss (LL) shape, so called Ichiro cavity as an ILC R&D. Ichiro cavity can produce a gradient higher than 50MV/m, of which principle proof has been done on the single cell cavities with center cell shape of Ichiro 9-cell cavity but not yet on the 9-cell cavity. We are still fighting on the 9-cell demonstration. To find out the reason of the difficulty, we are investigating the end cell cavity. Recently we have confirmed that its RF design has no problem to produce 50MV/m (Fig.1 left) and problem is in the beam pipe with a HOM coupler and an input coupler port (Fig.1 right). Qslope happens at higher than 35MV/m in such a cavity configuration. Motivation of the study One of the reasons might be in difficulty of cleaning after electropolishing. So we have studied to see it and searched more efficient cleaning methods for such a complicated end group. PRIMITIVE EXPERIMENTS We have made primitive experiments to visually observe the difficulty in the cleaning. We made a 1.3GHz demountable acryl model cavity (Fig.2, left). We sprayed MOLYKOTE, which is usually used as lubricant, on the inner surface and dried. Thus the contaminated surfaces was rinsing tested by various methods. Remained contamination by HPR Fig.3 shows the remained contamination by our regular HPR rinsing condition (6MPa, 15min. from Top to Bottom one pass at 22mm/min at down speed, 11 rpm). One can easily understand that HPR jets cannot shot fully inside of the input coupler port (Fig.3 left). HOM coupler is more difficult to be cleaned up due to the complicated structure (Fig.3, right). Rinsing difficulty even by Ultrasonic rinsing Fig.4 shows results of the ultrasonic rinsing subsequently done after the HPR mentioned above. The rinsing was done in an ultrasonic bath with 600W at 28kHz for 30 minutes. The contaminations are still remained. The real contamination with SRF cavity might be different from such the MOLYKOTE spraying. However, it has to be noticed that the real remained contamination would be difficult to be removed even by Ultrasonic rinsing. Thus, we have visually confirmed where contaminations remain on the HPR and seen how difficult to remove them by Ultrasonic rinsing. INVESTIGATION OF NEW POST EP CLEANING METHODS Nb
117369687
COMPACT HE II COOLING SYSTEM FOR SUPERCONDUCTING CAVITIES
This paper describes a compact He II cooling system for superconducting cavities. The cooling system mainly comprises a vacuum vessel, an 80 K liquid nitrogen bath, a 4 K He I bath, a He II bath, an evacuation pump, a single-stage GM cryocooler for the 80 K bath, and a 4 K GM cryocooler for the 4 K He I bath. Superfluid helium is generated and refilled into the He II bath via a heat exchanger and a JT valve by operating the evacuation pump. The refrigeration capacity attained was more than 10 W at 1.8 K. The cooling system was connected with a single-cell cavity cryostat. A superconducting cavity was immersed in superfluid helium. He II was supplied to the cavity vessel from the cooling system and evaporated helium gas was returned to it. High electric fields were obtained during superconducting cavity operations.
7147715
Design of a Low Loss SRF Cavity for the ILC
An international team comprising SLAC, KEK, FNAL, JLAB and DESY is collaborating on the design, fabrication and test of a low loss, 1.3 GHz 9-cell SRF structure as a potential improvement for the ILC main linac. The advantages of this structure over the TESLA structure include lower cryogenic loss, shorter rise time, and less stored energy. Among the issues to be addressed in this design are HOM damping, Lorentz force detuning and multipacting. We will report on HOM damping calculations using the parallel finite element eigenmode solver Omega3P and the progress made towards an optimized design. Studies on multipacting and estimates of the Lorentz force detuning will also be presented.
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.
55857127
PROMISING PERFORMANCE OF THE Nb/Cu CLAD SEAMLESS SUPERCONDUCTING RF CAVITIES
For future large applications of superconducting RF cavities, one has to fabricate cost-effective cavities with high electric-field gradients. We have proposed the fabrication of L-band seamless cavities from Nb/Cu clad material in order to eliminate the electron beam welding process. A feasibility study on the fabrication of 1.3 GHz Nb/Cu Clad single cell cavities from the clad sheet material was done. Three single cell Nb/Cu clad seamless cavities were fabricated by the collaboration with INFNLNL in Italy. In this paper, cold test results of seamless type cavities obtained by the spinning method are presented. The best performance of the cavities was Eacc = 25.1 MV/m with Qo=2.5X10 10 at a temperature of 1.4 K, which is very promising.