219401710
PROTOTYPE CRYOMODULE FOR THE ADS LINAC
For the future application of the superconducting LINAC to the accelerator driven system (ADS), a prototype cryomodule is being constructed under the collaboration of Japan Atomic Energy Research Institute (JAERI) and High Energy Accelerator Research Organization (KEK). The module contains two 9-cell structures of β=0.725 and f=972MHz. The design of the cryomodule and the status of the construction are reported. INTRODUCTION As the first step of the long-term R&D program of the ADS project, an ADS experimental facility and a 200MeV superconducting linac will be constructed in the second phase of the J-PARC project. The purposes of this program are to study and resolve technology issues of the system, and to demonstrate the feasibility of the ADS concept. The baseline design of the superconducting linac in the energy range of 400-600MeV was reported in the last SRF workshop [1]. In the late 2002, the construction of a prototype cryomodule was approved as a three years program. CRYOMODULE The cryomodule is similar to the TRISTAN cryomodule as is shown in Figure 1. The main changes adopted are 1: Jacket type He vessel of Titanium 2: 2K operation 3: Pulsed operation In order to cope with these changes, some new techniques, such as SUS/Ti joint, seals for 2K-He are used, so the system have to be examined experimentally. The main purpose of the cryomodule is to examine the cryogenic performance at 2K and the controllability of the accelerating gradient in the pulsed operation. 2K-He is provided from a He Dewar through a heat exchanger in a valve box and a J-T valve in the cryostat. Maximum design heat load at 2K is 7W for dynamic and 8W for static. Consumption of 4.4K-He is estimated to be 46 litter/hour for 2K-He production, and 35 litter/hour for 5K shield. Volume of a 2K-He reservoir is 17 litters. Figure 2 shows the vacuum vessel. Figure 1: A 972MHz prototype cryomodule. _________________________________________ shuichi.noguchi@kek.jp Proceedings of the 11th Workshop on RF Superconductivity, Lübeck/Travemünder, Germany
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.
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.
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
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.
56351344
RF SYSTEMS FOR JHF SYNCHROTRONS
Based on the measurements of the magnetic cores and R&D works, MA(Magnetic Alloy)-loaded cavity will be adopted for the RF cavity of JHF 50 GeV Main Ring and 3 GeV Booster. Because of high stability at large RF amplitude, high gradient of acceleration voltage (>50 kV/m) is available. By a test cavity, 2.5 kV/core has been already achieved in the CW operation using one MA core of 2.5 cm thickness. For the pulse operation, 5.5 kV/core has been obtained. Another advantage is that the system does not require the tuning system because of the cavity band width is wide enough to cover the RF frequency. A stability analysis shows that the RF system without the tuning loop has wider stable region than high Q cavity system with the loop. A multi-particle simulation shows that the RF system is also stable for the periodic transient and the RF bucket distortion. However, the distortion should be corrected when the Q value of the cavity is low (Q<2).
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.
123518493
Manifestation of Short-Range Few-Nucleon Correlations in Nuclear Structure Functions
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.
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.