20108614
SUPERIORITY OF ELECTROPOLISHING OVER CHEMICAL POLISHING ON HIGH GRADIENTS
Electropolishing (EP) offers a smoother surface, and that makes us expect high gradients in superconducting niobium cavities. EP has a little bit complicated procedure and needs annealing to avoid the hydrogen Q-disease. On the other hand, chemical polishing (CP) is easier and cheaper, so widely used in many laboratories. For the conventional field gradients ( ∪ 5 MV/m) in storage rings (TRISTAN-MR, HERA), no difference was seen on the cavity performance between EP and CP. In the high gradients research for TESLA, we have to establish the surface treatment method which has a high reliability on the high gradients over than 25 MV/m and is cheaper in the preparation cost. So far, CP has offered a nice cavity performance, but a concern on "European Headache" was developed recently on the high gradients at Saclay. KEK has intensively investigated the difference between the effect of CP and EP on high gradient performance since the last SRF workshop at Saclay. In this investigation "European headache" was also seen in chemically polished cavities at KEK, in addition these cavities often showed a new Q-degradation without x-ray signals which seriously limited the high gradient. EP offers the high gradient over than 30 MV/m reliably. At the moment, EP seems to have a superiority over CP on the high gradient over than 25 MV/m.
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
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.
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.
121746846
High momentum component in the deuteron
The high momentum component in the deuteron, which stems from the short range part of the nucleon-nucleon interaction, is studied in they-scaling function and the structure functionF2 of the deuteron. We use not only some non-relativistic wave functions but also relativistic ones. It is shown that the relativistic mechanism or a six-quark state in the nucleon-nucleon interaction yields a large high momentum component.
122485732
Axal Polarizability in the System of Two Chiral Nucleon Bags
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.
18385768
Hadron structure effect in finite nuclei
The quark-meson coupling model, based on a mean-field description of non-overlapping nucleon bags bound by the self-consistent exchange of $\sigma$, $\omega$ and $\rho$ mesons, is reviewed. In particular, I present the changes in the hadron masses of the (non-strange) vector mesons and the nucleon in a nucleus. I also give a new, simple scaling relation among the changes of the hadron masses.
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.