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
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.
125432193
State-of-the-art and future prospects in rf superconductivity
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.
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.
6356292
A Quark - meson coupling model for nuclear and neutron matter
Abstract An explicit quark model, based on a mean field description of non-overlapping nucleon bags bound by the self-consistent exchange of σ, ω and ϱ mesons, is used to investigate the properties of both nuclear and neutron matter. We establish a clear understanding of the relationship between this model, which incorporates the internal structure of the nucleon, and QHD. Finally, we use the model to study the density dependence of the quark condensate in-medium.
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.
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.
119432599
Flavour asymmetry of anti-quarks in nuclei
Abstract:A novel nuclear effect on the flavour asymmetry of anti-quarks in the nucleon bound in a nucleus is discussed in terms of the meson cloud model and the Pauli exclusion principle. It is expected that the flavour asymmetry is enhanced in a nucleus.
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).