132588620
HIGH FIELD Q-SLOPE PROBLEM IN END GROUP CAVITIES N=3
In our high gradient R&D of ICHIRO cavities at KEK, we have found some problems related to HOM coupler and high power RF input coupler port on beam tube: end group. One is the difficulty of rinsing in complex structures like HOM coupler. The other is Q-slope at high filed more than 40MV/m. The cavities without end group did not show such a high field Q-slope. At first step, we tested much stronger and aggressive rinsing method; wiping, brushing, and mega-sonic rinsing on the end group. The details and results of these rinsing effects will be reported. INTRODUCTION We have successfully demonstrated the principle proof of 50MV/m with KEK Low Loss (ICHIRO) single cell cavities (IS cavities) [1]. IS cavity has the centre cell shape of ICHIRO 9cell cavity (I9 cavity), but no end group. End group includes HOM coupler, high power RF input coupler port, and transmitted RF power pick up port on beam tube. For the pilot study of I9 cavity, we also made end single cell cavities (ISE cavities) that have end cell shape of I9 cavity. ISE#3 that has end cell shape but no end group successfully achieved 50MV//m using same recipe as IS cavities. It will be described later about the recipe. ISE#5, and #7, those have full end group except transmitted RF power pick up port, have achieved around 48MV/m with modified recipe but limited by Q-slope so far (Figure 2). We confirmed that RF design of ICHIRO cavity has no problem for 50MV/m, but end group has Qslope problem at more than 40MV/m. In this paper we focused on Q-slope problem of ISE cavities. ISE CAVITY AND RECIPE Our standard recipe for IS cavities consists of centrifugal barrel polishing (CBP, ~100μm), chemical polishing (CP, 10μm), annealing (AN, 750Cx3hrs), electropolishing (EP, 80μm+20μm), flash EP (3μm, new acid, no circulation), HPR, and Baking (120Cx48hrs). This recipe achieved 46.7±1.9MV/m with 6 IS cavities [2]. The key of this recipe is flash EP. We have found that sulphur contaminations generated during EP made scatter of performance. Some of sulphur remains underneath of the SRF niobium surface as niobium sulphide (NbxSy) after long EP durations [3]. The combination of light EP (20μm) + flash EP can remove NbxSy most effectively. We also understood the mechanism of sulphur generation during EP and how to reduce it [4]. For ISE cavities with end group, standard recipe did not work. They were limited by field emission (FE) at first. We considered one of the FE seeds of ISE cavities was sulphur contaminations remained at end group. End group has a complex structur, so it might be difficult to remove contamination by HPR only. We tried ethanol rinsing after EP which can dissolve sulphur. ISE#5 was improved but still limited around 40MV/m. We also tried wiping cavity inner surface directly. In common sense, RF surface is very sensitive, so nobody favours to touch the SRF surface after EP and before VT. We tried it to another cavity which limited by heavy FE as a pilot study. It was successfully improved. Then we tried it to ISE#5. We used very smooth cloth soaked in degreaser as wiper. ISE#5 was wiped whole SRF surface; cell, beam tubes, HOM cylinder and antenna by hand. The antenna was even rubbed by teeth brash. ISE#5 have achieved 48MV/m by combination of ethanol rinsing and wiping so far. We understood the problem of end group relates to the difficulties of rinsing in complex structures and post EP cleaning like ethanol rinsing and wiping are effective to rinse end group [5]. SERIES TEST OF POST EP CLEANINGS From the experience of ethanol rinsing and wiping, we confirmed that the contaminations generated during EP process is very sticky and stronger rinsing is needed for the complex structure like end group to remove them. In ___________________________________________ *fumio.furuta@kek.jp Proceedings of IPAC’10, Kyoto, Japan WEPE005 03 Linear Colliders, Lepton Accelerators and New Acceleration Techniques A03 Linear Colliders 3347 this chapter we will describe about 4 kinds of post EP cleanings we tried; ethanol rinsing, wiping, steam cleaning and Horn rinsing. Ethanol Rinsing Figure 3 shows the results of the yield test for ethanol rinsing. The tested recipe consists of light EP, flash EP, ethanol rinsing, degreasing, HPR, and baking. We repeated this recipe + VT 6times for ISE#5. The average of maximum gradient is 39.2±5.7MV/m, scatter is 15%. The average of FE onset is 35.2± 6.7MV/m. In our measurements, FE onset corresponded to the gradient where the level of radiation reached more than 0.3μSv/hr. It is radiation monitor’s sensitivity. The average Qo value at 40MV/m is (0.97±0.11)e10. Wiping Figure 3 shows the results of the yield test of wiping. Figure 4 shows the picture of wiping. The tested recipe consists of light EP, flash EP, ethanol rinsing, wiping with degreaser, HPR, and baking. We repeated this 5times for ISE#5. The average of maximum gradient is 42.6± 3.7MV/m, scatter is 9%. The average of FE onset is 31.8 ±7.1MV/m. The average Qo value at 40MV/m is (1.12± 0.21)e10. The Qo value is 15% higher than that of ethanol rinsing. Steam Cleaning Figure 4 shows steam cleaner and steam cleaning for end group. This steam cleaner is commercial one. We used pure water for the steam. Hot steam, about 100C, come out from nozzle of steam cleaner, we sprayed it all around end groups. The recipe for series test of steam cleaning did not include EP. It consists of steam cleaning, degreasing, HPR, short baking for degassing, and VT. We applied this for ISE#5, #7, and #8. We repeated this twice for ISE#7 and #8 to check the reproducibility. Qo vs. Eacc curves are summarized in figure 5. The average of maximum gradient is 41.6±3.9MV/m, scatter is 9%. The average of FE onset is 33.3±5.0MV/m. The average Qo value at 40MV/m is (0.93±0.19)e10.
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.
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.
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.
30324227
Towards a microscopic understanding of nuclear structure functions.
It has recently been shown that the twist-two valence quark distributions calculated in the MIT bag model are in reasonable agreement with world data. Furthermore, several authors have constructed mean-field theories which reproduce the saturation properties of nuclear matter in terms of a mean-field theory of nonoverlapping bags, self-consistently bound by scalar and vector meson exchange. By using a local density approximation we combine these developments to microscopically investigate the structure functions of finite nuclei. Not only do we obtain a semiquantitative description of the data (the so-called European Muon Collaboration effect) but we also show that the conventional treatment based on nucleon binding is quantitatively unreliable.
27396914
Properties of strange quark matter.
Assuming that the novel nuclei of [ital A]=370 amu and [ital Z]=14 recently observed in high-energy cosmic rays are really strange quark matter (SQM), the relationship between parameters describing SQM is discussed and the mass formula for SQM is derived by requiring that it yields the observed value of [ital A]=370 amu and [ital Z]=14.
45254853
Lattice thermodynamics for gauge theories.
We study the Stefan-Boltzmann formula for a free-gluon gas system in the lattice-regularized thermodynamics, and find that there arises a clear ''Debye effect'' above the temperature T/sub D/ = 1/a/sub sigma/ (a/sub sigma/ being the lattice spacing) and the Stefan-Boltzmann formula deviates from the conventional one in the high-temperature region T>T/sub D/.