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.
125432193
State-of-the-art and future prospects in rf superconductivity
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.
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.
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).
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.
11540608
The Nolen-Schiffer anomaly and isospin symmetry breaking in nuclear matter
Abstract The quark-meson coupling model which we have developed previously is extended to incorporate the δ meson. It is then used to study the Nolen-Schiffer anomaly and isospin symmetry breaking in nuclear matter. We find that, in combination with the u - d mass difference, the difference between quark scalar densities in protons and neutrons generates an effective neutron-proton mass difference of the right magnitude. Finally we find that isospin symmetry breaking in the quark condensates can be directly related to the δ meson field.
16595187
Luminosity Dependence of the Electron Temperature in the Bright Hard State of the Black Hole Candidate GX 339–4
We have analyzed 200 Rossi X-ray Timing Explorer observations of the black hole candidate GX 339� 4, all from bright hard state periods between 1996 and 2005. The purpose of our study is to investigate the radiation mechanisms in the hard state of GX 339� 4. The broadband 3–200 keV spectra were successfully modeled by as imple analytic model, power-law with an exponential cut-off modified with a smeared edge. The obtained energy cut-off (Ecut )w as distributed over 50–200 keV, and the photon index over 1.4–1.7. We found a clear anti-correlation (Ecut / L � 0:70˙0:06 )b etween the X-ray luminosity (L )i n2–200 keV and Ecut ,w henL is larger than 7 � 10 37 erg s � 1 (assuming a distance of 8 kpc), while Ecut is roughly constant at around 200 keV when L is smaller than 7 � 10 37 erg s � 1 .T his anti-correlation remained unchanged by adopting a more physical thermal Comptonization model, which resulted in an anti-correlation that can be expressed as kTe / L � 0:24˙0:06 .T hese anti-correlations can be quantitatively explained by a picture in which the energy-flow rate from protons to electrons balances with inverse Compton cooling.
118654996
Analytic Formulae for the Off-Center CMB Anisotropy in a General Spherically Symmetric Universe
The local void model has recently attracted considerable attention because it can explain the apparent accelerated expansion of the present universe without introducing dark energy. However, in order to justify this model as an alternative to the standard ΛCDM cosmology, the model should be tested by various observations, such as the CMB temperature anisotropy, besides the distance-redshift relation of SNIa. For this purpose, we derive analytic formulae for the dipole and quadrupole moments of the CMB temperature anisotropy that hold for any spherically symmetric universe model and can be used to compare consequences of such a model with observations of the CMB temperature anisotropy rigorously. We check that our formulae are consistent with the numerical studies previously made for the CMB temperature anisotropy in the void model. We also update the constraints concerning the location of the observers in the void model by applying our analytic dipole formula with the latest WMAP data. Subject Index: 400, 401, 402, 403, 468