Michiru Nishiwaki

Influence of electron irradiation and heating on secondary electron yields from non-evaporable getter films observed with in situ x-ray photoelectron spectroscopy

Nonevaporable getter (NEG) film has been used for the beam ducts of particle accelerators as a pump having a large area. NEG film has been considered to have a low outgas rate induced by energetic particle irradiation and a low secondary electron yield (SEY). In this article, we focused on SEY measurements and in situ surface characterization of four NEG film samples using x-ray photoelectron spectroscopy (XPS). The NEG samples were TiZrV thin films deposited by magnetron sputtering at 100 or 300°C on stainless steel. In addition, NEG samples saturated by CO gas exposure were prepared. SEY and XPS measurements of the surfaces of NEG samples were carried out under the conditions of as received, after electron beam irradiation, and after heating at 200°C for 24h. The maximum SEY values of the primary electron energy dependence, δmax, of all NEG samples decreased to around 1 by electron beam irradiation owing to a change in the carbon impurities, such as carbon oxide, carbon hydroxide, and hydrocarbon, to gr...

Surface analyses of electropolished niobium samples for superconducting radio frequency cavity

The performance of superconducting radio frequency niobium cavities is sometimes limited by contaminations present on the cavity surface. In the recent years extensive research has been done to enhance the cavity performance by applying improved surface treatments such as mechanical grinding, electropolishing (EP), chemical polishing, tumbling, etc., followed by various rinsing methods such as ultrasonic pure water rinse, alcoholic rinse, high pressure water rinse, hydrogen per oxide rinse, etc. Although good cavity performance has been obtained lately by various post-EP cleaning methods, the detailed nature about the surface contaminants is still not fully characterized. Further efforts in this area are desired. Prior x-ray photoelectron spectroscopy (XPS) analyses of EPed niobium samples treated with fresh EP acid, demonstrated that the surfaces were covered mainly with the niobium oxide (Nb2O5) along with carbon, in addition a small quantity of sulfur and fluorine were also found in secondary ion mass ...

Commissioning of the Phase-I SuperKEKB B-Factory and Update on the Overall Status

The SuperKEKB B-Factory at KEK (Japan), after few years of shutdown for the construction and renovation, has finally come to the Phase-1 commissioning of the LER and HER rings, without the final focus system and the Belle II detector. Vacuum scrubbing, optics tuning and beam related background measurements were performed in this phase. Low emittance tuning techniques have also been applied in order to set up the rings for Phase-2 with colliding beams next year. An update of the final focus system construction, as well as the status of the injection system with the new positron damping ring and high current/low emittance electron gun is also presented.

The Development of a Superconducting RF Electron Microscope

Fig. 2: 2-mode cavity We are developing a new type of electron microscope (EM), which adopts RF acceleration in order to exceed the energy limit of DC acceleration used in conventional EMs. It enables us to make a high voltage EM more compact and to examine thicker specimens, and possibly to get better spatial resolution. It also provides an ability to observe transient processes by employing a state of the art laser photocathode technology as electron source. Low energy dispersion ∆E/E, e.g. 1.0×10−6 or better, is required for good spatial resolution in EMs, while it is usually between 1.0×10−3 to 1.0×10−4 in accelerators. We have thus designed a special type of cavity that can be excited with the fundamental and second harmonic frequencies simultaneously; TM010 and TM020. With the 2-mode cavity, the energy dispersion of the order of 1.0×10−5 would be obtained by modifying the peak of accelerating field to be flattened. We also adopt a superconducting cavity in order to operate the EM in CW mode, so that we can obtain a beam flux comparable to conventional EMs. In addition, we can make the operation more stable. As the proof-of-principle of our concept, we are developing a prototype using a 300 keV transmission electron microscope (TEM), to which a new photocathode gun and the 2-mode cavity are attached(Fig.1). Now we have already manufactured the cavity(Fig.2). We have done the beam dynamics simulation using General Particle Tracer(GPT), using the realistic electromagnetic field of the gun and the cavity. As a result, it has been found that we can reduce the energy dispersion ∆E/E from 2.04×10−4 to 3.68× 10−5 with 2-mode cavity. Then we can get the spatial resolution of 376pm, which is only about 50% deterioration of the existing 300keV TEM, which is much smaller than 818pm, the expected value of 1-mode cavity. The required electric fields are 8.21MV/m for TM010, 9.25MV/m for TM020. The designed Q-values are 1.86 × 10 for TM010(1.3002GHz), 1.00 × 10 for TM020(2.5999GHz). Performance evaluation tests has shown that the maximum electric fields are (8.75±0.73)MV/m for TM010, (7.80±0.33)MV/m for TM020. And the measured Q-values are (1.41± 0.45)× 10 for TM010, (0.78± 0.12)× 10 for TM020. It proves that manufactured cavity’s Q-values are close to designed ones, therefore we can say that the manufacturing process of our specially-shaped cavity has been confirmed. The measured resonant frequencies are 1.2963GHz for TM010, 2.5851GHz for TM020, so that the frequency ratio is 1.994. Then next task is to modify the cavity in order to tune the frequencies. And gun is now under construction. The goal of this year is to acquire the electron beam from the cathode. APPC12 The 12th Asia Pacific Physics Conference