Kicker magnets are used to kick out the accelerated beam to the transport lines in the 3-GeV Rapid Cycling Synchrotron (RCS) of the Japan Proton Accelerator Complex (J-PARC). A high voltage is applied to kickers for a short period, so they must be installed in a vacuum to prevent discharge. Therefore, it is important to reduce the outgassing of water vapor from the ferrite cores. This time, we have decided to construct the reserve magnets with very low outgassing at high-voltage discharge. First of all, the thermal desorption behavior of the ferrite was investigated by thermal desorption spectroscopy (TDS). TDS spectra show two peaks of water vapor: at ∼100℃ and ∼300℃. Carbon dioxide is rather largely emitted with the peak around 275℃ and then decreases with the temperature. From these results, the ferrite cores were vacuum-fired at 450℃ for 48 h. Then the good properties for the magnetic cores were confirmed. And now the performances of the kicker magnet are examined.
The effect of exposure to ozone on the frequency shift (ΔF) and pressure (P) of a quartz oscillator was observed to check its resistance against the gas. After every ozone exposure, the ΔF-P characteristic curves shifted toward lower frequencies, indicating that the oscillator lost its repeatability. The oscillator electrode consisted of an Au-Cr film deposited on a quartz substrate; an evaluation using a scanning electron microscope (SEM) showed that each film layer had a thickness of 65 nm. The surface composition of the electrode was analyzed by Auger electron spectroscopy (AES). The AES intensities of Cr and Au showed that Cr oxide was present on top of the Au film layer; we speculate that ozone exposure may proceed the Cr oxidation with higher atomic valence. AES depth analysis showed that a small amount of Cr was detected in the Au film layer; we believe that Cr oxidation could progress by either Cr diffusion through the Au layer or by O diffusion from the surface.
In the field of high intensity beam accelerators, activation of the vacuum components has been a big problem. Until now, such materials as aluminum alloys and pure titanium have been used as low activation vacuum materials. However, the problem is that they have lower mechanical strength than stainless steel, which is generally used as a vacuum component material. As a candidate for a low activation vacuum material with high mechanical strength, we measured the radioactivity and vacuum characteristics of titanium alloy Ti-6Al-4V. For the radioactivity characteristics, we carried out proton beam irradiation experiments at 200 and 400 MeV beam energy. As a result, the dose rate of Ti-6Al-4V was found to decrease faster than that of stainless steel. Further, it was found that the relatively short half-life nuclides 44mSc(t1/2=58 h), 46Sc(t1/2=43 h), and 48V(t1/2=15d) are generated. It means that Ti-6Al-4V is a low activation material. To characterize the vacuum performance, the hydrogen concentration in a bulk of Ti-6Al-4V was measured. As a result, by performing the vacuum firing at 700℃ for 9 hours, the hydrogen concentration can be reduced to about 1 ppm, which is 1/70 of the untreated case. These experimental results suggest that it is possible to use Ti-6Al-4V as an ultra-high vacuum material with low activation.
Controlled-polarization-type ferroelectric gate thin film transistors (CP-type FeTFT) with nano-gap channel were fabricated by using a ZnO channel and a YMnO3 ferroelectric film. The electrical properties of the epitaxially grown (0001)ZnO/(0001)YMnO3 heterostructure fabricated by a pulsed laser deposition method were investigated by an impedance spectroscopy to discuss the carrier modulation by the spontaneous polarization of YMnO3. It was found that the ZnO layer surrounding the top electrode has low resistivity. 100 nm-gap electrode was formed by an inclined deposition method on the ZnO/YMnO3 heterostructure. The TFT showed non-volatile memory operation. However, the field-effect mobility is calculated to be 0.25 cm2/Vs, which is ten times lower than that of the micro-channel TFT. The decrease of the resistivity of the ZnO layer surrounding the top electrode is a possible origin of the decrease of the field-effect mobility.
Clarification of memory characteristics of tiny cells is important for practical use of resistive random access memory (ReRAM). However, the limitation of semiconductor micro-fabrication technology hinders to obtain memory characteristics in tiny cell with an area comparable to the size of ReRAM filaments. In this paper, we established a method to prepare a very small memory cell by fabricating ReRAM structure on the tip of the cantilever of atomic force microscope (AFM). We also established a method to avoid the overshoot of set current. As a result, reset current was successfully reduced enough to suppress serious damage to the cantilever. The effective cell size was estimated to be less than φ 10 nm due to electric field concentration at the tip of the cantilever, which was confirmed by an electromagnetic field simulator based on finite element method.
Triboluminescence spectra were measured by means of pin-on-disk method for several samples of natural diamond and a synthetic quartz disk in Ne or N2 gas at pressures between 10 and 105 Pa. At the gas pressure between 10 and 1000 Pa, a blue luminescence was observed besides the gas discharge luminescence due to triboelectricity. The spectrum of cathode-ray luminescence, which was measured by electron bombardment on the same diamond sample, was identical with that of the blue luminescence. The gas pressure dependence of the blue luminescence intensity also supports the model that the blue luminescence was induced by electron impact on the diamond surface in the gas discharge.
Gold film of a thickness of about 100 nm with extremely high resistivity was obtained through sputtering by neutral argon beam. The resistivity differed according to the angle of incidence for argon beam, indicating the lowest value in the vicinity of 60 degree. In the case of sputtering for the angle of incidence of 60 degree, the work function for gold film indicated the lowest value and the secondary electron emission current from gold target during the sputtering increased markedly. These results have suggested that the ionized gold particles play an important role at growth process, leading to enhanced the decrease of amorphous structure into the gold film.