Silicon carbide (SiC) is very attractive semiconductor material especially for power device use because of its excellent physical properties like as high critical electric field, high thermal conductivity, and so on. In this paper, the theoretical consideration about the advantages of SiC power devices compared with that of Si and the current status of the social implementation of SiC power devices are introduced.
Photocathodes that are capable of generating high-performance electron beams are one of the most important devices in an advanced accelerator and electron microscopes. In particular, bialkali photocathodes, such as cesium potassium antimonide (CsK2Sb) is of interest because it can generate a high-brightness electron beam using a high-power green laser. It is known that the quantum efficiency (QE) of these photocathodes is affected severely by their substrates; however, reusability of the substrates is not well known. In this study, we use graphene, silicon (Si), and molybdenum (Mo) substrates to evaluate the effects of substrates on the QE of redeposited CsK2Sb photocathodes after thermal cleanings. We found the QE of CsK2Sb photocathodes redeposited on a graphene substrate after a thermal cleaning at 500°C remained largely unchanged. On the other hand, the QE of redeposited photocathodes on Si and Mo substrates after thermal cleaning at the same temperature decreased drastically. We used X-ray photoelectron spectroscopy (XPS) to quantitatively evaluate the residues of photocathodes after thermal cleaning at 400°C and 500°C. We found that the Sb, K, and Cs are removed by thermal cleaning at 500°C for the graphene substrate, but all or the majority of these elements remained on the Si and Mo substrates. The results were consistent with our density functional theory (DFT) calculations for the case of Si, which we investigated. Furthermore, our angle-resolved photoemission spectroscopy (ARPES) on graphene indicated that its intrinsic electronic structure is preserved after photocathode deposition and thermal cleaning at 500°C. Hence, we attributed the difference in amount of photocathode residue to the unique dangling-bond-free surface of inert graphene. Our results provide a foundation for graphene-based reusable substrates for high-QE semiconductor photocathodes.
In STF at KEK, as the operational demonstration of the SRF accelerator for ILC, the STF-2 cryomodules (CM1+CM2a: one and half size CM with 12 cavities) have achieved 33 MV/m as average accelerating gradient with 7 cavities in Mar/2019. After that, one cavity with the lowest performance installed in CM2a was replaced with one N-infused cavity developed for High-Q/High-G R&D between Japan and US. From Apr/2021, the beam operation started again and those CMs achieved 33 MV/m as average accelerating gradient with 9 cavities including one N-infused cavity again. This is remarkably important milestone for the ILC project. In this report, the detailed results will be presented.
The Low Level RF (LLRF) control system for the Rapid Cycling Synchrotron (RCS) of the Japan Proton Accelerator Research Complex (J-PARC) plays an important role in acceleration of high intensity beams. The key functions of the original LLRF control system are the dual harmonic auto voltage control and the multiharmonic RF feedforward for compensation of the beam loading in the wideband cavity. The original system had been working well without significant problems for more than a decade, however, the long term maintenance became difficult due to the obsolesce of the old FPGAs in the system. Therefore we developed and deployed the next-generation LLRF control system. The next-generation system is based on the modern platform, MTCA.4. The most important new function of the system is the multiharmonic vector RF voltage control feedback, which compensate the heavy beam loading in the wideband cavity better than the feedforward at the beam intensity of the design beam power, 1 MW. The commissioning results are reported. The next-generation system has been successfully deployed.
RIKEN has built nine cyclotrons so far. The third RIKEN cyclotron was moved from Komagome, the former RIKEN site, to Wako campus in March 2021. It is good chance to describe its historical significance and the details of its design, looking back at the history of the RIKEN cyclotrons. Finally, if we were to revive this No. 3 cyclotron, I would consider what use it might have.
Semiconductor detectors are becoming essential in recent accelerator experiments with an ability of very precise position resolution. At recent high energy and luminosity experiments, high radiation tolerance is required. We have developed silicon detectors as an inner tracking detector for the LHC-ATLAS experiment with performing radiation tolerance studies using 70 MeV proton beam at the Cyclotron and Radioisotope Center (CYRIC), Tohoku University. In this article, the method of irradiation and evaluations of our developed detectors are presented.
The 2021 International Conference on RF Superconductivity (SRF’21) was held from the 28th of June to the 2nd of July 2021. Due to the COVID-19 pandemic, the conference was held as a virtual conference. The major focus of this biyearly conference series is to report on research and developments on superconducting radio frequency (SRF) technology. The conference was chaired by Kenji Saito from the Michigan State University (MSU), MI, USA.