High intensity cyclotrons for neutrino physics

In recent years, the interest in high intensity proton beams in excess of several milli-Amperes has risen. Potential applications are in neutrino physics, materials and energy research, and isotope production. Continuous wave proton beams of five to ten milli-Amperes are now in reach due to advances in accelerator technology and through improved understanding of the beam dynamics. As an example application, we present the proposed IsoDAR experiment, a search for so-called sterile neutrinos and non-standard interaction using the KamLAND detector located in Japan. We present updated sensitivities for this experiment and describe in detail the design of the high intensity proton driver that uses several novel ideas. These are: accelerating H2+ instead of protons, directly injecting beam into the cyclotron via a Radio Frequency Quadrupole (RFQ), and carefully matching the beam to achieve so-called vortex motion. The preliminary design holds up well in PIC simulation studies and the injector system is now being constructed, to be commissioned with a 1 MeV test cyclotron

Design study of a Split-Coaxial RFQ for IsoDAR

© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). The Isotope Decay-At-Rest experiment (IsoDAR) is a proposed experiment to search for sterile neutrinos by measuring neutrino oscillations. The electron-antineutrino generation requires a high intensity primary proton beam impinging on a beryllium target surrounded by lithium . In IsoDAR, H2+ ions are generated and accelerated to avoid space charge effects in the low energy region, which will be stripped into protons after extraction from a cyclotron. As part of the IsoDAR injection system, an RFQ buncher with 32.8 MHz of operation frequency provides 70 keV acceleration and strong bunching of the H2+ beam. The RFQ will be installed halfway inside the iron yoke of the cyclotron to be very close to the median plane. Because the beam starts diverging after the RFQ in both transverse and longitudinal direction, a re-buncher is employed in the end transition cell to re-focus the beam longitudinally. In this paper, we describe in detail the beam dynamics study and RF analysis of the IsoDAR RFQ for direct injection into a compact cyclotron

Development of Fast Protection System with Xilinx ZYNQ SoC for RAON Heavy-Ion Accelerator

The development of the fast protection system (FPS) was driven by the critical need to safeguard internal components of the accelerator from beam damage and minimize operational downtime. During accelerator operation, various faults can occur, posing a significant risk. The FPS acts as a rapid response system, initiating a shutdown signal to a reliable chopper system to prevent beam damage and ensure the operational availability of the accelerator. To meet the stringent shut off time requirements specific to critical faults, the FPS was designed to respond within 50 µs, while the total FPS time, including acquisition, redundancy, and processing, needed to be less than 20 µs. In order to achieve these goals, a customized FPS was developed for the RAON heavy-ion accelerator, utilizing the Xilinx ZYNQ system-on-chip (SoC). The FPS system comprised seven acquisition modules, one mitigation module with an embedded SoC, and employed optical fiber connections for efficient data transmission. This article provides a comprehensive account of the design, development, and testing of the FPS system. Experimental tests were conducted to validate its performance. These tests included verifying the accuracy of cyclic redundancy checks, acquiring interlock signals in short pulses, and measuring the delay time during abnormal signal occurrences. Of particular significance is the measurement of the total signal processing time for a 1 km optical cable in the RAON system, which was determined to be 9.8 µs. This result successfully met the stringent requirement of 20 µs for the FPS time. The ability of the FPS to operate within the desired time frame demonstrates its effectiveness in protecting the accelerator’s components from beam damage and minimizing downtime. Consequently, the FPS ensures the operational availability of the accelerator while maintaining the safety and integrity of its internal systems. By providing a detailed account of the FPS’s design, development, and testing, this article contributes valuable insights into the capabilities of the FPS in real-world accelerator scenarios. The successful implementation of the RAON-optimized FPS with the Xilinx ZYNQ SoC reaffirms its effectiveness as a fast and reliable protection system, thus enhancing the overall operational performance of the accelerator

Characterization of Tissue Equivalent Materials Using 3D Printing for Patient-Specific DQA in Radiation Therapy

Three-dimensional printing technology has the advantage of facilitating the construction of complex three-dimensional shapes. For this reason, it is widely used in medical and radiological fields. However, few materials with high electron density similar to that of bone exist for fabricating a human phantom. In this study, commercially available filament materials were used with an FDM 3D printer to perform delivery quality assurance (DQA) and were evaluated for medical use. For the bone filament material, BaSO4 was synthesized in five ratios of 2%, 4%, 6%, 8%, and 10% with 40% PBAT and 50~58% PLA. The electron density for the 3D printing material fabricated was obtained using kV energy CT and compared with the electron density of human organs and bones. The radiation beam properties of the 3D printed structures were analyzed as films for treatment using a linear accelerator. As a result, by changing the infill density of the material, it was possible to produce a material similar to the density of human organs, and a homogeneous bone material with HU values ranging from 371 ± 9 to 1013 ± 28 was produced. The 3D printing material developed in this study is expected to be usefully applied to the development of a patient-specific phantom to evaluate the accuracy of radiotherapy

Development of a polystyrene phantom for quality assurance of a Gamma Knife®

A polystyrene phantom was developed following the guidance of the International Atomic Energy Association (IAEA) for gamma knife (GK) quality assurance. Its performance was assessed by measuring the absorbed dose rate to water and dose distributions. The phantom was made of polystyrene, which has an electron density (1.0156) similar to that of water. The phantom included one outer phantom and four inner phantoms. Two inner phantoms held PTW T31010 and Exradin A16 ion chambers. One inner phantom held a film in the XY plane of the Leksell coordinate system, and another inner phantom held a film in the YZ or ZX planes. The absorbed dose rate to water and beam profiles of the machine-specific reference (msr) field, namely, the 16 mm collimator field of a GK Perfexion™ or Icon™, were measured at seven GK sites. The measured results were compared to those of an IAEA-recommended solid water (SW) phantom. The radius of the polystyrene phantom was determined to be 7.88 cm by converting the electron density of the plastic, considering a water depth of 8 g/cm2. The absorbed dose rates to water measured in both phantoms differed from the treatment planning program by less than 1.1%. Before msr correction, the PTW T31010 dose rates (PTW Freiberg GmbH, New York, NY, USA) in the polystyrene phantom were 0.70 (0.29)% higher on average than those in the SW phantom. The Exradin A16 (Standard Imaging, Middleton, WI, USA) dose rates were 0.76 (0.32)% higher in the polystyrene phantom. After msr correction factors were applied, there were no statistically significant differences in the A16 dose rates measured in the two phantoms; however, the T31010 dose rates were 0.72 (0.29)% higher in the polystyrene phantom. When the full widths at half maximum and penumbras of the msr field were compared, no significant differences between the two phantoms were observed, except for the penumbra in the Y-axis. However, the difference in the penumbra was smaller than variations among different sites. A polystyrene phantom developed for gamma knife dosimetry showed dosimetric performance comparable to that of a commercial SW phantom. In addition to its cost effectiveness, the polystyrene phantom removes air space around the detector. Additional simulations of the msr correction factors of the polystyrene phantom should be performed