arXiv subjects

Osamu Kamigaito

Publications and source records attributed to Osamu Kamigaito.

5 recordsLinked to original sources

arXiv2026

Space-charge compensation of a low-energy He2+ beam with fluorine-containing gases

This study investigates the space-charge compensation (SCC) of a low-energy He2+ beam by introducing fluorine-containing gases into the low-energy beam transport line (LEBT) of the RIKEN Heavy-Ion Linear Accelerator. The introduction of SF6, C3F8, and CHF3 improved beam transmission through the LEBT, and the largest improvement was obtained using SF6. In contrast, the increase in the beam current with Kr was relatively small, and its effect was less pronounced than that of the fluorine-containing gases. The introduction of fluorine-containing gases increased the rise time of the chopped beam to approximately 10 ms. Experiments performed without the prebuncher confirmed that the prebuncher was largely responsible for this slow rise. Furthermore, the substantial difference in the rise time between Kr and the fluorine-containing gases suggests that different charge carriers may contribute to the SCC in these two cases. Based on the results, a new grid-type beam chopper was installed immediately upstream of the radio-frequency quadrupole linac (RFQ). This configuration allows short beam pulses to be generated immediately before the RFQ while maintaining a direct-current beam in the LEBT, thereby achieving both an effective SCC and a fast beam-current rise. In an acceleration test using the new chopper, a 19.3 micro A He2+ beam was successfully and stably accelerated to the radioisotope-production beamline at a duty factor of 10%. This corresponds to approximately 193 micro A in continuous-wave mode operation, demonstrating that the proposed method is effective for realizing the acceleration of a 200 micro A-class He2+ beam.

physics.acc-ph↗

arXiv2026

Topological aspects of zero modes in cavity resonators

We discuss the relationship between the zero modes of electromagnetic fields in a cavity resonator and the cavity's topological characteristics. We show that the dimension of the electromagnetic zero-mode space coincides with the dimension of the corresponding homology group of the cavity. Moreover, we prove that the alternating sum of the dimensions of the electromagnetic zero-mode spaces is closely related to the Euler characteristic of the cavity boundary, and hence to the integral of the curvature.

physics.acc-ph↗

arXiv2025

Scale invariance of electrodynamics in radio-frequency linear accelerators

This study discusses the scale transformation of electromagnetic fields and trajectories of ions in radio-frequency linear accelerators. We will obtain a condition for mechanical similarity, where Maxwell equations with source terms and the equation of motion under Lorentz force remain invariant, including space charge fields, while the trajectories of ions are accordingly scaled. The possibility of linear accelerators for extremely high current beams will be considered based on this condition.

physics.acc-ph↗

arXiv2025

Nondestructive beam envelope measurements using beam position monitors for low-beta heavy ion beams in superconducting linear accelerator

In superconducting linear accelerators (linacs), accurately monitoring beam dynamics is essential for minimizing beam losses and ensuring stable operations. However, destructive diagnostics must be avoided in superconducting sections to prevent the occurrence of particulates and outgassing, rendering direct measurements of the beam envelope particularly challenging. This study presents a non-destructive method that uses beam position monitors (BPMs) to estimate the transverse beam envelope based on measurements of the quadrupole moment of the beam distribution. Although this concept was originally proposed in the 1980s, its application, especially to hadron beams, has been limited because of low signal sensitivity and the accuracy constraints associated with conventional BPM geometries. To overcome these challenges, we employed $\cos{2θ}$-type BPMs, which offer improved sensitivity to quadrupole components and are well-suited for low-$β$ heavy ion beams. This method was applied to the heavy ion beams in the superconducting RIKEN linac (SRILAC), for which data from eight BPMs were combined with transfer matrix calculations and supplemental wire scanner data. The resulting beam envelope estimates exhibited good agreement with conventional quadrupole scan results, demonstrating the feasibility of this technique for routine, non-destructive beam monitoring in superconducting accelerator sections.

physics.acc-ph↗

arXiv2022

Circuit-model formulas for external-Q factor of resonant cavities with capacitive and inductive coupling

The external-Q factor of a resonant mode of a cavity represents the strength of the electromagnetic coupling between this resonant mode and the transmission mode of a waveguide coupled to the cavity. In this paper, we derive formulas to explicitly give the external Q of the cavities coupled with the waveguide through capacitive and inductive coupling. The derivation is based on the classical method that uses the reflection coefficient to estimate the coupling strength. Although the external Q is evaluated via three-dimensional computer simulations currently, these formulas may be useful for making speculations in the initial stages of cavity design.

physics.acc-ph↗