arXiv subjects

Takuya Ishibashi

Publications and source records attributed to Takuya Ishibashi.

5 recordsLinked to original sources

arXiv2024

Coherent synchrotron radiation instability in low-emittance electron storage rings

Longitudinal impedances at high frequencies, which extend far beyond the width of the beam spectrum, can pose a threat to the performance of modern low-emittance electron storage rings, as they can establish a relatively low threshold for microwave instability. In such rings, coherent synchrotron radiation (CSR) emerges as a prominent contributor to these high-frequency impedances. This paper undertakes a systematic investigation into the effects of CSR on electron rings, utilizing Elettra 2.0, a ring of fourth-generation light sources, and the SuperKEKB low-energy ring, a ring of $e^+e^-$ circular colliders, as illustrative examples. Our work revisits theories of microwave instability driven by CSR impedance, extending the analysis to encompass other high-frequency impedances such as resistive wall and coherent wiggler radiation. Through instability analysis and numerical simulations conducted on the two aforementioned rings, the study explored the impact of high-frequency impedances and their interactions with broadband impedances from discontinuities in vacuum chambers.

physics.acc-ph↗

arXiv2023

Theories derived from Haissinski equation and their applications to electron storage rings

As a stationary solution of the Vlasov-Fokker-Planck equation, the Haissinski equation predicts the equilibrium line density of a bunch that circulates in a storage ring for a given wake function. This paper shows that some equations regarding the centroid shift of the bunch, the peak position of the bunch profile, bunch length, and extraction of impedance from the bunch profile can be derived from the Haissinski equation in a self-consistent manner. In particular, a generalized quadratic equation for potential-well bunch lengthening is obtained to accommodate any absolute impedance model, expanding upon Zotter's cubic equation, which is primarily applicable to inductive impedance. The equations derived in this paper are tested using computed impedance models for some electron storage rings, showing machine-dependent properties of impedance effects. We conclude that these equations can be employed in electron storage rings to effectively bridge the gap between impedance computations and beam-based measurements.

physics.acc-ph↗

arXiv2023

Potential-well bunch lengthening in electron storage rings

The cubic equation derived by B. Zotter has been popularly used for electron storage rings to describe the scaling law of potential-well bunch lengthening. This equation has also often been used to calculate the effective impedance when the bunch lengthening is measured or simulated. This paper discusses the validity of Zotter's equation and presents an alternative but self-consistent equation for potential-well bunch lengthening. Its applications to predicting bunch lengthening and extracting effective impedance from bunch length measurements are also addressed.

physics.acc-ph↗

arXiv2021

Measurements of Beam Backgrounds in SuperKEKB Phase 2

The high design luminosity of the SuperKEKB electron-positron collider will result in challenging levels of beam-induced backgro\ unds in the interaction region. Understanding and mitigating these backgrounds is critical to the success of the Belle~II experi\ ment. We report on the first background measurements performed after roll-in of the Belle II detector, a period known as SuperKE\ KB Phase 2, utilizing both the BEAST II system of dedicated background detectors and the Belle II detector itself. We also repor\ t on first revisions to the background simulation made in response to our findings. Backgrounds measured include contributions f\ rom synchrotron radiation, beam-gas, Touschek, and injection backgrounds. At the end of Phase 2, single-beam backgrounds origina\ ting from the 4 GeV positron Low Energy Ring (LER) agree reasonably well with simulation, while backgrounds from the 7 GeV elect\ ron High Energy Ring (HER) are approximately one order of magnitude higher than simulation. We extrapolate these backgrounds for\ ward and conclude it is safe to install the Belle II vertex detector.

physics.ins-det↗

arXiv2014

Investigation into electron cloud effects in the International Linear Collider positron damping ring

We report modeling results for electron cloud buildup and instability in the International Linear Collider positron damping ring. Updated optics, wiggler magnets, and vacuum chamber designs have recently been developed for the 5 GeV, 3.2-km racetrack layout. An analysis of the synchrotron radiation profile around the ring has been performed, including the effects of diffuse and specular photon scattering on the interior surfaces of the vacuum chamber. The results provide input to the cloud buildup simulations for the various magnetic field regions of the ring. The modeled cloud densities thus obtained are used in the instability threshold calculations. We conclude that the mitigation techniques employed in this model will suffice to allow operation of the damping ring at the design operational specifications.

physics.acc-ph↗