arXiv subjects

O. Kester

Publications and source records attributed to O. Kester.

10 recordsLinked to original sources

arXiv2026

The DarkLight Experiment at TRIUMF

This paper reports on the commissioning of the DarkLight experiment at the ARIEL superconducting electron linear accelerator located at TRIUMF in Vancouver, Canada. DarkLight was designed to utilize the ARIEL electron beam to search for a new boson, $A^\prime$, which preferentially couples to leptons, with a mass in the range 13-17 MeV/$c^2$. Such a boson could be produced via the $e^-~X\rightarrow e^-~X~A^\prime$ process, and the resulting $A^\prime\rightarrow e^+~e^-$ decay used to reconstruct the invariant mass of the $A^\prime$. The $e^+e^-$ pair is detected using a pair of magnetic spectrometers. Each spectrometer is instrumented with two triple GEM detectors and a scintillating strip hodoscope to trigger the event readout. Electron beam energies between 10 and 30 MeV were used to commission the experiment with a 1$~\mu$m thick carbon target. With both spectrometer polarities set to select electrons, elastic and M{\o}ller scattering were used to examine detector performance and compare with predicted distributions from Monte Carlo simulations. Planned upgrades to the e-linac will allow searches to be made with beam energies up to 50 MeV using a 1$~\mu$m thick tantalum target.

physics.ins-det↗

arXiv2026

Operational Accelerator Tuning via Model-Coupled Optics and Bayesian Steering

We present an on-line tuning strategy for the ISAC post-accelerator that pre-sets machine optics with a digital twin and then performs Bayesian optimization for steering under online operation with beam. The model computes end-to-end tunes in seconds and interfaces with the control system under device bounds, slew-rate limits, and loss interlocks. We report three experimental case studies demonstrating that decoupling optics from steering yields faster and more reliable convergence than a fully Bayesian optics-plus-steering baseline under identical conditions. Across these cases, iterations to high transmission tunes are reduced by a factor of 4-6, with final average transmissions in the mid- to high-90% range. By factorizing optics from steering, the dimensionality of the parameter space is reduced, convergence becomes more predictable, and operational safeguards are easier to enforce.

physics.acc-ph↗

arXiv2025

Matching Optimization for TRIUMF's Rare Isotope Linac

Fringe field effects are computed from simulated and measured quadrupole magnetic field gradients, enabling a more realistic modelling of the medium energy section optics in TRIUMF's RIB postaccelerator. Quantifying the fringe field optics using the method developed by Matsuda and Wollnik allows for the use of parallel modelling tune optimizations for machine operation, providing operators with an efficient means to re-tune the variable energy drift tube linac for RIB delivery.

physics.acc-ph↗

arXiv2025

Strategy for Bayesian Optimized Beam Steering at TRIUMF-ISAC's MEBT and HEBT Beamlines

In preparation for operation of multiple Rare Isotope Beams (RIBs) when the Advanced Rare Isotope Laboratory (ARIEL) becomes operational, TRIUMF embarked on a program of advanced beam tuning applications and machine learning tools. The strategy for operationalizing Bayesian Optimization for beam steering purposes is being developed. A previously reported centroid correction algorithm is used to tune accelerated charged particle beams at TRIUMF's ISAC postaccelerator facility. We present findings and results from multiple machine development experiments conducted between October and November 2024, as part of a pivot toward semi-automated machine tuning methods. These findings were instrumental in shaping the tuning strategy for the medium and high energy beam transport (MEBT, HEBT) lines at ISAC, by sequentially optimizing sub-sections of the beamlines.

physics.acc-ph↗

arXiv2022

Searching for New Physics with DarkLight at the ARIEL Electron-Linac

The search for a dark photon holds considerable interest in the physics community. Such a force carrier would begin to illuminate the dark sector. Many experiments have searched for such a particle, but so far it has proven elusive. In recent years the concept of a low mass dark photon has gained popularity in the physics community. Of particular recent interest is the $^8$Be and $^4$He anomaly, which could be explained by a new fifth force carrier with a mass of 17 MeV/$c^2$. The proposed DarkLight experiment would search for this potential low mass force carrier at ARIEL in the 10-20 MeV e$^+$e$^-$ invariant mass range. This proceeding will focus on the experimental design and physics case of the DarkLight experiment.

nucl-ex↗

arXiv2019

Characterization of a plasma window as a membrane free transition between vacuum and high pressure

A plasma window (PW) is a device for separating two areas of different pressures while letting particle beams pass with little to no loss. It has been introduced by A. Hershcovitch. In the course of this publication, the properties of a PW with apertures of 3.3 mm and 5.0 mm are presented. Especially the link between the pressure properties relevant for applications in accelerator systems and the underlying plasma properties depending on external parameters are presented. At the low pressure side around some mbar, high-pressure values reached up to 750 mbar while operating with volume flows between 1 slm and 4 slm (standard liter per minute) and discharge currents ranging from 45 A to 60 A. Unique features of the presented PW include simultaneous plasma parameter determination and the absence of ceramic insulators between the cooling plates. Optical analysis reveals no significant damage or wear to the components after an operation time well over 10 h, whereas the cathode needle needs replacement after 5 h.

physics.plasm-ph↗

arXiv2012

Preparation of an emittance transfer experiment

Flat beams feature unequal emittances in the horizontal and vertical phase space. Those beams were created successfully in lepton machines. Although a number of applications will profit also from flat hadron beams, to our knowledge they have never been created systematically. Multi-turn injection schemes, spectrometers, and colliders will directly benefit from those beams. The present paper covers the preparation of the experimental proof of principle for flat hadron beam creation in a beam transport section. Detailed simulations of the experiment, based on charge state stripping inside of a solenoid [L. Groening, Phys. Rev. ST Accel. Beams 14, 064201 (2011)], are performed. The matrix formalism was benchmarked with tracking through three-dimensional magnetic field maps of solenoids. An error analysis targeting at investigation of the impact of machine errors on the round-to-flat beam transformation has been performed. The remarkable flexibility of the set-up w.r.t. decoupling is addressed, as it can provide an one-knob tool to set the horizontal and vertical emittance partitioning. Finally, the status of hardware design and production is given.

physics.acc-ph↗

arXiv2007

HITRAP: A facility at GSI for highly charged ions

An overview and status report of the new trapping facility for highly charged ions at the Gesellschaft fuer Schwerionenforschung is presented. The construction of this facility started in 2005 and is expected to be completed in 2008. Once operational, highly charged ions will be loaded from the experimental storage ring ESR into the HITRAP facility, where they are decelerated and cooled. The kinetic energy of the initially fast ions is reduced by more than fourteen orders of magnitude and their thermal energy is cooled to cryogenic temperatures. The cold ions are then delivered to a broad range of atomic physics experiments.

physics.atom-ph↗

arXiv2007

Scintillation light produced by low-energy beams of highly-charged ions

Measurements have been performed of scintillation light intensities emitted from various inorganic scintillators irradiated with low-energy beams of highly-charged ions from an electron beam ion source (EBIS) and an electron cyclotron resonance ion source (ECRIS). Beams of xenon ions Xe$^{q+}$ with various charge states between $q$=2 and $q$=18 have been used at energies between 5 keV and 17.5 keV per charge generated by the ECRIS. The intensity of the beam was typically varied between 1 and 100 nA. Beams of highly charged residual gas ions have been produced by the EBIS at 4.5 keV per charge and with low intensities down to 100 pA. The scintillator materials used are flat screens of P46 YAG and P43 phosphor. In all cases, scintillation light emitted from the screen surface was detected by a CCD camera. The scintillation light intensity has been found to depend linearly on the kinetic ion energy per time deposited into the scintillator, while up to $q$=18 no significant contribution from the ions' potential energy was found. We discuss the results on the background of a possible use as beam diagnostics e.g. for the new HITRAP facility at GSI, Germany.

physics.atom-ph↗

arXiv2004

First Results on In-Beam gamma Spectroscopy of Neutron-Rich Na and Mg Isotopes at REX-ISOLDE

After the successful commissioning of the radioactive beam experiment at ISOLDE (REX-ISOLDE) - an accelerator for exotic nuclei produced by ISOLDE - first physics experiments using these beams were performed. Initial experiments focused on the region of deformation in the vicinity of the neutron-rich Na and Mg isotopes. Preliminary results show the high potential and physics opportunities offered by the exotic isotope accelerator REX in conjunction with the modern Germanium gamma spectrometer MINIBALL.

nucl-ex↗