Browsing by Author "Auchettl, R"

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    Applications of online optimization algorithms for injection at the Australian Synchrotron
    (JACoW Publishing, 2019-05-19) Auchettl, R; Dowd, RT
    Accelerators have hundreds of design parameters that makeup the design space. The optimization of complex nonlinear systems (like accelerators) is not straightforward. Trade-offs between competing nonlinear design variables means that optimizing a target objective (such as optics matching) can lack any obvious deterministic method. At the Australian Synchrotron, accelerator tuning predominantly occurs via manual optimization or traditional optimization techniques such as the Linear Optics from Closed Orbits (LOCO) algorithm. While we have had distinct success with the implementation of LOCO [1] and manual tuning, these strategies are not without their downsides. Some situations (such as the optimization of synchrotron beam dynamics) produce a design space too large and multifaceted for manual tuning while implementing LOCO can be computationally expensive. Also, without sufficient diagnostic systems, both LOCO and manual tuning do not necessarily guarantee that the optimal solution will be found. Motivated by the successful implementation of online optimization algorithms at SPEAR3 [2], this paper outlines the application of online optimization algorithms to improve the performance of the Australian Synchrotron injection system. We apply the efficient Robust Conjugate Direction Search (RCDS) Algorithm to reduce beam size in the storage ring.
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    Beam dynamics, injection and impedance studies for the proposed single pulsed nonlinear injection kicker at the Australian Synchrotron
    (JACoW Publishing, 2019-05-19) Auchettl, R; Dowd, RT; Tan, YRE
    The Australian Synchrotron are currently investigating the use of a single pulsed nonlinear injection kicker (NLK) to free floor space within the ring for future beamline development. The NLK has a zero and flat magnetic field at the stored beam to leave the stored beam undisturbed but has a maximum field off-axis where the injected beam is located. After the kick, the injected beam is stored. While NLKs have been prototyped at many facilities around the world, injection efficiency and heat loading have been the main impediment to deployment of the NLK. The wakefields that pass through the ceramic chamber aperture can cause severe heat loading and impedance. Despite achieving impressive injection efficiencies, a previous prototype at BESSY II * showed that strong interactions of the stored beam resulted in high heat load causing the thin 5µm Titanium coated ceramic chamber to reach temperatures > 500 °C and fail. To avoid beam induced heat loads, this paper presents studies of the wake impedance and thermal behaviour for our proposed NLK design. Injection simulations and future considerations for installation and operation at the Australian Synchrotron will be discussed.
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    Crystal structure of propio­nitrile (CH3CH2CN) determined using synchrotron powder X-ray diffraction
    (International Union of Crystallography, 2020-01) Brand, HEA; Gu, QF; Kimpton, JA; Auchettl, R; Ennis, C
    The structure and thermal expansion of the astronomical molecule propio­nitrile have been determined from 100 to 150 K using synchrotron powder X-ray diffraction. This temperature range correlates with the conditions of Titan's lower stratosphere, and near surface, where propio­nitrile is thought to accumulate and condense into pure and mixed-nitrile phases. Propio­nitrile was determined to crystallize in space group, Pnma (No. 62), with unit cell a = 7.56183 (16) Å, b = 6.59134 (14) Å, c = 7.23629 (14), volume = 360.675 (13) Å3 at 100 K. The thermal expansion was found to be highly anisotropic with an eightfold increase in expansion between the c and b axes. These data will prove crucial in the computational modelling of propio­nitrile–ice systems in outer Solar System environments, allowing us to simulate and assign vibrational peaks in the infrared spectra for future use in planetary astronomy. © 2020 International Union of Crystallography
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    Electronic structure and intramolecular interactions in three methoxyphenol isomers
    (AIP Publishing, 2018-10-07) Islam, SMA; Ganesan, A; Auchettl, R; Plekan, O; Acres, RG; Wang, F; Prince, KC
    Electronic structures and intramolecular interactions of three methoxyphenol positional isomers and their rotamers have been studied using core X-ray photoelectron spectroscopy and quantum mechanical calculations. The structural calculations are benchmarked against published calculations of enthalpy of formation and rotational constants, and published experimental data. The good agreement obtained confirms the accuracy of the results. A single rotamer of each isomer was then selected and the C 1s photoelectron spectra calculated and compared with experiment. Good agreement is obtained, and the calculations were extended to investigate the effects of conformation. For 3-methoxyphenol, the difference in the C 1s binding energy of the conformers is small, <0.15 eV. For 2-methoxyphenol, whose ground state includes an OH⋯OCH3 hydrogen bond, the higher energy rotamers show the largest shifts for the methyl carbon atom, whereas the ring carbon bonded to OH hardly shifts The theoretical differences in core level energies of the two rotamers of 4-MP are still smaller, <0.05 eV. By comparing calculations neglecting or including final state relaxation upon ionization, the relaxation energy of the phenyl carbons in all isomers is found to be ∼0.5 eV, while that of the methyl groups is ∼1.3 eV. © 2018 Author(s).