Slow collisions of hydride ion and deuteride ion with sodium, potassium and cesium

The cross sections of charge transfer and electron detachment in collisions of H\sp{-} and D\sp{-} with Na, K and Cs have been measured for collision energies ranging from 3 to 300 eV. Both charge transfer and electron detachment are significant electron-loss mechanisms for H\sp{-}(D\sp{-}); both processes exhibit velocity-dependent isotope effects for H\sp{-} and D\sp{-}. \sigma\sb{\rm cg}(E) displays high energetic thresholds for Na and K (about 20 eV for H\sp{-} + Na and 40 eV for H\sp{-} + K) yet no obvious one for Cs. \sigma\sb{\rm e}(E) does not depend on the target as much as \sigma\sb{\rm ct}(E) and displays near zero-energy thresholds. The relative importance of charge transfer as an electron-loss mechanism decreases as the mass of the alkali-metal increases

Particle Swarm Optimization for High Rigidity Spectrometer

The goal of this project is to find reliable parameter settings for a multi-dimensional global optimizer to optimize the performance of a large acceptance ion optical system for the requirements of nuclear physics experiments. We develop and test the Particle Swarm Optimization (PSO), a global optimization algorithm designed for continuous multi-dimensional problems, on a large acceptance particle beam separator, the High Rigidity Spectrometer (HRS) at the Facility for Rare Isotope Beams (FRIB), which is a laboratory specializing in the production and experimental study of short-lived nuclear matter. We split the HRS into two sections, the High-Transmission Beamline (HTBL) and the Spectrometer Section. The objective of the PSO is to improve the transmission rate for the Spectrometer Section and the beam spot size as well as dispersive foci for the HTBL, in both cases by adjusting the settings of the higher-order magnetic field elements—sextupoles and octupoles. We successfully improved the transmission rate of fission fragments from 57.5% to 63% in the Spectrometer Section and shrank the beam spot size in horizontal direction of 40Mg from 1.8 mm to 1.0 mm in the HTBL. Finally, we compare the performance of PSO with multiple, different internal parameter settings (inertia, acceleration). We find a significant difference in performance across the PSO parameter settings considered, with the best internal parameter setting for the PSO being (0.9, 0.45). Future work will explore the PSO parameter space for additional input particle distributions (e.g. fission fragments in the HTBL) and differently constructed objective functions to better understand the operation of the PSO in these ion optical systems

Contraction conditions with perturbed linear operators and applications

In this paper, we present some new fixed point theorems for both single-valued and multi-valued maps controlled by the contraction conditions with perturbed linear operators in continuous function spaces. Our results can be applied to various integral operators. Some previous results are generalized in this literature. As applications, the existence and uniqueness of solutions of impulsive periodic boundary value problems and functional differential inclusions are exhibited in the last section

Impedance-Based Stability Analysis for Interconnected Converter Systems with Open-Loop RHP Poles

Small-signal instability issues of interconnected converter systems can be addressed by the impedance-based stability analysis method, where the impedance ratio at the point of common connection of different subsystems can be regarded as the open-loop gain, and thus the stability of the system can be predicted by the Nyquist stability criterion. However, the right-half plan (RHP) poles may be present in the impedance ratio, which then prevents the direct use of Nyquist curves for defining stability margins or forbidden regions. To tackle this challenge, this paper proposes a general rule of impedance-based stability analysis with the aid of Bode plots. The method serves as a sufficient and necessary stability condition, and it can be readily used to formulate the impedance specifications graphically for various interconnected converter systems. Experimental case studies validate the correctness of the proposed method

Small-Signal Modeling of AC Power Electronic Systems: Critical Review and Unified Modeling

The harmonic state-space (HSS), the dynamic phasor (DP), and the generalized dq (GDQ) modeling are three widely used methods for small-signal analysis of ac power electronic systems. By reviewing their principles and deriving their mathematical relationships, this paper proposes a unified framework for all the three approaches. The unified modeling reveals that the linearization and transformation can be exchanged flexibly in the modeling process, and the initial phase takes a role in transforming the GDQ model into the HSS or DP model. Case studies on a three-phase voltage-source converter in unbalanced power grids are provided for validation. The relationships of three modeling methods are verified by mathematical proofs and time-domain simulations. The unified frequency-domain model is further validated through the frequency scan in experiments. Insights of the unified modeling framework and recommendations from engineering perspectives are finally discussed