Abstract: The feasibility of an acoustic-electrostatic hybrid levitator for small fluid and solid samples is evaluated. A proposed design and its theoretical assessment are based on the optional implementation of simple hardware components (ring electrodes) and standard laboratory equipment into typical commercial ultrasonic standing wave levitators. These levitators allow precise electrical charging of drops during syringe- or ink-jet-type deployment. The homogeneous electric 'Millikan field' between the grounded ultrasonic transducer and the electrically charged reflector provide an axial compensation of the sample weight in an indifferent equilibrium, which can be balanced by using commercial optical position sensors in combination with standard electronic PID position control. Radial electrostatic repulsion forces between the charged sample and concentric ring electrodes of the same polarity provide stable positioning at the centre of the levitator. The levitator can be used in a pure acoustic or electrostatic mode or in a hybrid combination of both subsystems. Analytical evaluations of the radial-axial force profiles are verified with detailed numerical finite element calculations under consideration of alternative boundary conditions. The simple hardware modification with implemented double-ring electrodes in ac/dc operation is also feasible for an electrodynamic/acoustic hybrid levitator.
Abstract: Recently. the SINQ time-of-flight (TOF) spectrometer FOCUS became operational. FOCUS is a cold neutron hybrid TOF machine that combines a doubly focusing crystal monochromator with a Fermi chopper. The concept provides a highly flexible instrument that can be optimized for both quasielastic and inelastic neutron scattering experiments. The layout of the machine as well as first experimental results are described. (C) 2000 Elsevier Science B.V. All rights reserved.
Abstract: The concept of the SINQ-time-of-flight (TOF) spectrometer FOCUS foresees a hybrid-TOF solution that combines a doubly focusing crystal monochromator with a Fermi-chopper. The spectrometer can be operated in time focusing (TF) and monochromatic focusing (MF) mode such that it can be optimised for quasielastic and inelastic scattering applications, respectively. BS the use of two interchangeable monochromators (PG and MICA) access is provided to incident energies in the range 0.25 meV < E-i < 20 meV.
