Long-pulse Spallation Source Research Articles

Neutron macromolecular crystallography at the European spallation source.

The long-pulse spallation source of the European Spallation Source-a facility under construction in Lund, Sweden-is well suited for macromolecular crystallography experiments. We review briefly the particular properties of the long-pulse source and the associated high-brilliance moderators from the point of view of instrument design. We then outline the design philosophy and current design of the NMX macromolecular diffractometer. We also briefly describe the supporting facilities available for users and finish by an evaluation of the expected performance.

Neutronic developments on TOSCA and VESPA: Progress to date

We report recent developments regarding the TOSCA (ISIS, UK) and VESPA (ESS, Sweden) neutron broadband chemical spectrometers, both joint ventures between CNR (IT) and ISIS (UK). TOSCA has seen the first major upgrade since it first became operational over fifteen years ago. The new design of the primary spectrometer, which exploits a state-of-the-art, high-m neutron guide and associated chopper system, is boosting the useful neutron flux by over an order of magnitude. Feasibility studies for an upgrade of the secondary spectrometer have been performed, outlining an additional order-of-magnitude gain in performance. In the case of VESPA, the novel characteristics and challenges arising from a long-pulse spallation source such as ESS are part of the drivers of the instrument design. For both the primary and secondary spectrometers, a detailed analysis of expected performance, supported by both simulations and analytical models, is being carried out, also capitalizing from experience on TOSCA. Indeed, for instrument design and optimization, extensive neutron-transport simulations and baseline studies of neutronic response have become a must, along with extensive benchmarking against much-needed experimental data. All these combined efforts represent the first opportunity to benchmark a broadband, high-resolution chemical spectrometer in terms of measured vs. simulated response.

Optimization of monochromator and ToF powder diffractometers at a long-pulse spallation source using Monte Carlo simulations

Recent development of the program package RESTRAX permitted us to carry out numerical optimizations of two generic types of powder diffractometers for the envisaged long-pulse structure of the European Spallation Source (ESS), namely a constant wavelength instrument equipped with a crystal monochromator (CM) and a narrow band time-of-flight (ToF) diffractometer. The aim was to compare properties of these two conceptually different instrument types. Optimization using particle swarm algorithm was carried out in the space of 10–15 free parameters for each instrument, while keeping the source, beam extraction optics, sample and detector fixed at the same values for both setups. The optimum performance was defined by the figure of merit based on the evaluation of complete simulated α-SiO2 diffractograms. As a result, we arrived at configurations yielding similar average resolution, but large difference (up to a factor of 40) in neutron intensity in favour of the ToF concept. The CM option is however competitive with ToF in terms of spectral flux density and instantaneous flux, which may find use in stroboscopic measurements or in-situ experiments under pulsed sample environments with millisecond duty times.

Beam Line Parameters for PERC at the ESS

Abstract Precision measurements of correlations in neutron beta decay test the standard model of particle physics. Here, pulsed neutron beams are invaluable to fight systematic effects. We show that the Proton Electron Radiation Channel PERC in pulsed mode is particularly well suited for a long-pulse spallation source, due to its long decay volume. We indicate how the optimum beam line parameters to run PERC at the ESS can be derived and compare the performance with that at the most powerful continuous source, the reactor of the ILL.

Target system neutronics study for NXGENS

The Materials Test Station (MTS) [E. Pitcher, G. Muhrer, H. Trellue, Neutronics Assessment of the LANSCE Materials Test Station as an Irradiation Facility for the JIMO Space Reactor, LA-CP-04-0903. [1]], a spallation target station, planned for construction at the Los Alamos Neutron Science Center (LANSCE), will provide the opportunity to test the prototype of a long-pulse spallation source neutron scattering instrument (NXGENS). In this paper, we present the target-moderator neutronics optimization study that was performed in support of NXGENS.

Powder diffraction on a long-pulse spallation source

Monte Carlo simulations have been performed for a time-of-flight monochromator powder diffractometer housed on a thermal moderator at a Long-Pulse Spallation Source and for a conventional crystal monochromator instrument on a thermal moderator of a reactor source of four times the time-averaged flux. By designing the time-of-flight instrument to utilise the inherent advantages of the technique whilst optimising to the peak performance of the crystal monochromator case, the performance of the TOF-instrument is shown to exceed that of the reactor-based diffractometer, despite the lower time-averaged flux of the source. Further, a simple extrapolation of the results obtained for the pulsed-source shows that such a TOF diffractometer would out-perform a conventional instrument if both were to be housed on the same reactor.

Next generation neutron source project in Japan Atomic Energy Research Institute (JAERI)

JAERI is carrying out a project to construct an intense-pulsed spallation source to promote a wide range of basic science and a CW source for nuclear power technologies such as nuclear transmutation of rare actinides from nuclear wastes. The most important basic science of the project is neutron scattering. The major facility is a 1.5 GeV superconducting H +/H − linac, with a peak current of 30 mA and a time-averaged beam current of 5.33 mA, which can provide 8 MW in total. For neutron-scattering experiments, 5 MW is available. A general view of the project and neutron-scattering facility are reported. Neutron-scattering experiments with a short-pulse spallation source (SPSS) are our final goal, but with a long-pulse spallation source (LPSS) might be optionally possible, if we have financial and/or technical difficulties.

Reflectometry at a long pulse spallation source

Abstract The layout criteria for a reflectometer at a long pulse spallation source (LPSS) are discussed. It is shown how the most important instrument parameter, the wished resolution of the measured reflectivity profile, determines the choice of the wavelength and available wavelength band, the length of the instrument and the position of the disc choppers, which are necessary for applying the time-of-flight method. Using 4 disc choppers it is possible to measure the same spectrum with different resolutions without changing the beam geometry and the available wavelength band. All considerations are tested with Monte Carlo simulations, which were performed with a 2 ms pulse of a source working at 25 Hz.

Long-pulse spallation source neutronic performance

There are potential gains of about a factor of seven in the time-average neutron brightness for a coupled liquid H2 moderator compared to a decoupled one, and a factor of around five for a H2 0 moderator. However, these gains come at the expense of p

A multilayer ultracold neutron turbine source for a long-pulse spallation source

We have developed a concept for an ultracold neutron (UCN) turbine source based on a long-pulse spallation source. Using a single reflection from a receding blade, the turbine converts cold neutrons from the primary moderator to UCN. The UCN pulse length is spread out in time and is comparable to the primary pulse interval, producing a quasi-continuous UCN source. The principal parameters for such a design are the primary source pulse length, the flight path distance, and the velocity acceptance interval of the reflector. Taking advantage of recent advances in multilayer reflector preparation, we propose W 11B 4C multilayer reflectors with a high-reflectivity plateau in the velocity range of 80±5 m/s. We have simulated a multilayer turbine which converts 160±5 m/s neutrons from a 1 ms primary source with a 2.5 m incident flight path to UCN with an efficiency, in terms of phase space density, of about 4.4%. For a ∼1 MW long-pulse spallation source with 1 ms pulse length and 60 Hz frequency, and a time average flux in a liquid hydrogen moderator of 1 × 10 14 n/cm 2 s, this corresponds to a UCN source flux of 1.9 × 10 5 n/cm 2 s, a total UCN current of 3.3 × 10 7 n/s, and a UCN density (for velocity ≤6.2 m/s) of 500 n/cm 3.

Neutron scattering instruments on long pulse spallation sources

Abstract About one year after the workshop at Berkeley aimed at assessing the opportunities offered by a 1 MW long pulse spallation source (LPSS) as proposed to be built at the LAMPF linear proton accelerator at Los Alamos, the next meeting devoted to neutron scattering potentials of LPSS was held at the Hahn-Meitner-Institut in Berlin from June 24–27, 1996.The scope of the workshop was to consider instrumentation concepts and advance quantitative evaluation of instrumentation performance in view of an optimization of source design options for neutron scattering research. The workshop was attended by over 50 colleagues, over 30 of them from outside HMI, the host laboratory. Earlier this year, the neutron scattering group at HMI embarked on a broad program of Monte-Carlo evaluation and comparison of instrument performance, complementing the well established effort at Los Alamos. The proceedings of the workshop will be published in the Journal of Neutron Research.