CAMEA—A novel multiplexing analyzer for neutron spectroscopy

The analyzerdetector system continuous angle multiple energy analysis will be installed on the cold-neutron triple-axis spectrometer RITA-2 at SINQ, PSI. CAMEA is optimized for efficiency in the horizontal scattering plane enabling rapid and detailed mapping of excitations. As a novelty the design employs a series of several sequential upward scatteringanalyzer arcs. Each arc is set to a different, fixed, final energy and scattersneutrons towards position sensitive detectors. Thus, neutrons with different final energies are recorded simultaneously over a large angular range. In a single data-acquisition many entire constant-energy lines in the horizontal scattering plane are recorded for a quasi-continuous angular coverage of about 60°. With a large combined coverage in energy and momentum, this will result in a very efficient spectrometer, which will be particularly suited for parametric studies under extreme conditions with restrictive sample environments (high field magnets or pressure cells) and for small samples of novel materials. In this paper we outline the concept and the specifications of the instrument currently under construction

Design and performance of the multiplexing spectrometer CAMEA

The cold neutron multiplexing secondary spectrometer CAMEA (Continuous Angle Multiple Energy Analysis) was commissioned at the Swiss spallation neutron source SINQ at the Paul Scherrer Institut at the end of 2018. The spectrometer is optimised for an efficient data collection in the horizontal scattering plane, allowing for detailed and rapid mapping of excitations under extreme conditions. The novel design consists of consecutive, upward scattering analyzer arcs underneath an array of position sensitive detectors mounted inside a low permeability stainless-steel vacuum vessel. The construction of the world's first continuous angle multiple energy analysis instrument required novel solutions to many technical challenges, including analyzer mounting, vacuum connectors, and instrument movement. These were solved by extensive prototype experiments and in-house developments. Here we present a technical overview of the spectrometer describing in detail the engineering solutions and present our first experimental data taken during the commissioning. Our results demonstrate the tremendous gains in data collection rate for this novel type of spectrometer design

MultiFLEXX - The new multi-analyzer at the cold triple-axis spectrometer FLEXX

The first experimental characterization of a multiple energy analysis wide angle backend for a cold triple-axis spectrometer is reported. The multi-analyzer module MultiFLEXX employs 155 detection channels which simultaneously probe an extensive range in wavevector and energy transfer. Successful mapping of magnetic excitations in MnF2 and Ho demonstrate order of magnitude gains in data collection efficiency using this novel type backend. MultiFLEXX is competitive to standard triple-axis spectroscopy in terms of energy resolution and signal-to-noise ratio. A minority of the detector channels is affected by spurious signals inherent to this multiplexing concept. The characteristic signature of these spurious signals easily allows for their discrimination. The instrument concept focuses on detection efficiency in the horizontal scattering plane which makes it an ideal technique for fast mapping and parametric studies including extreme sample environment

Prototype of the novel CAMEA concept—A backend for neutron spectrometers

The continuous angle multiple energy analysis concept is a backend for both time-of-flight and analyzer-based neutron spectrometers optimized for neutron spectroscopy with highly efficient mapping in the horizontal scattering plane. The design employs a series of several upward scattering analyzer arcs placed behind each other, which are set to different final energies allowing a wide angular coverage with multiple energies recorded simultaneously. For validation of the concept and the model calculations, a prototype was installed at the Swiss neutron source SINQ, Paul Scherrer Institut. The design of the prototype, alignment and calibration procedures, experimental results of background measurements, and proof-of-concept inelastic measurements on LiHoF4 and h-YMnO3 are presented here

Hochauflösende Spektroskopie mit der Neutronen Resonanz Spin Echo Methode

Der erste Teil dieser Arbeit erkundet Neuland für die hochauflösende Neutron Resonanz Spin-Echo (NRSE) Spektroskopie über die Messung von Lebensdauern elementarer Anregungen hinaus. Die Datenanalyse solcher Experimente erfordert ein detailliertes Modell der Echoamplitude als Funktion der Korrelationszeit. Das Model bietet zudem eine Hilfestellung für die Experimentplanung in Bezug auf die Wahl der Parameter. Des Weiteren erlaubt es eine quantitative Vorhersage des Informationsgehaltes von NRSE Messungen, z.B. im Bereich der Linienformanalyse oder der Aufspaltung von Anregungsenergien. Wichtige, in dieser Arbeit entwickelte Verallgemeinerungen des existierenden Formalismus berücksichtigen Depolarisationseffekte durch Spin-Echo-Bedingungen, die nicht exakt erfüllt sind. Lokale Gradienten der Dispersion mit einer Orientierung, die nicht parallel zum Wellenvektor q sein muss, und geringfügige Abweichungen der Parameter des Dreiachsen-Spektrometers (DAS), welche zu zusätzlichen, zuvor vernachlässigten Depolarisationseffekten führen, werden jetzt berücksichtigt. Ferner kann der Formalismus nun auf beliebige Symmetrieklassen angewendet werden. Das Modell wurde erfolgreich mit Experimenten an Phononen in einem Pb-Einkristall mit exzellenter Mosaizität überprüft. Die Ergebnisse demonstrieren die Notwendigkeit, Depolarisationseffekte zweiter Ordnung zu berücksichtigen. Der Formalismus wurde dahingehend erweitert, die Analyse von Anregungsdubletts zu ermöglichen. Dadurch werden nun Dejustageeffekte für beide Anregungen berücksichtigt. Das Modell wurde durch elastische und inelastische NRSE Messungen an einem eigens dafür entwickelten Aufbau, welcher künstlich aufgespaltene Moden realisiert, überprüft. Die Ergebnisse zeigen das Potenzial der NRSE Spektroskopie, Anregungsdubletts aufzulösen, deren Energieaufspaltung unter der Energieauflösung eines Standard-DAS liegt. Weitere hier durchgeführte NRSE Experimente widmeten sich der Linienformanalyse temperaturabhängiger asymmetrischer Linienverbreiterungen. Dafür wurden inelastische NRSE Messungen an Cu(NO3)2•2.5D2O sowie an Sr3Cr2O8 durchgeführt. Hierfür wurden eigens hochwertige Cu(NO3)2•2.5D2O -Einkristalle gezüchtet. Die Ergebnisse zeigen deutlich, dass die NRSE Methode in der Lage ist, eine temperaturabhängige asymmetrische Linienverbreiterung zu bestimmen. Erstmalig wurde dieser Effekt mit NRSE gemessen. Im Zuge dieser Arbeit wurde außerdem die NRSE-Option des kalten Dreiachsen-Spektrometers FLEXX an der Neutronenquelle BER II am HZB, Berlin, aufgerüstet. Die dafür neu gefertigten NRSE Bootstrap-Spulen erlauben eine effektivere Ausnutzung des größeren Strahlquerschnitts, der durch das FLEXX Upgrade zur Verfügung steht. Höhere erreichbare Spulenkippwinkel bieten zusätzlich Zugang zu steileren Dispersionen. Das durch die neu entwickelten Spektrometerarme kompaktere Instrument ermöglicht Kalibrationsmessungen im direkten Strahl für den gesamten zugänglichen Wellenvektor-Bereich. In Kombination mit höheren Spulenkippwinkeln wird der zugängliche Q-Bereich in der Larmor Diffraktionsgeometrie vergrößert. Umfangreiche Kalibrationsmessungen zeigen deutlich die Zuverlässigkeit und Leistungsfähigkeit der neuen NRSE-Option, die nun einer breiten Nutzerschaft zu Verfügung steht.The first part of this thesis is dedicated to explore new territory for high resolution Neutron Resonance Spin Echo (NRSE) spectroscopy beyond measuring lifetimes of elementary excitations. The data analysis of such experiments requires a detailed model for the echo amplitude as a function of correlation time. The model also offers guidance for planning NRSE experiments in terms of a sensible choice of parameters and allows predicting quantitatively the information content of NRSE spectroscopy for line shape analysis or energy level separation. Major generalizations of the existing formalism, developed in this thesis, allow for violated spin echo conditions, arbitrary local gradient components of the dispersion surface and detuned parameters of the background triple axis spectrometer (TAS) giving rise to important additional depolarizing effects, which have been neglected before. Furthermore, the formalism can now be applied to any crystal symmetry class. The model was successfully tested by experiments on phonons in a high quality single crystal of Pb and the results demonstrate the stringent necessity to consider second order depolarization effects. The formalism was subsequently extended to analyze mode doublets. As a major step forward, detuning effects for both modes are taken into account here. The model was verified by NRSE measurements on a unique tunable double dispersion setup. The results prove the potential of NRSE spectroscopy to resolve mode doublets with an energy separation smaller than the typical energy resolution of a standard TAS. The second class of NRSE experiments was dedicated to line shape analysis of temperature dependent asymmetric line broadening. Inelastic NRSE spectroscopy was performed on two systems, Cu(NO3)2•2.5D2O and Sr3Cr2O8. For this purpose high quality single crystals of Cu(NO3)2•2.5D2O were grown in the course of this thesis. As a proof of principle the results clearly show that the NRSE method can be used to detect temperature dependent asymmetric line broadening. For the first time this effect was measured with NRSE. The second major part of this thesis was the upgrade of the NRSE option of FLEXX at the BER II neutron source at HZB, Berlin. Redesigned NRSE bootstrap coils allow for a more efficient exploitation of the larger beam cross section, given due to the overall upgrade of FLEXX. Higher accessible coil tilt angles enable measurements on steeper dispersions. The newly designed spectrometer arms result in a more compact instrument, enabling direct beam calibration measurements for the entire accessible wavevector range. In combination with higher coil tilt angles the accessible Q-range in Larmor diffraction geometry is enhanced. Extensive calibration measurements were performed and the results clearly demonstrate the reliable performance of the new NRSE option, now available for the broader user community at FLEXX

High Resolution Spectroscopy with the Neutron Resonance Spin Echo Method

The first part of this thesis is dedicated to explore new territory for high resolution Neutron Resonance Spin Echo NRSE spectroscopy beyond measuring lifetimes of elementary excitations. The data analysis of such experiments requires a detailed model for the echo amplitude as a function of correlation time. The model also offers guidance for planning NRSE experiments in terms of a sensible choice of parameters and allows predicting quantitatively the information content of NRSE spectroscopy for line shape analysis or energy level separation. Major generalizations of the existing formalism, developed in this thesis, allow for violated spin echo conditions, arbitrary local gradient components of the dispersion surface and detuned parameters of the background triple axis spectrometer TAS giving rise to important additional depolarizing effects, which have been neglected before. Furthermore, the formalism can now be applied to any crystal symmetry class. The model was successfully tested by experiments on phonons in a high quality single crystal of Pb and the results demonstrate the stringent necessity to consider second order depolarization effects. The formalism was subsequently extended to analyze mode doublets. As a major step forward, detuning effects for both modes are taken into account here. The model was verified by NRSE measurements on a unique tunable double dispersion setup. The results prove the potential of NRSE spectroscopy to resolve mode doublets with an energy separation smaller than the typical energy resolution of a standard TAS. The second class of NRSE experiments was dedicated to line shape analysis of temperature dependent asymmetric line broadening. Inelastic NRSE spectroscopy was performed on two systems, Cu NO3 2 2.5D2O and Sr3Cr2O8. For this purpose high quality single crystals of Cu NO3 2 2.5D2O were grown in the course of this thesis. As a proof of principle the results clearly show that the NRSE method can be used to detect temperature dependent asymmetric line broadening. For the first time this effect was measured with NRSE. The second major part of this thesis was the upgrade of the NRSE option of FLEXX at the BER II neutron source at HZB, Berlin. Redesigned NRSE bootstrap coils allow for a more efficient exploitation of the larger beam cross section, given due to the overall upgrade of FLEXX. Higher accessible coil tilt angles enable measurements on steeper dispersions. The newly designed spectrometer arms result in a more compact instrument, enabling direct beam calibration measurements for the entire accessible wavevector range. In combination with higher coil tilt angles the accessible Q range in Larmor diffraction geometry is enhanced. Extensive calibration measurements were performed and the results clearly demonstrate the reliable performance of the new NRSE option, now available for the broader user community at FLEX