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Experiments and theoretical studies are being conducted for :;A?A on critical assemblies with 1-m-diara by 1-m-long lowdensity cores surrounded by a thick beryllium reflector. These assemblies make extensive use of existing nuclear propulsion reactor components, facilities, and instrumentation. Due to excessive porosity in the reflector-, the initial critical r.ass was 19 ke ! J(93.2). Addition cf a 17-em-thlek by 59-cm-diar. beryllium flux tra^ in the cavity reduced the critical rr.ass to 7 kf when all the uranium was ir. the :cnc .'us*, outside the flux '.rat. A mockup aluminum '.'?,< coritalr.t-r was r laced inside the flux trap and fueled with uraniun-.'ra; hi-.e elements. Fission distributions and reactivity worths of fuel and structural materials were measured. Finally, ar; ?•"• ijO-orialur.Inum ;:anlster in the central replon was fueled with VFr as and f.'.ssion Jer.sity distributions jeterrsine J. These results will be used to guide the design of a prototype f lasma core reactor which will test energy removal ty optical radiation.
Schlagwörter: Sensoren, Brillouin-Streuung, Lichtleitfasern, frequenzanaloges Ausgangssignal, Stokeswelle, Brillouin-Laser Stimulierte Brillouin-Streuung (SBS) ist ein nichtlinearer Effekt in optischen Glasfasern, der durch die Wechselwirkung elektromagnetischer Lichtwellen mit den Gitterschwingungen des Festkörpers entstehen kann. Dabei bildet sich eine kohärente rückgestreute Stokeswelle, die gegenüber der eingestrahlten Frequenz der Pumpwelle um einige Gigahertz rotverschoben ist. Bei entsprechender Dimensionierung der Wechselwirkungsparameter tritt SBS bereits bei Pumpschwellen im Sub-Milliwatt-Bereich auf. So störend dieser Effekt für die optische Nachrichtenübertra-gung mittels Glasfasern ist, so interessant ist er für die optische Sensorik, da er die inhärente Konversion physikalischer Größen in eine Signalfrequenz liefert.
Stimulated Brillouin Scattering (SBS) is a nonlinear effect in optical fibres, which can be generated by interaction of electromagnetic light waves and acoustic phonons in the glass material. As a consequence a coherently backscattered stokeswave builds up with an emission frequency, which is red-shifted by a few GHz compared to the pump frequency. Suitably configuring the interaction parameters allows for pump thresholds in the microwatt region.Although the phenomenon is considered as potentially perturbing in fibre optic communication systems, it is of interest for fibre optic sensors, which, as an inherent feature, convert the physical measurement value in a frequency Signal.
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