593 research outputs found
Making ICRF power compatible with a high-Z wall in ASDEX Upgrade
No full textA comparison of the ASDEX Upgrade 3-strap ICRF antenna data with the linear electro-magnetic TOPICA calculations is presented. The comparison substantiates a reduction of the local electric field at the radially protruding plasma-facing elements of the antenna as a relevant approach for minimizing tungsten (W) sputtering in conditions when the slow wave is strongly evanescent. The measured reaction of the time-averaged RF current at the antenna limiters to the antenna feeding variations is less sensitive than predicted by the calculations. This is likely to have been caused by temporal and spatial fluctuations in the 3D plasma density distribution affected by local non-linear interactions. The 3-strap antenna with the W-coated limiters produces drastically less W sputtering compared to the W-coated 2-strap antennas. This is consistent with the non-linear asymptotic SSWICH-SW calculations for RF sheaths
Perturbation of nuclear excitons by ultrasound
No full textThe coherent decay of a nuclear exciton created by synchrotron radiation in spatially separated targets is studied in the presence of ultrasound (US) vibrations in one of the targets. The time evolution of the nuclear exciton perturbed in such a way is described by interference between the wave packets re-emitted by both targets and radiative coupling between the targets. Since the condition for initial phasing of the wave packets and coupling can be restored periodically by US, strong intensity enlargements in the time response, called nuclear exciton echoes, are observed. If the targets have different resonant energies quantum beats arise which are frequency modulated by the US perturbation. A complete dynamical theory is presented which provides a quantitative description of all experimental results discussed
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MÖSSBAUER STUDY OF ELECTROMAGNETIC PHENOMENA IN LOW TEMPERATURE COPPER
No full textL'émission Mössbauer à basse température d'une feuille de cuivre doppée au 57Co est absorbée de façon résonnante par du Be(57Fe) stationnaire. L'utilisation d'un courant radiofréquence de 700 MHz envoyé à travers la source entraîne une augmentation importante de la transmission, principalement à la fin de l'impulsion. Ce phénomène est attribué à un mouvement oscillatoire dans le plan de la feuille à une fréquence plus petite que 10 MHz. Ce phénomène ne dépend pas de la fréquence du courant r-f et n'apparaît pas pendant la pulsation r-f. Les relations avec d'autres processus bien connus de production d'ultrason ne sont pas immédiates.Mössbauer radiation from a low température copper foil doped with 57Co is resonantly obsorbed in a stationary Be(57Fe) absorber. Radio frequency current puises at 700 MHz through the source cause large increases in transmission, mainly after the end of the puise. The phenomena is attributed to ascillatory motion in the place of the foil and with motional fraquencies ≤ 10 MHz. As it occurs neither with the r-f current frequencies nor mainly during the r-f puise, its connection with other well-studied processes of direct production of ultrasound is not immediate
CRESST II background discrimination: Detection of W-180 natural decay in a pure alpha-spectrum
No full textFor the first time the natural alpha decay of W-180 has been unambiguously detected in a (gamma, beta and neutron)-free background spectrum. This has been obtained by simultaneously measuring phonon and light signals with CRESST 11 cryogenic detectors. Results on the radio purity of the detectors and on the measured half-life of W-180 are presented
Neganov-Luke amplified cryogenic light detectors for the background discrimination in neutrinoless double beta decay search with TeO2 bolometers
No full textWe demonstrate that Neganov-Luke amplified cryogenic light detectors with Transition Edge Sensor read-out can be applied for the background suppression in cryogenic experiments searching for the neutrinoless double beta decay of 130Te with TeO2 based bolometers. Electron and gamma induced events can be discriminated from α events by detecting the Cherenkov light produced by the β particles emitted in the decay. We use the Cherenkov light produced by events in the full energy peak of 208Tl and by events from a 147Sm source to show that at the Q-value of the neutrinoless double beta decay of 130Te (Qβ β = 2.53 MeV), a separation of e-/γ events from α events can be achieved on an event-by-event basis with practically no reduction in signal acceptance
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