Berlin 2005 – wissenschaftliches Programm
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VA: Vakuumphysik und Vakuumtechnik
VA 2: Quanten, Neutronen und Positronen
VA 2.5: Vortrag
Montag, 7. März 2005, 12:20–12:40, TU E20
Positron remoderation device for brightness enhancement of the reactor based positron beam at the FRM-II — •C. Piochacz1, C. Hugenschmidt1,2, K. Schreckenbach1,2, and B. Straßer2 — 1TUM, Lehrstuhl für Experimentalphysik E21, James-Frank-Str., 85747 Garching — 2ZWE FRM2, Lichtenbergstr. 1, 85747 Garching
Recently, the positron beam facility NEPOMUC was set into operation at the new research reactor FRM-II in Garching. In order to enhance the brightness of the beam a positron remoderation apparatus was developed. The remoderator is build up in transmission geometry: positrons from the source are focused on to a 0.1 µm thin mono-crystalline W-foil where they thermalize and diffuse to the back side of the foil. At the surface, low energy positrons (∼ 3 eV) leave the foil with a small angular divergency. The focusing is magnetically achieved by adiabatic beam compressing with a water-cooled copper coil. It is expected to reach a magnetic field of about 280 mT resulting in a beam diameter of less than 1 mm. The energy distribution and the angular spread of the remoderated beam as well as the moderation efficiency is measured. An overview of the the assembly will be given and first measurements will be presented.