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VA: Fachverband Vakuumphysik und Vakuumtechnik

VA 1: Large instruments for science

VA 1.4: Talk

Monday, March 26, 2007, 10:45–11:00, H9

Gas moderation of positrons — •Benjamin Löwe, Klaus Schreckenbach, and Christoph Hugenschmidt — Physik Department E21 und FRM II, TU München, Lichtenbergstr. 1, 85747 Garching

A variety of low energy positron experiments need an improved brilliance of the beam by means of a remoderator. Conventionally a tungsten single crystal is used as a remoderator in transmission or reflection geometry. In this project a novel remoderation unit is developed and is presently tested at the positron beam facility NEPOMUC at the FRM II. This remoderation is based on inelastic positron scattering and the drift of positrons in a suitable gas.

Positrons of an energy of approximately 500 eV from NEPOMUC are decelerated at the entrance of the remoderation chamber to about 50 eV by an electric field and enter into the gas region (about 1 mbar). They are stopped in the gas, drift along the focusing electric field lines and are accelerated into the UHV region at the exit. By differential pumping the pressure in front and behind the chamber must be as low as possible in order to avoid positron losses by positron-atom collisions at higher energies. Later on it is planned to couple the device to a positron trap.