Beam chopper development at LAMPF |
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Authors: | R L Hutson D W Cooke R H Heffner M E Schillaci S A Dodds G A Gist |
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Institution: | (1) Los Alamos National Laboratory, NM 87545 Los Alamos, USA;(2) Rice University, 77251 TX, Houston, USA;(3) Present address: Exxon Production Research Corporation, 77252 Houston, TX, USA |
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Abstract: | In order to reduce pileup limitations on μSR data rates, a fast chopper for surface muon beams was built and tested at LAMPF.
The system allowed one muon at a time to be stopped in a μSR sample in the following way: A surface beam from the LAMPF Stopped
Muon Channel was focused through a crossed-field beam separator and onto a chopper slit. With the separator E and B fields
adjusted properly, the beam could pass through the slit. The beam to the μSR sample was turned on or off (chopped) rapidly
by switching the high voltage applied to the separator plates on or off within approximately 500 ns; with the E field off,
the B field deflected the beam, dumping it near the slit. We demonstrated that, with improved electronics, we will be able
to stop a single muon in a μSR sample as frequently as once every 20 μs and that data rates for the system can be a factor
of five higher than is attainable with unchopped beams. The observed positron contamination of the beam was less than five
percent, and the ratio of the muon rate with beam on to the rate with beam off was 1540. |
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