MEPHISTO (under construction)

MEPHISTO scheme

Since the start of user operation, the FRM II provides a cold white neutron beam for long-term user-dedicated experimental set-ups.

Such an experiment is normally planned and built up by external groups, but additional help during the commissioning of the experiment is necessary. So, this work must be organised closely with the local instrument scientist. The desired precision is reached inter alia by good statistics, which means long-term experiments over several reactor cycles.

The experimental area MEPHISTO, the measurement facility for particle physics with cold neutrons, is dedicated to experiments in the field of nuclear and particle physics. Currently, the experimental area moves from the Neutron Guide Hall West to the Neutron Guide Hall East. The solely used neutron guide SR-4b will deliver a white cold spectrum for experiments. A removable 11% velocity selector at the end of the guide will complete the beam line.

The MC-simulation for this beam with a dimension of 60 × 106 mm² proposes a mean wavelength of 4.5 Å and a gold capture flux of 2 ×10¹⁰ n cm^-1 s^-1. The experimental area is 5 × 25 m², diagonally built-in in the Neutron Guide Hall East. The spectrum shows a shoulder to smaller wavelengths, and the maximum of the spectrum is located at 3.3 Å.

Currently, the instrument PERC [1] is installed at MEPHISTO for the first years of operation in the Neutron Guide Hall East. This instrument is a precise, bright, and intense source of protons and electrons from the neutron decay. The instrument PERC itself is open for external user groups with spectrometers to measure the protons and electrons.

[1] Dubbers, D. et al., NIM- A 596, 238 (2008).