Low-Energy Muon Facility (LEM)

1) the source of the low-energy muon beam and the low-energy muon beam transport system (the µE4 surface muon beam line, the cryogenic moderator to convert energetic muons to epithermal muons, and a system of electrostatic elements for reacceleration and low-energy muon transport)

2) the low-energy µSR spectrometer (LE-µSR).

Documentation

Electronic logbook:

• lem00, web access http://lem00:8000 (PSI intranet only)
• pc8582, elog mirror of lem00, readonly, web access http://pc8582:8000 (PSI intranet only)

General Specifications

• location: area mue4
• Positive muons
  • momentum of muE4 beam: 27.7 MeV/c
  • momentum(energy) of low-energy muon beam: 0.45 - 2.5 MeV/c (1 - 30 keV)
  • mean range of low-energy muon beam: 10 - 200 nm
• muE4 muon beam polarization >90%; low-energy muon beam polarization >90%
• Direction of muon spin at sample: -90 - +90° where +90° is in beam direction
• Positron detectors: 8;
  4 downstream detectors Left/Top/Right/Bottom (with respect to muon momentum)
  4 upstream detectors Left/Top/Right/Bottom

Detector arrangement

• The muon detector, "trigger detector" (TD), about 0.5 m upstream of the sample
• With WEW magnet: eight positron detectors (with respect to the beam direction):
  • Left downstream (LD), histogram 1
  • Top downstream (TD), histogram 2
  • Right downstream (RD), histogram 3
  • Bottom downstream (BD), histogram 4
  • Left upstream (LU), histogram 5
  • Top upstream (TU), histogram 6
  • Right upstream (RU), histogram 7
  • Bottom upstream (BU), histogram 8
• With Bparallel magnet: four positron detectors (with respect to the beam direction):
  • Left downstream (LD), histogram 1
  • Right downstream (RD), histogram 3
  • Left upstream (LU), histogram 5
  • Right upstream (RU), histogram 7

• histograms without post-pileup rejection ("npp" histograms), No. 1-8
• histograms with post-pileup rejection ("ppc" histograms), No. 9-17
  Use this set of histograms, if background is not fitted but is determined at "negative" times;
  Statistics is reduced by 7-10% compared to npp histograms
• histogram identifiers in the original root files:
  • npp histograms: IDs 1-8
  • ppc histograms: IDs 21-28

Sample environment

• Konti flow cryostats, 4 - 320 K at sample plate
  • Konti-1: for special experiments (current injection, illumination with LEDs) and tests
  • Konti-2: normal user operation
  • Konti-3: normal user operation, application of electric fields, current injection
  • Konti-4: testing small sample plates (42 mm diameter instead of 70 mm)
• lowTemp cryostat:
  • 2.7 - 300 K with sample plate
  • 2.3 - 300 K without sample plate; sample directly mounted on sapphire
• Furnace: RT - 200°C, commissioning planned in 2013
• Sample size:
  • Ideally 25x25² mm or ∅ = 25 mm
  • mosaic of four pieces of 10x10²mm
  • 10x10² mm possible, but only 30-50% of muons hitting the sample

Magnetic Fields

• WEW magnet (TF and LF): 0 - 0.34 T parallel to the beam
• Bparallel magnet (TF and ZF) : 0 - 25 mT, vertical, perpendicular to the beam

Data acquisition server and analysis clients

• DAQ server: lem00, midas access through http://lem00 (PSI intranet only).
  (backup system: pc8584)
• client pc8581, Linux SL54, for online analysis and experiment control
• client pc7962, Linux SL51, for online analysis and experiment control

Printers in LEM counting room

• WEHA_LEM_1: black/white, duplex
• WEHA_LEM_2: color, duplex

Data format, storage and analysis

On the Linux client PCs histogram files (root and other formats) and online analysis files are accessible on

• /mnt/data/nemu/his/<year>, root histogram files
• /mnt/data/nemu/psibin/<year>, psi-bin histogram files
• ...

• /mnt/home/nemu/analysis/<year>/ subdirectories

• /afs/psi.ch/project/nemu/data
• /afs/psi.ch/project/nemu/analysis

For fitting of the µSR data the program musrfit is used. No file conversion necessary to use it with root, psi-bin, psi-mdu, mud, nexus, and several ascii formats. Documentation is available here.