Low-Energy Muon Facility (LEM)

The low-energy muon facility consists of two instruments:
  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

See http://lmu.web.psi.ch/docu/nemu/html.

Electronic logbook:

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
Note, that four sets of decay histograms are saved in the histogram files (two sets for external stimulus off (ExtOff), two sets for external stimulus on (ExtOn)):
  • ExtOff histograms without post-pileup rejection ("npp" histograms), No. 1-8
  • ExtOff histograms with post-pileup rejection ("ppc" histograms), No. 9-16
    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
  • ExtOn histograms without post-pileup rejection ("npp" histograms), No. 17-24
  • ExtOn histograms with post-pileup rejection ("ppc" histograms), No. 25-32
    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:
    • ExtOff npp histograms: IDs 001-008
    • ExtOff ppc histograms: IDs 021-028
    • ExtOn npp histograms: IDs 041-048
    • ExtOn ppc histograms: IDs 061-068

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: normal user operation
  • lowTemp cryostat:
    • 2.4 - 300 K with sample plate, In coated sapphire
    • 2.2 - 300 K without sample plate; sample directly mounted on sapphire
  • Furnace: -50 - 300°C (can be cooled by LN2)
  • Sample size:
    • Ideally 25x25 mm2 or ∅ = 25 mm
    • mosaic of four pieces of 10x102mm
    • 10x10 mm2 possible, but only 30-50% of muons hitting the sample, depending on implantation energy (30% for 1keV, 50% for zero or negative sample bias)
  • Magnets
    • WEW magnet (TF and LF): 0 - 0.34 T parallel to the beam
    • Bparallel magnet (TF and ZF) : 0 - 30 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 pc12438, Linux RHEL7 64-bit, for online analysis and experiment control
  • client pc12439, Linux RHEL7 64-bit, 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

The histogram files are saved in root format (see ROOT web page ). The root histogram files can be converted to psi-bin, TRIUMF mud, and ascii formats, using the any2many program on the Linux client PCs.

On the Linux client PCs histogram files (root and other formats) and online analysis files are accessible on:
  • /mnt/data/nemu/his/, root histogram files
  • /mnt/data/nemu/psibin/, psi-bin histogram files
Online analysis results are usually saved in:
  • /mnt/home/nemu/analysis// subdirectories
After each run, or once per day, files are copied to the nemu afs project disk:
  • /afs/psi.ch/project/nemu/data or
    /afs/psi.ch/project/bulkmusr/data/lem/dYYYY
    where YYYY is the year of the experiment
  • /afs/psi.ch/project/nemu/analysis
For fitting of the µSR data the program musrfit is used. No file conversion is necessary to use it with root, psi-bin, psi-mdu, nexus, mud and several ascii formats.
Documentation is available here.