FLexible Advanced MuSR Environment (FLAME)

Location
Area piM3.3

Beam
Positive surface muons with momentum of 28MeV/c

Muon Polarization
~ 100% (spin rotation ~6 - 60 degrees)

Detectors
8 positron detectors + muon detector + forward and backward veto

Sample size
Area: >4x4 mm², Thickness: > 250 mg/cm²

Magnet
Cryogenic Ltd. dry superconducting magnet (up to 3.5 T) with three shim coils for highest homogeneity and vector magnets for zero field compensation, wTF measurements and alpha calibration.

Cryostat
Oxford Instruments Variox cryostat with or without KelvinoxJT dilution refrigerator insert.

Magnetic Field

Magnetic field up to ±3.5 T can be applied along the beam by using the dry Cryogenic Ltd. superconducting magnet. Shim coils may be used to improve homogeneity of the magnetic field in the sample space which is better than 10ppm.

Three vector magnets, X (vertical, ±200G), Y (horizontal, ±100G), and  Z (longitudinal, ±100G) can be used to adjust for true zero field conditions better than 50 mG. They also be used for weak longitudinal and transverse µSR as well as alpha calibration.

Cryostat

The experiment is equipped with a Oxford Instruments Variox cryostat and a KelvinoxJT dilution fridge insert.

Variox with sample stick
 Temperature range: ~ 1.8 K < T < 300 K

Variox with the KelvinoxJT dilution fridge insert
 Temperature ranges:
 ~ 30 mK < T < 2.5 K with circulating mixture with a weak link
~ 1.8 K < T < 100 K passively using KelvinoxJT as a sample stick inside Variox

Sample size and holder

Two samples can be mounted simultaneously  (both the Variox sample stick and the KelvinoxJT). During the experiment, the cryostat can be moved from one sample to the other. Each sample should at least cover an area of >4x4 mm² with a thickness: > 250 mg/cm².
A drawing of the sample holder is available here. 

Detector Arrangement

8 positron detectors + muon detector + forward and backward veto

Eight positron detectors are arranged around the sample. Each scintillator is directly connected to the silicon photomultipliers (SiPM), which are unaffected by the magnetic field up to 3.5 T and ensure a time resolution of about 150ps. A backward veto system acts as active collimator and the forward veto rejects muons which did not stop in the sample. Both veto systems also reject decay positrons that did not originate from the sample region.

Front-end Electronics

The TDC electronics is characterized by a logic performed exclusively at the software level.

A manual (html / pdf) is available.

The acquisition software DeltaT (html / pdf) is based entirely on the DAQ software package MIDAS.

Computers

The µSR data acquisition system hardware consists of a frontend PC running Scientific Linux and controlling the VME DAQ unit which is located in the GPS counting room and a Linux back-end server (psw422) located in the central computing center at PSI.

There are several PCs in the FLAME counting room for instrument control and data analysis. The area is equipped with a Linux PC for instrument control as well as with two Windows PCs which run the dedicated operation software for the KelvinoxJT dilution fridge and the superconducting magnet.

Printer

• WEHA_PIM3_1 in the FLAME counting room

The histogram files are saved in the MusrRoot format, see Software and Data storage for more information.

On the Linux client PCs histogram files are accessible on:

• /afs/psi.ch/project/bulkmusr/data/flame/dYYYY
   where YYYY is the year of the experiment

Files can be retrieved via the discovery.psi.ch data catalog and via the database on musruser.psi.ch .

For fitting of the µSR data the program musrfit is used. This package also contains a conversation tool called any2many to convert between different µSR file formats.
The documentation of musrfit is available here.

• Project Description