General Purpose Decay-Channel Spectrometer (GPD)

General Description

  • Beam properties:
    • Area: µE1
    • Positive or negative muons: momentum ranges ~60-125MeV/c.
    • Muon range: ~1.5-20g/cm2, range width ~30mg/cm2-~4g/cm2 FWHM in CH2.
  • Polarization: Longitudinal (direction of the muon momentum; no spin rotation).
  • Collimation: Cylindrical collimation with dia. 16, 12, 10, 8, or 6mm. Rectangular collimation 4x10 mm.
  • Collimated beam: Beam profile monitor is available for checking quality of beam and tuning collimator positoins in magnetic field (see instructions here ).
  • Degrader: Silver or kapton layers are used as muon degraders.
  • Detectors (fast plastic scintillators, Hamamatsu-PTs R1828-01, PSI voltage deviders PHVR100,  iseg HV-powersupply HPp 30 107):
    • Incoming muons: 'M' (between collimator and sample; 2mm thick plastic scintillator).
    • Decay positrons (electrons): 'forward' (single, fork), 'backward' (single, fork),  'up' (pair), 'down' (pair), 4mm thick each.
    • System time resolution: ~1ns.
    • For more information on the detectors click here.
  • Magnetic fields operating instructions
  • Static zero field compensation (dynamic compensation is in preparation).
    • Main field 0-0.66T, parallel or perpendicular to the muon spin (rotatable coils).
  • Remotely controlled movable parts: The following parts are equiped with stepper motor drives and can be controlled by DELTAT under Modify Devices... smngpd...: GPD_VERTICAL, GPD_HORIZONTAL, DEWAR, DEGRADER, COLLIMATOR and DETECTOR (more channels are available).
Please note: It is extremely dangerous to run the motor drives without checking the free mobility. Because in most cases remote motion is necessary when working with transverse field, instructions and warnings are given in detail under operating instructions for magnetic fields and for the motor drives. Please read it carefully.
  • Available temperature range 0.3 - 500 K using different types of cryostats (see below).


Recommended Sample Holder and Maximum Sample Size:

For an overview of all available drawings, click here.  Please note:
  • The users are expected to bring their own sample holders and make sure that the samples are safely sealed and fixed on the holder.
  • Users who intend to bring hazardous sample materials (radioactive, toxic, flammable, etc.) to PSI should read the instructions on our safety page well in advance of their scheduled beam time.

Available Sample Cryostats 

Oxford Sorption Pumped 3He Cryostat type Heliox/Variox

The VARIOX-cryostat is a top loading 4He-bath cryostat with variable temperature insert useful in the temperature range 0.3 - 300 K (details). The large sample chamber (50 mm diameter) is filled with 4He contact gas and contains the sample suspended on a sample stick. Alternatively, the sample stick can be replaced by a 3He-insert type HELIOX.

The HELIOX-insert is a sorption pumped single-shot 3He-cryostat. Its main components, the sorption pump, the condenser and the 3He-pot are connected to form a closed 3He-system. The 3He-pot is inclosed in a separate vacuum chamber which also contains the sample mounted on the pot. The sorption pump and the condenser are cooled through the 4He contact gas by the VARIOX variable temperature insert.
  • Temperature Range: 0.3 - 300 K
  • Holding Time: >40 hours
  • Coolant
    • 40 litres/day liq-4He consumption, automatic refilling
    • 10 litres/day liq-N2 consumption, automatic refilling
  • Maximum Sample Size: 40 mm diameter. See a drawing with main dimensions.
The system is relatively easy to operate. A specialized Mercury iTC temperature controller called "Heliox" must be used to control the temperature of the VARIOX-cryostat and the 3He-insert and to automatically handle the recondensation. However, sample change is rather time consuming. It takes 6 - 8 hours to change a sample in the HELIOX including cooling down.

A standard Mercury iTC temperature controller ("Variox") must be used to control the temperature of the VARIOX-cryostat and the sample stick.
  • Sample rotation: 0 - 360o available on request
For more details refer to the QUICK REFERENCES Manual.

Janis 4He Vaporizer Cryostat2)

Top loading type with continuous He-flow through sample chamber, mounted on vertical spectrometer axis, sample rotation about vertical axis, pneumatic retraction of the sample from beam axis.  (more details to be published soon).
  • Temperature Range / Coolant
    • 2.5 - 300 K
    • 4 - 0.7 litres/hour LHe at 4 - 25 K
    • 0.7 - 0.4litres/hour LHe at 25 - 75 K
    • 0.4 - 0.2 litres/hour LHe at 75 - 300 K
  • Sample rotation: 0 - 360o available on request
2) Please Note: the Janis and Oxford cryostats can only be allocated separately in larger beam-time blocks (separated by at least one week) because of long changeover times.

For more details refer to the QUICK REFERENCES Manual.

Closed-Cycle Cryostat (CCR)3)

  • Cold finger type CCR, no contact gas. Mounted on horizontal spectrometer axis. Temperature Range / Coolant
    • 10 - 300 K
    • No coolant (He-gas compressor) Recommended Sample Holder and Maximum Sample Size: For an overview of all available drawings, click here.

New Chemistry Cryostat3)

Top loading type with continuous N2-gas flow through sample chamber, mounted on horizontal spectrometer axis (details).
  • Temperature Range / Coolant
    • 80 - 500 K
    • Coolant: liquid N2
    • Recommended Sample Holder and Maximum Sample Size: Special design for glass bulbs, max. bulb diameter 35 mm, cylindrical shaft 8 mm diameter, adjustable sample stick length. Drawing.
3) Note: CCR and New Chemistry Cryostat use the same vacuum chamber. Changing cryostats is easy.

Temperature Control

  • A LakeShore Model 336 controller for CCR, New Chemistry liq.N2 and Janis 4He in a rack on the platform in the area. The first heater of the controller is used to control the 10K-CCR-Cryostat in single-loop mode or the Janis 4He-Cryostat or the Chemistry-Cryostat in two-loop mode using the second heater as the second loop. Click on the cryostat name to see the PID and gas flow tables for CCR, New Chemistry and Janis (to be published soon).
  • Two OXFORD Mercury iTC controller for Oxford VARIOX-cryostat and 3He in a rack on the platform in the area.

Electronics / Data Acquisition

Data Format and Storage The users are responsible to store in a safe place their own data. Every week a backup of the data is performed in the PSI Archive system and the specific muSR ftp-server (see here for more information). You are strongly adviced to retrieve your data ("bin"-format) using our new ftp-server.


The new TDC electronics is characterized by a logic performed exclusively at the software level. A manual is available in PDF format and HTML format.

For the old electronics, the logic diagram based on the PTA ORTEC 9308 Unit is available here.

A manual for the DELTAT graphic-users-interface application is also available in HTML format and PDF format.


  • The Experiment Console (PC11317 running Scientific Linux) is located in Studio A. You can start the programm DELTAT on this machine.
  • A Midas Back-End Linux-PC (PSW412) for the data acquisition system is located in WHGA/U121.
  • A Linux-PC (PC9684) for local access to the AFS-files by PSI-software e.g. LOOK_MUSR (local account name: l_musr_tst, ask instrument scientist for password).
  • A Windows-PC (PC8576) used for remote control (vnc) of the Area-PC (PC7746) is located in Studio A.
  • The HIPA secondary beam-line control system controls the beam-line elements (magnets, slit systems, etc.) between the target and the experiment. The area is equipped with an EPICS Console (hipa-mue1) to set the EPICS Process Variables of the beam-line elements, to optimize beam settings and to diagnose. Please don't use this PC for other applications.
  • A Windows-PC used for Camera Control is located on the platform in the area (PC7746).
  • A Linux Workstation (PC12023) controlling the VME data acquisition electronics.
  • A number of different devices (e.g. temperature controllers, Gossen magnet power supply, etc.) are controlled by the Deltat slow control 'front ends'. Modify Devices or Exp. Magnets by means of GPIB bus, RS-232 serial line, TCP port or EPICS Process Variable.
    • An Agilent LAN/GPIB Gateway is used in Studio A (psgs009) for the Gossen magnet power supply.
    • A Lantronix ETS8PS 8-channel RS-232 terminal server (psts220) located in the area is used to control the stepper motor drive controller and other devices.
    • A Moxa Nport 5110 1-channel RS-232 terminal server (psts266) located in Studio A to control the high voltage power supply Iseg HPx30107.


Information about how to print at PSI is available here (reachable only through the intranet at PSI).

Printing from Unix and Linux is performed using the CUPS system. The nearest printer located in the blue cabin near the piE5 area has the name: weha_e5_2.

From UNIX/Linux-Cluster you can either use the glp command and choose the appropriate printer (WEHA_E5_2). You can also set the environment variable PRINTER to be equal to the name of your printer, and use the lpr command.

For more information on CUPS, just look here.

To print from a Windows Laptop, one should just install the corresponding printer:

Click the Start button and choose Run... option. When prompted for a command just type \\winprintw\ If a account and password is requested, just use "guest" as account and disregard the password by pressing ENTER On the list choose the corresponding printer (WEHA_E5_2). Right click and choose Install... Top