General Purpose Surface-Muon Instrument (GPS)

Written Documentation available

A short list of what is new in 2015 is available here (PDF).

A User Guide is available containing useful information on the sample environment, field, beam, etc... The guide is available in a PDF Version (2.0 Mbytes).
Quick References are also available:
A manual for the acquisition software deltat is available in PDF format or in HTML format

A manual for the new electronics (so-called TDC-Electronics) is available in PDF format] or in HTML format

General Specifications

  • Location: area piM3.2
  • Positive muons, standard momentum: 28MeV/c)
  • Muon polarization >95%
  • Direction of spin ~10-55° with respect to muon beam axis
  • Positron detectors: 2 longitudinal, 4 transverse
  • Look also here to obtain information on our Muon On REquest ("MORE") setup.

Detector Arrangement

The detector arrangement consists of A muon detector (M) 6 positron detectors (with respect to the beam direction): Forward Backward Up Down Right Left A Backward veto detector (B_veto).

This detector consists of a hollow scintillator pyramid with a 7x7 mm hole facing the M counter. The purpose of B_veto is to collimate the muon beam to a 7x7 mm spot and to reject muons (and their decay positrons) missing the aperture ("active collimation"). A forward veto detector (F_veto), rejecting muons which have not stopped in the sample (and their decay positrons). It is used with small samples. When the sample/holder assembly stops all muons, F_veto can be added to the F detector to increase the forward solid angle.

Sample Environment


Type: Quantum Technology Corp. "top (or side) loading" continuous-flow He-4 evaporation cryostat. Sample in He-4 exchange gas. Temperature Range 2-300K, liquid-He consumption approx. 2.5l/h at base temperature. (Liquid He comes in dewars with approx. 230 litres capacity). Liquid He is supplied at regular intervals (Mondays and Fridays) at the filling station in the experimental hall (west gallery). While the orders for liquid He are placed by the instrument scientist, the users are expected to take care of the transport of the He dewars betweeen the filling station and the experimental area, to change them on the specified days and to return empty dewars immediately to the filling station. Two sample holders per cryostat allow fast sample change. Remote-controlled sample rotation (360°, rotation axis perpendicular to muon polarisation). For the manual, please look into the GPS User Guide (PDF-format or Postscript-format)

Maximum Sample Size and Recommended Sample Mount Free diameter of the sample chamber: 23mm. Maximum sample length (including mount): 45mm. Sample region drawing available in GIF (12kB) or PostScript(80kB) format. Sample holder platform as in the CCR and Janis cryostats of the GPD Instrument. Drawings of a possible sample mount are available here. For more details please contact the Instrument Scientist.

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.


Type: Janis with Sumitomo Heavy Industries Cold-Head: "top (or side) loading". Sample in He-4 exchange gas when operated between 4K and 300K. Used as a "warm finger" when operated between 300K and 475K. Installed on the 2nd cryogeny port. For the manual, please look into the GPS User Guide (PDF-format)

Zürich Oven

Type: Zürich University design. Used as a "warm finger" when operated between 300K and 1000K. For the manual, please look into the GPS User Guide (PDF-format) Magnetic Fields

Main magnetic field (WED): 0-0.6T parallel to the beam Auxillary field (WEP): 0-10mT perpendicular to the beam Earth-field compensation is usually better than 0.001mT for all directions. To cope with the external magnetic field sources present in the Experimental Hall, an automatic compensation is now performed. When performing experiments in zero-field mode, the compensation is done dynamically to ensure true zero-field conditions independently of the status of the external magnetic field sources.

When performing experiments in applied-field, the compensation is done according to tabulated values depending on the status of the external magnetic field sources.

Electronics / Data Aquisition

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 new ftp-server (


The TDC electronics is characterized by a logic performed exclusively at the software level. A manual is available in PDF format] or in HTML format. Also the main Manual of GPS (GPS User Guide) provides information about the logic diagram.


The area is equipped with a Experiment Console (running Scientific Linux) pc11318. The µSR data acquisition system hardware consists of this console and a Linux back-end server (psw415) located in the computing building (Hauptgebäude). This back-end is connected to a front-end PC running Linux controlling the VME data acquisition electronics.

A number of different devices (temperature controlers, magnetic field power supplies, etc...) are used for the slow control of the experiment. These devices are mainly controlled via GPIB (IEEE-488) bus, RS-232 serial line, TCP port or EPICS Process Variables. GPIB : The GPIB devices are controlled through a Agilent LAN/GPIB Gateway (E5810A). RS-232 : The RS-232 devices are controlled through either a Moxa Nport 5150 which supports one RS-232 line or a Lantronix ETS8PS 8-channel RS232 terminal server.

The acquisition software deltat is based entirely on the DAQ software package MIDAS.

Two Linux Workstations (PC11319 and PC8577) are also available and can be used through a usual AFS account or a local account (ask the instrument scientist for information). From these machines, one can connect also to the Linux cluster.

The HIPA secondary beam-line control system controls the beam-line elements (magnets, slit systems, etc.) between the target and the experiments. For the GPS and the LTF instrument the area is equipped with an EPICS Console (hipa-pim3) located in the GPS counting room to set the EPICS Process Variables of the beam-line elements, to optimize beam settings and to diagnose.


Information about how to print at PSI is available is available only through the intranet at PSI.

Printing from Unix and Linux is performed using the CUPS system. The nearest printer is WEHA_PIM3_1 on the passage between the GPS counting room and the LTF barrack. There is another color printer located in the blue cabin near the piE5 area named WEHA_E5_2.

From UNIX/Linux-Cluster you can either use the glp command and choose the appropriate printer (WEHA_PIM3_1 or 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_PIM3_1 or WEHA_E5_2). Right click and choose Install...