SµS • Swiss Muon Source

General Specifications

• Location: area piE1.
  
• Positive muons, standard momentum 28 MeV/c (other momenta possible).
  
• Degree of polarization >95%.
  
• Direction of spin ~180° with respect to muon momentum (longitudinal polarization; spin rotator for transverse polarization under construction).
  
• Positron detectors: 2 longitudinal, 2 transverse.
  

Detector Arrangement

• A muon detector (M).
• Four positrons detectors (with respect to the beam direction) :
  Forward (F),
  Backward (B),
  Left (L),
  Right (R).
• A backward veto detector (B_veto), consisting 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 cup-shaped forward veto detector (F_veto) for use with samples that do not cover the entire beam spot.
  Its purpose is to reject muons (and their decay positrons) that have missed the sample.
  When the sample/holder assembly stops all muons, the F_veto signal may be added to the F signal to increase the forward solid angle.
  

Available drawings of the detector arrangement:

• GIF :
  Horizontal cross section (15 kB).
• PostScript:
  Horizontal cross section (160 kB).

Sample Environment

Cryostat

• Type: Oxford Variox (top loading, sample in He-4 exchange gas).
• Temperature range: 1.6-300 K.
• Sample holders: Two sample sticks are available.
• Sample rotation: Remote-controlled 360° rotation of the sample stick for orientation-dependent measurements can be made available on request. Please contact the instrument scientist.
• Manual: is available.
• Liquid He is supplied in two 100 litre dewars. While one dewar is in use, the second one is being refilled by PSI staff at the filling station in the experimental hall (west gallery). Therefore it is vital that the empty dewar is immediately brought back to the filling station and not left in the area. Contact the instrument scientist for help. The dewars should not be emptied completely. Leave about 10% level.

         In preparation:  Oxford Heliox He3 insert for the temperature range 0.3 -- 300 K (contact the instrument scientist).

Sample Size and Recommended Sample Mount

• Sample chamber (Variox): Free diameter 31 mm, distance from bottom of sample chamber to center of beam spot is 41 mm.  A sample of 10 mm diameter and a thickness of 0.2 g/cm^2 at the correct position will stop the majority of the incoming muons.
• Drawings of the sample region (Variox with Heliox insert) are available here.
• Sample holder: Drawings of the sample holders recommended are available (standard / modular).
• Please note:
  • The users are expected to bring their own sample holders and to 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.

Temperature Control (see manual)

 Temperature Sensor History  is here.

Magnetic Fields

• Main field (WEU): 0-0.49 T parallel to the beam (the coil design allows 0.8 T when an appropriate power supply becomes available).
  
• Auxillary field (WEV): 0-15 mT perpendicular to the beam.
• Earth-field compensation: Two pairs of coils for the components perpendicular to the beam (horizontal and vertical) and one pair for the component parallel to the beam (longitudinal). Compensation is usually better than 0.001 mT for all components.
   

Electronics / Data Aquisition

A manual for the acquisition software deltat is available in HTML fomat or in PDF format

Logic Diagram

• The logic diagram is available as pdf-file (780 kB).

Computers

• DAQ Linux Backend
• DAQ Windows XP Frontend
• Linux Console: PC6169 running Scientific Linux 3 for run control (deltat), user PC5531 for analysis etc.
• PC SEP1 (Windows XP) for control of separator
• Area PC: Intel processor running under Windows XP. Standard software: beam-line programs (Set Point, Optima etc.), remote printing and plotting (VPP), Netscape, Norton pcAnywhere, WS_FTP. 

The secondary beam-line control system controlling all beam-line elements (magnets, slit systems, separator etc.) between the target station and the experiment consists of a CAMAC crate containing the interfaces and modules needed for the beam line, a server PC (connected via RS232 to the CAMAC crate) and an area PC. The server and area PC's are connected via Ethernet.