Fast closing shutter

 

The windowless connection of experiments to large ultrahigh vacuum (UHV) systems like storage rings include the risk of accidental venting provoked by operational errors or bursts of a vacuum-parts at the connected experiment. The consequent shock wave enters the evacuated system at a speed of about 1000m/sec. Fast closing shutter (FCS) systems with closing times in the 10msec range are mandatory, to stop the shock wave of such an event. The strong radiation background in storage ring tunnels requires the installation of all metal valves.

A new small fast closing shutter with a closing time <10msec was developed. The all metal sealing principle achieves leak rates smaller than 10mbarl/sec. This leak rate of FCS combined in the case of a storage ring application with an all metal valve prevents venting of the whole system and thus beam time losses for all users
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Problem

The previous UHV-compatible FCS type developed at the “Deutsches Elektronen Synchrotron” DESY for large apertures (40 x 200mm2) is characterized by a complex in vacuum drive unit of the shutter plate. This complicated in vacuum design has disadvantages regarding to UHV-compatibility, maintenance and compactness.
More compact FCS systems require a different mounting of the shutter plate with matched drive and release units outside the UHV system.

Innovation

The new compact FCS is characterised by the following properties:

  • A flexible joint serves as guidance of the shutter plate inside the UHV system.
  • The vacuum pipe which forms the plate seat is shaped elliptical. A setting angle of the valve seat results in a circular shutter plate.
  • The plate drive of the FCS is located outside the vacuum.
  • The design of the release latch (outside the vacuum) enables small trip delays.
  • The FCS module can easy be separated from the plate seat and simplifies the maintenance.
  • The closing time is less than 10 msec.

Benefit

The presented fast closing shutter simplifies the shutters which have been used at DESY in the past in a considerable way. The flexible joint of the shutter plate avoids the higher maintenance risk of in vacuum bearings. The complete actuator is positioned outside the vacuum and permits service without breaking the vacuum. The production and the installation of the system are simple.

Development status

More than 20 FCS have been built at DESY. 17 are successful in use at the storage ring PETRA III and the free electron laser experiment FLASH.