Left: drift tube installed in the vacuum chamber. Right: schematic of the drift tube showing the mounting rod fabricated in Alloy K-500.
The Science & Technology Facilities Council (STFC) selected Alloy K-500 to fabricate the inner sleeve of the mounting rod inside its linear particle accelerator. The alloy was chosen because it stays non-magnetic across the operating temperature range, carries a suspended magnet on a thin support, and resists degradation in a chamber that cannot be repaired once it is irradiated.
About STFC
STFC is one of Europe's largest multidisciplinary research organisations, supported by the UK Government. It employs more than 1700 people across two main sites - the Rutherford Appleton Laboratory at Harwell and Daresbury Laboratory near Runcorn - and supports around 800 PhD researchers at any one time. Its research spans fundamental fields including particle physics, nuclear physics and astronomy, with the objective of understanding how the universe works and ultimately supporting the UK economy.
The application
The linear accelerator is an extremely large vacuum chamber used to conduct particle physics experiments. Within this 12m long, 1m diameter tank, particles are accelerated to great speeds by a radio frequency generator and collided with each other. They are focused by passing through drift tubes - the rugby-ball-shaped units seen hanging from the wall in the image.
STFC approached Langley Alloys for a material to fabricate the inner sleeve of the mounting rod. Alloy K-500 met each of the key criteria:
- Non-magnetic over the wide range of operating temperatures, so it does not influence the particle focusing process
- Compatible with the other materials in the fabrication, specifically the thermal expansion coefficient of Alloy 304 stainless steel and copper sheet
- High strength and stiffness to robustly support the suspended magnet on a relatively thin support
- Resistance to general degradation, as units cannot subsequently be repaired due to the presence of radiation in the chamber