Design and certification of the chopper disks for the NEAT II TOF spectrometer: A lesson learned

The NEAT II TOF spectrometer utilizes a set of seven chopper disks with an outer diameter of 700 mm and different window configurations with a maximum window depth of 135 mm. A relatively thick (1.5 mm) boron coating is required, together with a maximal operational speed of 20,000 rpm. When the Institute of Lightweight Structures (LLB) of the Faculty of Mechanical Engineering at Technische Universität München was asked to design and produce the set of disks for the instrument, the major challenge seemed to be that of achieving the operational speed in accordance with the given requirements. In particular, the large area with the boron coating, adding a non-structural weight in a highly loaded area, appeared to be the most challenging design parameter. A common cross section for all the disks, which could sustain the load for all the different window configurations, was manufactured. A hub was designed which fitted in the system and fulfilled the given requirements. Due to recurring vibrations at about 16,000 rpm during the certification test, it was not possible to achieve the required rotational speed with the original configuration, although all parts of the system seemed to work properly and no initial failure had occurred. This paper presents all the steps that led to the final design of the system, consisting of disk and hub, which allowed the certification for the desired operational speed.      «

The NEAT II TOF spectrometer utilizes a set of seven chopper disks with an outer diameter of 700 mm and different window configurations with a maximum window depth of 135 mm. A relatively thick (1.5 mm) boron coating is required, together with a maximal operational speed of 20,000 rpm. When the Institute of Lightweight Structures (LLB) of the Faculty of Mechanical Engineering at Technische Universität München was asked to design and produce the set of disks for the instrument, the major challeng...     »