Thomson parabola spectrometer

In the summer of 2022, we were approached by a customer from the Institute of Plasma Physics of the CAS with a request for the production of a spectrometer with a Thomson parabola. This is a device used to analyse accelerated charged particles and their energy and charge distribution. The principle of operation is based on deflecting incoming particles from their direct path by means of magnetic and electric fields and then recording their position on a flat panel detector.

In the case of our customer, the spectrometer was to be used to analyse the plasma produced by the interaction of a high-energy laser pulse with a solid target. The main goal of the project was to obtain a device with higher resolution than before, which can be achieved mainly by higher electric and magnetic field strength. Furthermore, the customer's requirement was that the spectrometer be mounted on a movable and angularly adjustable frame so that the system as a whole could be added to the experiment as required.

Although the principle of the Thomson parabola has been known for over a century, the layout and processing quality of the individual parts can have a major impact on the performance of this spectrometer. Thus, great care had to be taken in the design of the assembly itself.

The Thomson parabola spectrometer is at its core a vacuum system. Its main chamber was manufactured according to our own design and then fitted with standard vacuum parts. The achievable vacuum level is around 10-6 mbar. Attached to this chamber is a powerful electromagnet which is capable of generating a field of over 0.7 T via pole attachments located inside.

As a detector, we chose a microchannel plate (MCP) from Hamamatsu with a 2-stage arrangement of MCP elements. The input photocathode is located in the vacuum part of the system, and the output phosphor plate is located outside the vacuum so that a readout camera can be placed next to it.

The spectrometer is mounted on a rigid aluminium frame with castors to allow convenient movement. The connection between the vacuum apparatus and the frame is made via two aluminium plates on top of each other, the position and angle of which can be adjusted to each other, thus ensuring the desired adjustability of the spectrometer's inlet aperture.