3D Temperature Monitoring for Ultra-High Vacuum Spectrometers in KATRIN Experiment

A crucial phase of the KATRIN (Karlsruhe TRItium Neutrino) experiment involves the heating and cooling of both spectrometer vessels to obtain a UHV (Ultra-High Vacuum). These large vessels are hidden under a thick (~40cm) thermal insulation layer, making non-contact observation of the temperature distribution of the vessel surfaces impossible. Therefore, about 400 temperature sensors are mounted directly along the surface of the vessels beneath the insulation layer. The temperature data is acquired and visualized in real-time using the software NI LabVIEW and NI DIAdem INSIGHT from National Instruments. INSIGHT allows the visualization of measurement data on a 3D-CAD-model of the object. In this application color shading of the model surface indicates real-time temperature changes on the vessel. INSIGHT also allows the user to rotate and zoom the model, providing easy visual access to real-time measurement data at any position of a complex object. In the KATRIN experiment the resulting 3D-view of the vessels with a colored temperature profile on the surface allows the operator to monitor heating and cooling processes and to avoid vacuum leaks that may occur due to thermal stresses.

Introduction

The Karlsruhe Tritium Neutrino Experiment KATRIN aims to measure the mass of the electron neutrino with a high degree of accuracy, improving the sensitivity of its current value of 2.2eV/c2 by one order of magnitude to 0.2 eV/c2 (3s) corresponding to a 5s discovery potential of 0.35 eV/c2.



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Fig. 1: General View of KATRIN Experiment

Spectrometers Vacuum Requirements

The experimental system consists of two spectrometers and has an overall length of ~70m (Fig 1). They serves as a very precise filter that rejects all electrons with energies less then 200 eV below the endpoint E0 because they carry no information about the neutrino mass. The most important parameter for both components is the extreme ultra-high vacuum (UHV) of below 10-11 mbar which minimizes the background effects of any residual gas on the energy measurement. To achieve this, several vacuum pump systems are used together with heating (outbaking) and cooling of the surfaces whilst running KATRIN experiment.

Diadem and Temperature Visualization

The heating or cooling of an object of about 24 m length and 10 m diameter (main spectrometer) is a major technical challenge of itself. It has to be carried out very uniformly to avoid induced mechanical stresses due to varying temperatures of different parts of the spectrometer. Therefore temperature control of the surface plays a crucial role in this procedure. Thermal imaging camera techniques are not suitable for monitoring the surface temperature, because both spectrometers are covered by a thermal insulation layer of 40 cm thickness.




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Fig 2, Data Path


Therefore, about 120 temperature sensors are used for the prespectrometer and about 300 sensors for the main spectrometer. The data is collected using compactFieldPoint banks and a LabVIEW program running on the operator’s Control PC communicating with the hardware via an OPC (OLE for Process Control) connection (Fig. 2). For online visualization of the temperature data of both vessels 3D-displays are used (Fig. 3,4).


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Fig. 3: 3D Model of Pre-Spectrometer



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Fig 4: 3D Model of Main Spectrometer


The software was built with the help of NI DIAdem INSIGHT where each temperature signal is assigned to a grid point of the 3D-CAD-model of the vessels according to the position of the respective sensor (Fig. 5).


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Fig. 5: Grid point view of the pre-spectrometer 3D-CAD model

Using a configurable temperature color scheme, the current temperature values are visualized online as color shading on the models surface. This allows the operator to observe easily the temperature distribution on the very complex shapes of both spectrometers. It also offers rich graphical presentation features for rotating and zooming of the object in order to inspect any point of interest.
In the KATRIN experiment the resulting 3D-view of the vessels with a colored temperature profile on the surface (Fig. 6) allows the operator to easily monitor and influence the heating and cooling processes in order to avoid thermal stresses that otherwise could result in vacuum leaks.



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Fig. 6: Colored temperature profile of prespectrometer.First tests at the prespectrometer of KATRIN experiment showed a good consistency between data and object’s color shading. Such application can be used to monitor remote processes and display data from any kind of measurements on predefined 3D-models of objects with complex profile.

References

[1] See the KATRIN Design Report at http://www-ik.fzk.de/katrin
[2] National Instruments Corporation http://www.ni.com/insight

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