Multi-channel magnetic flux detector comprising a magnetometer modular construction in a vessel containing a cooling medium

DETAILED DESCRIPTION With the present invention, a substantial improvement to the prior art is gained.
The features characteristic to this invention are as follows.
The body of the instrument has been subdivided into separate modules that are easily disconnected and assembled; these modules have been attached to each other by means of commercially available connectors.
Especially the neck plug of the insert is made of stiff thermal radiation insulation, which also effectively prevents backward convection, and of ribbon cable made of parallel twisted pairs of resistive wire; they make up a single piece that acts as a support structure.
The invention has several advantages.
Especially the neck plug is of solid and light construction, a good thermal insulator but at the same time, constructionally simple.
The plug-like structure prevent effectively the turbulent convection between the radiation shield baffles, and the thermal conductivity of the foam plastic used is small.
The foam plastic plug can be thought as a continuous stack of radiation shield baffles; the emissivity as compared to conventional metallic baffles is poor, though, but this drawback is effectively compensated by the large number of the "equivalent floating baffles".
To equalize the lateral temperature distribution inside the plug, metallic plates inside the foam plastic can be used.
By making the gap between the neck of the dewar and the radiation shield plug narrow enough, the cooling by the outflowing cold helium gas can be effectively utilized.
Especially, if the cables are placed against the outer wall of the neck plug, a good thermal contact with the outflowing gas is reached, and the amount of heat conducted via the cables is reduced.
This heat leak can be made completely negligible by choosing a conductor material of high resistivity.
However, because the thermal noise of the sensors increases as well, this solution cannot be used as such.
Here, the problem has been solved by compensating the excess noise, for example by increasing the SQUID gain be means of positive feedback