| 摘要 |
A cryostat-screen for measurements of magnetic susceptibility of materials in strong magnetic fields up to 10 tesla intended for screening against external electromagnetic noises of samples of materials at implementation of supersensitive measurements by means of SQUIDs for study of structural properties of those materials is a Dewar vessel and includes metal vessel for liquefied nitrogen (nitrogen tank), vessel for liquefied helium (helium tank) in which measuring volume is placed, with holder for sample and controller of temperature of measured sample, and superconductive solenoid that generates magnetic field for magnetization of the sample. The helium tank is surrounded with radiation screens and screen-vacuum thermal insulation and is placed to thick-wall metal body that has a temperature of environment. The helium tank does not have non-split joints of different metals. The helium tank is made of metal with high level of purification that in presence of strong magnetic fields does not have residual magnetization at helium temperatures and at cycles of cooling-heating – does not have structural transitions as well. To the outer side of the body of toroidal nitrogen tank suspended nitrogen screen is attached, this is arranged as multi-layer construction shells of which to each other and to the body are fixed by means of dielectric plates with high thermal conductivity. Between the additional nitrogen screen and the body of cryostat, to mouth of the cryostat, heat screen is fixed, at that dimensions and positions of all radiation screens and helium tank are arranged with account of thickness of skin-layers of metals of which those are made, at working temperatures of those, minimum of effects on signal measured from the sample, and minimal duration of decay of natural electromagnetic pickup as well. The screens are made of metal strips without electric contact between those. At least one cavity between any neighboring screens is filled with screen-vacuum thermal insulation, or between helium screen and helium tank. |
