A cryostat, comprising - a first helium tank, which is filled in a lower part with liquid helium, in particular superfluid helium, at a temperature < 2.5 K and in an upper part at least partially with liquid helium, in particular normal fluid helium, at a temperature > 4 K, such that the first helium tank has a first area that is continuously filled with liquid helium from a lower end of the lower part to a first liquid surface in the upper part, - a Joule-Thomson cooling unit, with which the liquid helium in the lower part of the first helium tank can be cooled by expanding helium via a heat exchanger, - a second helium tank, which is at least partially filled with liquid helium, in particular normal fluid helium, at a temperature > 4 K, such that the second helium tank has a second area that is continuously filled with liquid helium from a lower end of the second helium tank to a second liquid surface in the second helium tank, wherein the first helium tank and the second helium tank are separated from each other in a liquid-tight manner at least below the liquid surfaces (27, 28), wherein the Joule-Thomson unit for cooling the lower part of the first helium tank can withdraw liquid helium from the second helium tank - directly via drawing liquid helium from the second helium tank, - or indirectly via evaporation of liquid helium from the second helium tank, recondensing the evaporated helium in the upper part of the first helium tank, and drawing liquid helium from the first helium tank, and wherein - a thermal barrier is arranged between the upper and lower part of the first helium tank, in which a temperature gradient of at least 1 Kelvin is formed and/or an interface runs between superfluid helium and normal fluid helium and/or - the first helium tank comprises an access tube that is narrower than a section of the first helium tank lying thereunder, such that in the access tube, a temperature gradient of at least 1 Kelvin is formed and/or an interface between the superfluid helium and normal fluid helium is present in the access tube. - a first helium tank, which is filled in a lower part with liquid helium, in particular superfluid helium, at a temperature < 2.5 K and in an upper part at least partially with liquid helium, in particular normal fluid helium, at a temperature > 4 K, such that the first helium tank has a first area that is continuously filled with liquid helium from a lower end of the lower part to a first liquid surface in the upper part, - a Joule-Thomson cooling unit, with which the liquid helium in the lower part of the first helium tank can be cooled by expanding helium via a heat exchanger, - a second helium tank, which is at least partially filled with liquid helium, in particular normal fluid helium, at a temperature > 4 K, such that the second helium tank has a second area that is continuously filled with liquid helium from a lower end of the second helium tank to a second liquid surface in the second helium tank, - directly via drawing liquid helium from the second helium tank, - or indirectly via evaporation of liquid helium from the second helium tank, recondensing the evaporated helium in the upper part of the first helium tank, and drawing liquid helium from the first helium tank, - a thermal barrier is arranged between the upper and lower part of the first helium tank, in which a temperature gradient of at least 1 Kelvin is formed and/or an interface runs between superfluid helium and normal fluid helium and/or - the first helium tank comprises an access tube that is narrower than a section of the first helium tank lying thereunder, such that in the access tube, a temperature gradient of at least 1 Kelvin is formed and/or an interface between the superfluid helium and normal fluid helium is present in the access tube.