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 , 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 . <EOS>