Cryostat with a first and a second helium tank, which are separated from one another in a liquid-tight manner at least in a lower part

A cryostat comprising:

• a first helium tank, which is filled in a lower part with subcooled liquid helium at a temperature <2.5 K, and which is filled in an upper part at least partially with normal fluid helium, such that the lower part of the first helium tank is continuously filled with liquid helium between a lower end of the lower part and a first liquid surface in the upper part;
• a Joule-Thomson cooling unit configured to cool the subcooled liquid helium in the lower part of the first helium tank by expansion of helium via a heat exchanger;
• and
• a second helium tank, which is at least partially filled with liquid helium, such that the second helium tank is continuously filled with liquid helium between a lower end of the second helium tank and 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 first liquid surface and the second liquid surface, and wherein the Joule-Thomson unit withdraws liquid helium from the second helium tank either directly via drawing liquid helium from the second helium tank, or indirectly via evaporation of liquid helium from the second liquid surface in 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.