Presentation on theme: "1 Cooling the Hydrogen (Helium) Absorbers with Small Coolers Michael A. Green University of Oxford Department of Physics Oxford OX1 3RH, UK MICE Video."— Presentation transcript:
1 Cooling the Hydrogen (Helium) Absorbers with Small Coolers Michael A. Green University of Oxford Department of Physics Oxford OX1 3RH, UK MICE Video Meeting 22 September 2004
2 Cooler Options for H 2 and He Either the Gifford McMahon (GM) coolers or the pulse tube (PT) coolers can be used for cooling MICE liquid hydrogen absorbers. At 20 K, the PT cooler and the GM cooler puts out about the same amount of cooling. At 4.2 K the GM cooler puts out more cooling (1.5 W) than the PT cooler (1.0 W). MICE absorbers can be cooled with small coolers, because there is no beam heating in MICE.
4 The Key Issues Connection of the cooler to the absorber Reducing the heat leak for 4 K operation Simplification of an absorber exchange Cool down of the absorber and filling of the absorber with liquid hydrogen or helium
5 How to reduce the Absorber Heat Leak If one is going to operate the absorber with liquid helium, one must reduce the absorber heat leak to about 1 watt. The forces on the absorber are low (< 400 N in the r direction and <5000 N in the z direction), so getting the cold mass support heat load down can be done even with low design stress supports made of a material such as G-10 (40 MPa). Liquid helium operation requires that the absorber body have at least 10 layers of MLI. The absorber windows must have at least 4 layers of MLI. All of the pipes coming into the absorber must be well insulated with at least 10 layers of MLI. The MLI on the absorber is also needed to reduce the heat flow in the event the absorber vacuum goes bad. (The vent line diameter is a problem.) Ducts into the absorber must be tied to the cooler 1 st stage
6 Absorber Cooling with 1 RDK-415 Cooler First Stage of Cooler (up in the neck) 1 RDK-415 MLI Radiation Heat Leak (W) 1.0 Cold Mass Support Heat Leak (W) --- Plumbing Heat Leak (W) 2.4 Instrumentation Lead Heat Load (W) 0.1 Total Heat Load to 1st Stage per Cooler (W) 3.5 First Stage Temperature (K) ~27 Second Stage of Cooler (the Absorber and LH2 System) Absorber Body MLI Radiation Heat Leak (W) 0.36 Cold Mass Support Heat Leak, buttons plus longitudinal (W) ~0.20 Plumbing Heat Leak and Instrumentation Lead Heat Leak (W) 0.10 Radiation Heat Leak on Window (4 layers of MLI) ~0.37 Total Heat Load to 2nd Stage (W) ~1.03 2nd Stage Temperature (K) ~ 4.0* * Extra Heat (about 14 W) is required to keep cooler cold head above 15 K. Cooler Cost = <45 k$
8 Absorber Cool Down and Warm Up The fastest cool down and fill occurs when the absorber is filled with LN 2 and LH 2 directly. The absorber cool down and hydrogen liquefaction can be done using LN 2 and LHe in the absorber heat exchanger. The freezing of H 2 is an issue. The absorber cool down and hydrogen liquefaction can be done using the cooler alone. The absorber can be warmed up by heating the absorber with a heater or circulating warm helium through the heat exchanger. 2 to 4 hours 6 to 8 hours 24 to 40 hours 6 to 8 hours
9 Why Simple May Be Better Simplify the absorber by eliminating the wall heat exchanger and its pipes. This gives one more room for additional MLI and a low heat leak support. Connect the absorber to the cooler through a copper strap as well as the 2 pipes of gravity feed heat pipe. The absorber can be cooled down using the cooler. The hydrogen gas liquefied in the absorber must be pre-cooled using the cooler first stage. The absorber can be cooled down and filled in 36 to 40 hours using the simplest system. A fast cool down and fill can be done using liquid hydrogen directly.
12 Concluding Comments One RDK-415, RDK-408, PT-410, or PT-810 cooler can cool each liquid hydrogen absorber. Added heat is needed to keep 2 nd stage above 15 K. If the absorbers are to be run with liquid helium in them, the best cooler to use is the RDK-415 cooler. Liquid helium operations requires that the absorber body have at least 10 layers of MLI. The absorber windows must have at least 4 layers of MLI. All of the pipes coming into the absorber must be well insulated with at least 10 layers of MLI The cold mass support system for the absorber body must be made from a composite like G-10. Ducts into the absorber must be tied to the cooler 1 st stage.
13 Concluding Comments cont. The MLI on the absorber body and the windows is important for safety (pressure rise during a fault), when the absorber is filled with liquid helium. The T from the hydrogen absorber to the cooler cold head is less important, but the use of a liquid hydrogen heat pipe ensures that there will be liquid hydrogen flow through the absorber. The T from the helium absorber to the cooler cold head is very important. The heat pipe is needed for a low T from the absorber to the cold head. The absorbers can be cooled down and filled with liquid hydrogen using the cooler, provided there is a copper strap between the absorber and the cooler.
14 Concluding Comments cont. The absorber body can be cooled to 4.2 K using the cooler alone as long as the heat leak is low enough. A liquid helium absorber must be designed to be filled with liquid from an external liquid dewar. If the absorber is designed to be cooled down using the cooler, the heat exchanger and its pipes can be eliminated. This simplifies the absorber and the changing of absorbers. If one wants to cool and fill the absorber quickly the absorber must be cooled down and filled with liquid (N 2 then H 2 or He) from an external dewar.