MICE Collaboration Meeting CM-15 1

Is the the pulse tube cooler a must or is it simply better for

the MICE AFC module?

Michael A. Green

Lawrence Berkeley Laboratory

Berkeley CA 94720, USA

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What are the Cooler choices for the AFC Module?

• The AFC module has the need for three coolers. Two coolers are needed for the superconducting magnet and one cooler is needed for the absorber.

• The coolers for the MICE AFC module will be will deliver 1.5 W at 4.2 K and > 40 W at 55 K.

• Two types of coolers can be used. These machines are the Sumitomo RDK-415D GM cooler or the Cryomech PT-415 pulse tube cooler.

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Cryomech PT415 Cooler

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PT415 Pulse Tube Cooler in its Test Stand

Rotary Valve

Surge Tank

Test Cryostat for Machine

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Computer Display of the PT415 Cooler in Operation

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25 35 45 55 65 752

3

4

5

6

84W63W42W21W0 W3.0W2.5W

2.0W

1.5W

1.0W

0.5W

SECOND STAGE TEMPERATURE, K

FIRST STAGE TEMPERATURE, K

CRYOMECH TEST

0 W

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5

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2

SEC

ON

D S

TA

GE T

EM

PER

ATU

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Operating Points of the PT415 Cooler

The measured test data is from Tom Painter of Florida State University.

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PT415 Cooler Rotary Valve and Motor

Rotary Valve Motor

Rotary Valve

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Typical Tube Cooler Compressor Package

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A Comparison of the PT415 Coolerwith the RDK-415D Cooler

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Advantages of the Pulse Tube Cooler

• More cooling on 1st stage at a given temperature.• Faster cool down of cooler and load.• Same performance at 50 Hz as at 60 Hz.• There is lower cold head vibration (a factor of >30). • There is a longer maintenance interval with less

loss of performance between maintenances.• Can use snap-in integration with a magnet.• Remote valve motor permits cold head operation in

magnetic fields of 1 to 2 T. • Liquefaction rate is higher than other cooler types. • Lower magnetic distortion due to cooler pulsation.

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Advantages of the GM Cooler

• Orientation of the cooler cold head is not an issue.• Cooler cold head assembly is smaller.

• Compressor module takes up less space.

• There is lower input power to the compressor for a given amount of refrigeration. As a result, less cooling water needed for the compressor.

• The machine capital cost is lower.

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Performance Comparison of the RDK-415Dand the PT415 Coolers at 50 Hz

PT415Parameter

SumitomoRDK415 normal Remote

1st Stage Temp @ 40 W (K) 54 40 43

2nd Stage Temp @ 1.5 W (K) 4.2 4.2 4.35

Base Temperature (K) ~2.9 ~2.8 ~3.0

Input Power @ 50 Hz (kW) 6.5 10.5 10.5

Machine Efficiency (%) ~4.4 ~3.5 ~3.3

* The remote valve is 1.0 meters from the cooler cold head.

*

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Size Comparison of the RDK-415Dand the PT415 Coolers

PT415Parameter

SumitomoRDK415 normal Remote

Top Flange to 1st Stage (mm) 156.0 195.7 195.7

1st Stage to 2nd Stage (mm) 236.5 212.4 212.4

Top Flange Diameter (mm) 180.0 186.7 186.7

1st Stage Diameter (mm) 126.0 129.5 129.5

2nd Stage Diameter (mm) 58.0 94.0 94.0

Cold Head Height (mm) 557.0 759.0 414.4

Cold Head Length (mm) 294.0 339.0 186.7

*

* The remote valve is 1 meter from the cold head. The buffer tank iswith the remote rotary valve. The cold head height is the top flangeand the cold parts of the machine.

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The Magnetic Field on the CoolerIs it an important issue?

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PT415 Pulse Tube

Displacer <0.08 T perpendicular Displacer <0.3 T parallel

Displacer Motor <0.08 T Valve Motor <0.1 T

Regenerator <1.5 T

Places where Magnetic Field is a Concern

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Worst Case Field Map Flip Mode for AFC Module (radial)

From H. Witte & J. Cobb Oxford University

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Worst Case Field Map Flip Mode for AFC Module (axial)

From H. Witte & J. Cobb Oxford University

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Worst Case Field Map Non-flip Mode for AFC Module (radial)

From H. Witte & J. Cobb Oxford University

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Worst Case Field Map Non-flip Mode for AFC Module (axial)

From H. Witte & J. Cobb Oxford University

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The Cooler Magnetic Field Issue

RDK-415D Displacers from Y. MatsubaraICEC-20 Proceedings (2005) p 189

A magnetic field perpendicular to the movingdisplacer increases wear and reduces the GM coolermaintenance interval. The field parallel to the displacer can be four times the perpendicular field.

A magnetic field on the cooler motors causes the motors to stall. The RDK-415D AC motor is a little more sensitive to field than the PT415 stepper motor. Neither motor will operate in fields much above 0.1 T. Motor shielding is an option for both coolers.

Magnetic field saturates the regenerator material at ~1.5 T. This reduces the output at 4.2 K 10 to 15 percent.

Private communicationGeoff Green, NRL

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PT-410 Pulse Tube Cooler Valve Motor

The PT410 or PT415 valve motor can be shielded to operate in a field of 0.5 T.Cryomech will provide a custom shield for the valve motor at minimal cost.

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PT415 Cooler Remote Motor without Surge Tanks

Rotary Valve Motor

Rotary Valve

The surge tank should be attached to the rotary valve.

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Comments on Magnetic Shielding• Iron shielding of the displacer tube on a GM cooler

is difficult. The field perpendicular to the tube must be kept below 0.08 T for long life.

• Iron shielding of the rotary valve on a pulse tube cooler is easier than shielding the motor assembly of a GM cooler. The valve motor shield would be included with the pulse tube cooler.

• The rotary valve can be moved to a low field region away from the cooler by 1 meter if the field at the valve is greater than 0.4 to 0.5 T

• Shielding of the 2nd stage regenerator is not necessary if the field on the regenerator is <1.5T.

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Snap-in Integration of thePulse Tube Cooler to the Magnet

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Snap-on Coolers for the Magnets

• Since the magnets will be cooled down with liquid cryogens, the pulse tube coolers can be installed in the magnets just before they are cooled down.

• The condenser is attached to the second stage of the PT cooler. (This is included in the price of the cooler.) The PT cooler is connected directly into the LHe space of the cryostat. The PT cooler will reduce the cooler neck heat leak over a factor of 5.

• The PT coolers can be removed without warming up the magnets. A new cooler can be installed and cooled down without warming the magnets

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2nd Stage Cold Head Helium CondenserQ/A = ~40 W m-2

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Snap-on Integration continued

• Snap-on integration is doable when GM cooler is used. The cooler neck heat losses are much higher. This will affect the overall performance of the cooler and magnet combination.

• Snap-on integration of a PT cooler to the absorber is possible provided one can eliminate air leaks into the hydrogen space. An liquid absorber cooler should be designed for hydrogen and helium liquefaction. I am willing to work with Cryomech to see how this might be accomplished safely.

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Hydrogen and Helium Liquefactionwith a Pulse Tube Cooler

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The H2 and He Liquefaction Problem

• The goal is to fill absorber with LH2 using the cooler in 15 to 24 hours. One wants to fill the absorber with LHe in about 24 hours using the cooler.

• This means that the H2 or He gas must be pre-cooled by the cooler before it can be liquefied*. The pre-cooling rate is >100 W for H2 and >50 W for He.

• The pre-cooling is applied through a heat exchanger attached to the 1st stage or the tube between the 1st and 2nd stages and or a liquid nitrogen pre-cooler.

• The heat exchangers can not be part of the hydrogen vent circuit.

* See MICE notes 108 and 113 concerning the need for this heat exchanger.

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Why is the type of cooler used important?

• The only way that one can pre-cool the gas being liquefied using a GM cooler is to attach a laminar flow heat exchanger to the 1st stage. LN2 cooling should also be used.

• With a pulse tube cooler, one can pre-cool off of the regenerator tubes of both stages. Liquefaction using the pulse tube cooler is much more efficient.

• Using the pulse tube cooler, the neck heat leak into the cryostat is reduced by over a factor of five. This benefit is not available from a GM cooler.

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The Cryomech PT410 used as a Liquefier

• A PT-410 cooler (1 W @ 4.2 K) was used. The actual cooler capacity is not known

• Input power = 8 kW @ 60 Hz

• Liquefaction into a 60 liter storage dewar. The heat leak into the dewar is unknown

• The liquefaction rate for helium gas was 15.2 l/d (0.022 g/s).

• Dewar cool down took ~20 hrs until liquid accumulation starts. The start temperature is not known.

• The data was published in Cryogenics 45 (2005), pp 719-7240.0250.0200.0150.0100.0050.000

0.0

0.2

0.4

0.6

0.8

1.0

Helium Liquefaction (g/s)

Refrigeration from the PT-410 Cooler (W)

2 liters per day (G = 42.8 j/g)

5 liters per day (G = 38.9 J/g)

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The Cryomech Helium Liquefier

Now a Commercial Product

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PT410 Helium Liquefier for the South Pole Dewar

Liquefaction Pot

2nd Stage

Helium HeatExchanger

1st Stage

1st Stage Tubes

Rotary Valve Assembly

Pulse Tubes

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60 He Liter Test Dewar for the South Pole Station PT410 Helium Liquefier

In a wide mouth 60 liter dewar, the He liquefier makes up to 15 liters per day. The 4000 liter South Pole dewar had a boil off rate of 14 liters per day w/o a cooler. With the PT410 liquefier, there is a net liquefaction of 2 to 3 liters per day.

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He Liquefaction using a Pulse Tube Cooler, Two GMCoolers and Two GM Coolers with a J-T Circuit

ParameterCryomech

PT410Sumitomo

K3004110

GM+JT

Liquefaction Rate (L day-1) 15.2 6.0 8.0

Liquefaction Rate (g s-1) 0.022 0.0086 0.0116

Number of Coolers 1 2 2

4.2 K Refrigeration (W) 1.0 3.0 ~2.0

Input Power (kW) 8.0 15.0 8.0

Liquefaction Coefficient (J g-1) ~45 ~350 ~130

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Capital Cost and OperatingCost Issues

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Cooler Cost and Other Related Issues

• The manufacturer’s list price in the US for a 1.5 W Sumitomo GM cooler is 37.5 k$. The list price for the Cryomech PT cooler is 46.0 k$. The cooler list price is like the MSRP on a car. The price can be negotiated lower, particularly when one orders multiple coolers.

• Part of the PT cooler higher price is the larger He compressor. The PT cold head is simpler, so its cost should be lower. Much of the higher price for the PT cooler is due to the lower production rate at Cryomech (500 units per year versus 10000+ units per year at Sumitomo).

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Cost and other issues continued

• The capital cost of the cooler is not the only thing that should be considered. The maintenance interval and the cost of maintenance should also be considered.

• The method of installation of the cooler on the magnets will affect the cost of the magnet cryostat. I believe that the use of the PT cooler on the magnets will reduce the cost of the magnets enough to offset the increased cooler price.

• The PT compressor can be located 30 to 40 meters from the cooler cold head.

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Concluding Comments

• The PT415 cooler is now in production.

• The PT415 cooler is larger than the RDK-415D GM cooler. The diameter of the top flange is not very different. The cold portion of the PT cooler is not very different either.

• Pulse tube coolers are less sensitive to magnetic field, particularly when a remote valve is used.

• Snap-in installation into the magnets is a plus. More engineering is needed to see if this feature can be applied to the absorbers.

• Pulse tube coolers work very well as liquefiers.

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Is the the pulse tube cooler a must or is it simply better for the MICE AFC module?

In my opinion, the pulse tube cooler is a must if one wants to fill an absorber using the cooler. For the magnets, the pulse tube cooler is better in many respects, but not all.

The pulse tube cooler is a must for the coupling coils.