Performance of the Liquid Hydrogen Target

Performance of the Liquid Hydrogen Target Presented by Chad Gillis Indiana University at NPDGamma Collaboration Meeting July 2012, Oak Ridge, Tennessee

Since upgrading the target for operation at the SNS, we have successfully completed: A partial fill and vent test using liquid neon at Indiana. Another partial fill and vent test using liquid neon at ORNL. A complete fill and vent test using hydrogen at ORNL. Stable operation with a target full of liquid hydrogen from mid-april to mid-june of 2012.

Temperature measurement We use silicon diode thermometers. Specified by the manufacturer as accurate to 0.5 K at the temperatures of interest. Read by Lakeshore and Scientific Instruments thermometer readouts which report to the DAQ digitally.

Upstream side of vessel Filling elbow Downstream bottom corner of vessel Ortho-para converter

Vapor pressure measurement PT106 Pressure transducer Omega PX303-100A5V. Analog output with repeatability accuracy of 2.5 torr. Read by an Omega meter which has an analog output with 0.2 % linearity read by the data acquisition system through the ADC card. In February/2012 its calibration was verified to be in 1 torr agreement with a calibrated gauge that was in turn in 1 torr agreement with two other calibrated gauges.

Hydrogen mass measurement Volume of vessel up to end of elbow curve in fill/vent line is 16.48 liters based on Walt's (engineer at Indiana) calculation. Including the small extra contribution from the recirculation line and the OPC filled with catalyst, the volume is 16.6 +/- 0.1 liters.

flowmeter flowmeter

Cylinder pressure method In total, we need measurements of temperature, pressure and volume. Since the supply shed is located outside, data on outside temperature from NOAA (http://www.ncdc.noaa.gov/crn/) were used. An extra uncertainty of 5 K was assumed. Pressure was measured using the pressure gauge on the regulator. It is model 1535 by Ametek Inc. and has specified accuracy of +/- 30 psi. Volume is the difficult one.

Cylinder pressure method To measure the internal volume of the pressurized cylinder to 3 %: Measure the external dimensions of the cylinder using a tape measure. The important contributions are: h1 (known to +/- 3/8 ) h2 (known to +/- 1/2 ) C1 (known to +/- 3/8 ) The difficult part is knowing the actual shape of the top dome. It is somewhere between: a half sphere of radius h2 and the top slice of height h2 of a sphere of circumference C1. The difference in these two possibilities is incorporated into the uncertainty. Measure weight of cylinder to +/- 3 pounds using a regular bathroom scale. Use known density of alloy steel and assume 5 % uncertainty: 7.9 +/- 0.4 g/l. (based on a survey of a large number of alloy steels at matweb.com) The internal volumes were: Cylinder 1: 50.5 +/- 1.5 liters Cylinder 2: 51.4 +/- 1.5 liters Cylinder 3: 50.3 +/- 1.5 liters Expected volume from talking to an Air Liquide technical specialist is 49.6 +/- 0.5 liters.

Cylinder pressure method To measure the internal volume of the pressurized cylinder to 3 %: Measure the external dimensions of the cylinder using a tape measure. The important contributions are: h1 (known to +/- 3/8 ) h2 (known to +/- 1/2 ) C1 (known to +/- 3/8 ) The difficult part is knowing the actual shape of the top dome. It is somewhere between: a half sphere of radius h2 and the top slice of height h2 of a sphere of circumference C1. The difference in these two possibilities is incorporated into the uncertainty. Measure weight of cylinder to +/- 3 pounds using a regular bathroom scale. Use known density of alloy steel and assume a 5 % uncertainty: 7.9 +/- 0.4 g/l. (based on a survey of a large number of alloy steels at matweb.com) The internal volumes were: Cylinder 1: 50.5 +/- 1.5 liters Cylinder 2: 51.4 +/- 1.5 liters Cylinder 3: 50.3 +/- 1.5 liters Expected volume from talking to an Air Liquide technical specialist is 49.6 +/- 0.5 liters.

Cylinder pressure method At internal pressures of 2000 psi, the ideal gas law needs significant (~ 10 %) corrections. We used three methods: 1) The van der Waals equation of state: cubic in the density with coefficients independent of temperature. 2) The virial expansion: also cubic in the density, but the coefficients depend on temperature. [Michels, de Graaff, ten Seldam, Physica 26, 393-408 (1960)] 3) A formula recommended by the NIST hydrogen website that determines density of hydrogen gas in terms of ten pressure and temperature-dependent terms that are determined by a total of 27 constants. Provides 1E-4 agreement with the standard at our temperature and pressure. [Lemmon, Huber, Leachman, J Res Natl Inst Stand Technol 113, 341-350 (2008)]

Flowmeter method We have a very nice brand new flowmeter that was factory calibrated specifically for hydrogen in January of 2012. Specified accurate to 1.5% of 15 slpm and was seen to work at better than 0.5% when it was calibrated. The flowmeter is recorded once every three seconds. Integration of the flow rate gives us the mass of hydrogen loaded to the target. Flowmeter Gas Handling cabinet

We loaded 16.1 +/- 0.6 liters of 17 K liquid hydrogen to the target.

Performance of target during production running of May 26-June 2 saturation pressure of temperature just above elbow in filling line actual measured pressure (PT106) saturation pressures of temperatures on the vessel temperature just above elbow in filling line distribution of temperatures on vessel and recirculation line

Performance of target during production running of June 11-15 saturation pressure of temperature just above elbow in filling line actual measured pressure (PT106) saturation pressures of temperatures on the vessel temperature just above elbow in filling line distribution of temperatures on the vessel and recirculation line

Vessel pressure and temperatures during venting Temperatures and pressure drift upwards Turn off condensing refrigerator

Status of Target DAQ During running, aside from a couple loose wiring connections that arose, the target DAQ system was very stable. It has written to disk once every three seconds continually for 70 days without having to restart the computer or the acquisition program. Software exists to integrate the target data with the rest of the NPDGamma data.

FIN.

Supplementary slides follow.

Source: 2012 CRC tables

Performance of target during production running of May 26-June 2/2012

Performance of target during production running of June 11-15/2012

NPDGamma Apparatus Our goal is to measure Aγ to a statistics-limited precision of 10-8 Observed quantity A= Pn Aγ. Polarized pulsed cold neutron beam.

NPDGamma Apparatus Beam Choppers monitors Guide field Liquid H2 Beam Supermirror RF guide polarizer Spin Rotator Cryostat Gamma detector array Guide coils Our goal is to measure Aγ to a statistics-limited precision of 10-8. Observed quantity A= Pn Aγ. Polarized pulsed cold neutron beam. Beam monitor

NPDGamma Goal Measure A γ to a statistics-limited precision of 10-8. dω dω 1+A γ cosθ+

Requirements for Hydrogen target Observed quantity depends on beam polarization must use para hydrogen so that beam doesn't depolarize significantly inside the target. At 17 K, hydrogen has a high para fraction, but natural conversion is slow use a catalytic chamber. chamber Measurement of the ortho-para ratio using the beam monitor analysis is discussed in L. Barrón-Palos et al., Nucl. Instrum. and Meth. A, 659 (2011), 579-586

Why Parahydrogen? Distance (cm) MCNP simulations of the distribution of an initially collimated neutron beam inside targets of pure ortho- and parahydrogen Distance (cm) pure orthohydrogen Distance (cm) pure parahydrogen

The NPDGamma liquid parahydrogen target has been successfully commissioned at the SNS Data taking for a measurement of Aγ is now commencing. For more detailed information about our liquid parahydrogen target: S. Santra et al., Nucl. Instrum. and Meth. A, 620 (2010) 421-436 L. Barrón-Palos et al., Nucl. Instrum. and Meth. A, 659 (2011), 579-586

Fill and vent test: Commissioning the target with hydrogen Pressure drops as warmest limiting point reaches liquefaction temperature Pressure reaches constant limit determined by check valves. System passively vents. Constant temperature indicates liquid until liquid level drops below this thermometer. Pressure and Temperature lie approximately on hydrogen vapour pressure curve. Flow is manually increased as liquefaction has started. Vessel is full Manually Introduce heat load to vessel.

cryostat Helium channels Helium supply

1. Hydrogen vessel 2. 6Li doped plastic neutron shielding 3. 18 K Cu radiation shield with Al front and back 4. Superinsulation 5. G10 plastic ring supports 6. 80 K Cu radiation shield with Al front window 7. Superinsulation 8. G10 supports (not visible in left photo) 9. Outer Al wall of cryostat Photograph from behind of midway through installation Inside cryostat superinsulation outer radiation shield Engineer's drawing of 6Li shielding around vessel 6 Cryogenic wiring to feedthrough inner radiation shield Outer wall of cryostat Li plastic G10 supports collimation to beam monitor vessel