Nonboiling Liquid Hydrogen TargetNelson Jarmie Citation: Review of Scientific Instruments 37, 1670 (1966); doi: 10.1063/1.1720080 View online: http://dx.doi.org/10.1063/1.1720080 View Table of Contents: http://scitation.aip.org/content/aip/journal/rsi/37/12?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Liquid Hydrogen Target Experience at SLAC AIP Conf. Proc. 823, 1043 (2006); 10.1063/1.2202518 Liquid Hydrogen: Target, Detector AIP Conf. Proc. 710, 16 (2004); 10.1063/1.1774662 Mechanically Refrigerated Liquid Hydrogen Target Rev. Sci. Instrum. 39, 1348 (1968); 10.1063/1.1683669 Refluxing Liquid Hydrogen Target Rev. Sci. Instrum. 29, 732 (1958); 10.1063/1.1716311 A Liquid Hydrogen Target Rev. Sci. Instrum. 22, 1006 (1951); 10.1063/1.1745801

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP:

130.113.111.210 On: Sat, 20 Dec 2014 02:05:43

THE REVIEW OF SCIENTIFIC INSTRUMENTS VOLUME 37, NUMBER 12 DECEMBER 1966

N onboiling Liquid Hydrogen Target*

NELSON JARMIE

University of California, Los Alamos Scientific Laboratory, Los Alamos, New Mexico 87544

(Received 10 August 1966; and in final form 30 August 1966)

A thin 2 mm liquid hydrogen target is described. It operates at conditions away from the boiling curve and can therefore absorb considerable (200 m W) power from an accelerator beam without serious boiling. Construction and operation are discussed and several additional advantages are presented.

INTRODUCTION

LIQUID hydrogen has been frequently used in nuclear and particle physics as the best proton target.l -4

More recently, liquid hydrogen targets have been con­densed at the site using liquid helium as a coolant. 5,6 The advantages of this method are versatility, and, in addition, safety because only a small amount of hydrogen liquid is used.

This article describes a helium cooled, liquid hydrogen target with additional advantages. The unique character­istic of this target is its maintenance in the liquid phase of hydrogen away from the boiling curve (Fig. 1). Such a target can absorb without boiling large amounts of energy deposited by a beam. (In the experiment in which this target was used,7 the target was a thin 2 mm lamina in which the avoidance of boiling was imperative.) Another advantage is the exclusion of various contaminants.

TARGET CONSTRUCTION

A schematic diagram of the target is shown in Fig. 2. Most of the constructional details are omitted, and the diagram is not drawn to scale. In equilibrium, liquid hydrogen exists in the target proper (about 6 cc) and in the hydrogen gas supply tube (about 1 cc). The beam passes through thin (0.0038 mm HavarS) foils roughly 2 cm in diameter. These foils, soft soldered tautly to a steel plate, bulged surprisingly little (for example, the center of a 20 rom diam foil deviated 0.5 mm from a plane) and formed a laminar target about 2 rom thick. The steel plates were attached with epoxy cement9 through an

* Work performed under the auspices of the U. S. Atomic Energy Commission.

1 R. S. Hickman, R. W. Kenney, R. C. Mathewson, and R. A. Perkins, Rev. Sci. Instr. 30, 983 (1959).

2 E. A. Whalin, Jr., and R. A. Reitz, Rev. Sci. lnstr. 26, 59 (1955). 3 L. Marshall, Rev. Sci. Instr. 26, 614 (1955). 4 C. Barrow, G. H. Guest, and L. Riddiford, J. Sci. Instr. 40, 260

(1963). 6 C. A. Swenson and R. H. Stahl, Rev. Sci. Instr. 25, 608 (1954). 6 G. S. Janes, L. G. Hyman, and C. J. Strumski, Rev. Sci. lnstr.

27,527 (1956). 7 N. Jarmie et al., "Spin Correlation in Proton-Proton Scattering

at 27 MeV" (submitted to Phys. Rev.). 8 A complex alloy of 9 elements, mainly Co, Ni, Cr, and Fe. It is

manufactured by the Hamilton Watch Company, Lancaster, Pennsylvania.

'Armstrong adhesive A-4, Armstrong Products Company, Warsaw, Indiana.

1670

expansion joint to the body of the target, which was made of copper. The temperature of the target was sensed by a gold alloy-copper thermocouple.lO The reference junction was attached to the liquid helium tank so that small changes in the hydrogen target temperature were then reflected in relatively large fractional changes in the thermocouple voltage-an important key to sensitive control. The thermocouple voltage (typically 100/-lV) was amplified and, through a nonlinear feedback system, con­trolled the "on" time of a 5 V 127 n wire heater shown in Fig. 2. A permanent heat short of 10.5 cm of 1.628 mm diam electrolytic tough pitch copper wire connected the target with the liquid helium reservoir.

450

400

350

300

II: II: 0 .... ..; 250 II: :>

"' "' ... II: ... 200

150

100

50

SOLID

LIQUID

~NING POINT

GAS

O~--~~--~--~ __ ~ __ ~ __ 4-~ 14 15 16 17 18 19

TEMPERATURE, OK

FIG. 1. Pressure-temperature phase diagram for hydrogen. Shown is the normal running region for equilibrium operation. -----

102.1 at. % Co in Au wire made by Cohn Sigmund Corp., Mount Vernon, New York. For characteristics, see R. L. Powell and M. D. Bunch, BUll. lnst. Intern. Froid. Suppl. 1, 129 (1958).

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP:

130.113.111.210 On: Sat, 20 Dec 2014 02:05:43

HYDROGEN TARGET 1671

H2 GAS SUPPLY

I

MENISCUS

LIQ. He TANK

I I I I I I

L_~ ____ J "-4° HEAT SHIELD

He GAS SUPPLY

j

BEAM _.--+

FIG. 2. Schematic diagram of the target. For details, see the text. The diagram is not to scale, and most construction details are omitted.

The target was suspended, but insulated thermally (by stainless steel) from the helium tank.. Helium gas may be admitted as shown in Fig. 2 to provide a large heat leak (1 mm spacing) for the initial condensation.

The pressure of the hydrogen gas was controlled by an external system, the heart of which was a Moore sub­atmospheric regulator,ll model 43-20. This system could be set to and maintain a given pressure of hydrogen, supplying or withdrawing gas as needed. Relatively small amounts (a few hundred cubic centimeters per hour) were needed to maintain equilibrium.

OPERATION

Initially the system was evacuated. After the liquid helium reservoir was filled and the system was fairly well cooled, hydrogen gas was admitted. A few Torr of helium gas were admitted into the heat leak space for rapid condensation which took about 20 min. As the target filled with liquid hydrogen, the temperature indicated by

11 Moore Products Company, Philadelphia, Pennsylvania.

the thermocouple was the boiling temperature12 corre­sponding to the pressure of the input gas. When the target was full, the meniscus moved up the input tube and out of the liquid helium region. At that time, the temperature of the target began to fall away from the boiling curve. The helium heat leak gas was then pumped away, the heater feedback system turned on, and the system rapidly reached the running point shown in Fig. 1. The conditions at the meniscus were on the boiling curve shown at point Min Fig. 1, but heat transmission down the liquid hydrogen in the input tube was very low.

The beam of protons (27 MeV) deposited on the average about SO m W, and sometimes was turned off suddenly or fluctuated. The system handled these changes by auto­matically changing the heat input from the heater coil. The combined energy of the beam and the heater balanced the loss in the copper heat short wire, which was designed for a 200 mW conduction at normal conditions. At high beam tests, the system did indeed perform well up to 200 m W of beam deposition.

DISCUSSION

The system ran well, maintaining without special atten­tion the target at the design condition of lS.l°K and 340 Torr to within ± O.2°K and 2 or 3 Torr for the duration of the experiment.

In addition to the nonboiling feature of this target, several other advantages were realized. In most hydrogen targets, many contaminants are frozen out. Running at lS.1°K is additionally advantageous because even deu­terium (and tritium) are eliminated as possible targets­the triple point of HD is 16.6°K and that of DD is 18.7°K. Also, the density of the target hydrogen is greater by about 10% than at boiling conditions at 1 atm.

ACKNOWLEDGMENTS

The aid of J. W. Jordan, M. Wallis, T. Carroll, and the Cryogenics Group of this Laboratory is gratefully acknowledged.

12 Most of the cryogenic data used came from the following refer­ences: V. J. Johnson, Ed., "A Compendium of the Properties of Materials at Low Temperature (Phase 1), Part 1. Properties of Fluids," Rept. WADD-TR-60-56 (July 1960); and D. B. Chelton and D. B. Mann, "Cryogenic Data Book," Univ. Calif. Rad. Lab. Rept. UCRL-3421 (15 May 1956).

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP:

130.113.111.210 On: Sat, 20 Dec 2014 02:05:43