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A mylar liquid hydrogen target with thin mylar side walls
By taking the same steps to improve the heat exchanger as .for ordinary dilution refrigerators, 4 it would evidently be possible to obtain the same low temperatures with a refrigerator using a condensation pump, ~(5 to 8) x 10 -3 K. The author is grateful to M. S. Khaikin for supporting the work and to A. Ya. Parshin and K. N. Zinov'eva ¢or valuable discussions.
References 1 London, H., Clarke, G. R., Mendoza, E. Phys Rev 128 (1962) 1993 2 Peshkov, V. P. Prib i Tekh/fksper No 5 (1969) 193 3 Betts, D. S., Edmonds, D. T., Keen, B. E., Matthews, P. W. JScilnstr41 (1964) 515 4 Wheatley, J. C., Rapp, R. E., Johnson, R. T. J Low Ternp Phys4 (1971) 1
A mylar liquid hydrogen target with thin mylar side walls L. M. Vasil'ev, I. A. Radkevich, T. G. Smotyakina, and V. V. Sokolovskii
When studying the interaction between elementary particles and protons, it is desirable to have a liquid hydrogen target with walls as thin as possible in the paths both of the primary beam and of the secondary particles emitted from the target at large angles. Mylar targets have been described. 1 The vacuum jackets of such targets are relatively large so the dimensions of the counting equipment have to be increased. We have developed and built a liquid hydrogen target with a vacuum jacket which has wide windows on all sides covered with thin mylar. The solid angle cut out by thick metal parts is very small so that particles emitted from the target inside a practically 47r solid angle can be counted. The design of the target is shown in Fig.1. The tank 1 is made of mylar in the way described elsewhere] The tank, surround by two 14/a thick aluminium foil passive shields 2 with foam plastic support rings 3, hangs freely on the inlet tubes 6, soldered to shell 5. The case of the The authors are with the Institute of Theoretical and Experimental Physics, Moscow, USSR. Prib i Tekh Eksper No 4 (1971) 56. Received 2 December 1971.
Fig.2
EJ
Cross-section of case of the vacuum jacket
vacuum jacket 4 of welded construction is made of stainless steel (for work with a magnetic field). The case is welded to tube 1, which contains the inlet and evaporation tubes 6. The tubes are secured with foam plastic mounts 8. The target tank is 250 mm long and 50 mm in diameter. The thickness of the bottom is about 80/am and of the side walls 120/am. The cross-section of the case of the vacuum jacket is shown in Fig.2. The profile chosen for the side fins of the case, with a small amount of metal, is strong enough and e~,~ures reliable covering of the case with mylar. The case is 100 x 100 x 30 mm 3.
/
8-
7¸
6-
I
L_~X~q
5 Fig.1
~I
S c h e m a t i c section o f t h e target
CRYOGENICS.
O C T O B E R 1972
2
3
The side walls of the case with the hydrogen tank previously fixed inside (see Fig.3) were covered with two layers of 60/am mylar. The mylar was stretched in two perpendicular directions while it was being stuck. The stretching ensured a smooth join of the mylar to the uneven surfaces, made it appreciably easier to remove the adhesive when laying the second layer and, of special importance, it reduced the sagging of the mylar when the vacuum jacket was pumped. After sticking the side faces, the extra mylar was cut off so that an approximately 1 cm wide strip remained at the
387
ends. Previously formed mylar domes (radius of the spherical part 15 cm) were stuck to the end of the case. The strips left after sticking the side faces were bent down onto the ends and stuck to the fiat part of the bottom. To protect the edges from being knocked and to increase the reliability of the joins, a casing of stainless steel foil (0.1 mm thick) was stuck to the ends of the vacuum jacket. The mylar was stuck to the vacuum jacket with E D - 5 epoxy resin to which was added about 30% by weight of mixture of active thinner T E G - 1 and polyethylenepolyamine. The target was heated for 24 h at 60°C after sticking. The vacuum in the target was maintained at less than 3 x 10 -5 tor~ before filling with liquid hydrogen by pumping with a TsVL-100 diffusion pump, and after filling the pressure in the vacuum jacket was <10 -5 torr (1 torr = 133 N m'2). The rate of evaporation of the liquid hydrogen from the target tank did not exceed 0.1 I h "1 .
References Fig.3 A photograph of the case of the vacuum jacket w i t h the target t a n k inserted
1 Mehr, D. L., McLaughlin, E. F. Rev Scilnstr 34 (1963) 104
An apparatus for studying dry friction at low temperatures A. M. Arkharov, G. I. Voronin, and L. D. Kharitonova
Special apparatus for measuring the coefficient of friction tribometers 1-5 _ are used to study frictional processes. We shall call tribometers for studying frictional processes at low temperatures, cryotribometers. The KT-1 cryotribometer is designed to study the processes of dry friction for rotational motion in various media or in vacuo at low temperatures. The coefficient of sliding friction and static friction can be measured for different pairs of material on 'finger' shape specimens, and also facial friction on ring and sole shaped specimens.
Principle o f the action. The 65 mm diameter horizontal rotating table, specimen 3 (Fig.l) is made from the material to be studied. A second, hemispherical, specimen 2 (the indenter) is pressed onto the table from above by the norreal force N; the sphere radius is 2.5 mm and it is fastened on the end of the measuring lever arm 10. The frictional force Ff, when the table is rotated, deflects the arm from its equilibrium position. Measurement of the frictional force is based on the measurement of the compensating force F c, necessary to maintain the arm in its equilibrium position. (A small constant force F o is applied to keep the
The authors are w i t h the Moscow Technical High School, Moscow USSR. Prib i Tekh ~ksper No 4 (1971) 235. Received 2 December 1971.
388
7
B
9
\ 5"
IO i 1 / .
t2 ~ -
ii \ \
e
,
'3
Fig. 1 L a y - o u t of the c r y o t r i b o m e t e r 1 -- sealed electrical unit w i t h screened magnetic coupling; 2 -- indenter; 3 -- rotating specimen; 4 -- viewing tube; 5 -- test chamber; 6 -- nitrogen cooling jacket; 7 -- lid; 8 -- siphon; 9 -- hinge; 10 -- measuring arm; 11 -- elastic unit (ring) w i t h strain gauges stuck on; 12 -- roller; 13 -- tube f o r supplying liquid nitrogen to the indenter
unloaded arm against an external shoulder). The measuring arm can move freely in the horizontal and vertical planes by using hinge 9. The indenter is pressed onto the table with the normal force N by externally loading the arm with a force N e. The frictional couple, the frictional force,
CRYOGENICS. OCTOBER 1972
the normal force, and the coefficient of friction are calculated by the relations
M f = ( F c -Fo)13; /~f=(-bc
F o) / 3 . lI
l2 N = N
e
(F c
•
F o ) 13
N e l2 (for a "finger' specimen with d 4{ r; d is the indenter diameter, r the distance of the indenter from the axis of the table).
Design o f the cm,otribometer. This meets, in the main, the requirements set out by Kharitonova. 6 Special attention is paid to maintaining the cleanliness o f the surface of the specimens, to the reliability o f the cooling, and to the stability in measuring characteristics of the strain gauges. The cryotribometer is provided with a sealed means of rotation, with bellows sealing off the measuring arm, fixed to a universal joint, and with viewing windows for observing the measuring the rate of rotation visually with a stroboscopic tachometer. The frictional couple is measured with strain gauges placed outside the measuring chamber. The cryotribometer consists of the case of the sealed chamber 5, the rotating specimen table, the measuring arm 10, the hinge 9, and the electrical unit 1 with the sealed rotation mechanism. All the main components are made of Xh 18N 9T steel. The cylindrical case o f chamber 5 is provided with viewing tubes 4, side tubes for letting in and removing gas, and jacket 6 for cooling the specimens and media in the chamber with liquid nitrogen or air. Lid 7 with the viewing window can be replaced by a flange for evacuating the chamber. The internal diameter o f the chamber is 93 mm and the height 200 mm. Arm 10 is a double walled hollow rod 25 mm in diameter with an evacuated heat insulating jacket. It is designed to transmit a normal force to the indenter and transmit the frictional force to the ring-shaped spring element 11 with strain
gauges stuck on. The specimen being studied, the indenter 2, is fixed to the lower face of the rod. The movable sealing of the arm into the test chamber is achieved by bellows 8. The indenter is cooled by introducing liquid nitrogen inside the rod. Hinge 9 is the point of support of tire rod and has 4 rocking bearings. The drive for the rotating table is a sealed constant current electric unit with screened magnetic coupling. The bearing shafts o f the rotor are the self-lubricating dry friction rocking bearings with permanent F - 3 separators. A smooth change in the number of revolutions is achieved by varying the voltage to the motor.
Measuring syswm. The balancing force F c is measured by four strain gauges stuck to ring 11 and connected into a bridge circuit; a P Sr 1 recording potentiometer is used in conjunction with them. The potentiometer is calibrated by loading the ring with standard weights. The error in measuring the balancing force does not exceed 0.02 N. The temperature of the specimens and of the medium between 90 and 300 K are measured by copper-constantan thermocouples using an E P P - 0 9 potentiometer; the accuracy is -+2 K. The rate of rotation of the table is measured with an S T - 5 strobscopic tachometer, and the vacuum in the chamber goes down to 10 -5 tort. The main technical data o f the K T l cryotribometer. The maximum frictional couple is 0.1 N m, the rate of rotation can be varied from 600 to 6 000 rev min -1 : the indenter temperature varies from 90 to 300 K; the radius of rotation is 0 to 25 ram; the nom~al load is 0.5 to 5 N; the drive voltage (constant current) 3 to 27 V; the weight of the cryotribomeler (without the associated equipment) is 50 kg; the dimensions are 1 100 x 860 x 420 mm 3.
References 1 Braun, Barton Apparatus Jor Scientific Im'esti~,ations No 12 (1966) 61 2 Bruske, Ekman Apparatusfi~ Scientific lm'esti,eations No 9 (1963) 17 3 Buckley, D. H., Johnson, R. L. ASLE Trans 8 (1965) 123 4 King, R. F., Tabor, D. ProcPhysSoc B 66 (1953) 728 5 El'kim, A. 1., Bartenev, G. M. hMustrial Laboratory No 2 (1963) 227 6 Kharitonova, L. D. {h~h'ersiO,Proceedin,es: Mechanical f:'n~uneer in,~ No 6 11969) 43
A cryogenic temperature controller A. Tominaga The device described here was designed for use with resistance thermometers in the measurement and control of temperature. It has been used successfully with carbon and germanium resistance thermometers to control the temperature in several types of low temperature cryostats over a range of 0.3 to about 6 K.
was versatile, simple to operate, and very reliable. The sensitivity was to be as high as possible, consistent with the opposing goal of low dissipation in the themlometer resistante. The secondary objective was to produce a design which could be quickly and easily duplicated.
Numerous designs exist for thermometer controllers.1 7 The design objective here was to produce a controller which
Description of the circuit
The author is with the Department of Physics, Tokyo University of Education, Tokv,, !a'~an. Received7 January 1972.
C R Y O G E N I C S . O C T O B E R 1972
The bridge circuit (Fig.2) which compares the resistance of the thermometer with the precision decade resistor 8 is the same type as that used by Royer P. Ries and B. Keith Moore. 7 An input transformer is used as a bridge trans-
389
References 1 London, H., Clarke, G. R., Mendoza, E. Phys Rev 128 (1962) 1993 2 Peshkov, V. P. Prib i Tekh/fksper No 5 (1969) 193 3 Betts, D. S., Edmonds, D. T., Keen, B. E., Matthews, P. W. JScilnstr41 (1964) 515 4 Wheatley, J. C., Rapp, R. E., Johnson, R. T. J Low Ternp Phys4 (1971) 1
A mylar liquid hydrogen target with thin mylar side walls L. M. Vasil'ev, I. A. Radkevich, T. G. Smotyakina, and V. V. Sokolovskii
When studying the interaction between elementary particles and protons, it is desirable to have a liquid hydrogen target with walls as thin as possible in the paths both of the primary beam and of the secondary particles emitted from the target at large angles. Mylar targets have been described. 1 The vacuum jackets of such targets are relatively large so the dimensions of the counting equipment have to be increased. We have developed and built a liquid hydrogen target with a vacuum jacket which has wide windows on all sides covered with thin mylar. The solid angle cut out by thick metal parts is very small so that particles emitted from the target inside a practically 47r solid angle can be counted. The design of the target is shown in Fig.1. The tank 1 is made of mylar in the way described elsewhere] The tank, surround by two 14/a thick aluminium foil passive shields 2 with foam plastic support rings 3, hangs freely on the inlet tubes 6, soldered to shell 5. The case of the The authors are with the Institute of Theoretical and Experimental Physics, Moscow, USSR. Prib i Tekh Eksper No 4 (1971) 56. Received 2 December 1971.
Fig.2
EJ
Cross-section of case of the vacuum jacket
vacuum jacket 4 of welded construction is made of stainless steel (for work with a magnetic field). The case is welded to tube 1, which contains the inlet and evaporation tubes 6. The tubes are secured with foam plastic mounts 8. The target tank is 250 mm long and 50 mm in diameter. The thickness of the bottom is about 80/am and of the side walls 120/am. The cross-section of the case of the vacuum jacket is shown in Fig.2. The profile chosen for the side fins of the case, with a small amount of metal, is strong enough and e~,~ures reliable covering of the case with mylar. The case is 100 x 100 x 30 mm 3.
/
8-
7¸
6-
I
L_~X~q
5 Fig.1
~I
S c h e m a t i c section o f t h e target
CRYOGENICS.
O C T O B E R 1972
2
3
The side walls of the case with the hydrogen tank previously fixed inside (see Fig.3) were covered with two layers of 60/am mylar. The mylar was stretched in two perpendicular directions while it was being stuck. The stretching ensured a smooth join of the mylar to the uneven surfaces, made it appreciably easier to remove the adhesive when laying the second layer and, of special importance, it reduced the sagging of the mylar when the vacuum jacket was pumped. After sticking the side faces, the extra mylar was cut off so that an approximately 1 cm wide strip remained at the
387
ends. Previously formed mylar domes (radius of the spherical part 15 cm) were stuck to the end of the case. The strips left after sticking the side faces were bent down onto the ends and stuck to the fiat part of the bottom. To protect the edges from being knocked and to increase the reliability of the joins, a casing of stainless steel foil (0.1 mm thick) was stuck to the ends of the vacuum jacket. The mylar was stuck to the vacuum jacket with E D - 5 epoxy resin to which was added about 30% by weight of mixture of active thinner T E G - 1 and polyethylenepolyamine. The target was heated for 24 h at 60°C after sticking. The vacuum in the target was maintained at less than 3 x 10 -5 tor~ before filling with liquid hydrogen by pumping with a TsVL-100 diffusion pump, and after filling the pressure in the vacuum jacket was <10 -5 torr (1 torr = 133 N m'2). The rate of evaporation of the liquid hydrogen from the target tank did not exceed 0.1 I h "1 .
References Fig.3 A photograph of the case of the vacuum jacket w i t h the target t a n k inserted
1 Mehr, D. L., McLaughlin, E. F. Rev Scilnstr 34 (1963) 104
An apparatus for studying dry friction at low temperatures A. M. Arkharov, G. I. Voronin, and L. D. Kharitonova
Special apparatus for measuring the coefficient of friction tribometers 1-5 _ are used to study frictional processes. We shall call tribometers for studying frictional processes at low temperatures, cryotribometers. The KT-1 cryotribometer is designed to study the processes of dry friction for rotational motion in various media or in vacuo at low temperatures. The coefficient of sliding friction and static friction can be measured for different pairs of material on 'finger' shape specimens, and also facial friction on ring and sole shaped specimens.
Principle o f the action. The 65 mm diameter horizontal rotating table, specimen 3 (Fig.l) is made from the material to be studied. A second, hemispherical, specimen 2 (the indenter) is pressed onto the table from above by the norreal force N; the sphere radius is 2.5 mm and it is fastened on the end of the measuring lever arm 10. The frictional force Ff, when the table is rotated, deflects the arm from its equilibrium position. Measurement of the frictional force is based on the measurement of the compensating force F c, necessary to maintain the arm in its equilibrium position. (A small constant force F o is applied to keep the
The authors are w i t h the Moscow Technical High School, Moscow USSR. Prib i Tekh ~ksper No 4 (1971) 235. Received 2 December 1971.
388
7
B
9
\ 5"
IO i 1 / .
t2 ~ -
ii \ \
e
,
'3
Fig. 1 L a y - o u t of the c r y o t r i b o m e t e r 1 -- sealed electrical unit w i t h screened magnetic coupling; 2 -- indenter; 3 -- rotating specimen; 4 -- viewing tube; 5 -- test chamber; 6 -- nitrogen cooling jacket; 7 -- lid; 8 -- siphon; 9 -- hinge; 10 -- measuring arm; 11 -- elastic unit (ring) w i t h strain gauges stuck on; 12 -- roller; 13 -- tube f o r supplying liquid nitrogen to the indenter
unloaded arm against an external shoulder). The measuring arm can move freely in the horizontal and vertical planes by using hinge 9. The indenter is pressed onto the table with the normal force N by externally loading the arm with a force N e. The frictional couple, the frictional force,
CRYOGENICS. OCTOBER 1972
the normal force, and the coefficient of friction are calculated by the relations
M f = ( F c -Fo)13; /~f=(-bc
F o) / 3 . lI
l2 N = N
e
(F c
•
F o ) 13
N e l2 (for a "finger' specimen with d 4{ r; d is the indenter diameter, r the distance of the indenter from the axis of the table).
Design o f the cm,otribometer. This meets, in the main, the requirements set out by Kharitonova. 6 Special attention is paid to maintaining the cleanliness o f the surface of the specimens, to the reliability o f the cooling, and to the stability in measuring characteristics of the strain gauges. The cryotribometer is provided with a sealed means of rotation, with bellows sealing off the measuring arm, fixed to a universal joint, and with viewing windows for observing the measuring the rate of rotation visually with a stroboscopic tachometer. The frictional couple is measured with strain gauges placed outside the measuring chamber. The cryotribometer consists of the case of the sealed chamber 5, the rotating specimen table, the measuring arm 10, the hinge 9, and the electrical unit 1 with the sealed rotation mechanism. All the main components are made of Xh 18N 9T steel. The cylindrical case o f chamber 5 is provided with viewing tubes 4, side tubes for letting in and removing gas, and jacket 6 for cooling the specimens and media in the chamber with liquid nitrogen or air. Lid 7 with the viewing window can be replaced by a flange for evacuating the chamber. The internal diameter o f the chamber is 93 mm and the height 200 mm. Arm 10 is a double walled hollow rod 25 mm in diameter with an evacuated heat insulating jacket. It is designed to transmit a normal force to the indenter and transmit the frictional force to the ring-shaped spring element 11 with strain
gauges stuck on. The specimen being studied, the indenter 2, is fixed to the lower face of the rod. The movable sealing of the arm into the test chamber is achieved by bellows 8. The indenter is cooled by introducing liquid nitrogen inside the rod. Hinge 9 is the point of support of tire rod and has 4 rocking bearings. The drive for the rotating table is a sealed constant current electric unit with screened magnetic coupling. The bearing shafts o f the rotor are the self-lubricating dry friction rocking bearings with permanent F - 3 separators. A smooth change in the number of revolutions is achieved by varying the voltage to the motor.
Measuring syswm. The balancing force F c is measured by four strain gauges stuck to ring 11 and connected into a bridge circuit; a P Sr 1 recording potentiometer is used in conjunction with them. The potentiometer is calibrated by loading the ring with standard weights. The error in measuring the balancing force does not exceed 0.02 N. The temperature of the specimens and of the medium between 90 and 300 K are measured by copper-constantan thermocouples using an E P P - 0 9 potentiometer; the accuracy is -+2 K. The rate of rotation of the table is measured with an S T - 5 strobscopic tachometer, and the vacuum in the chamber goes down to 10 -5 tort. The main technical data o f the K T l cryotribometer. The maximum frictional couple is 0.1 N m, the rate of rotation can be varied from 600 to 6 000 rev min -1 : the indenter temperature varies from 90 to 300 K; the radius of rotation is 0 to 25 ram; the nom~al load is 0.5 to 5 N; the drive voltage (constant current) 3 to 27 V; the weight of the cryotribomeler (without the associated equipment) is 50 kg; the dimensions are 1 100 x 860 x 420 mm 3.
References 1 Braun, Barton Apparatus Jor Scientific Im'esti~,ations No 12 (1966) 61 2 Bruske, Ekman Apparatusfi~ Scientific lm'esti,eations No 9 (1963) 17 3 Buckley, D. H., Johnson, R. L. ASLE Trans 8 (1965) 123 4 King, R. F., Tabor, D. ProcPhysSoc B 66 (1953) 728 5 El'kim, A. 1., Bartenev, G. M. hMustrial Laboratory No 2 (1963) 227 6 Kharitonova, L. D. {h~h'ersiO,Proceedin,es: Mechanical f:'n~uneer in,~ No 6 11969) 43
A cryogenic temperature controller A. Tominaga The device described here was designed for use with resistance thermometers in the measurement and control of temperature. It has been used successfully with carbon and germanium resistance thermometers to control the temperature in several types of low temperature cryostats over a range of 0.3 to about 6 K.
was versatile, simple to operate, and very reliable. The sensitivity was to be as high as possible, consistent with the opposing goal of low dissipation in the themlometer resistante. The secondary objective was to produce a design which could be quickly and easily duplicated.
Numerous designs exist for thermometer controllers.1 7 The design objective here was to produce a controller which
Description of the circuit
The author is with the Department of Physics, Tokyo University of Education, Tokv,, !a'~an. Received7 January 1972.
C R Y O G E N I C S . O C T O B E R 1972
The bridge circuit (Fig.2) which compares the resistance of the thermometer with the precision decade resistor 8 is the same type as that used by Royer P. Ries and B. Keith Moore. 7 An input transformer is used as a bridge trans-
389