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An apparatus for measuring the length of liquid hydrogen targets
The consumption of liquid hydrogen in this target is exactly the same as in that described above. One can work with an electron beam without ref'dling with hydrogen for 4 to 5 days. If necessary, the hydrogen reservoir and one of the targets can be f'dled with liquid He4 and the other with He 3 by condensing the gas. The authors are very grateful to O. V. Evlanov, I. M. Arkatov, and V. I. Petran'for organizing the test runs and for help in the development and adjustment of the target control system.
References 1 2 3 4 5 6 7
Cook, L. Rev Scilnstr 22 (1951) 1006 Wdson, R. Rev Scilnstr 29 (1958) 732 Whalin, E. A., Reitz, R. A. Rev Scilnstr 26 (1955) 59 Nagle,D. E. Phys Rev 97 (1955) 480 Montelatici, V. NucllnstrandMethods 29 (1964) 121 Svenson, C. A., Stahl, R.H. Rev Scilnstr 25 (1954) 608 Chambers, B., Hofstadter, R., Marcum, A., Yearian, M. Rev Scilnstr 34 (1963) 1019 8 Ritson, D. Experimental Methods in High Energy Physics (Nauka, 1964) 9 Afanas'ev, N. G., God'dshtein, V., A., Dementii, S. V., Evlanov, O. V. et al Prib i Tekh Eksper No 3 (1968) 30
An apparatus for measuring the length of liquid hydrogen targets Yu. P. Dmitrevskii, V. V. Elestratov, and A. F. Prudkoglyad Liquid hydrogen and liquid deuterium targets, which are essential instruments in experiments on the interaction of high energy particles with protons and neutrons, consist of vessels for liquefied hydrogen and deuterium enclosed in vacuum jackets which provide the necessary thermal insulation. In many experiments with an increased accuracy in measuring the cross-sections of the interacting particles, the accuracy in determining the target length along the beam must be improved. While it is not always possible to fit plane target windows, and a determination of the mean effective length of target becomes inadequate, it is necessary to measure the target geometry in directions transverse to the beam. The usual procedure for determining the target length or the distribution of lengths (the geometry) across the beam is to measure the corresponding sections at room temperature and convert them to hydrogen temperature. However, considerable errors arise in such calculations because the integrated expansion coefficients of real materials used in constructing targets are either different from tabulated values or have not been measured. The beam windows of target vacuum jackets are now generally made from Mylar or Lawsonite film, which reduces the amount of unwanted matter in the path of the particles and at the same time makes visual observation of the geometry of the ends of the target possible. In our experiments we had to measure with an accuracy of a few hundredths of a per cent the length of liquid hydrogen targets made of 1 Kh 18N 10T steel, M3S copper, domestic Lawsonite film, and various type of imported material. For this purpose we constructed an optical apparatus to measure directly the length of the target in the working state through the transparent Lawsonite windows of the vacuum jacket, focusing the image of sections of the surface of the target in the object plane The authors are w i t h Institute of High Energy Physics, Serpukhov, USSR. 1972.
310
Prib i Tekh Eksper No 4 (1972) 238. Received 4 December
of a microscope. The essential part of the method is the comparison by optical means of the length of various parts of the target with an end gauge of just the same length as the target. The length of the gauge is determined to high accuracy by standard methods. The difficulty of such methods lies in the rather large distance from the vacuum jacket to the target windows because of constructional or physical considerations. For example, in our case these distances were from 150 to 600 mm. The optical system of the apparatus used is shown in Fig. 1. Objective 1 produces an image of the object, placed at twice the focal distance to the left of it I - I , in a plane at twice the focal distance to the right I I - I I . The object is viewed through the long focus microscope 2 - 3 . On moving the object along the optic axis of the objective, its image goes outside the object plane of the microscope and if this movement is more than the depth of definition of the mic~uscope, the image seen in the microscope loses
5
4
1
Fig.1 Optical system of the instrument 1 - interchangeable photo-objective, 2 -- MG microscope objective, 3 -- MG microscope eyepiece, 4 - 0 | - 1 9 lamp, 5 - half-silvered mirror, 6 -- transparent target vacuum jacket w i n d o w , | - I -- object measuring plane, l [ - | [ -- imaging plane of the object
CRYOGENICS. MAY 1973
References 1 2 3 4 5 6 7
Cook, L. Rev Scilnstr 22 (1951) 1006 Wdson, R. Rev Scilnstr 29 (1958) 732 Whalin, E. A., Reitz, R. A. Rev Scilnstr 26 (1955) 59 Nagle,D. E. Phys Rev 97 (1955) 480 Montelatici, V. NucllnstrandMethods 29 (1964) 121 Svenson, C. A., Stahl, R.H. Rev Scilnstr 25 (1954) 608 Chambers, B., Hofstadter, R., Marcum, A., Yearian, M. Rev Scilnstr 34 (1963) 1019 8 Ritson, D. Experimental Methods in High Energy Physics (Nauka, 1964) 9 Afanas'ev, N. G., God'dshtein, V., A., Dementii, S. V., Evlanov, O. V. et al Prib i Tekh Eksper No 3 (1968) 30
An apparatus for measuring the length of liquid hydrogen targets Yu. P. Dmitrevskii, V. V. Elestratov, and A. F. Prudkoglyad Liquid hydrogen and liquid deuterium targets, which are essential instruments in experiments on the interaction of high energy particles with protons and neutrons, consist of vessels for liquefied hydrogen and deuterium enclosed in vacuum jackets which provide the necessary thermal insulation. In many experiments with an increased accuracy in measuring the cross-sections of the interacting particles, the accuracy in determining the target length along the beam must be improved. While it is not always possible to fit plane target windows, and a determination of the mean effective length of target becomes inadequate, it is necessary to measure the target geometry in directions transverse to the beam. The usual procedure for determining the target length or the distribution of lengths (the geometry) across the beam is to measure the corresponding sections at room temperature and convert them to hydrogen temperature. However, considerable errors arise in such calculations because the integrated expansion coefficients of real materials used in constructing targets are either different from tabulated values or have not been measured. The beam windows of target vacuum jackets are now generally made from Mylar or Lawsonite film, which reduces the amount of unwanted matter in the path of the particles and at the same time makes visual observation of the geometry of the ends of the target possible. In our experiments we had to measure with an accuracy of a few hundredths of a per cent the length of liquid hydrogen targets made of 1 Kh 18N 10T steel, M3S copper, domestic Lawsonite film, and various type of imported material. For this purpose we constructed an optical apparatus to measure directly the length of the target in the working state through the transparent Lawsonite windows of the vacuum jacket, focusing the image of sections of the surface of the target in the object plane The authors are w i t h Institute of High Energy Physics, Serpukhov, USSR. 1972.
310
Prib i Tekh Eksper No 4 (1972) 238. Received 4 December
of a microscope. The essential part of the method is the comparison by optical means of the length of various parts of the target with an end gauge of just the same length as the target. The length of the gauge is determined to high accuracy by standard methods. The difficulty of such methods lies in the rather large distance from the vacuum jacket to the target windows because of constructional or physical considerations. For example, in our case these distances were from 150 to 600 mm. The optical system of the apparatus used is shown in Fig. 1. Objective 1 produces an image of the object, placed at twice the focal distance to the left of it I - I , in a plane at twice the focal distance to the right I I - I I . The object is viewed through the long focus microscope 2 - 3 . On moving the object along the optic axis of the objective, its image goes outside the object plane of the microscope and if this movement is more than the depth of definition of the mic~uscope, the image seen in the microscope loses
5
4
1
Fig.1 Optical system of the instrument 1 - interchangeable photo-objective, 2 -- MG microscope objective, 3 -- MG microscope eyepiece, 4 - 0 | - 1 9 lamp, 5 - half-silvered mirror, 6 -- transparent target vacuum jacket w i n d o w , | - I -- object measuring plane, l [ - | [ -- imaging plane of the object
CRYOGENICS. MAY 1973