RU2465620C1 - Drift chamber for operation in vacuum - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: base of the chamber used is a full ring with pairs of holes for drift tubes lying in a quasi-checkered order. Drift tubes, having tips with insulating inserts at the ends are tightly mounted in bushings which are in turn leak-tightly fitted in pairs of holes in the chamber with possibility of movement, and the tips for the tubes and insulators for supporting the anode wire have an external cross-section which is in form of a convex n-sided regular polygon.

EFFECT: high accuracy of restoring coordinates of charged particles passing through the chamber operating in a vacuum.

6 cl, 2 dwg

Description

Technical field

The invention relates to ionization multiwire coordinate detectors and can be used in experimental nuclear physics to detect nuclear radiation, in particular, to accurately determine the coordinates of charged particles passing through the chamber in a vacuum medium with low energy loss or at atmospheric pressure. It can also be used in other branches of science, where the determination of the coordinates of ionizing radiation passing through the chamber is required.

Over the past few decades, in experimental nuclear physics, wire drift chambers have been widely used, based on the principle of measuring the time of arrival of the first electrons to the anode, which appear when charged particles pass through them, and multiplied in a strong radial electric field near the anode in the form of a thin wire. In particular, such electrons are also formed in chambers consisting of thin-walled drift tubes of metal or insulating material metallized from the inside, with a thin anode wire at high potential in the center. To obtain the exact coordinates of the particles passing through the tubes, it is necessary to match the real mechanical parameters of the chamber to its calculated geometric characteristics — the accuracy of the location of the ends of the tubes in the chamber, their straightness, the constancy of the diameter of the tubes along the entire length, the accuracy of the location of the anode along the axis of the tubes, etc., and also high temporal resolution of used electronics.

State of the art

Drift chambers based on thin-walled tubes made of insulating material metallized from the inside and anode wire located along their axis with a tube length of up to 4000 mm and containing coordinate planes in an amount of 2 ÷ 4 (X, Y, U, V) are known and widely used in experiments. ), see for example [1-5].

Analogs of such chambers [6] and [7], close to this invention, have two rows or more closely spaced tubes to create geometric tightness of the chamber and to resolve the left-right uncertainty that occurs when a charged particle passes through the tube to the right or left from the anode wire. In the chamber [6], the tubes are arranged in two circles between two metal disks with holes and are glued together, and the camera from [7] represents a rectangular structure with openings for the tubes on the sides. But such a scheme for constructing chambers when they are working in a vacuum, where a high vacuum density of each tube is required, significantly complicates the problem of sealing them and, moreover, does not allow each tube to be individually pulled to increase their straightness. This is their fault.

Closest to the proposed drift chamber (prototype) is a drift chamber for working in a vacuum volume, described in [8], which includes a design with nodes located on opposite sides of the chamber and having paired coaxial through cylindrical holes. In them, with the possibility of their coaxial movement relative to each other, thin-walled metallized inside, parallel to the plane drift tubes made of flexible insulating material serving as a cathode, with an anode wire along their axis, having metal lugs at both ends with insulating inserts inside hermetically fixed on one side at the ends of the tubes, and on the other hand, in the pair of holes on the chamber and used to center the anode wires, isolate them from the cathodes, seal the tubes, going outside in a vacuum, and inside at high pressure, supplying working gas inside the tubes, as well as zero potential, high voltage and output electrical signals.

The disadvantage of this device is that the tips inserted into the ends of the tubes are used without taking into account their variation in diameter, and thus they do not allow the tube ends to be positioned as precisely as possible in the chamber, and therefore the tubes themselves. This remark is also true for the arrangement of wires passing through the center of these tubes. In addition, the tubes in the device are arranged in two rows, close to each other, which complicates their sealing. In addition, this design has a complex system for simultaneously pulling out all the tubes in order to improve their linearity with the transfer of mechanical motion to vacuum, while simultaneously pulling all the tubes, due to the obvious scatter in the initial tension, can lead to pulling some of the tubes more than acceptable, or part the tubes will have insufficient tension. In addition, if it is necessary to measure two or more particle coordinates in an experiment, it is impossible to place a second or more coordinate in the device. This will require the manufacture of two or more practically independent cameras, which will complicate the device and, at the same time, due to the large distance between the coordinate planes, will significantly increase the parallax, which directly affects the accuracy of restoring the coordinates of the particles in the camera. We also note that when replacing a tube that has failed in the chamber, it will be necessary to drill glued tips with tubes and gluing new ones, which is not easy to carry out in an already assembled chamber.

Disclosure of invention

The invention solves the problem of increasing the accuracy of restoring the coordinates of particles passing through the chamber by simplifying the design and increasing its rigidity, reducing the dead zone of the chamber and, at the same time, makes it possible to arrange two, three, four or more coordinate planes in one chamber, which reduces parallax; and also allows you to simplify the change of the tube that failed.

The technical problem in the proposed chamber is solved by making the structural unit of the chamber in the form of a solid ring, and the pair of holes are located in a quasi-chessboard order on its side surface, parallel to its diameter. Drift tubes having tips at both ends with inserts are hermetically sealed on the outside in additional bushings, which, on the other hand, are vacuum-tightly mounted in pair holes with the possibility of movement and have an inner diameter equal to the maximum diameter of the tubes used dmax. = Dav . + Δd, taking into account their scatter - dtp. = Dcp. ± Δd, where Δd is the scatter of the diameter of the tubes, in addition, the tips with inserts are made with an external cross section in the form of a convex regular n-sided polygon, which is derived from the condition The number of the parties:

Δl = dmax. (Π-2nSin (π / n)) = 2Δd,

where Δl is the difference between the length of the circumscribed circle and the perimeter of the polygon, dmax. is the maximum diameter of the tubes used, n is the number of sides of the polygon, and Δd is the variation in the diameter of the tubes; with the diameter of the circumscribed circle equal to d = dmax.-2h-ε, where h is the tube wall thickness, ε is the accuracy tolerance; the tips themselves, sealed at one end in the tubes and free at the other end, the vertices of the polygon always rest on the inner surface of the tubes, centering them, and through them on the inner surface of the bushings; at the same time, within each tube, within the length of the bushings, self-centering insulators with a hole in the center for the anode wire are introduced, also having the shape and dimensions of a convex regular polygon in cross section and also satisfying the conditions

Δl = dmax. (Π-2nSin (π / n)) = 2Δd,

where Δl is the difference between the length of the circumscribed circle and the perimeter of the polygon, n is the number of sides of the polygon, and Δd is the spread in the diameter of the tubes.

In addition, all the holes in the ring have two diameters - the inner one, equal to the fit size of the bushings, and the outer one, with a large diameter, with a vacuum seal installed in it; while the bushings located in the holes on the side of the tube entry into the chamber have a girdle for abutment in this seal, and on the other end of the sleeve they have a smooth surface, with the possibility of moving in the holes by pulling the end, for example, with a spring or nut, for each tube separately. In this case, the landing dimensions of each hole, from the side of the tube entry into the chamber, are 0.05 ÷ 0.2 mm larger than its paired hole and the landing dimensions of the bushings at the ends of each tube differ by the same amount; all tips with an insert on the outside are provided with a shoulder that abut against the outer end of the sleeve; and with a long tube length, self-centering insulators are also installed along their axis, every 700 ÷ 1000 mm, with supports on the outside of the tubes in these places.

The second, third, fourth and more coordinate planes shifted along its axis are additionally introduced into the whole ring with corresponding paired holes and drift tubes, also located in a quasi-chessboard order at an angle to the horizon (or to each other) within 0 ÷ 180 °.

Distinctive features of the invention are:

- an integral ring, as the base of the chamber, which, in view of its stiffness, can significantly simplify its design. Moreover, when the chamber is operated in a vacuum, atmospheric pressure does not distort its shape, unlike other forms of the chamber. Consequently, there will be less mechanical distortion both from atmospheric pressure and from the tension of the tubes, which will significantly affect the accuracy of the location of the tubes;

- the quasi-chessboard arrangement of the holes for the tubes allows the chamber to be opaque to the incident particles, practically not increasing their number, and thereby not increasing the amount of substance in the beam. This arrangement eliminates the gaps that occur when the tubes are separated, through which particles pass through unregistered ones. With the known maximum angle of incidence of particles on the plane of the chamber, which is usually determined by the experimental conditions, it is possible to sequentially move the tubes in the chamber toward its center with a small step determined by this angle (usually not exceeding 5 degrees), and thus block all the cracks. Since this arrangement of tubes is slightly different from staggered, it can be called quasi-chessboard;

- drift tubes have tips at both ends with a cross section of a regular polygon and outside their ends are hermetically fixed in additional bushings, which for their part are vacuum-tightly mounted in pair holes, with the possibility of moving each tube separately in them, which allows them to be individually pulled and thereby straighten them;

- the inner diameter of the bushings is equal to the maximum diameter of the tubes used dmax. = dcp. + Δd, taking into account their dispersion - dtr. = dcp. ± Δd, where Δd is the magnitude of the variation in the diameter of the tubes;

- tips with inserts are made with an external cross-section in the form of a convex regular n-sided polygon, the number of sides of which is derived from the condition:

Δl = dmax. (Π-2nSin (π / n)) = 2Δd,

where Δl is the difference between the length of the circumscribed circle and the perimeter of the polygon, dmax. is the maximum diameter of the tubes used, n is the number of sides of the polygon, and Δd is the variation in the diameter of the tubes;

- lugs with a polygon cross-section, hermetically fixed at one end in the tubes, and loose at the other end, the vertices of the polygon always rest on the inner surface of the tubes, centering them, and through them on the inner surface of the bushings; the difference between the maximum diameter of the tubes and the perimeter of the polygon allows the tip to penetrate into the tube and center it relative to the sleeve within ± Δd, while the round tip, with a small diameter of the tube, cannot penetrate the tube or, having a diameter smaller than that of the tube , will not be able to center it;

- Self-centering insulators with a hole in the center for the wire, also having a cross-sectional shape and dimensions of a convex regular polygon and also satisfying the conditions

Δl = dmax. (Π-2nSin (π / n)) = 2Δd,

where Δl is the difference between the length of the circumscribed circle and the perimeter of the polygon, n is the number of sides of the polygon, and Δd is the magnitude of the dispersion of the diameter of the tubes;

- the presence in the holes of two diameters - an inner one, equal to the fit size of the bushings, and an outer one with a large diameter, with a vacuum seal installed in it, allows you to install the bushings in the chamber strictly and, at the same time, vacuum seal them with the ability to move;

- the presence of a belt on the bushings located in the holes on the side of the tube entry into the chamber to abut this seal does not allow the vacuum to draw the tubes into the vacuum volume; and at the other end, sleeves having a smooth surface, with the possibility of movement, are held in the holes by pulling the end, for example, with a spring or nut, for each tube separately, to straighten the tubes and, at the same time, to hold the tubes in place;

- an increase in the mounting dimensions of each hole from the side of the introduction of the tubes into the chamber by 0.05 ÷ 0.2 mm compared to its paired hole and by the same size and the landing dimensions of the bushings at the ends of each tube makes it easier to install tubes with bushings in the workplace without compromising landing accuracy.

The combination of all of the above features allows you to increase the accuracy of restoring the coordinates of particles passing through the chamber by simplifying the design and increasing its rigidity, rigorous installation of tubes using additional bushings, as well as tips and insulators with a polyhedron cross-section. At the same time, the dead zone of the chamber is significantly reduced and the flow rate of tubes is reduced, and it becomes possible to arrange three, four or more coordinate planes in one chamber under vacuum conditions.

List of figures

Figure 1. A drawing of a two-coordinate drift chamber in the form of a single ring with tubes and quasi-chessboard holes.

Figure 2. Drawing of tubes assembly with lugs with insert and bushings.

A diagram of a two-coordinate drift chamber in the form of a solid ring is shown

figure 1 of application 1, where:

(1) - a camera in the form of a ring;

(2) - paired holes;

(3) - tubes.

Figure 1 presents the annular chamber. The one-piece ring (1) is the structural basis of the chamber. On its opposite sides, parallel to its diameter, there are paired coaxial through holes (2) located quasi-chessboard for drift tubes (3).

The diagram of the device tubes with lugs with inserts and bushings is shown in figure 2 of Appendix 2, where:

(4a) - flange tips;

(46) - inserts;

(5a) - sleeve from the input side of the tubes;

(5b) - smooth sleeve;

(6) - self-centering insulators;

(7) - anode wire;

(8) - vacuum seal;

(9) - girdle on the sleeve from the input side of the tubes;

(10) - spring with a holder.

Figure 2 presents a fully assembled drift tube in the chamber. Shown here is a tip (4a) with an insert, a sleeve (5a) on the tube entry side of the chamber, a smooth sleeve (5b) on the opposite side, self-centering insulators (6) with an anode wire (7) passing through them, a vacuum seal (8) located in the holes (2), the belt (9) on the sleeve (5a) and a spring with a stand for pulling tubes.

The implementation of the invention

A device for the case of a two-axis camera can be implemented as follows: a solid aluminum ring (1) {see Appendix 1, Figure 1} with flanges on both sides for connection to a vacuum system is made of forgings and processed in size. Then, a pair of holes (2) are drilled on the coordinate boring machine, on opposite sides of its side surface, parallel to its diameter; for a two-coordinate camera, the same holes are drilled, but shifted along the axis of the ring and at right angles to the first set of holes. Handsets (3) {see also Appendix 2, FIG. 2} the ends are hermetically glued into the bushings (5a and 5b), insulators (6) with anode wire (7) within the bushings are installed in them and, at the same time, lugs with a polyhedron cross-section and a shoulder (4a) are glued ) {flanges resting against the ends of the bushings (5a and 5b) do not allow the tips to penetrate further} with inserts (4b). Thus assembled tubes are inserted into the chamber from the inlet side into pairs of holes (2) on the chamber, sealed with vacuum seals (8) and abut with a girdle (9) located on the sleeve from the inlet side, into vacuum seals (8). Then, at the other end, the straightening tubes are pulled out using a spring with a stand (10) or a nut, the thread of which can be cut into an insulating insert. The magnitude of the tension of the tubes is measured with a dynamometer. After that, the anode wires are pulled to the desired size from the opposite side of the tubes and fixed by soldering or clipping.

After completing the assembly, testing the chamber for leakage, electrical testing, gas is supplied to the tubes, grounding, high voltage are supplied through the copper bus and control electronics are installed. Thus, the camera is prepared for registration of charged particles.

Charged particles passing through any tube create pairs of ions that begin to move to the corresponding electrodes. Electrons sent to the anode, getting into a strong electric field near it, multiply and give an impulse. By launching the trigger at the moment of the particle passage, using the control electronics, it is possible to measure the electron drift time and, therefore, at a known drift velocity, the exact place of the particle passage in the tube can be determined. In order to obtain high accuracy in measuring the coordinate of a particle, a high temporal resolution of the used electronics is required, but the closer the real mechanical parameters of the camera to its geometric characteristics - first of all, structural rigidity, exact location of the ends of the tubes relative to the structure, their straightness, accuracy the location of the anode along the axis of the tubes.

Literature

1. W. W. W. Ash et al. Nuclear Instruments and Methods, A261 (1987) 399-419.

2. M. Alvarez et al. Nuclear Instruments and Methods, A255 (1987) 486-492.

3. J. Adler et al. Nuclear Instruments and Methods, A276 (1989) 42-52.

4. K. Maeshima et al. Nuclear Instruments and Methods, A307 (1991) 52-62.

5. J.L. Popp. Nuclear Instruments and Methods, A472 (2001) 354-358.

6. P. Baringer et al. Nuclear Instruments and Methods, A254 (1987) 542-548.

7. K. Lang et al. Nuclear Instruments and Methods, A522 (2004) 274-293.

8. C. Kendziora et al. A Straw Drift Chamber for Operation in Vacuum Tank, Preprint FERMILAB - Pub-02/241-E.

Claims (6)

1. A drift chamber for working in a vacuum, including a design with nodes located on opposite sides, having paired coaxial, through cylindrical holes, with the possibility of coaxial movement relative to each other, containing thin-walled, metallized from the inside, drilled tubes parallel to it on the plane made of flexible insulating material, serving as a cathode with an anode wire along their axis, having metal tips at both ends with insulating inserts inside, g Sealed on one side at the ends of the tubes, and on the other in the pair of holes on the chamber, used to center the anode wires, isolate them from the cathodes, seal the tubes that are outside in vacuum, and inside at high pressure, supply the working gas inside the tubes as well as zero potential, high voltage voltage and output of electrical signals, characterized in that the structural unit of the camera is made in the form of a single ring, and the pair of holes are located in a quasi-chessboard order on its side surface and parallel to its diameter; in addition, drift tubes having tips fixed at the ends with inserts are externally sealed with their ends in additional bushings, which, for their part, are vacuum-tightly mounted in paired holes, with the possibility of movement, and have an inner diameter equal to the maximum diameter of the tubes used dmax = dav + Δd, taking into account their scatter - dav = dav ± Δd, where Δd is the magnitude of the variation in the diameter of the tubes; in addition, the tips are made with an external cross section in the form of a convex regular n-sided polygon, the number of sides of which is derived from the condition
Δl = dmax (π-2nsin (π / n)) = 2Δd,
where Δl is the difference between the length of the circumscribed circle and the perimeter of the polygon; dmax is the maximum diameter of the tubes used; n is the number of sides of the polygon, and Δd is the variation in the diameter of the tubes; with the diameter of the circumscribed circle of the polygon equal to d = dmax-2h-ε, where h is the wall thickness of the tubes; ε is the accuracy tolerance; the tips themselves, sealed at one end in the tubes and free at the other end, always rest on the inner surface of the tubes with the vertices of the polygon, centering them, and through them onto the inner surface of the bushings; at the same time, inside each tube, within the length of the bushings, self-centering insulators with a hole in the center for the wire are introduced, also having the cross-sectional shape and dimensions of a convex regular polygon and also satisfying the conditions:
Δl = dmax (π-2nsin (π / n)) = 2Δd,
where Δl is the difference between the length of the circumscribed circle and the perimeter of the polygon; n is the number of sides of the polygon, and Δd is the variation in the diameter of the tubes. 2. The device according to claim 1, characterized in that all the holes in the ring have two diameters - the inner one, equal to the fit size of the bushings, and the outer one with a large diameter, with a vacuum seal installed in it; while the bushings located in the holes on the side of the tube entry into the chamber have a girdle for abutment in this seal, and at the other end the sleeve has a smooth surface that can be moved in the holes by pulling it over the end, for example, by a spring or nut, for each tube separately. 3. The device according to claim 1, characterized in that the mounting dimensions of each hole on the input side of the tubes into the chamber are 0.05-0.2 mm larger than its paired hole, and the mounting dimensions of the bushings differ by the same amount at the ends of each tube. 4. The device according to claim 1, characterized in that on the outside all the tips with an insert are provided with a girdle that abuts against the outer end of the sleeve. 5. The device according to claim 1, characterized in that the self-centering insulators with a large length of the tubes are also installed along their axis, every 700 ÷ 1000 mm, with supports from the outside of the tubes in these places. 6. The device according to claim 1, characterized in that the second, third, fourth and more coordinate planes with corresponding paired holes and drift tubes, also located in a quasi-chessboard order, are angled to each other limits 0 ÷ 180 °.

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