RU993762C - Duoplasmatron - Google Patents

Description

duoplasmatron chambers. Two tungsten filaments and a crucible, which is usually made of tantalum or graphite (for various starting materials) with a chamber temperature limit of 1 ° C, are placed in a chamber (usually molybdenum), which is the anode.

The disadvantages of the known sources are the low working currents of ions (100 μA and a low coefficient of ionization of the substance -

The closest technical solution is an ion source - a duoplasmatron containing an anode with a conical expander, an intermediate electrode with a cavity, in which a working substance input device is located in the form of a crucible with a conical body and a channel made at its apex, a cathode located in the crucible cavity, and an extractor with a hole.

The known source provides a large ion current of up to 10-20 shA, which is achieved due to the location of the cathode in the inner cavity of the intermediate electrode C. The cavity of the intermediate electrode is equipped with an additional pumping system. The working substance is placed in an evaporator, which is inserted into the cavity of the intermediate electrode with a set of heat-insulating screens. The working substance is heated sequentially by thermionic emission current 31 with a cathode and an arc current ignited between the cathode and the intermediate electrode. After ignition of the cathode, the anode is extracted from the plasma surface filling the anode expander cup by applying a high potential difference between the anode and the extractor

(15-20 kV). . i

A disadvantage of the known source is the limited operating time with maximum efficiency due to overgrowth of the hole in the expander,

The aim of the invention is to increase the operating time of the source with

This goal is achieved by the fact that in the source of ions, a duoplasmotron, containing an anode with a conical expander, an intermediate electrode with a cavity in which the input device of the working substance in

a crucible with a conical body and a channel made at its apex, a cathode located in the crucible cavity, and an extractor with an aperture, between the conical body of the crucible and the anode expander there is a system of screens located in contact with each other, electrically connecting the intermediate electrode and the anode, and in the outlet of the extractor from the side opposite to the anode, a thermal cathode is installed in the ring, so that the focus of the electron beam emitted by it coincides with the channel exit to the crucible orpus facing the anode

In Fig. A shows a source, a section; in FIG. - the main elements of the source, forming the path, Forming an ion beam; Fig. 3 design of the crucible

The source contains an anode 1, which is a cylinder made of Hbiid steel Sts 3 with a hollow cavity - for water cooling. An expander 3 is inserted into the hole of the anode 1 1b mm, made in the form of a cone made of steel Sts 3 with an angle at the apex of 9 °, inside the cone a cylindrical cavity is machined 10 mms. The diameter of the hole at apex 1, mms

To feed the cathode made from the tantalum cavity, there are water-cooled copper bushings mounted in the water-cooled cover 5 of the cup 6 made of stainless steel 12Xl8MlOTj insulated from it using ceramic-metal insulators 7. Intermediate electrode 8 made of steel St 3, ends with poles with a channel along the discharge axis 1 and a length of 5 mm “T-, gel 9 assembly and intermediate electrode 8 placed in a water-cooled case made of steel X18H10T, on which a solenoid coil of a U-shaped electromagnet is mounted Volume 10, The magnetic flux from the coil is closed using an external magnetic wire 11 made in the form of a set of armco iron plates, which are isolated from the anode using fluoroplastic gaskets.

For cooling the source casing, it has a water-cooled cavity for its convenience. For convenience, when developing and assembling the source, a junction of current-carrying wires from

power supply with flexible wires by means of pressure contacts 12

The extractor 13 is made of STOZ in the form of a cone-shaped electrode with an apex angle of 110 and a hole with a diameter of 10 mMo. The extractor is separated from the anode by a vacuum gap of 5 mMo. On the side of the extractor opposite the anode, a ring tungsten thermal cathode 14 (0.2 mm) is mounted so that the focus position of the electron beam coincides with the output of the crucible channel 9

In the cavity of the intermediate electrode 15 there is a crucible 9o enclosed in a molybdenum case. Fig. 3 shows a crucible for receiving carbon ions. The crucible 9 contains an output channel 16, a set of heat shields 17, cathode glow electrodes 18 and a cathode A enclosed in a 19o molybdenum. Consider more the crucible design for carbon in detail Since graphite evaporates without passing into the liquid, it is introduced into the evaporator in the form of a cup 20 with a wall thickness of 3 mm, which adheres tightly to the inner surface of the evaporator.

The crucible (Fig. 3) is a cylinder at the base with a cone, the angle at the apex of which is 90 /, the cone has a 3 mm hole at the apex. Two tantalum cathode feed electrodes are inserted into the evaporator through two holes in the set of upper screens for sealing and high-temperature ceramics. The source cathode is made in the form of a 12 mm ring from a tantalum cavity (0.1 mm thick, 2 mm wide), attached by spot welding to electrodes 18 „

The evaporator is surrounded on all sides by heat-insulating screens 17 made of tantalum and molybdenum foil with a thickness of 0.2 mm. “Top screens - a set of flat disks with extruded conical protrusions that prevent the screens from sticking together; side screens - a set of cylinders with the same protrusions, the bottom - a set of coaxial truncated cones. By calculations and experimentally it was established that the optimal number of screens for the case of carbon is 13-1 ppm. When assembling the source, the evaporator unit is installed in such a way that mechanical and electrical contact between the lower screens and the expander is ensured and the channel output of the intermediate electrode is connected to the channel input of the expander.

Let us consider the operation of a source using the example of carbon-ion production. Heating graphite to a temperature that ensures its vapor pressure rToSTo, necessary for arc burning, is carried out in 2 atana: l) before ignition of the arc, heating is carried out by thermionic current from the heated cathode 4 to the internal walls of the evaporator 1b 0 4-0.5 A, 220-. 250 V 2) after ignition of the arc, which occurs when the required vapor pressure is reached, heating is performed by the same arc (5-6 A,

0 IfO-50 c) Simultaneously with the ignition of the arc between the cathode and the inner walls of the evaporator, the main arc between the cathode and the anode and the duoplasmatron ignites;

for operating mode „

The extraction of the ion beam from the surface of the plasma filling the expander is carried out with the quasi-Pierce electrode system, the first

0 the electrode of which is the conical shape of the anode 1, the second extractor is 13 °. The ion source, which is in the process of working under a voltage of 20 kV, is separated from the vacuum

5 cameras (not shown) with a high-voltage isolator,

During long-term operation of the source (10 hours or more), as already noted, the channel of the intermediate electrode overgrows with working substances (in the graphite case under consideration), which leads to a significant (1.52-fold) decrease in the ion current

5, the drawback that exists during long-term operation is eliminated by introducing an annular tungsten, male cathode l (Fig. 2) concentrically to the hole in the extractor, below

0 to the top edge of the extractor opening by 0.5-1 MMo Such an additional cathode located under the ground potential, together with the central part of the source anode located

5 under high positive potential, form a ring electron gun, the electron beam of which is focused at the output of channel 1b crucible 9 about

Pe |;) And (; L 1che; a short inclusion of the munga for a short period of time (not ;;; ko, seconds) completely restored the channel diameter to the original Beliyiina and thereby practically unlimitedly extends the period of continuous stable operation of the source And dlkte.pos for continuous operation, source 5-: and;: a is determined by the amount of working solution introduced into the evaporator 70 M);,

Due to the fact that it is always used in ion sources such as Luoplg13ma iPOH, it is located in the middle of the electrode and the anode in the isoform of the intermediate electrode) and in the invention of the intermediate electrode by means of a system: shields 17 (FIG. 2) connected to anode expander was dripping in. At 3TOf-i, the electric value is 1: .op;: the interference between them in the operating mode is several hundred ohms, then the ignition cathode is ignorant. In this case, the path of the passage of high concentration plasma from the channels of the intermediate electrode DS-) is reduced. - It maintains its high 1 - :: og center 11, and by decreasing the dispersion (lack of clearance) s, this pair is either ionized by fast e-electron in the channel of the intermediate electrode, or, when it enters the channel of the expander, it is ionized, which also increases the concentration of positive ionoses , and therefore the value of the maximum recoverable

0 ion current, The ion current to the walls also decreases, which leads to a similar positive effect. The described technique allowed to increase the current of positive ions at the output

5 sources for 20-25, obtain currents of 1225 nijii for ions of the indicated substances. at an accelerating voltage of 18 to 20 kP (against the usually obtained 1020 A)

Moreover, the proposed source allows for a normal pumpdown system 1 and to obtain a vacuum in the working volume not x: / same 10

This ion source, while retaining all the positive qualities of a duoplasmatron type swirl source, provides the possibility of producing solid ions, has a higher efficiency and a longer period of continuous operation,

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