Patent Number: 054065941
Section: description

With reference to FIG. 1 the injection system of the present invention is formed of a supporting construction, not shown in the figure, to which a pneumatic propulsion system, a cryogenic device and a vacuum system are connected. The pneumatic system includes a pneumatic propulsion system 1 formed of a first; stage 2, a second stage 4 and two valves 3 and 6 which will be described in more detail afterwards. The first valve 3 separates stage from stage 4, the other valve 6 separates the propulsion system 1 from the launching barrel 7. Within the second stage 4 the compression piston 5 (or more pistons) is placed. The feeding of said propulsion system 1 is provided by gas cylinders 8 through a set of valves and pressure reducers 9. The gases ejected by the propulsion system 1 flow through launching barrel 7 of cryogenic device, valve 10, diagnostic station D, and valve 10A into decompression chambers 11 and 12, from which the gases are evacuated through a vacuum system. The decompression chambers are separated from each other by valve 13, and a valve 14 separates chamber 12 from the machine using the pellet. The cryogenic device is formed of a Dewar flask 15 from which the fluid for refrigerating one or more copper flanges 18 is sucked through a special transferring pipe 16 which will be described afterwards. The flanges are placed within cryostat 17 and are welded to the launching barrel 7 so as to generate a cold point along the barrel at which the pellet will solidify. At the sides of flange 18 two electric resistances 19A and 19B limiting the cold zone are connected to barrel 7 in thermal contact therewith. The whole assembly is protected by a radiation screen 20 which is also cooled by the fluid conveyed then to a recovery line 21 provided with valves 22 and 23 and a differential pressure gage 24. The gas (isotopes of hydrogen) necessary to the construction of the pellet is supplied by a gas cylinder 25 through line 26 provided with a pressure reducing valve 27, a flowmeter 28, a pressure switch 29 and a valve 30. The gas is then sucked to the cold point by cryopumping. The vacuum system includes a rotating pump 31 which evacuates second stage 4, cryostat 17 and launching barrel 7 through valves 32, 33 and 34, respectively, the vacuum measurement being effected in the above cryostat by means of two vacuum gages 35 and 36. Decompression chambers 11 and 12 are evacuated through valves 37 and 38 by turbomolecular pump 39, valve 40 and rotating pump 42. Downstream of valve 40 the vacuum gage 41 is provided. The turbomolecular pump is provided with a water cooling circuit; 43 and a gas nitrogen circuit 44 used in the stopping phase of the turbine. The vacuum is monitored by means of a pressure transducer 45 and two vacuum gages 46 and 47. FIG. 4 shows a preferred embodiment of valve 3. It includes a pressure-containing member or shutter 3a and a valve seat 3b separating first stage 2 from second stage 4. The shutter is pneumatically driven by high pressure gas through an inlet port, 52 and a conduit 54 upstream of chamber 50. The gas flows along the walls of the shutter and fills first stage 2. As shown shutter 3a is cylindrical and provided with a little shoulder 56 to start the stroke when the upstream chamber 50 is evacuated to the atmosphere through electrovalve 58 at one end of conduit 54. As shutter 3a is separated from valve seat 3b the high pressure in stage 2 acts on the section of the shutter and causes the latter to move very quickly backwards. When electrovalve 58 is closed the gas supplied from inlet 52 pushes quickly shutter 3a forwards, thus closing valve seat 3b, and then is drawn down to fill stage 2 again. FIGS. 5a and 5b show a preferred embodiment of valve 6. The main feature of such valve is of assuring the separation between cryostat and propulsor with a good vacuum sealing, which is essential when cold components are processed with a very small volume in order to keep a good compression ratio and then a good performance of the propulsor. Such valve includes a body 61 in which the sliding seat of a slide 65 is formed, the latter being a blade provided with a small hole 66 and a slot 68 receiving a pin 70. The slot restricts the stroke of the slide which opens or closes the cross channel 72 connecting second stage 4 to launching barrel 7. The movement of the slide is controlled by a pneumatic actuator, not shown, which is rigidly connected to bracket 74. FIG. 6 shows a preferred embodiment of the transferring pipe 16. Pipe 16 allows the saturated vapours of tie to be drawn at a temperature of about 42K disregarding the amount of liquid contained in Dewar flask 15. It includes two branch pipes 16a and 16b which are inserted into Dewar flask 15 and cryostat 17, respectively. The pipe is insulated by a vacuum sheath, and its end which is intended for the suction of the cold gas from the Dewar flask is provided with four holes formed at an upper level than the height which can be reached by the liquid in the Dewar flask. Thus the pipe may draw only the vapour which is cooled through the sheath 16c and flows in the inner coaxial pipe 16d to reach cryostat 17. The circulation of only the vapours avoids the drawback of the thermal oscillations produced in case of a cycling liquid. FIG. 7 shows a preferred embodiment of the expansion or decompression chambers 11 and 12. These chambers are formed of two identic tanks connected in series with the interposition of valve 13. As shown, the gases are conveyed in each tank through a pipe 82 the diameter of which is essentially lower than the width of the tank but considerably larger than the diameter of the pellet. Pipe 82 extends axially and is provided with dynamic impedances formed by suitable shaping of inlet ports 84 and output nozzles 86. Because of the supersonic rate of the pellets said chambers provide a good separation of the propelling gas even with reduced overall dimensions with respect to the systems of the status of art and without guide pipes which cannot be used for very rapid pellets. The decompression chamber system seeks to combine three criteria to separate the propelling gas from the pellet: 1) expanding the gas in a volume (100+100 liters) which is evacuated to bring down the pressure; PA1 2) retarding the gas in crossing pipes and impedances; PA1 3) cutting off the system by closing quick valves which are actuated after the pellet is passed in order to entrap the gas upstream thereof. The quick closure of valve 3 and the relatively quick closure of valve 6 contribute to the reduction of the gas flow. A propulsion system provided with two pistons is schematically shown in FIG. 2b. In this case the main compression piston 5 is placed downstream of a secondary piston 5a provided with a suitable hole. An injector provided with several barrels is shown in FIG. 3 where there are four pneumatic propulsors 1 and four launching barrels 7. The completely automized operation of the system according to the invention is controlled by a programmable logic controller PLC, in which the operative sequence for the case of gaseous deuterium is stored, as follows. After the whole system is supplied with power, second stage 4 of propulsion system 1, cryostat 17 and launching barrel 7 are evacuated by rotating pump 31. A preliminary vacuum is established in decompression chambers 11 and 12 through rotating pump 42 and afterwards a lard vacuum is provided by turbomolecular pump 39. After the limit vacuum in cryostat 17 is reached, the cooling circuit of the cryogenic system is activated. As the temperature of cryostat 17 is reduced below 100K, valve 33 is closed so that cryostat 17 remains under static vacuum conditions. The subsequent cooling causes the vacuum grade to improve by cryopumping. When the temperature of the system reaches a value lower than 20K, gaseous deuterium from gas cylinders 25 is allowed to flow into launching barrels 7. The flow of the gaseous deuterium is monitored, regulated and integrated in the time by suitable instruments, flowmeter 28, and pressure gage 29, so as to assure a constant pressure lower than that of the triple point of the gas in the barrel during the solidification of the pellet. When the desired amount of gas has flown through the barrel, the flow is interrupted by closing valve 30. At this time the system is subjected to a thermal regulation by the PLC and simultaneously the propulsion system 1 is loaded. High pressure gas (5 to 100 bars) is allowed to flow into first stage 2, and low pressure gas (&lt;2 arm) is allowed to flow into second stage 4. At this point, after the programmable logic controller has checked the processing of the system, the pellet is shot. Soon after valves 6, 10, 10A, 13 and 14 are simultaneously opened, valve 3 causing the propulsion system 1 to shoot the pellet is also opened. The operation is as follows: The opening of valve 3 causes the high pressure gas contained in first, stage 2 to flow towards piston 5 which is strongly pushed forwards, thus causing the gas contained in second stage 4 to be subjected to a substantially adiabatic compression. The produced pressure pulse accelerates the pellet along the launching barrel 7 and expels it from the latter so that it is allowed to pass through the diagnostic section D and the two decompression chambers 11 and 12 up to the centre of the plasma column. The closure of valve 3 soon after the shooting of pellet P is followed by the closure of valves 6, 10, 10A, 13 and 14 so as to restore the starting conditions and to produce a new pellet. In particular second stage 4, launching barrel 7 and decompression chambers 11 and 12 are evacuated, and the transfer of the cooling fluid is stopped so that the cryostat is naturally heated to a temperature of about 20-25K. Now another cycle of the system can be started again so as to produce a further shot. In alternative to the described use of a cryostat in situ the use of a novel cryostat intended to produce pellets with better mechanical properties is provided according to the present invention. The problem of the fragility of the solid hydrogen causing a restricted limit, to be imposed to the maximum acceleration of the cryogenic pellet and then to the injection rate thereof has been already disclosed above. On the other hand, it is well known that the mechanical properties of a solid are strongly reduced by structural defects and imperfections in the crystal lattice; it is then reasonable to suppose that an alternative method of solidification of the pellet directed to minimize such imperfections could allow the mechanical properties of the cryogenic pellet to be improved so as to obtain better performances as far as the injection rate is concerned. To this end the present invention suggests the use of a cryostat allowing the pellet to be solidified by a technique similar to that of the growth of the single crystals, as better illustrated afterwards. FIGS. 9, 10a and 10b show a preferred but not restricted embodiment of a device which unlike that described previously is placed vertically. As one can see from these figures, the cryogenic pellet is not manufactured any longer directly "in situ", i.e. in the location from which it is then shot, but it is solidified in the location of FIG. 10b and then transferred to be shot to the location of FIG. 10a by a properly moved vacuum sealing system. Such system is schematically comprised of a body 94 supporting the launching barrel 7 and adapted to axially move and to rotate with respect to the fixed base 95, in which two seats are formed, a dead seat 97 and a seat; connected to the propulsor through pipe 98. The operation is as follows: after the launching barrel 7 placed as shown in FIG. 10b is evacuated, a desired amount of reactant (for example deuterium) is supplied; the volume of the gas to be solidified is sufficiently small as to cause the pressure to be brought to a value grater than that of the triple point. When the temperature of the cryostat falls below the equilibrium value corresponding to the pressure in the barrels, the gas starts to liquefy and to be collected by gravity in chamber 90 at the lower end of barrel 7 corresponding to the cold point. The liquid starts then to solidify slowly under a thermal gradient which is suitably controlled by heater 100, for example an electric resistance, so as to simulate the typical conditions of the growth of the single crystals which is as free as possible from lattice imperfections and then provided presumably with better mechanical properties. Once the solidification phase is completed, the pellet is carried to the location of FIG. 10a and then shot. The present invention has been illustrated and described in some preferred embodiment but, it should be understood that operative and/or construction modifications can be made from those skilled in the art without parting from the scope of the present invention as defined in the appended claims.