vacuum for fusion technology by more science.pptx

we discuss about usage of vacume techniqs for fusion reaction

1. Introduction for Fusion Technology Worldwide there are great hopes that fusion technology will be a clean alternative source of energy. Since the 1950s, scientists all over the world have been attempting to use nuclear fusion for peaceful purposes. Despite the fact that the process works perfectly on our sun, it is difficult to reproduce these extreme conditions on earth. For these experiments two types of large fusion reactors are used: tokamak and stellarator. Both reactor types work on the same principle. The differences lie in the shape and arrangement of the coils that generate the toroidal magnetic field. The tokamak reactor has a symmetrical design. Stellarators on the other hand, have a complex asymmetrical reactor form .

2. How does it work ? Basically, it is a matter of fusing together two hydrogen isotopes at a time to form a new helium nucleus. In the course of this process, not just helium and a single neutron are formed but also an extraordinarily large amount of energy. Fusion can only take place in high vacuum at a high plasma temperature of some 100 to 150 million Kelvin. The aim of the heating process is to separate the nuclei from the electrons to form a plasma. The charged nuclei are guided within the reactor with the aid of an extremely strong magnetic field (of several Tesla) maintaining separation from the reactor walls. When two atomic nuclei approach each other or collide, they fuse and release a large quantity of energy. A part of this energy is needed to keep plasma at the same temperature in order to retain the system without any additional energy input. The generated heat is then used to produce steam which drives a generator.

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5. Vacuum system requirements One of the important requirements for operating a fusion reactor is a strong, reliable, and powerful vacuum system. The plasma vessel of a fusion reactor must be evacuated to a base pressure of < 10-6 Pa (< 10-8 mbar) and the pressure in the cryostat system should be below 10-3 Pa (< 10-5 mbar). The process gases in the experiment vessel are usually hydrogen, deuterium or tritium Due to the high magnetic field of several Tesla (short T) the vacuum equipment need to be installed at a distance of 4 to 9 meters to the plasma vessel. Even at this distance, the magnetic field can still reach strength of 100 mT. All components must therefore be provided with magnetic shielding. It is especially important for turbopumps, to prevent the rotor from heating up as a result of eddy current

6. Vacuum system requirements All vacuum components used require their electronics to be installed at a distance from the actual pump or measuring device. This is because modern digital electronics are damaged by radioactivity

7. Turbomolecular Pumps Turbomolecular pump operating principle The pumping effect of an arrangement consisting of rotor and stator blades is based upon the transfer of impulses from the rapidly rotating blades to the gas molecules being pumped. Molecules that collide with the blades are adsorbed there and leave the blades again after a certain period of time. In this process, blade speed is added to the thermal molecular speed. To ensure that the speed component that is transferred by the blades is not lost due to collisions with other molecules, molecular flow must prevail in the pump, i . e. the mean free path must be greater than the blade spacing

8. Turbomolecular Pumps In the case of kinetic pumps, a counterpressure occurs when pumping gas; this causes a backflow. The pumping speed is denoted by S0 . The volume flow rate decreases as pressure increases and reaches a value of 0 at the maximum compression ratio K0

9. Turbomolecular Pumps Compression ratio :The compression ratio, which is denoted K0

10. Turbomolecular Pumps

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13. Turbomolecular Pumps The points plotted in Figure 4.23 are determined by Pfeiffer Vacuum on the basis of the measured values of the indicated pumps. Points far above the plotted curve are physically not possible.

14. Turbomolecular Pumps The pumping speeds thus determined still tell nothing about the values for light gases, e.g. for hydrogen. If a turbopump is designed for a low ultimate pressure, pump stages with various blade angles are used and the gradation is optimized for maximum pumping speeds for hydrogen. This produces pumps with sufficient compression ratios for both hydrogen (approximately 1,000) and nitrogen, which should be 109 due to the high partial pressure of nitrogen in the air. In the case of pure turbomolecular pumps, backing-vacuum pressures of approximately 10-2 mbar are required due to their molecular flow .

15. Turbomolecular Pumps

16. Turbomolecular Pumps