the devices are called "plasma mass filter" or "plasma centrifuge" (not to be confused with medical). The centrifugal separation of isotopes was first suggested by Aston and Lindemann in 1919 and the first successful experiments were reported by Beams and Haynes on isotopes of chlorine in 1936. However attempts to use the technology during the Manhattan project were unproductive. In modern times it is the main method used throughout the world to enrich uranium and as a result remains a fairly secretive process, hindering a more widespread uptake of the technology. In general a feed of UF6 gas is connected to a cylinder that is rotated at high speed. Near the outer edge of the cylinder heavier gas molecules containing U-238 collect, while molecules containing U-235 concentrate at the center and are then fed to another cascade stage. Use of gaseous centrifugal technology to enrich isotopes is desirable as power consumption is greatly reduced when compared to more conventional techniques such as diffusion plants since fewer cascade steps are required to reach similar degrees of separation. In fact, gas centrifuges using uranium hexafluoride have largely replaced gaseous diffusion technology for uranium enrichment. As well as requiring less energy to achieve the same separation, far smaller scale plants are possible, making them an economic possibility for a small nation attempting to produce a nuclear weapon. Pakistan is believed to have used this method in developing its nuclear weapons. Vortex tubes were used by South Africa in their Helikon vortex separation process. The gas is injected tangentially into a chamber with special geometry that further increases its rotation to a very high rate, causing the isotopes to separate. The method is simple because vortex tubes have no moving parts, but energy intensive, about 50 times greater than gas centrifuges. A similar process, known as jet nozzle, was created in Germany, with a demonstration plant built in Brazil, and they went as far as developing a site to fuel the country's nuclear plants. Electromagnetic Electromagnetic separation is mass spectrometry on a large scale, so it is sometimes referred to as mass spectrometry. It uses the fact that charged particles are deflected in a magnetic field and the amount of deflection depends upon the particle's mass. It is very expensive for the quantity produced, as it has an extremely low throughput, but it can allow very high purities to be achieved. This method is