the chamber through radiation, collisions, or lack of confinement. The inner wall of the chamber is water-cooled and the heat from the particles is removed via conduction through the wall to the water and convection of the heated water to an external cooling system. Turbomolecular or diffusion pumps allow for particles to be evacuated from the bulk volume and cryogenic pumps, consisting of a liquid helium-cooled surface, serve to effectively control the density throughout the discharge by providing an energy sink for condensation to occur. When done correctly, the fusion reactions produce large amounts of high energy neutrons. Being electrically neutral and relatively tiny, the neutrons are not affected by the magnetic fields nor are they stopped much by the surrounding vacuum chamber. The neutron flux is reduced significantly at a purpose-built neutron shield boundary that surrounds the tokamak in all directions. Shield materials vary but are generally materials made of atoms which are close to the size of neutrons because these work best to absorb the neutron and its energy. Good candidate materials include those with much hydrogen, such as water and plastics. Boron atoms are also good absorbers of neutrons. Thus, concrete and polyethylene doped with boron make inexpensive neutron shielding materials. Once freed, the neutron has a relatively short half-life of about 10 minutes before it decays into a proton and electron with the emission of energy. When the time comes to actually try to make electricity from a tokamak-based reactor, some of the neutrons produced in the fusion process would be absorbed by a liquid metal blanket and their kinetic energy would be used in heat transfer processes to ultimately turn a generator. Experimental tokamaks Currently in operation (in chronological order of start of operations) 1960s: TM1-MH (since 1977 as Castor; since 2007 as Golem) in Prague, Czech Republic. In operation in Kurchatov Institute since the early 1960s but renamed to Castor in 1977 and moved to IPP CAS, Prague. In 2007 moved to FNSPE, Czech Technical University in Prague and renamed to Golem. 1975: T-10, in Kurchatov Institute, Moscow, Russia (formerly Soviet Union); 2 MW 1983: Joint European Torus (JET), in Culham, United Kingdom 1986: DIII-D, in San Diego, United States; operated by General Atomics since the late 1980s 1987: STOR-M, University of Saskatchewan, Canada; its predecessor, STOR1-M built in 1983, was used for the first demonstration of alternating current in a tokamak. 1988: Tore