1096 C. Llewellyn Smith and S. Cowley conceivably reach 1000◦C. The heat will be extracted through a primary cooling circuit, which could contain water or helium, which in turn will heat water in a secondary circuit that will provide the steam/gas to drive turbines. These turbines generate about 1.5 GW of electricity (enough for more than a million people) in the conventional way. For economic viability, the blanket must operate robustly for many years. Because this component is both critical and unique to fusion it will contain much of the intellectual property in fusion. A 1.5 GW plant would use about 10–20 kg of natural lithium and 0.6 kg of deuterium per day and the electricity is estimated to cost in the range 5–9 Eurocents per kW h. 5. Status of fusion research: tokamaks The leading magnetic conﬁguration for conﬁning fusion plasmas is called a tokamak (a contraction of a Russian phrase meaning toroidal chamber with a magnetic coil). The basic layout of a tokamak is shown in ﬁgure 2. In this section we outline the basic operation of a tokamak. A fusion plasma conﬁguration is made in the tokamak via the following steps: — A small amount of gas (hydrogen or deuterium in most experiments; deuterium and tritium in some experiments at JET and in an actual fusion reactor) is injected into the toroidal (doughnut shaped) vacuum chamber after the magnetic ﬁeld coils have been switched on. — A rising current is raised in the inner poloidal ﬁeld coils (see ﬁgure 2) that drives an electric current (approx. 5 MA in JET and approx. 15 MA in ITER) through the gas, via transformer action. — The electric current heats the gas, and turns it into a plasma. It also produces a magnetic ﬁeld which, combined with the magnetic ﬁeld produced by the external coils, generates a helical ﬁeld that is necessary to ‘conﬁne’ the plasma, i.e. hold it away from the walls and provide very good thermal insulation. — The electrical resistivity of a plasma drops rapidly with temperature and the current induced by transformer action can heat the plasma to only about one-third of the temperature needed for copious fusion to occur. Additional heating power (of many megawatts) must then be supplied by microwaves or beams. — The transformer can sustain the plasma current only while the current is rising in the inner poloidal ﬁeld—thereafter the current must be driven by the microwaves and or beams of energetic neutral atoms which transfer energy to the plasma through collisions. — When the plasma reaches temperatures of about 100 million degrees Celsius the D–T fusion reactions begin. The helium (alpha particles) nuclei from the fusion reaction then heat the plasma. In addition to heating and current drive systems, experimental tokamaks are equipped with ‘diagnostic’ devices that measure the magnetic ﬁeld, electron and ion temperatures and densities, the plasma pressure, position and shape, neutron and photon production, impurities, etc., and monitor the development of instabilities. Phil. Trans. R. Soc. A (2010)