Fusion triple product

Fig. 2.1. Fusion triple product uTte, vs. temperature (KeV), and contours of constant plasma surfaces interaction intensity p (definition see text). Q is the ratio of output fusion power to input heating power. The upper left part (beyond the radiation limit line) is not accessible, due to unavoidable radiation losses (Bremsstrahlung) already exceeding fusion power production...

In the above treatment, it was assumed that alpha heating compensates all the losses from the plasma. This condition is called ignition. One can set similar Lawson condition for various Q = Pf/Pioss values. Abundantly used is the case when the total (alpha + neutron) fusion power reaches the losses, that is Q = 1. This condition is called breakeven. In a given experiment, the value of the product n tE and its deviation from the minimum requirement is a measure of fusion performance. From the above derivation, it is clear that the actual value of the number before the factor 10 s/m in the Lawson criterion depends on the plasma temperature. In the early decades of controlled fusion research, the fusion performance of the plasmas was so far from the Lawson criterion that its use was satisfactory. In the recent years, however, the use of another quantity cailed fusion triple product TiU tE became more popular, because it also contains the ion temperature T and describes the Lawson criterion off the optimal temperature as well ... 

When the tokamaks appeared in the 1960s, most of the countries and laboratories switched to tokamak research, and abandoned or rebuilt their stellarators into tokamaks. The overwhelming success of tokamaks lies in their robust equilibrium within the operational space and relative simplicity of design. Achieved values of the fusion triple product had doubled every 1.8 years and now (in 2010) it is believed, that the first fusion reactors will be tokamak based. 

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