The closeness of a plasma to power plant conditions is measured in terms of the triple product nTtE, the product of density, i.e. the number of fuel particles per unit volume (n), the temperature (T) and the energy confinement time (tE). For a 50-50 D-T plasma at about 20 keV, to achieve ignition condition in a power plant, (i.e., when the fusion reaction is self-sustained through alpha particle heating), one would need this triple product to have the value
Another important parameter for fusion based power plant is Q, the ratio of fusion power to input auxiliary heating power. While fusion power plant generating electricity would need Q≥10, an ignited power plant would correspond to Q=∞ , since there is no externally injected heating power in such a device. Present day fusion experiments have brought the triple product to within a factor of 3-5 of its final required value and have already exceeded conditions equivalent to a Q=1 operating power plant.