The fusion energy confinement time is very important , and EAST tokamak experiment has achieved 101.2 seconds of continues operation time, and it is different from energy confinement time τ， or if a fusion tokamak system can realize steady-state operation by a lot of subsystems, such as NBI injection system, plasma heating system; is this system exist fusion energy confinement time? and what is the difference between fusion energy confinement time and operation time of the tokamak system.
The energy confinement time measures the rate at which the confined plasma loses energy to its environment. According to the Lawson criterion for ignition, the minimum energy confinement time for optimal D-T fusion is somewhat order of 1 second while the temperature is approximately 15 keV. After the plasma is ignited within the energy confinement time, the energetic alpha particles as one of the fusion products can collide with the fuel nuclei in the plasma and heat it, reducing the amount of external heat needed (strictly speaking, the ignition point means that the internal self-heating is enough to keep the reaction going without any external heating). Therefore, the operation time can be much longer than the energy confinement time(for example, the ITER aims at operation of long pulses of 400 to 600 seconds). The pulse duration is even longer than the particle confinement time so that the refills of fuels are necessary due to the losses of particles. All the subsystems for plasma heating should exist within the energy confinement to help ignite the plasma.
Confinement time and operation time are totally different concepts. Let's consider the confinement time of water in a leaky container. The confinement time of water is 1/rate of leaking. But the operation time of the container can be very very long, as long as you keep filling in new water from outside.
The energy confinement time depends on various plasma processes taking place in the tokamak. However operation time of the tokamak can be increased by pumping energy in the plasma by different processes.
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