pulse length is the total duration of a single plasma discharge in a pulsed 📝fusion device, measured from the start of 📝ramp-up through flattop to the end of ramp-down.
Pulse length is often conflated with its most important subset: the 📝flattop is the steady, productive plateau, while pulse length counts the transient phases on either side of it. Its companion figure is duty cycle — the fraction of total time a machine is actually running pulses — and together the two describe how much of a pulsed plant's life is spent producing. In a conventional 📝Tokamak, pulse length is capped by the finite flux swing of the 📝central solenoid that sustains the 📝plasma current through 📝inductive current drive; when the solenoid's swing is exhausted, the discharge must end.
Superconducting machines have pushed far past the seconds-long pulses of copper-coil tokamaks: EAST in China and KSTAR in South Korea have sustained discharges for hundreds of seconds, with EAST exceeding a thousand. For a power plant, pulse length is as much an economic quantity as a physics one — every pulse thermally cycles the machine's components, and the ratio of productive flattop to the dead time between pulses feeds directly into how much electricity the plant can sell. The escape from the limit altogether is 📝steady-state operation, in which 📝non-inductive current drive sustains the current indefinitely.