Pulsed merging compression in a spherical tokamak reactor
A method of operating a nuclear fusion device. The nuclear fusion device comprises a toroidal plasma chamber and has poloidal field coils configured to form a plasma within the plasma chamber by one of merging compression and double null merging. A varying current is provided to the poloidal field coils. The varying current comprises a plurality of pulses. Each pulse comprises a plasma formation period having a rate of change of current which is opposite in sign to the current; and a merging period following the plasma formation period and having a current sufficiently low in magnitude as to allow plasmas within the chamber to merge into a single plasma. The current during the plasma formation period is varied such that the energy density of the single plasma immediately after merging is sufficient for fusion to occur.
1. A method of operating a nuclear fusion device including a toroidal plasma chamber and having poloidal field coils configured to form a plasma within the plasma chamber by one of merging compression and double null merging, the method comprising:
providing current to the poloidal field coils, the current is varied through applying a plurality of pulses, each pulse including:
a plasma formation period where the sign of the current is opposite to its derivative; and
a merging period following the plasma formation period, where the magnitude of the current is reduced to zero to allow plasmas within the chamber to merge into a single plasma,
wherein the plasma formation period comprises a first plasma formation period with a positive current, and a second plasma formation period with a negative current.
2. The method according to claim 1 , wherein the varying current is always greater than or equal to zero.
3. The method of generating neutrons, the method including operating a nuclear fusion device by a method according to claim 1 .
4. The method according to claim 1 wherein the pulses are applied periodically.
5. The method according to claim 4 , wherein a frequency of the pulses is greater than 1 Hz, more preferably greater than 10 Hz, more preferably greater than 100 Hz.
6. The method according to claim 4 , wherein the varying current has half-wave symmetry.
7. The method according to claim 1 , wherein a frequency of the pulses varies over time.
8. A method according to claim 7 , and including, for each pulse:
monitoring conditions within the plasma chamber or poloidal field coils following the merging period;
initiating a subsequent pulse in dependence upon the monitored conditions.
9. A nuclear fusion device comprising:
a toroidal plasma chamber;
poloidal field coils configured to form a plasma within the plasma chamber by one of merging compression and double null merging;
a controller configured to provide current to the poloidal field coils and to vary the current through applying a plurality of pulses, each pulse including:
a plasma formation period where the sign of the current is opposite to its derivative; and
a merging period following the plasma formation period where the magnitude of the current is reduced to zero to allow plasmas within the chamber to merge into a single plasma,
wherein the plasma formation period comprises a first plasma formation period with a positive current, and a second plasma formation period with a negative current.