A method of accelerating charged particles in a plasma, the method comprising: creating a region of non-uniform electric field (24; 110; 210) within the plasma which propagates through the plasma, using the non-uniform electric field (24; 110; 210) to accelerate a first plurality of charged particles in the direction of propagation of the region of non-uniform electric field (24; 110; 210), once the accelerating first plurality of charged particles have propagated part-way through the plasma: adding a second plurality of charged particles (45; 115; 215) to the plasma, such that; the second plurality of charged particles (45; 115; 215) propagates through the plasma, the second plurality of charged particles (45; 115; 215) creates a local distortion (50; 120; 220) in the non-uniform electric field experienced by the accelerating first plurality of charged particles, and the local distortion (50; 120; 220) in the non-uniform electric field (24; 110; 210) propagates through the plasma with the accelerating first plurality of charged particles ; and using the local distortion (50; 120; 220) in the non-uniform electric field (24; 110; 210) to accelerate the first plurality of charged particles in the direction of propagation of the region of non-uniform electric field (24; 110; 210). creating a region of non-uniform electric field (24; 110; 210) within the plasma which propagates through the plasma, using the non-uniform electric field (24; 110; 210) to accelerate a first plurality of charged particles in the direction of propagation of the region of non-uniform electric field (24; 110; 210), once the accelerating first plurality of charged particles have propagated part-way through the plasma: adding a second plurality of charged particles (45; 115; 215) to the plasma, such that; the second plurality of charged particles (45; 115; 215) propagates through the plasma, the second plurality of charged particles (45; 115; 215) creates a local distortion (50; 120; 220) in the non-uniform electric field experienced by the accelerating first plurality of charged particles, and the local distortion (50; 120; 220) in the non-uniform electric field (24; 110; 210) propagates through the plasma with the accelerating first plurality of charged particles ; and using the local distortion (50; 120; 220) in the non-uniform electric field (24; 110; 210) to accelerate the first plurality of charged particles in the direction of propagation of the region of non-uniform electric field (24; 110; 210). adding a second plurality of charged particles (45; 115; 215) to the plasma, such that; the second plurality of charged particles (45; 115; 215) propagates through the plasma, the second plurality of charged particles (45; 115; 215) creates a local distortion (50; 120; 220) in the non-uniform electric field experienced by the accelerating first plurality of charged particles, and the local distortion (50; 120; 220) in the non-uniform electric field (24; 110; 210) propagates through the plasma with the accelerating first plurality of charged particles ; and the second plurality of charged particles (45; 115; 215) propagates through the plasma, the second plurality of charged particles (45; 115; 215) creates a local distortion (50; 120; 220) in the non-uniform electric field experienced by the accelerating first plurality of charged particles, and the local distortion (50; 120; 220) in the non-uniform electric field (24; 110; 210) propagates through the plasma with the accelerating first plurality of charged particles ; and using the local distortion (50; 120; 220) in the non-uniform electric field (24; 110; 210) to accelerate the first plurality of charged particles in the direction of propagation of the region of non-uniform electric field (24; 110; 210). <EOS>