ELM activity

ELM activity may evolve as e short, intense heat load on the plates causes erosion of the divertor materials. During the instability, the edge pressure gradient is reduced until the plasma becomes stable again. Then the pressure gradient starts recovering to the level where it reaches the stability limit so that another ELM occurs. If the conditions stay constant, the cycle can continue indefinitely. Depending on the ELM type and the details of a plasma device, each ELM removes 1 – 7 % of the plasma energy and particles.

Sound corresponding to density fluctuations due to ELM bursts can be downloaded here. The signal was obtained from a probe inserted into the plasma edge of the TCV tokamak. Note that the signal has been slowed down so that ELMs appear at a rate of five per second whilst in reality they are nearer two hundred per second. Courtesy of CRPP EPFL.