A plasma channel has a low electrical resistance and, once formed, will permit continuous current flow if the energy source that heats the plasma can be maintained. Unlike a normal electrical conductor, the resistance (and voltage drop) across an unconfined plasma channel decreases with increasing current flow, a property called negative resistance. As a result, an electric spark that initially required a very high voltage to initiate avalanche breakdown within the insulating gas will rapidly evolve into a hot, low-voltage electric arc if the electrical power source can continue to deliver sufficient power to the arc. Plasma channels tend to self constrict (see plasma pinch) due to magnetic forces stemming from the current flowing through the plasma.