Necromancer spell

Any Necromancer user that know the spell "Mark of Pain" can tell me if its only one time in the 30 seconds or its EVERY time in the 30 seconds? i mean it can work even 10 times in that 30 seconds or after 1 time it ends

For 30 seconds, whenever target foe takes physical damage, mark of pain deals 10...34 damage to adjacent enemies. 10 energy/2 sec cast/30 sec recharge.