A surgical access port assembly for providing access for a medical instrument into an intracorporeal cavity of a patient undergoing surgery, the access port assembly comprising: - a cannula; - an electrode; - a first passage which extends along the cannula and along which a medical instrument is able to pass, the passage comprising a first entrance portion disposed at a proximal region the of the cannula and a first exit portion disposed at a distal region of the cannula; - a second passage which extends along the cannula and along which the electrode is able to pass, the second passage comprising a second entrance portion disposed at a proximal region of the cannula and a second exit portion disposed at a distal region of the cannula; - wherein the second entrance portion of the second passage converges toward the first passage in a direction which is from the proximal end to the distal end of the cannula, and wherein the first exit portion of the first passage and the second exit portion of the second passage diverge along the cannula in a direction which is from the proximal end to the distal end of the cannula; wherein - the surgical access port assembly further comprising an electrode receiver housing having a receiver passage which extends there through; - wherein the electrode comprises an ion emission zone disposed at the distal region thereof, which in use, is arranged to extend out from a second exit port (124/129) and a head disposed at a proximal end thereof, which is arranged to abut the receiver housing; and, - wherein the ion emission zone is spaced from the cannula by a distance in the range of 5-50mm to minimise the reduction in output voltage caused by a decrease in the resistance between the electrode and the cannula. - a cannula; - an electrode; - a first passage which extends along the cannula and along which a medical instrument is able to pass, the passage comprising a first entrance portion disposed at a proximal region the of the cannula and a first exit portion disposed at a distal region of the cannula; - a second passage which extends along the cannula and along which the electrode is able to pass, the second passage comprising a second entrance portion disposed at a proximal region of the cannula and a second exit portion disposed at a distal region of the cannula; - wherein the second entrance portion of the second passage converges toward the first passage in a direction which is from the proximal end to the distal end of the cannula, and wherein the first exit portion of the first passage and the second exit portion of the second passage diverge along the cannula in a direction which is from the proximal end to the distal end of the cannula; wherein - the surgical access port assembly further comprising an electrode receiver housing having a receiver passage which extends there through; - wherein the electrode comprises an ion emission zone disposed at the distal region thereof, which in use, is arranged to extend out from a second exit port (124/129) and a head disposed at a proximal end thereof, which is arranged to abut the receiver housing; and, - wherein the ion emission zone is spaced from the cannula by a distance in the range of 5-50mm to minimise the reduction in output voltage caused by a decrease in the resistance between the electrode and the cannula.