The three dimensional distribution of the net production rate of excit
ed species in an inductively coupled plasma (ICP) reactor in Ar has be
en measured as a function of pressure and discharge power. The ICP rea
ctor is driven by a single turn radio-frequency current coil at 13.56
MHz. Robot assisted optical emission tomography was used in order to o
btain radial profiles of emission at different distances from the coil
thus giving effectively a three dimensional distribution of the net e
xcitation rate as well as the number density of excited states. Under
some conditions azimuthal symmetry of the discharge is broken mostly a
t higher pressures and higher powers. We have covered a range of press
ures between 15 and 500 m Torr and powers between 50 W and 400 W. The
conditions for producing a uniform distribution of excited atoms as a
representative of active species, are discussed.