a substrate for placement in the plasma processing system and exposed to the plasma;

an ion energy analyser disposed in the substrate for measuring the ion energy distribution at the substrate surface during plasma processing, the analyser comprising a first conductive grid, G0, a second conductive grid, G1, a third conductive grid, G2, a fourth conductive grid G3, and a collection electrode, C, each grid separated by an insulating layer;

a battery power supply and a battery manager integrated in the substrate, for supplying and controlling voltage to each of the grids and the collection electrode of the ion energy analyser; and

a high voltage generating circuit within the substrate, the high voltage generating circuit comprising a low voltage to high voltage transformer feeding a voltage multiplier, wherein the high voltage generating circuit takes the output voltage of the battery manager and supplies a voltage sweep to the third conductive grid.