A variable capacitor is provided within a radiofrequency (RF) power transmission path to a bias electrode, in addition to an impedance matching circuit provided within the RF power transmission path to the bias electrode. An RF power supply is operated in a pulsed mode to transmit pulses of RF power through the RF power transmission path to the bias electrode. A capacitance of the variable capacitor is set to control a rate at which a DC bias voltage builds up on a substrate present above the bias electrode during each pulse of RF power. The rate at which the DC bias voltage builds up on the substrate controls an ion energy distribution and an ion angular distribution within a plasma exposed to an electromagnetic field emanating from the substrate.