A multi-track magnetron having a convolute shape and asymmetric about the target center about which it rotates. A plasma track is formed as a closed loop between opposed inner and outer magnetic poles, preferably as two or three radially arranged and spirally shaped counter-propagating tracks with respect to the target center and preferably passing over the rotation axis. The pole shape may be optimized to produce a cumulative track length distribution conforming to the function L=arn. After several iterations of computerized optimization, the pole shape may be tested for sputtering uniformity with different distributions of magnets in the fabricated pole pieces. If the uniformity remains unsatisfactory, the design iteration is repeated with a different n value, different number of tracks, or different pole widths. The optimization reduces azimuthal sidewall asymmetry and improves radial deposition uniformity.