A turbo charger driven by exhaust gas from a combustion engine via an exhaust inlet to the turbo charger, the turbo charger having an axial inlet for combustion air generally at atmospheric pressure, from an outlet at a bent pipe portion with an inlet from an inlet channel from an air inlet, the inlet channel having at least one arched wall of non-magnetic material, with an inward facing surface and an outward facing surface relative to the inlet channel, wherein along the arched wall is arranged a series of at least three magnets having sequentially opposite magnetization directions directed mainly orthogonal to the wall, and with a pole surface of each magnet generally in level with the wall, and with a mutual separation between the magnets being at least as long as a half of a first width of the inlet channel's cross-section.