Abstract: This disclosure relates to a proton beam degrader and a cooling assembly. The proton beam degrader includes a degrader foil that is positioned within a path of a particle beam directed to strike a target. The degrader can include a plurality of fins positioned outside of a conduit within which the degrader foil is positioned to transfer heat away from the degrader foil and into a cooling channel formed in conjunction with the cooling assembly. The degrader foil can have chamfered corners to further improve heat transfer. The degrader foil can include at least one aperture to aid in forming a vacuum condition across the degrader foil. In some examples, where a target cannot operate in a vacuum environment, the degrader can include a degrader foil devoid of any apertures.