An apparatus and methods are disclosed for ion beam extraction. In an implementation, the apparatus includes a plasma source (or plasma) and an ion extractor. The plasma source is adapted to generate ions and the ion extractor is immersed in the plasma source to extract a fraction of the generated ions. The ion extractor is surrounded by a space charge formed at least in part by the extracted ions. The ion extractor includes a biased electrode forming an interface with an insulator. The interface is customized to form a strongly curved potential distribution in the space-charge surrounding the ion extractor. The strongly curved potential distribution focuses the extracted ions towards an opening on a surface of the biased electrode thereby resulting in anion beam.