A robustness of a thin-foil tailored hole target is demonstrated by particle simulations in laser-produced proton generation. The hole target has a hole at the target rear surface. When an intense short pulse laser illuminates the thin-foil target with the hole, transverse edge fields of an accelerated electron cloud and an ion cloud are shielded by a protuberant part of the hole so that the proton beam divergence is suppressed [Sonobe et al., Phys. Plasmas 12, 073104 (2005)]. This paper presents the robustness of the hole target against laser parameter changes in a laser spot size and in a laser pulse length against a contaminated proton source layer and against a laser alignment error. The 2.5-dimensional particle-in-cell simulations also show that a multiple-hole target is robust against a laser alignment error and a target positioning error. The multihole target may serve as a robust target for practical uses to produce a collimated proton beam.
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