Spectrum tailoring of low charge-to-mass ion beam by the triple-stage acceleration mechanism

Lower charge-to-mass ions are more difficult to be accelerated during the traditional single accelerating progress, because they are generally modulated by the weaker charge-separated electric field. In this paper, the cascaded target normal sheath acceleration (TNSA) mechanism is proposed to solve this issue in experiments, where the low charge-to-mass ions (C²⁺) generated from the first TNSA stage can be further tailored to a mono-energetic bunch by the peak of the sheath field in the additive TNSA stages. A simple numerical model is used to explain the experimental result and shows that the energetic spread of the ion beam can be further reduced from 27% to ∼1% by expanding the two-stage acceleration to triple-stage acceleration. Here, the sheath field works like a spectral knife that can control the peak energy and bandwidth of the spectra for the ions with any charge-to-mass ratio. More choices can be provided for many potential applications, such as ion therapy and nuclear physics.