H.  Higaki, Kuroda, N., K. Franzen, Y., Wang, Z., Hori, M., Mohri, A., Komaki, K., and Yamazaki, Y., ?Radial compression of protons and H_{3}^{+} ions in a multiring trap for the productionof ultralow energy antiproton beams?, Physical Review EPhys. Rev. E, vol. 70, p. 026501 -, 2004.