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TY - CONF AU - Hofmann, I. ED - Schaa, Volker RW TI - Revisiting the Longitudinal 90 Degree Limit for Superconducting Linear Accelerators J2 - Proc. of HB2018, Daejeon, Korea, 17-22 June 2018 C1 - Daejeon, Korea T2 - ICFA Advanced Beam Dynamics Workshop T3 - 61 LA - english AB - In the design of high-intensity linear accelerators one of the generally adopted criteria is not to exceed a zero-current phase advance per focusing period of 90 degrees in order to avoid the space charge driven envelope instability, or a coinciding fourth order space charge resonance. Recently it was claimed that in certain structures, predominantly applicable to super-conducting linac lattices - such a constraint is not always necessary in the longitudinal plane (I. Hofmann and O. Boine-Frankenheim, Phys. Rev. Lett. 118, 2017). This applies primarily to such focusing structures, where the transverse focusing period only induces a weak space charge dependent modulation in the longitudinal plane, and a different periodicity is applicable to the longitudinal plane. Hence the longitudinal 90 degree stopband is practically absent, and phase advances significantly above 90 degrees should be possible in such structures, with a corresponding additional design freedom. As a consequence, we suggest that the 90 degree rule should no longer be taken as standard criterion in the longitudinal plane of linac design. PB - JACoW Publishing CP - Geneva, Switzerland SP - 369 EP - 372 KW - space-charge KW - lattice KW - emittance KW - resonance KW - focusing DA - 2018/07 PY - 2018 SN - 978-3-95450-202-8 DO - 10.18429/JACoW-HB2018-THP2WB01 UR - http://jacow.org/hb2018/papers/thp2wb01.pdf ER -