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TY - UNPB AU - Checchin, M. ED - Ramberger, Suitbert ED - Draper, Mick ED - Schaa, Volker RW TI - High-Q R&D at FNAL J2 - Proc. of ERL2017, Geneva, Switzerland, June 18-23, 2017 C1 - Geneva, Switzerland T2 - ICFA Advanced Beam Dynamics Workshop T3 - 59 LA - english AB - Modern projects of accelerators for High Energy Physics and FEL accelerators (PIP II, LCLS II, etc.) demand operation of the SRF cavities in CW regime. In this situation, low cryogenic losses are essential. Decrease of the losses or, thus, increase of the cavity unloaded quality factor Q0 allows great savings in capital and operational cost. The new N-doping technique for the SRF cavity processing in order to achieve high Q0 is described, which is now a ready-to-use technology for SRF accelerators. The current implementation of this technique for the LCLS-II cavity production, allow us to present how ultra-high Q-factors can be maintained from the vertical to the horizontal test. In particular, efficient cooling and optimization of shielding design will be discussed to address potential Q degradation from the remnant magnetic fields in the cryomodule. The talk will go through the physics and fundamental studies performed at FNAL that allowed us a) to define the best nitrogen doping treatment which minimizes the Q sensitivity to trapped magnetic field, b) to maximize magnetic flux expulsion based on cavity treatment. PB - JACoW Publishing CP - Geneva, Switzerland ER -