A Cold SCU Phase-Shifter P. Emma, H.-D. Nuhn (SLAC), D. Arbelaez, L. Fajardo, S. Prestemon (LBNL) May 17, 2016

Motivation Superconducting undulators (SCU) provide much higher fields allowing higher power, more tunable FELs. Recent R&D at ANL/LBNL/SLAC successfully built and tested a 1.5-m SCU FEL prototype (NbTi). If put in production, this prototype can deliver > 6 keV at LCLS-II.

Project Scope Next R&D steps should be a full cryostat, but costs are high (15M$) To keep moving (at low cost) we propose component R&D (a cold phase-shifter as next challenge) Each und. break needs a phase- shifter to control electron-photon phasing over the FEL spectral tuning range An SCU requires a cold phase shifter (4 K) for efficiency We will design, build, and test a cold phase shifter with LCLS-II-like parameters (1 yr plan)

Design Concept -2k +k Phase-Shifter (PS) Design Concept: Three pole phase shifter Iron dominated design with NbTi coils to minimize PS length Conduction cooled to ~ 5 K Incorporates steering correction Two power supplies for PS (main + out-of-plane steering correction) Four power supplies for SCU (main + entrance steering correction + exit steering correction + dipole field correction) +k -2k SCU1 SCU2 Phase Shifter Cryostat SCU1 Exit steering correction SCU2 Entrance steering correction +k -2k PS Trajectory Steering correction

Minimum Required PS Range Design Objectives Phase-Shifter (PS) Design Objectives: Provide sufficient phase adjustment range Provide sufficient PS step-size resolution Minimize PS length (< 15 cm) for efficiency Minimize coupling of PS and undulator fields Minimize PS net field integrals Include field-integral correctors (x & y) Minimize PS Hysteresis Define modes of operation Cryostat Minimize Coupling PS SCU SCU Minimize Length Minimum Required PS Range

Wire inside vacuum chamber Phase Shifter R&D Plan Test Cryostat at LBNL PS Design Conceptual design 3D design including investigation of coupling and hysteresis Fabrication PS parts and NbTi coil winding Cryostat prep., including support structure and magnetic measurements Testing Pulsed wire measurements of PS strength and coupling effects Simulate undulator structure with steel cores and end correctors Pulsed Wire Feedthroughs In-Vacuum Pulsed Wire Wire inside vacuum chamber Detector

Budget & Milestones Project costs (based on a resource-loaded schedule, includes LBNL overhead rates) Labor: 214.5 k$ Hardware: 29 k$ Schedule milestones:

Schedule (1 yr) Magnetic design and optimization Prepare magnetic measurement capability (benefit from other projects) Detailed design and fabrication Parallel effort to prepare and commission test cryostat Final testing

Phase shifter does not impact any existing facilities Summary Phase shifter does not impact any existing facilities However, development of phase shifter advances SCU R&D, without high cost, while “keeping the team together” Future SLAC FEL branch lines or LCLS upgrades will benefit, as will FEL community This 1-yr component R&D keeps the SCU effort alive and advances the effort at low cost P. Emma, H.-D. Nuhn (SLAC), D. Arbelaez, L. Fajardo, S. Prestemon (LBNL)