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

2. 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.

3. 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)

4. 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

5. 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

6. 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

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

8. 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

9. 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)