1. LCLS-II CMTF@LERF Technical Requirements
E. Daly / K. Jordan / C. Hovater / M. Wiseman with help from Accel Ops and Engineering
03-AUG-2017

2. Fast cooldown – Modified Bayonet Box L1 Configuration Summary
Outline
Overview
Introduction
Requirements
Fast cooldown – Modified Bayonet Box
L1 Configuration
Summary
REV2, 03-AUG-2017

3. Introduction
LCLS-II CMs have requirements similar to XFEL in terms of integrated testing of 8 channels in an effort to confirm performance requirements and identify early collective effects that may limit performance
JLab and FNAL have set-up CM testing facilities to support LCLS-II with parallel production and testing lines
Fast cooldown is a challenge for JLab’s CTF
An additional testing facility providing full testing capability would allow the project to
Perform more testing cycles due to rework of poorly performing CMs
Perform testing cycles earlier if a backlog of CMs begins to develop
Test set-up is similar to L1 (2 CM segment of LCLS-II)
May derive benefits from this specific testing configuration
REV2, 03-AUG-2017

4. LCLS-II CM Layout in LERF – Testing 2 CMs per Cycle
CM Slot
CM Slot
CM Slot
Access
Storage
Current machine contains slots for 3 full CMs and 1 Injector CM
Shielded vault
Existing PSS including radiation and ODH monitoring
Utilities include cryo, water, electrical
Propose 2 CMs installed in middle of FEL machine
REV2, 03-AUG-2017

5. Acceptance Criteria can be achieved in LERF
Production acceptance criteria includes 18 items includes:
Min cavity gradient MV/m
Min CM gradient – 128 MV
Min cavity gradient for FE onset – 14 MV/m
Captured dark current < 1 nA
Full CM operation for 10 hours continuous at nominal gradient
2K, 5K and 50K static and dynamic heat loads
Verify thermometry, liquid level readback and valve/heater operations
Tuner performance – coarse (mechanical) and fine (peizo)
FPC maximum operating temperatures
HOM coupler Q_external > 5 x 10E11 & < 1 W at 16 MV/m
SC magnet operation
BPM electrical measurements
Verify beamline, coupler and insulating vacuum levels
REV2, 03-AUG-2017

6. J1.3-02 Minimum Requirements
Qo specification
>2.7 x 10E10 at 16 MV
Implied by the dynamic heat load at 2K of 86 W/CM (~ 3.0 x 10E10)

7. Attaining High Qo in CMs
Nitrogen doping technique has raised the bar for Qo performance
More than half of the production cavities have been delivered
Routinely measure Qo’s > 3 x 10E10 in VTA for production LCLS-II cavities
Nb material impacts performance (grain size, hardness) – both Qo and maximum gradient
Requires low magnetic field environment during testing, achieved by a combination of magnetic shielding and flux expulsion
Flux expulsion from niobium is enhanced by fast cooldowns that create large temperature differences across cavity as it cools through the transition temperature of 9.2 K
CM contains piping modifications to leverage this effect
REV2, 03-AUG-2017

8. Recent Production Cavity Test
Cavity vertical tests at Jlab since last weekly update:
L2-271 (TD), first test
Q(16)= 3.2 e10; Admin limited 24 MV/m
FE free
Qualified
3 – 5 mG field
Fast cooldown

9. LERF Cryogenic Specifications Achieved
Primary supply – 3K, 3 atm
Primary return – 2.07 K, atm
Primary mass flow - > 15 g/s achieved per C100-style CM in steady state operations
Primary heat load - ~ 300 W static + dynamic per C100-style CM
Shield supply – 35K, 3 atm
Shield return – 50K, < 3 atm
Shield mass flow – 10 g/s nominal per CM
Shield heat load - ~ 200 W static + dynamic per CM
Cooldown header for helium gas return – 1.05 atm
Diverts cooldown flow from primary return to recovery compressors
ODH / Upset conditions – FEL design for 3 CMs (4500 liters at 2K) + 1/4CM (300 liters at 2K)
REV2, 03-AUG-2017

10. LERF Cryogenic Specifications for LCLS-II
Primary return – 2.07 K, atm – higher return pressure during operations
dP/dt using RT valve on TL
Apply same correction algorithm to measured Qo’s as done in CMTF currently
5K circuit – mix return with shield return flow
Modified Bayonet Box
LCLS-II CM
Use cooldown header and large Cv control valve to achieve fast cooldown (~ 30 g/s)
Similar application – SNS cooldown valve integrated in End Can
REV2, 03-AUG-2017

11. Bayonet Box & U-tubes Concept
REV2, 03-AUG-2017

12. LCLS-II contains four segments – L0, L1, L2 and L3
L1 Configuration
LCLS-II contains four segments – L0, L1, L2 and L3
L1 contains 2 CMs with end cap connections to the cryogenic distribution system
L1 Configuration may be beneficial for additional test studies
Cooldown of 1 CM while other is cold or warm
Microphonics environment
HPRF/LLRF controls development
REV2, 03-AUG-2017

13. Technical requirements for testing CMs in the LERF can be met
Summary
Technical requirements for testing CMs in the LERF can be met
Correction algorithm for Qo measurement exists
Fast cooldown achievable with cooldown header to ~ 30 g/s
L1 Configuration may be beneficial for additional test studies
REV2, 03-AUG-2017

14. Back Up
REV2, 03-AUG-2017