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LCLS-2 Cavity and Cryomodule Test Workshop 2015

29–30 Oct 2015
US/Central timezone

Working group outline

  1. Vertical Test
 
 
  1. Motivation/Purpose – Cavity Acceptance Criteria
 
  1. what range of Q0 for qualification? should we look at Rs_res, Rs_BCS for acceptance? (example, if cavity has good BCS but very large residual that can be from mag field, triggers re-test under improved field conditions)
  2. What minimum gradient for qualification? Do we set an admin limit? at what field?
  3. what FE level and what field triggers reprocessing?
  4. for reprocessing, how many times? when to re-EP?
 
  1. Test Procedure – (including infrastructure and instrumentation)
  1. Active pumping or not
  2. Standardizing the instrumentation - decide what, how many, locations
    1. Field emission instrumentation: two locations (top, bottom, discuss)
    2. Fluxgates
    3. Temperature sensors
  3. Cooldown procedure, acceptable mag field levels? should we use PID controller to zero the mag field during the cooldown via coils?
  4. Conditioning procedures, administrative limits?
  5. Q disease test – not needed?
  6. Test at different T? only 2K? 2, 1.8, 1.5K?
 
  1. Test Reports format and content
 
 
  1. Horizontal Test
Motivation/Purpose
Unlike vertical testing, HTS testing is not intended to determine if a cavity meets the project- specified performance requirements. Likewise, HTS does not provide a final assurance that a cryomodule or its components are ready for installation into the linac, as cryomodule testing does. Rather, it is used in the context of cryomodule production to provide the following information as a kind of secondary check and risk-mitigation:
  1. Are the processes, procedures, tooling, and staffing yielding the required performance of the combined SYSTEM when assembled from qualified individual components and
  2. Are the vendor-supplied components conforming (or still conforming) to required performance specifications when used/operated under conditions similar to those encountered during cryomodule operation (and which cannot be duplicated “on the bench”).
  3. If unforeseen performance issues arise in early cryomodule tests that require either iterative investigations in a cryomodule environment or evaluation of a modified or re-designed component or procedure, this can be done with a scheduled HTS test.
  4. Facilities at other partner labs (e.g, Cornell) could be dedicated to long-term stability or lifetime tests of systems/components (tuner, LLRF) long before they could be pursued in cryomodules, and allowing for timely feedback into production.
Measured Parameters
  1. Determine cavity gradient limit (16MV/m + margin (TBD), administratively limited), with little or no FE. (verifies that the cavity assembly (FPC) or transport/handling has not introduced any contaminants to the RF surface)
  2. Determine cavity Q0 at Eop . (Verifies that the RF surface treatment has not been compromised, that there is no undue influence from magnetized parts, no unacceptable heating of end group from HOMs/FPC)
  3. Verify Tuner operation (range, center freq, deadband, pre-load, PZT & stepper operation). verifies that the complicated tuner assembly has been performed correctly and that parts’ tolerances are acceptable, that PZTs and tuner motor operate reliably in a cryogenic/vacuum environment, and that warm pre-load/pre-tuning achieves desired 2K cavity frequency.
  4. Verify acceptable HOM and FPC heating, HOM power extraction (perfomed concurrently with 1.) above). Verifies that notch frequency and HOM antenna lengths are correct and more importantly that HOM and FPC thermal strapping provides adequate thermal management, and that the FPC can reliably operate at full power level and Qext target and adjustment range is being achieved
                                                                                                                                                                    
Since this is a restricted number of tests which would have well-defined acceptance criteria, the cold test duration is compressed to about 7 working days (potentially less). Reserving about 2 ½ working weeks for installation, cooldown, warmup, and removal, an entire HTS cycle can be accomplished in just under 4 weeks.
 
3a) Prototype Cryomodule (pCM) Test
Motivation/Purpose
 
pCM testing will verify engineering design that was not fully tested during the horizontal cavity test, namely the fast cool down and warmup for an entire cavity string. pCM testing should provide optimized cryogenic operational procedures for maximized cavity performances.
pCM testing should also validate production test plan, identify changes that need to be made and ensure that we are getting the same information from both test facilities.  This is separate from topics to be addressed in production CM testing session.
Goals:
  1. A complete written test plan for the production CM testing.
  2. The first 2 CMs for LCLS-II.
  3. An optimized cryogenic operational procedures for linac operation
 
  1. Measured Parameters - pCM Module Testing acceptance criteria ( 25 min)
 
  1. Usable Gradient
  2. Maximum testing gradient ( VT max – 2 MV/m?) (nominal Eacc + 2 MV/m, whichever is smaller)
  3. Q0 of each cavity or only average Q0 of module
  4. Q­0 as a function of temperature
  5. Q0 as a function of coupler Qext
  6. Resistance calculations RBCS, Rs_res
  7. HOM Qext
  8. Static heatload and total heatload of 2K, 5K, 50K circuits
  9. FE onset
  10. FE@nominal
  11. FE maximum – admin limit
  12. Dark current measurement
  13. Ancillary component measurements
    1. Quadrupole magnet operation and temperature measurement
    2. Magnetic operational effect to cavity Q
    3. FPC adjustment range verification
    4. FPC load to 5K intercept and 50K shield
    5. Off- resonance coupler conditioning
    6. Tuner & piezo range test and resolution
    7. Microphonics measurements
    8. Cavity pressure sensitivity
    9. Cavity Lorentz force coefficient
    10. BPM function test
    11. Operation of new LLRF and SSA systems – needs to be integrated with SLAC – beyond scope of this workshop (RF bandwidth, amplitude and phase control, interlocks, machine protection for cryomodule)
  14. Cavity magnetic hygiene
    1. Magnetic shield temperature monitoring
    2. Mag shielding performance
    3. Active compensation implementation
 
  1. Test Procedure /  Measurements need to be standardized – (including infrastructure and instrumentation)
 
  1. What is the cryogenic configuration at each lab?
  2. How do we ensure the module cooldown plan is the same at both labs?
  3. How will this be transferred to cooldown process at SLAC?
  4. How is the fast cooldown performed & documented?
  5. Fluxgate magnetometers mounted inside the HV on cavities 1,4,5 & 8.
  6. Active magnetic field compensation coils on the module (time to study operation will be during pCM testing)
  7. Instrumentation and layout for field emission measurements
  8. Temperature measurements
  9. Connection between Cryo and RF measurements (including fast and slow cool down)
  10. Connection between fast cool down and active magnetic coil condition
  11. RF components and calibration methods, including phasing process if possible
  12. Cavity gradient measurement methods
  13. Cavity Q0 measurement methods
  14. Q0 vs. time of 2K soaking
  15. Cavity RF conditioning limit
  1. Test Reports format and content
    1. Development of Standardized test report
    2. Development and use of CM testing Travelers
 
3b) Production Cryomodule Test
  1. Motivation/Purpose – Production CM Acceptance Criteria
    1. When to reject; how long does one troubleshoot before warming up and removing?
    2. What is the Rework plan?
    3. Magnetic Shielding
    4. Acceptance criteria – How are tests ranked?
    5. Usable Eacc (operating vs. breakdown or administrative limit)
    6. Q0
    7. Rs_res,Rs_BCS (are R measurements possible on a CM?)
    8. Onset of FE, magnitude at nominal gradient
    9. Dark current
    10. Coupler condition
    11. QE range
    12. Tuner/piezo range & resolution
    13. Microphonics/LFDC
 
  1. Test Procedure
    1. What are the critical Cryogenic operating parameters and acceptable limits? How long a cold soak after cool down is needed?
    2. What are the acceptable vacuum limits in all three circuits – beam tube, coupler, insulating. Are RGA scans needed?
    3. What instrumentation needs to be standardized especially with respect to position relative to the cryomodule and readout (especially for Field Emission)?
    4. Cooldown/Test procedure – how to verify flux expulsion/minimization given different test set ups
    5. What to test – overall performance with all cavities on, and with single cavities For many couplers this will be the first operation at cold. How extensive are single cavity tests?
    6. Ancillary systems – what and how does one measure/verify thermometry, BPM, magnet, etc?
  2. Test Reports format and content
    1. Standardized test report definition
    2. Development and guidance for the use of CM testing Travelers
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