1. Ari D. Palczewski, SRF Scientist
Current state of LCLS-II recipe development and ongoing research to maximization flux expulsion for the already in production cavity material
Ari D. Palczewski, SRF Scientist
Jefferson Lab, USA
MOBA07

2. 100% recrystallized. Uniform size and equal-axed grains
LCLS-II Material
Parameter
Unit
E-XFEL / LCLS II
Year -
2007&2010 / 2014
RRR
> 300
CHEMICAL COMPOSITION Ta
% or weight ppm
≤ 0.05 % W
≤ 0.007% Ti
≤ 0.005% Fe
≤ 0.003% Si Mo Ni H2
≤ 2 w-ppm N2
≤ 10 w-ppm O2 C
MICROSTRUCTURE
100% recrystallized. Uniform size and equal-axed grains
Grain size
ASTM µm
Predominantly ≥ 6
≤ 45
Maximal grain size
> 4
< 90
MECHANICAL PROPERT.
Tensile strength, Rm *
N/mm2
> 140
Yield strength, Rp0.2 *
50 < Rp0.2 < 100
Elongation, AL 30 * %
≥ 30
Hardness, HV (min. load 10 N)
≤ 60
26 Total heat lots from Tokyo Denkai (TD) material sheets
16 heat lots from Ningxia Orient Tantalum industry co ltd (OTIC or Ningxia or NX) sheets
Compiled by Jacek Sekutowicz DESY/LCLS-II

3. How is material specification defined/tested
Parameter
Unit
E-XFEL / LCLS II
Year -
2007&2010 / 2014
RRR
> 300
CHEMICAL COMPOSITION Ta
% or weight ppm
≤ 0.05 % W
≤ 0.007% Ti
≤ 0.005% Fe
≤ 0.003% Si Mo Ni H2
≤ 2 w-ppm N2
≤ 10 w-ppm O2 C
MICROSTRUCTURE
100% recrystallized. Uniform size and equal-axed grains
Grain size
ASTM µm
Predominantly ≥ 6
≤ 45
Maximal grain size
> 4
< 90
MECHANICAL PROPERT.
Tensile strength, Rm *
N/mm2
> 140
Yield strength, Rp0.2 *
50 < Rp0.2 < 100
Elongation, AL 30 * %
≥ 30
Hardness, HV (min. load 10 N)
≤ 60
Each sheet is tested for hardness – must be less than HV 60, if harder they are sent back to Manufacture for annealing again.
The hardest and softest sheet from each lot then goes to analysis (Done by DESY) for LCLS-II.
Lots are defined by heat lots, not by ingot - TD uses more than one ingot per heat lot while Ningxia uses one ingot per heat lot.

4. LCLS-II Material Distribution
Gigi Ciovati - JLab plots
TD distribution is more expected “Predominately ASTM 6.0”
OTIC/NX in predominately “ASTM 5.8” but strange distribution

5. OTIC/NX Material sorting based on ASTM crystal size – this was a guess
Gigi Ciovati - JLab plots
“Lot A” ~ from softest/largest crystal sheets (ASTM 5 to <6)
“Lot B” ~ from the middle sheets (ASTM 6 to>7)
“Lot C” ~ from the largest/smallest crystal sheets (ASTM 7 to 8)
TD material was not sorted or actively tracked

6. Current status
LCLS-II recipe by cavity vendor, material vendor, heat treatment/EP recipe by cavity counts

7. Comments on testing conditions – Magnetic field
Cavities
JLab
FNAL
DESY
First 20 from RI (TD)
First 8 from Zanon (NX)
1-2mG (Dewar 7-8)
1-2mG (Dewar 1)
3-5mG (Dewar 2)
Cavity after first articles Through April 15th 2017
5-7mG (Dewar 7-8)
6mG max
3-5mG (D2)
3-10mG (D3) – mostly D2
1-10mG large Dewar with 4 cavities. (8TD and 4 NX-A 900 tested for JLab)
Cavities after April 15th 2017 (JLab change)
3-5mG (Dewar 5, 7, 8) 6mG max
Magnetic field at JLab can be controlled on all Dewar's in the axial position, perpendicular position is ~ 0-1.5mG
D1 at FNAL had composition coils around the cavities to minimize the fields
JLab and D2 & FNAL hold 3 cavities.

8. TD 140µm/800°C
Two tested in ~1-3mG at JLab and the other two and 3-5mG at FNAL.
1-3mG too low for modual
3-5 about modual spec
This recipe will not be good enough – this was a verification from single cell results at FNAL and JLab 800°C degassing temperature is not enough
Gonnella SRF2017 thxa09

9. TD 200µm/900°C
FNAL data all pass
Gonnella SRF2017 thxa09

10. NX 200µm/900°C
FNAL data all pass
Gonnella SRF2017 thxa09

11. TD 200µm/900°C vs NX 200µm/900°C
Most data tested in 3-7mG field depending on time, and location.
Gonnella SRF2017 thxa09

12. NX-A 900 vs DESY
Tested in 2 different Dewar's and two different test stands.

13. NX-A 900°C retest from DESY @ JLab Dewar 7
When tested at DESY the cavity had a Q0 of 1.9e10.
Q0 change appears to be both magnetic field and cooling rate related changes – See JLab D5 data later.

14. Re-testing at JLab D5 (position 1) vs. D7 standard cool down
Sorry for scales, 2.2e10 in Dewar 5 to 3.1e10 in Dewar 7

15. Testing at JLab D5 (three on one test stand) – standard cool down
Position 3 is on the inlet and outlet side.
Positions 1 and 2 are on far side.
Cooldown data corrupt, but looks like cavity 3 cooling like D7/D8 Cavities 1/2 top and bottom cool at the same time, trapping all the flux

16. Testing at JLab D5 (three on one test stand) – modified cooldown
Standard cooldown
Dewar warm at 300K, ramp up time 20 minutes 0 to 8-10 grams per second.
Modified cooldown
Dewar and cavity thermalize at 100K, , ramp up time 10minutes 0 to 8-10 grams per second.
Cooldown data corrupt, but looks like cavity 3 cooling like D7/D8 Cavities 1/2 top and bottom cool at the same time, trapping all the flux

17. D5 modified cooldown from 100K

18. RF D5 standard vs. modified 100K

19. NX-B 900°C vs. 950°C

20. NX-A 950°C from Vendor A vs. NX-A 900°C Vendor B

21. NX-C 900°C from Vendor A vs. NX-C 975°C Vendor B

22. Back-up

23. Reminder - Flux expulsion 800°C vs 900°C
SRF2017 Tutorial July 13-15th
Reminder - Flux expulsion 800°C vs 900°C
Ningxia Lot A
Flux expulsion baseline 800°C (JLAB data)
Flux expulsion post 900°C 3 hours (FNAL data)
Ningxia Lot C
Flux expulsion baseline 800°C (FNAL data)
Tokyo Denkai Lot B-C
Tokyo Denkai Lot A
Flux expulsion post 900°C 3 hours (JLAB data)* ΔT 2K
10%
46% 2% 5%
23%
69%
14%
71% 6K
21%
70%
15%
35%
30%
95%
26%
90%
10K
80%
20%
42%
34%
100% NA
Absolute value between different labs and different test setups have not been fully calibrated, look at relative changes.
Both TD material lots show excellent expulsion after 900°C
NX-A material shows “ok” expulsion after 900°C, 950°C would maximize it.
Lot “C” NX material shows minimal expulsion after 900°C, and acceptable after 975°C, 9 cell prototypes results later.
*Different test setup than 800°C data (800°C D7 and 900°C D3)
Table initially compiled by Anna Grassellino FNAL, modified here