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Labo-EP tests with Nb samples for stain problem

Labo-EP tests with Nb samples for stain problem. Jlab-FNAL-KEK S0 meeting 18 Sept. 2009 T. Saeki and P.V.Tyagi. Labo-EP of samples at Nomura. 11 Aug. 2009. Exposing the samples to the air for 70 min. w/o Pure-Water (P.W.) rinse. No stain appeared.

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Labo-EP tests with Nb samples for stain problem

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  1. Labo-EP tests with Nb samples for stain problem Jlab-FNAL-KEK S0 meeting 18 Sept. 2009 T. Saeki and P.V.Tyagi

  2. Labo-EP of samples at Nomura 11 Aug. 2009 Exposing the samples to the air for 70 min. w/o Pure-Water (P.W.) rinse. No stain appeared. Labo-EP (20 um) with new EP acid ([Nb] = 0 ~ 0.4 g/L) at Nomura Stains appeared within a minute after exposing the samples to the air. Light P.W. rinse for a few 10’s seconds.

  3. Exposing samples to the air after P.W. rinse stains P.W. remaining Stains appeared within a minute after exposing the samples to the air. The stains appeared in the area where P.W. dried. (EP acid of [Nb] = 0.4 g/L)

  4. Modification of first U.P.W. rinse process First U.P.W. rinse duration after EP-acid-draining at STF/KEK was extended. Horizontal for 5 min. Drain EP acid for 10 min. Then UPW rinse starts. Drain EP acid for 15 min. The first U.P.W. rinse was extended with overflow for a longer time. Original sequence: [pouring U.P.W. for 7 min. + draining for 5 min. ] x 5 Modified sequence: [pouring U.P.W. for 60 min. + draining for 10 min.] + [pouring U.P.W. for 20 min. + draining 7 min. ] x 3. MHI#9 (9-cell cavity) was processed with this modified sequence and reached Eacc = 27 MV/m at Q0 = 9x10^9 (quench), even still with some field emission.

  5. Additional labo-EP tests with samples • Additional labo-EP tests were done with the EP acid of two different [Nb] of ~4 g/L and ~8 g/L. • The EP acid of [Nb] = 4.4 g/L was prepared by removing a dummy Nb-plate. • Samples were EP’ed (20 um) with EP acid of [Nb] = 4.4 ~ 4.8 g/L. Samples were exposed to the air, lightly P.W.-rinsed and exposed to the air. • The EP acid of [Nb] = 8.2 g/L was prepared by removing a dummy Nb-plate again. • Samples were EP’ed (20 um) with EP acid of [Nb] = 8.2 ~ 8.6 g/L. Samples were exposed to the air, lightly P.W.-rinsed and exposed to the air.

  6. Labo-EP of samples at Nomura 8 Sept. 2009 Exposing the samples to the air for 30 min. w/o Pure-Water (P.W.) rinse. No stain appeared. Labo-EP (20 um) with EP acid ([Nb] = 4.4 ~ 4.8 g/L) at Nomura No stains appeared after exposing the samples to the air. Light P.W. rinse for a few 10’s seconds.

  7. Exposing samples to the air after P.W. rinse No stains P.W. remaining No stain appeared after exposing the samples to the air. (EP acid of [Nb] = 4.8 g/L at the end)

  8. Labo-EP of samples at Nomura 11 Sept. 2009 Exposing the samples to the air for 30 min. w/o Pure-Water (P.W.) rinse. No stain appeared. Labo-EP (20 um) with EP acid ([Nb] = 8.2 ~ 8.6 g/L) at Nomura No stains appeared after exposing the samples to the air. Light P.W. rinse for a few 10’s seconds.

  9. Exposing samples to the air after P.W. rinse No stains P.W. remaining Sulfur ? No stain appeared after exposing the samples to the air. (EP acid of [Nb] = 8.6 g/L at the end)

  10. Summary

  11. Considerations • I think that DESY/JLab EP-facilties might use new EP acid for each EP process and dump it at the end of process . • If so, [Nb] is 0 g/L at the beginning of EP, but [Nb] might be large at the end of each EP process. Then DESY/JLab EP-facilities would have no stain problem. • Question from KEK: What is the final value of [Nb] for each EP process of 9-cell cavity at JLab? • KEK EP-facility has a big EP-tank of 1000L. When we replace the EP acid with new one, we will keep using new EP acid with some 9-cell cavities for a while. Should we change this style to DESY / JLab style? Or should we develop a new U.P.W. rinse method, like introducing N2 during first U.P.W. rinse duration?

  12. Planned/possible analysis • 4 samples with stains will be analyzed by XPS/SEM at KEK. The analysis will start soon. • I already sent 3 samples with stains to JLab. It is a very interesting idea to analyze samples by Auger and FSEM at JLab. In particular, the FSEM is the unique method to see if the stains are the source of field emission. • Analysis of [F-] is ongoing at KEK for the EP acid sampled at [Nb]= 4.8 g/L and 8.6 g/L, because [F-] is another parameter of EP acid.

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