Stain appeared after EP acid renewal Field emission at low gradient happened on MHI-06, MHI-07, in VT. Kyoto-camera found brown stain trace in beam pipes, irises and equators. Now we are investigating STF EP process using old MHI-#0 cavity (with simple beam pipe). They seems to be Niobium-Oxide. However, the problem is not yet solved, not yet fixed H. Hayano, KEK ???

BL#6 1-cell equator, t = 306 deg. Downstream : Outside weld area BL#6 #9-BP, t = 241 deg. -1 BL#6 #9-BP, t = 241 deg. -2 Brown spot and traces; MHI-06 ： spot or traces on BP-#1 、 #1 、 #2 、 #3 、 #4 、 #8 、 #9 、 #9-BP (red indicate bad) MHI-07 ： BP-#1 、 #1 、 #2 、 #3 、 #4 、 #5 、 #6 、 #7 、 #8 、 #9 、 #9-BP Kyoto-camera picture examples using new LED illumination

BL#6 9-cell equator, t = 034 deg. Upstream : Outside weld area BL#6 3-cell equator, t = 291 deg. BL#6 3-4 iris, t = 055 deg. BL#6 8-9 iris, t = 053 deg. BL#6 9 equator, t = 037 deg. BL#6 9-cell equator, t = 184 deg. Upstream : Outside weld area

OLD_MHI-#0 cavity EP test 2009/07/07 EP condition ： 4 th EP after acid renewal removal ： 20 um cavity surface area ： 9000 cm2 acid soaking area ： 5400 cm2 target average current ： 270 A acid flow ： 15 litter / min cavity rotation ： 1 rpm cavity acid temp at start ： 20.9 ℃ acid tank temp ： 20.1 ℃ room temp ： 31 ℃ Typical EP parameter

2009/5/27, BL#6, 1 st EP after acid renew2009/6/10, BL#7, 2 nd EP after acid renew 2009/7/01, BL#8, 3 rd EP after acid renew 2009/4/08, BL#5, EP before acid renewal 4div 2div

2009/3/25, ERL-2cell #1, EP before acid renew 2div 2008/12/10, BL#6, EP before acid renew 2div 2009/7/07, OLD_MHI-#0 4 th EP after acid renew 4div 2009/7/07, OLD_MHI-#0 5 th EP after acid renew 4div

After EP-20um, 5min rotate, HPR #1 equator, t = 248 deg. After EP-20um, 5min rotate, HPR #1 equator, t = 304 deg. After EP-20um, 30min rotate, HPR #1 equator, t = 248 deg. After EP-20um, 30min rotate, HPR #1 equator, t = 304 deg. after 4 th EPafter 5 th EP after 4 th EPafter 5 th EP

After EP-20um, 5min rotate, HPR #1 equator, t = 349 deg. After EP-20um, 30min rotate, HPR #1 equator, t = 349 deg. stains went away by EP 20um. after 4 th EPafter 5 th EP

After EP-20um, 30min rotate, HPR #1 equator, t = 342 deg. After EP-20um, 30min rotate, HPR #1 equator, t = 328 deg. After EP-20um, 30min rotate, HPR #1 equator, t = 000 deg. new stains comes up after 5 th EP

stain in beam pipe edge scrape out scraped sample sample was glued by silver paste on Si substrate. Then, apply XPS analysis. results; Nb 11 at% O 48 at% C 27 at% Si 14 at% (substrate) No special material, just Niobium-oxide, maybe. MHI#0 cavity

AES001 had also similar stains, observed as received. ( Jlab EP )

AES001 #2-3 iris 212° 1mm iris back side of EL Other spots that have no wall gradients Appendix back side of EL to Equator of #3 cell to Equator of #2 cell arc scar? The result of SI measurements shows that this spot is flat. This spots looks like a sign of Field Emission or Arcing. Many spots like this were observed.

Appendix AES001 #4-5 iris 233° 1mm iris back side of EL bright belt to Equator of #5 cell All the Iris regions are yellowish. This spot is locally bright. It may be caused by EP? to Equator of #4 cell

Appendix AES001 #4-5 iris 136° 1mm iris to Equator of #5 cell Dropped coffee smear? back side of EL to Equator of #4 cell

Appendix AES001 #7-8 iris 279° 1mm iris to Equator of #8 cell back side of EL to Equator of #7 cell Dropped coffee smear? scar?