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Elas%c	
  Recoil	
  Detec%on	
  and	
  Positron	
  
   Annihila%on	
  Studies	
  of	
  the	
  Mild	
  
              Bakin...
Different	
  mild	
  baking	
  mechanisms	
  
•  Models	
  previously	
  considered	
  	
  
    –  Inters%%al	
  oxygen-­‐b...
Historical	
  Prospec%ve	
  
•  “Stage	
  III	
  controversy”	
  
•  Origin	
  -­‐	
  observa%ons	
  of	
  resis%vity	
  r...
D.	
  E.	
  Peacock,	
  A.	
  A.	
  Johnson,	
  Philosophical	
  Magazine,	
  Volume	
  8,	
  Issue	
  88	
  April	
  1963...
L.	
  Stals	
  and	
  J.	
  Nihoul,	
  Phys.	
  Stat.	
  Sol.	
  8,	
  785,	
  1965	
  

                                 ...
P.	
  Hautojarvi	
  et	
  al,	
  Phys.	
  Rev.	
  B,	
  
   Vol.	
  32,	
  Num.	
  7,	
  1985	
  


Positron	
  annihila%o...
Physica	
  Scripta.	
  Vol.	
  20,683-­‐684,	
  1979	
  
Annealing	
  of	
  Defects	
  in	
  Irradiated	
  Niobium	
  
0.	...
Hydrogen-­‐induced	
  defects	
  
                                                                                        ...
Inves%ga%on	
  of	
  near-­‐surface	
  hydrogen	
  
•  Mo%vated	
  by	
  the	
  possible	
  driving	
  mechanism	
  
   fo...
Elas%c	
  Recoil	
  Detec%on	
  
              Sample	
  
                                              He+	
             ...
Hydrogen Concentration profiles obtained from energy spectra
                           simulations




•  Area under each...
Samples	
  inves%gated	
  with	
  ERD	
  
Sample	
                        Origin	
                                  Treatm...
Experimental	
  data	
  (Overview)	
  




Incident	
  energy	
  =	
  1.6MeV	
  He+	
  
Incident	
  angle	
  =	
  75o	
   ...
Experimental	
  data	
  (vs	
  Energy)	
  
Different	
  posi%ons	
  at	
  the	
  surface	
  
                                                                         ...
Different	
  posi%ons	
  at	
  the	
  surface	
  




ERD	
  results	
  for	
  different	
  posi%ons	
  on	
  the	
  surface...
Different	
  posi%ons	
  at	
  the	
  surface	
  




ERD	
  results	
  for	
  different	
  posi%ons	
  on	
  the	
  surface...
HA-­‐X	
  ERD	
  Summary	
  

Sample	
   Treatment                                                                       S...
Data	
  on	
  cutout	
  samples	
  
•  Used	
  samples,	
  which	
  were	
  cut	
  out	
  of	
  real	
  RF	
  
   cavi%es	...
Cutouts	
  Data	
  




Incident	
  energy	
  =	
  1.6MeV	
  He+	
  
Incident	
  angle	
  =	
  75o	
                      ...
Large	
  grain	
  BCP	
  hot	
  spot	
                             Fine	
  grain	
  EP	
  baked	
  cutout	
  




Sample  ...
Sample	
  2	
  from	
  baked	
  EP	
  cavity	
  –	
  no	
  
                                high	
  field	
  Q-­‐slope,	
  ...
Positron	
  Annihila%on	
  	
  
Doppler	
  Broadening	
  Spectroscopy	
  
                         • 	
  Positron	
  life%...
Doppler	
  broadening	
  spectroscopy	
  –	
  
          preliminary	
  results	
  
  UMich/NCSU	
  data	
                ...
Conclusions	
  
•  Hydrogen	
  seems	
  to	
  be	
  uncorrelated	
  with	
  the	
  
   mild	
  baking	
  improvement	
  in...
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Romanenko - Elastic Recoil Detection and Positron Annihilation Studies of the Mild Baking Effect

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Elastic recoil detection and positron annihilation studies of the mild baking effect (Alexander Romanenko - 30')
Speaker: Alexander Romanenko - Fermilab | Duration: 30 min.
Abstract
In this contribution we will present the results of mild baking experiments performed at Fermilab and through FNAL-University collaboration, which include investigations of vacancies and hydrogen in niobium coupons and cavity cutouts utilizing positron annihilation spectroscopy and elastic recoil detection analysis. The implications of the findings to the high field Q-slope problem mitigation will be discussed.

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Romanenko - Elastic Recoil Detection and Positron Annihilation Studies of the Mild Baking Effect

  1. 1. Elas%c  Recoil  Detec%on  and  Positron   Annihila%on  Studies  of  the  Mild   Baking  Effect   A.  Romanenko     Fermilab   L.  Goncharova,  P.  Simpson     Univ.  of  Western  Ontario   D.  Gidley     UMich  
  2. 2. Different  mild  baking  mechanisms   •  Models  previously  considered     –  Inters%%al  oxygen-­‐based  models   –  Natural  oxide  modifica%on   •  Inters%%al  hydrogen  in  the  near-­‐surface  region     •  LaJce  defects   –  Local  misorienta%on  (disloca%on  density)   reduc%on  with  baking  revealed  by  EBSD  studies  
  3. 3. Historical  Prospec%ve   •  “Stage  III  controversy”   •  Origin  -­‐  observa%ons  of  resis%vity  recovery  (strong   change)  in  different  group  V  metals  (tungsten,   molybdenum,  niobium)  aSer  either  deforma%on  or   irradia%on  in  1960-­‐70s   •  Controversy  essence  -­‐  is  it  inters%%al  impuri%es  or   laJce  defects,  which  are  changing  in  Stage  III   •  Stage  III  happens  in  niobium  around  -­‐50C  without  any   hydrogen  and  at  around  120C  with  hydrogen  presence     •  Near-­‐surface  niobium  is  exactly  that  -­‐  niobium  with   some  hydrogen  
  4. 4. D.  E.  Peacock,  A.  A.  Johnson,  Philosophical  Magazine,  Volume  8,  Issue  88  April  1963  ,  pages  563  -­‐  577     A  clear  resis%vity  recovery  stage   in  neutron  irradiated  niobium   iden%fied  at  around  100-­‐120C   •   Radia%on  damage  –  laJce   defects  –  mostly  vacancies  and   disloca%on  loops   •   Degree  of  recovery  depends   on  the  amount  of  damage  –  the   “recovering”  en%ty  is  laJce   defects   •   Similar  stage  found  in  Mo  
  5. 5. L.  Stals  and  J.  Nihoul,  Phys.  Stat.  Sol.  8,  785,  1965   Same  resis%vity  recovery  stage   in  heavily  cold  worked  niobium   iden%fied  at  around  100-­‐120C   •   Heavy  cold  work  –  laJce   defects  –  mostly  disloca%ons   and  vacancies   •   From  the  analysis  of  recovery   at  different  temperatures  –   driving  process  most  likely   bimolecular  process  –  vacancies   annihila%ng  with  self-­‐ inters%%als   •   Abributed  to  the  recovery  of   point  defects  
  6. 6. P.  Hautojarvi  et  al,  Phys.  Rev.  B,   Vol.  32,  Num.  7,  1985   Positron  annihila%on  –  studies   of  open  volume  defects   (vacancies)   •   Temperature  of  the  Stage  III   recovery  depends  on  the   hydrogen  presence  -­‐  vacancies   are  bound  by  hydrogen  up  to   100-­‐120C     •   Similar  effect  found  in  Ta  
  7. 7. Physica  Scripta.  Vol.  20,683-­‐684,  1979   Annealing  of  Defects  in  Irradiated  Niobium   0.  K.  Alekseeva  et  al.   Positron  annihila%on  –  studies   of  open  volume  defects   (vacancies)   •   Clear  decrease  in  open   volume  defects  (i.e.  vacancies)   starts  at  around  120C  
  8. 8. Hydrogen-­‐induced  defects   •  Hydrogen  can  cause  laJce   defects  –  vacancies  and   disloca%ons  depending  on   the  concentra%on  –   equivalent  to  heavy  cold-­‐ work   •  Superabundant  Vacancies   (SAVs)  –  general   phenomenon  recently   uncovered  for  M-­‐H  systems   –  emerges  when  surface   chemisorp%on  is  preferable   to  inters%%al  solu%on   For  review  –  A.  Pundt  and  R.  Kirchheim,  Annu.  Rev.  Mater.  Res.  2006.  36:555–608   29  orders  of  magnitude  higher  concentra%on  of  vacancies  in  the  presence  of  hydrogen  as   compared  to  thermal  equilibrium  
  9. 9. Inves%ga%on  of  near-­‐surface  hydrogen   •  Mo%vated  by  the  possible  driving  mechanism   for  the  mild  baking  effect  –  Vac-­‐H  complexes   dissocia%on  occuring  around  100-­‐120C   •  Leading  to  the  elimina%on  of  the  HFQS  by   –  LaJce  defect  density  reduc%on  in  the  near-­‐ surface  layer?  [A  Romanenko  and  H  Padamsee  2010  Supercond.  Sci.  Technol.   23  045008]   –  Or  hydrogen  concentra%on  decrease?  -­‐   inves%gated  by  Elas%c  Recoil  Detec%on  (ERD)  
  10. 10. Elas%c  Recoil  Detec%on   Sample   He+   Incident  energy  =  1.6MeV  He+   Incident  angle  =  75o   Scabering  Angle  =  29o   H+   Dose:  normalized  to  1µC   Facility  at  the  Univ.  of  Western  Ontario  (Prof.  L.  Goncharova)   •  Based  on  the  detec%on  of  recoiled  H  ions   •  Sensi%vity  of  order  1  at.%   •  Depth  resolu%on  achievable  ~  1  nm   •  Depth  profile  is  reconstructed  from  energy   spectrum  of  ions  
  11. 11. Hydrogen Concentration profiles obtained from energy spectra simulations •  Area under each peak corresponds to the concentration of the element in a 1nm slab •  Peak shapes and positions come from energy loss, energy straggling and instrumental resolution. •  The sum of the contributions of the different layers describes the depth profile.
  12. 12. Samples  inves%gated  with  ERD   Sample   Origin   Treatment   HA-­‐1   Single  grain  Nb     BCP  150  um   HA-­‐2   Single  grain  Nb   BCP  150  um  +  800C  4  hrs   HA-­‐3   Single  grain  Nb   BCP  150  um  +  800C  4  hrs  +   110C  74  hrs   HA-­‐4   Single  grain  Nb   BCP  150  um  +  800C  4  hrs  +   110C  74  hrs  +  HF  rinse  10   min   HA-­‐5   Single  grain  Nb   BCP  150  um  +  600C  10  hrs   HA-­‐6   Single  grain  Nb   BCP  150  um  +  600C  10  hrs   +  110C  54  hrs   LE1-­‐37  hot  spot   Large  grain  Nb  cavity   BCP  200  um   cutout   TE1AES004  cold  spot   Fine  grain  Nb  EP  cavity   EP  100  um  +  120C  48  hrs   cutout    
  13. 13. Experimental  data  (Overview)   Incident  energy  =  1.6MeV  He+   Incident  angle  =  75o   He+   Scabering  Angle  =  29o   Dose:  normalized  to  1µC   H+  
  14. 14. Experimental  data  (vs  Energy)  
  15. 15. Different  posi%ons  at  the  surface   BCP+800C  2  hrs   BCP   ERD  results  for  different  posi%ons  on  the  surface  are  shown;  integrated  intensi%es  for  bulk  (ch.100-­‐240)  and  surface  (ch.240-­‐320)  hydrogen  yield  are   listed  below   •  difference  between  different  spots  is  noted  in  the  table   Sample Spot Integrated Yield, ch 100-240 Integrated Yield, ch 240-310 HA-1 1 566 1038 2 513 925 HA-2 1 383 761 2 347 756 3 347 846
  16. 16. Different  posi%ons  at  the  surface   ERD  results  for  different  posi%ons  on  the  surface  are  shown;  integrated  intensi%es  for  bulk  (ch.100-­‐240)  and  surface  (ch.240-­‐320)  hydrogen  yield  are   listed  below   •  difference  between  different  spots  is  noted  in  the  table   Sample Spot Integrated Yield, ch 100-240 Integrated Yield, ch 240-310 HA-3 1 355 860 2 365 882 3 354 918 HA-4 1 472 1041 2 521 1136 3 533 1102
  17. 17. Different  posi%ons  at  the  surface   ERD  results  for  different  posi%ons  on  the  surface  are  shown;  integrated  intensi%es  for  bulk  (ch.100-­‐240)  and  surface  (ch.240-­‐320)  hydrogen  yield  are   listed  below   •  difference  between  different  spots  is  noted  in  the  table   Sample Spot Integrated Yield, ch 100-240 Integrated Yield, ch 240-310 HA-5 1 393 1220 2 417 1045 HA-6 1 375 855 2 347 696
  18. 18. HA-­‐X  ERD  Summary   Sample   Treatment Surface  Content Bulk  Content # HA-­‐1 BCP 53Å  Nb0.79H0.21 Nb0.994H0.008 HA-­‐2   BCP  +  800C  4hrs 48Å  Nb0.80H0.20 Nb0.994H0.006 HA-­‐3   BCP  +  800C  4  hrs  +  110C  54  hrs 53Å  Nb0.80H0.20 Nb0.994H0.006 HA-­‐4 BCP  +  800C  4  hrs  +  110C  54  hrs  +  HF  10   110ÅNb0.91H0.09/   Nb0.992H0.008 min 170Å  Nb0.96H0.04 HA-­‐5   BCP  +  600C  10  hrs 62Å    Nb0.77H0.23 Nb0.994H0.006 HA-­‐6 BCP  +  600C  10  hrs  +  110C  72  hrs 65Å    Nb0.85H0.15 Nb0.994H0.006
  19. 19. Data  on  cutout  samples   •  Used  samples,  which  were  cut  out  of  real  RF   cavi%es  characterized  with  thermometry   during  the  tests     •  One  sample  from  the  “hotspot”  in  Cornell  high   field  Q-­‐slope  limited  large  grain  BCP  cavity   •  One  sample  from  FNAL  baked  fine  grain  EP   cavity  –  no  high  field  Q-­‐slope,  cavity  limited  by   local  quench  at  around  150  mT  at  the  other   loca%on    
  20. 20. Cutouts  Data   Incident  energy  =  1.6MeV  He+   Incident  angle  =  75o   He+   Scabering  Angle  =  29o   Dose  =  4µC   H+  
  21. 21. Large  grain  BCP  hot  spot   Fine  grain  EP  baked  cutout   Sample Spot Integrated Yield, ch 100-240 Integrated Yield, ch 240-310 Large grain BCP cutout 1 464 1666 2 528 1877 3 511 2075 4 506 2082 EP baked cutout 1 579 1829 2 596 2292 3 558 2279 4 636 2121
  22. 22. Sample  2  from  baked  EP  cavity  –  no   high  field  Q-­‐slope,  losses  negligible   Sample  1  –  Hot  Spot  in  the  high  field  Q-­‐ slope  of  large  grain  BCP  cavity  –  strong   dissipa%on  detected  by  thermometry   But  –  hydrogen  profile  is  the  same!   Sample Surface Content Bulk Content # 1 7.6 nm Nb0.78H0.22 Nb0.994H0.006 2 7.5 nm Nb0.77H0.23 Nb0.994H0.006
  23. 23. Positron  Annihila%on     Doppler  Broadening  Spectroscopy   •   Positron  life%me  depends  on   the  electron  density  –  lives   longer  at  open  volume  defects   (i.e.  vacancies)   •   Width  of  the  spectra  of  gamma   quants  produced  on  annihila%on   depends  on  the  local  electron   density  and  momenta   •   Characterized  by  S-­‐ parameter  –  roughly  the   higher  S  the  larger  the   concentra%on  of  open   volume  defects     •   Varying  positron  energy  –  non-­‐ destruc%ve  depth  profiling  
  24. 24. Doppler  broadening  spectroscopy  –   preliminary  results   UMich/NCSU  data   UWO  data   Baking  120C  in  situ   Baked/unbaked   Decrease  in  the  density  of  vacancies  detected   Life%me  spectra   in  both  cases  
  25. 25. Conclusions   •  Hydrogen  seems  to  be  uncorrelated  with  the   mild  baking  improvement  in  the  HFQS   –  Same  H  content  with/without  HFQS   •  HF  rinsing  results  in  the  smearing  of  H-­‐profile   •  Preliminary  positron  annihila%on  data  –   decrease  in  near-­‐surface  laJce  defects  during   mild  baking   •  Same  samples  from  ERD  are  going  to  be  used   for  further  positron  annihila%on  studies  

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