LE-SEY @ e - -cloud meeting

1. LE-SEY@ e--cloud meeting R. Cimino, LNF INFN, Frascati, Italy & CERN, Geneva, CH. partially founded by INFN-Gr.Vnta-IMCA project. R. Cimino

2. We set up and operate twoSurface Science “state of the art” systems to study, lowSEY films @ Dafne Light Laboratory The XPS system Manipulator Farady Cup Sample Prep. Chamber for reactions Electron Analyser LEED + e- gun e- gun X-ray Lamp

3. We set up and operate twoSurface Science “state of the art” systems to study, lowSEY films @ Dafne Light Laboratory • µ-metal chamber; • En. & angle res. analyser; • Low T manipulator; • LEED - Auger RFA; • Faraday cup. • Low energy el. gun • Mass spectrometer • Sample preparation • Monochromatic high flux-high resolution VUV Lamp The UPS system

4. Measure of Secondary e- Yield: 2 methods SEY= = = Iout Iin Igun Igun-Isample

5. Measure of Secondary e- Yield What we have now @ LNF: • 2 µ-metal chamber; • (2 different En. & angle res. analyser) • 2 sample manipulators ( 1 for Low T ) • 2 LEED - Auger RFA; • 2 Faraday cup. • 2 Low energy electron gun • 2 Mass spectrometer • 2 (different) Samples preparation systems. Isample SEY= = = Iout Iin Igun 1mm slot • e- beam Stable between 30 - 500 eV • Currents from few nA to µA (20µC/h/mm2 - 20mC/h/mm2) • Intense spot (f< 0.5 mm) with low background Igun Igun-Isample

6. Measure of Secondary e- Yield: 2 methods SEY= = = Iout Iin Igun • Iout and Iin(Noel) • Advantages: • Simultaneously measure d at each energy: very fast. • Effective also for “dispersive samples” (i.e. Sponges) • Disadvantages • Gun far from the sample • Big(er) spot and no LE-SEY • ISample and Iin • Advantages: • Gun close to sample. • Reduce noise for insulators • LE-SEY accessible? • Disadvantages • Gun need to be very stable (takes time) • More work (2 separate runs) Igun-Isample

7. Measure of Secondary e- Yield = SEY=  Igun-Isample Igun At each Primary energy we can measure Igun(with the Faraday cup)andIsample. secondary electron emission three-stepprocess:  production of SEsat a depthz transport of the SE toward the surface  emission of SE across the surfacebarrier R. Cimino et al. Phys. Rev. Lett.93, 14801 (2004).

8. Measure of Secondary e- Yield = SEY=  Igun-Isample At each Primary energy we measure Igun(with the Faraday cup)andIsample. Igun • Each point in d is the integral of the energy distribution of the emitted electrons R. Cimino et al. Phys. Rev. Lett.93, 14801 (2004).

9. SEY of LHC Cu @ Low energy Integrating the curves gives the Percentage of Secondaries and Reflected electrons To separate “true secondaries from“re-diffused electrons is arbitrary and has not been considered in this analysis. We observe that the contribution to of the reflected electronsat very low primary energy is, in this material, very high. R. Cimino et al. Phys. Rev. Lett.93, 14801 (2004).

10. Theoretical • Quantum diffraction from potential barrier • Experimental • Difficulties of measurements at low incident electron energy • Previous careful measurements showing contrary observation • Probe measurements in plasma will not work Recently A. N. Andronov, A. S. Smirnov, I. D. Kaganovich, E. A. Startsev, Y. Raitses, and V. I. Demidov, (in Proceedings of ECLOUD’12 (2013), CERN-2013-002, p. 161) questioned this result based on the fact that: Long (forgotten) history of secondary electron emission studies suggests otherwise.

11. While I will leave the theoretical aspects to others….

12. Previous careful measurements showing contrary observation 1. R. Cimino, et al, Phys. Rev. Lett. 93, 014801 (2004). 2. I. M Bronshtein, B. S Fraiman. Secondary Electron Emission. Moscow, Russia: Atomizdat, p. 408 (1969). Other measurements reported the reflection coefficient of about 7% for incident electron energy below few electron volts for most pure metals. I.H. Khan, J. P. Hobson, and R.A. Armstrong, Phys. Rev. 129, 1513 (1963). H. Heil, Phys. Rev. 164, 887, (1967). Z. Yakubova and N. A. Gorbatyi, Russian Physics Journal, 13 1477 (1970). From: A. N. Andronov, A. S. Smirnov, I. D. Kaganovich, E. A. Startsev, Y. Raitses, and V. I. Demidov, (in Proceedings of ECLOUD’12 (2013), CERN-2013-002, p. 161) Total secondary electron yield of Cu as a function of incident electron energy. 1. from the letter for fully scrubbed Cu (T=10 K). 2. Experimental data for bulk Cu after heating in vacuum (room temperature).

13. Previous careful measurements showing contrary observation Total secondary electron yield of Ge. I. M Bronshtein, B. S Fraiman. Secondary Electron Emission. Moscow, Russia: Atomizdat, p. 60 (1969). From: A. N. Andronov, A. S. Smirnov, I. D. Kaganovich, E. A. Startsev, Y. Raitses, and V. I. Demidov, (in Proceedings of ECLOUD’12 (2013), CERN-2013-002, p. 161) Total secondary electron yield of Mo as a function of incident electron energy after degassing by prolong heating of target.

14. Thanks to this contribution we decided to address in details the capability of our setup to study LE-SEY. Setting the energy scale. Expected Setup limitations at Low energy Study in identical conditions (same geometry etc.) atomically clean (XPS) Cu obtained by cycles of Ar+ sputtering of the “as received” Cu. Compare it to “as received” Cu samples. Warning: “As received” is NOT a well defined chemical state!

15. Setting the energy scale for metals Vacuum field free region At Sample Surface Gun E Ek+ Vlenses= Eg Ep= Eg – Vbias - DW Vlenses Vbias e- e- Ek DW WS WG EF EF e- Gun Cathode Metallic Sample

16. Setting the energy scale for insulator/semic. Vacuum field free region At Sample Surface Gun E Ek+ Vlenses= Eg Ep= Eg – Vbias - DW Vlenses Vbias e- e- Ek DW Egap+ cS cS WG EF EF Egap e- Gun Cathode Insulator or Semic. Sample

17. Expected Setup limitations @ low energy

18. Clean (Ar+ Sputtered) Polycrystalline Cu

19. Clean (Ar+ Sputtered) Polycrystalline Cu

20. Over the “blind region” It scales with the e- beam resolution

21. Correcting Ip by the Eg resolution

22. Over the “blind region” • = • 1 – Is/Ip d*= 1 – Is/I*p

23. “As received” vs. Clean Cu

24. “As received” vs. Clean Cu

25. For the LHC: test HL simulations.

26. For the LHC: test HL simulations. R= d(0) = 0.8 in all cases

27. For the LHC: test HL simulations.

28. LE-SEY vs Dose @ RT (preliminary)

29. LE-SEY vs Dose @ RT (preliminary)

30. LE-SEY vs Dose @ RT (preliminary)

31. LE-SEY vs Dose @ RT (preliminary)

32. Conclusion • R d(0) tend to: • ~ 0 for metals (in agreement with previous data) and stay low in the entire LE region. • ~ 0.6 - 1 for “as received” metals and stay high in the entire LEregion Preliminary: • LE-SEY: Not big action during Scrubbing • Need to be repeated at LT and in presence of co-deposited gas • The setup (Faraday+Isample) can measure LE-SEY (in construction also at CERN) • Can extract info on Ws changes.

33. Acknowledgment A. Di Gaspare and L. Gonzalez INFN-LNF, Frascati (RM), Italy A.L. Romano Universita’ del Sannio and INFN Napoli/Salerno Rosanna Larciprete CNR-ISC, Roma, Italy V. Baglin, D. Letant-Delrieux, M. Taborelli, H. Neupert , G. Iadarola, and G. Rumolo CERN, Geneva, Switzerland