CERN, e - cloud meeting, R. Cimino e - -cloud meeting R. Cimino, LNF INFN, Frascati, Italy & CERN, Geneva, CH. partially founded by INFN-Gr.V nta-IMCA project. 1 R. Cimino

CERN, e - cloud meeting, R. Cimino We set up and operate two Surface Science “state of the art” systems to study, low SEY Da  ne Light Laboratory Manipulator Farady Cup LEED + e - gun X-ray Lamp e - gun Electron Analyser Sample Prep. Chamber for reactions The XPS system

CERN, e - cloud meeting, R. Cimino We set up and operate two Surface Science “state of the art” systems to study, low SEY Da  ne 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  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

CERN, e - cloud meeting, R. Cimino Measure of Secondary e - Yield: 2 methods Igun - Isample Iin SEY =  = Iout = Igun

CERN, e - cloud meeting, R. Cimino Measure of Secondary e - Yield What we have 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. 1mm slot e - beam Stable between eV Currents from few nA to µA (20µC/h/mm mC/h/mm 2) Intense spot (  < 0.5 mm) with low background Igun - Isample Iin SEY =  = Iout = Igun Isample Igun

CERN, e - cloud meeting, R. Cimino Measure of Secondary e - Yield: 2 methods I out and I in (Noel) Advantages: Simultaneously measure  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 Igun - Isample Iin SEY =  = Iout = Igun I Sample and I in 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)

CERN, e - cloud meeting, R. Cimino Measure of Secondary e - Yield At each Primary energy we can measure Igun (with the Faraday cup) and Isample. R. Cimino et al. Phys. Rev. Lett. 93, (2004). Igun - Isample SEY =  = Igun three-step process:  production of SEs at a depth z  transport of the SE toward the surface  emission of SE across the surface barrier secondary electron emission

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

CERN, e - cloud meeting, R. Cimino SEY of LHC Low energy R. Cimino et al. Phys. Rev. Lett. 93, (2004). 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 electrons at very low primary energy is, in this material, very high.

CERN, e - cloud meeting, R. Cimino 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 , p. 161) questioned this result based on the fact that: Long (forgotten) history of secondary electron emission studies suggests otherwise. 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

CERN, e - cloud meeting, R. Cimino While I will leave the theoretical aspects to others….

CERN, e - cloud meeting, R. Cimino Previous careful measurements showing contrary observation 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). 1. R. Cimino, et al, Phys. Rev. Lett. 93, (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, (1970). 12 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 , p. 161)

CERN, e - cloud meeting, R. Cimino Previous careful measurements showing contrary observation Total secondary electron yield of Mo as a function of incident electron energy after degassing by prolong heating of target. I. M Bronshtein, B. S Fraiman. Secondary Electron Emission. Moscow, Russia: Atomizdat, p. 60 (1969). 13 Total secondary electron yield of Ge. 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 , p. 161)

CERN, e - cloud meeting, R. Cimino 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!

CERN, e - cloud meeting, R. Cimino Setting the energy scale for metals e - Gun Cathode e - Gun Cathode E EFEF Metallic Sample Metallic Sample WGWG WSWS EkEk E k + V lenses = E g EFEF Vacuum field free region e-e- Gun At Sample Surface V lenses V bias WW E p = E g – V bias -  W e-e-

CERN, e - cloud meeting, R. Cimino e - Gun Cathode e - Gun Cathode E EFEF Insulator or Semic. Sample Insulator or Semic. Sample WGWG EkEk E k + V lenses = E g EFEF Vacuum field free region e-e- Gun At Sample Surface V lenses V bias WW E p = E g – V bias -  W e-e- E gap E gap +  S SS Setting the energy scale for insulator/semic.

CERN, e - cloud meeting, R. Cimino Expected Setup low energy

CERN, e - cloud meeting, R. Cimino Clean (Ar + Sputtered) Polycrystalline Cu

CERN, e - cloud meeting, R. Cimino Clean (Ar + Sputtered) Polycrystalline Cu

CERN, e - cloud meeting, R. Cimino Over the “blind region” It scales with the e- beam resolution It scales with the e - beam resolution

CERN, e - cloud meeting, R. Cimino Correcting Ip by the Eg resolution

CERN, e - cloud meeting, R. Cimino Over the “blind region”  = 1 – I s /I p  = 1 – I s /I p  * = 1 – I s /I * p  * = 1 – I s /I * p

CERN, e - cloud meeting, R. Cimino “As received” vs. Clean Cu

CERN, e - cloud meeting, R. Cimino “As received” vs. Clean Cu

CERN, e - cloud meeting, R. Cimino For the LHC: test HL simulations.

CERN, e - cloud meeting, R. Cimino For the LHC: test HL simulations. R=  (0) = 0.8 in all cases

CERN, e - cloud meeting, R. Cimino For the LHC: test HL simulations.

CERN, e - cloud meeting, R. Cimino LE-SEY vs RT (preliminary)

CERN, e - cloud meeting, R. Cimino LE-SEY vs RT (preliminary)

CERN, e - cloud meeting, R. Cimino LE-SEY vs RT (preliminary)

CERN, e - cloud meeting, R. Cimino LE-SEY vs RT (preliminary)

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

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