Importance of realistic surface related properties as input to e-cloud simulations.

Transcription

1 Importance of realistic surface related properties as input to e-cloud simulations. R. Cimino LNF Frascati (Italy) The problem of input parameters: a detailed analysis by a test case (the cold arcs of LHC). Results of relevance for LHC and ILC Future experiments and open problems ILC 2007, DESY, May31, 07. R. Cimino 1

2 Radial Distance Cold 1.9 K Static Beam 5K< T <20K Extreme High Static Vacuum (<< Torr) T=0, without beam ILC 2007, DESY, May31, 07. R. Cimino 2

3 Synchrotron Radiation: Ec = 44 e LHC CB Radial DistanceBS Photon Flux [ph/(mm 2 s 0.1%BW)] p L.H.C. calculation Photon energy (ev) Time = 0 ILC 2007, DESY, May31, 07. R. Cimino 3

4 Photon reflectivity: SR & Surface Science Radial Distance CB BS p+ Flat Cu N. Mahne et al. App. Surf. Sci. 235, Saw tooth , (2004). Time = 2 nsec ILC 2007, DESY, May31, 07. R. Cimino 4

5 CB Radial DistanceBS Photon reflectivity: p + SR & Surface Science TiN reflectivity Vs Angle of incidence and Energy (to be pub.) Time = 2 nsec N. Mahne et al. App. Surf. Sci. 235, , (2004). N. Mahne et al. To be published ILC 2007, DESY, May31, 07. R. Cimino 5

6 Photoemission:(vs. hν, Θ, E,T, B) CB Radial DistanceBS p + Intensity (a.u) SR and Surface Science Cu E.D.C Kinetic Energy (ev) R. Cimino, V. Baglin, I. R. Collins. Phys.Rev. ST-AB (1999). Time = 5 nsec ILC 2007, DESY, May31, 07. R. Cimino 6

7 Photoemission:(vs. hν, Θ, E,T, B) SR and Surface Science Radial Distance CB BS TiN TEY (still in a.u) Vs Angle of incidence and ph. Energy (to be pub.) p+ N. Mahne et al. To be finalized if possible.. ILC 2007, DESY, May31, 07. R. Cimino 7

8 The project: two new DAΦNE-L beam lines. If partially dedicated to ILC related studies need support from this community! FLUX photons/s/mrad/0.1%bw Daφne N.S.L.S.-UV Adone Elettra Undulators (Central Cone) Elettra XUV1 ( ev) XUV2 (5-150 ev) ENERGY (ev) 10 5 ILC 2007, DESY, May31, 07. R. Cimino 8

9 Beam induced el. acceleration CB Radial DistanceBS p + (F.Zimmermann) simulation Time = 10 nsec ILC 2007, DESY, May31, 07. R. Cimino 9

10 CB Radial DistanceBS e - induced e - emission δ Fully scrubbed Cu Surface Science δ total Contribution of secondaries to δ Contribution of reflected electrons to δ Primary Energy (ev) R. Cimino et al Phys. Rev. Lett. 93, (2004). Time = 15 nsec ILC 2007, DESY, May31, 07. R. Cimino 10

11 Does low energy Implication reflectivity explain the memory effect? Low energy electrons have a long survival time. This may explain observations at KEK, SPS, PSR, LANL. ILC 2007, DESY, May31, 07. R. Cimino 11

12 CB Radial DistanceBS e - induced e - emission vs. E Surface Science Energy Distribution Curves as function of Ep Secondaries Reflected electrons Ep=11 ev Kin. En. (ev) Secondaries Ep=3.7eV Reflected electrons Kin. En. (ev) R. Cimino et al Phys. Rev. Lett. 93, (2004). Time = 20 ns ILC 2007, DESY, May31, 07. R. Cimino 12

13 e - ind. e - em. vs. Emission Angle CB Radial DistanceBS Surface Science P. Barone et al to be published Time = 20 ns (EDC) from Cu surface vs. incident angle θ i at a fixed observation angle θ e =55, ILC 2007, DESY, May31, 07. R. Cimino 13

14 CB Radial DistanceBS P + e - cloud Build-up P + simulation (F. Zimmermann) Time structure vs Simulations. Time = 25 ns ILC 2007, DESY, May31, 07. R. Cimino 14

15 e - induced heat load (@ LHC) CB Radial DistanceBS p + p + Simulation R. Cimino et al Phys. Rev. Lett. 93, (2004). Time = 25 ns ILC 2007, DESY, May31, 07. R. Cimino 15

16 CB Radial DistanceBS ph. or e - induced desorption Dynamic p + p + Surface Science and simulation It is a Vacuum issue! pressure increase!!! Desorbed gas Time = 25 ns ILC 2007, DESY, May31, 07. R. Cimino 16

17 Beam scrubbing effect with photon Radial Distance CB BS P + P + Intensity (a.u.) Surface Science and SR OFE Colaminated Copper As received surface; (dose<1 min. LHC operation) PY=0.103 After ~ 1 day LHC operation; PY= Electron energy above the vacuum level (ev) See: R. Cimino et al Phys. Rew. AB-ST (1999) Time = 25 ns ILC 2007, DESY, May31, 07. R. Cimino 17

18 Beam scrubbing effect with e - CB Radial DistanceBS P + P + Surface Science The nominal LHC operation relies on SCRUBBING Time = 25 ns ILC 2007, DESY, May31, 07. R. Cimino 18

19 Scrubbing (LHC) and stability vs. Time(ILC) from LHC PR 472 (Aug. 2001): Although the phenomenon of conditioning has been obtained reproducibly on many samples, the exact mechanism leading to this effect is not properly understood. This is of course not a comfortable situation as the LHC operation at nominal intensities relies on this effect Surface science Can give a deeper understanding of the chemical processes occurring at surfaces. ILC 2007, DESY, May31, 07. R. Cimino 19

20 Surface Science vs. Scrubbing on Cu We can study the chemistry with photoemission before and after 11 mc of e 500 ev ILC 2007, DESY, May31, 07. R. Cimino 20

21 Surface Surface Science Science vs. vs. Scrubbing Scrubbing. on Cu We can analyze differences with SR-spectroscopies Secondaries O 1s Core L O 1s Core L ILC 2007, DESY, May31, 07. R. Cimino 21

22 Surface Science vs. Scrubbing on Cu We can analyze differences with X-ray Absorbtion Secondaries O K-edge C K-edge ILC 2007, DESY, May31, 07. R. Cimino 22

23 New results from M. e - cloud 07 ILC 2007, DESY, May31, 07. R. Cimino 23

24 Are there differences between Scrubbing (or stability studies vs time) in the laboratory and in the machine? This issue need to be carefully studied, with more realistic input parameters and more powerful spectroscopy analysis. For the observed differences, we have strong evidence that the actual energy of the electrons responsible for the scrubbing does affect their scrubbing effects and efficiency. ILC 2007, DESY, May31, 07. R. Cimino 24

25 Are there differences between Scrubbing in the laboratory and in the machine? We need to measure the actual energy of the e - forming the cloud in the ring and measure their scrubbing efficiency in the lab for all material. The question being: Simulations from F. Zimmermann: Dose= N e - x Ee - (ev) x t(s) xa (mm 2 ) does 1 e 500 ev scrub as 50 e 10 ev? ILC 2007, DESY, May31, 07. R. Cimino 25

26 At DaΦne we plan to measure it by inserting in the machine Energy-resolved El. Detectors. a) 5 grids for: - mass screening - energy resolution - Sensitivty to low energy electrons b) Channeltron / channelplate for high counting rate ILC 2007, DESY, May31, 07. R. Cimino 26

27 Energy-resolved El. detectors on DaΦne To be inserted in 3 positions looking trough the existing slots at the beam: - electron-ring (for reference) - Positron ring (Uncoated chambrer) - Positron ring (TiN coated chambrer?) ILC 2007, DESY, May31, 07. R. Cimino 27

28 CONCLUSION: SURFACE SCIENCE can produce essential inputs to tackle the e-cloud problem. High quality study and use of frontiers techniques like photoemission with Synchrotron radiation seems to be important to understand material properties as required to correctly predict accelerators performances in presence of an e-cloud. ILC 2007, DESY, May31, 07. R. Cimino 28

29 For ILC-DR one need to circulate Samples, to put resources (also for SR) and manpower to study: 1) 0-1keV Electron induced el. emission yield (SEY) 2) and its angular dependence 3) Photoemission Yield and Photoemission induced el. energy distribution (also Angle resolved!) 4) Photon - reflectivity 5) Electron induced energy distribution curves 6) Heat load 7) Photon and electron induced desorption 8) Surface properties changes during conditioning. 9) Chemical modifications vs. conditioning. 10) Relation between photon and electron conditioning. and this on all vacuum high tech. materials ILC 2007, DESY, May31, 07. R. Cimino 29

30 Acknowledgments: - C. Vaccarezza, M. Biagini, M. Commisso, P. Barone, A. Bonanno, S. Guiducci, M. Zobov, A. Drago and the LNF-INFN accelerator group - V. Baglin, G. Bellodi, I.R Collins, M. Furman, O. Gröbner, A. G. Mattewson, M. Pivi, F. Ruggero, G. Rumolo, F. Zimmermann, etc.. ILC 2007, DESY, May31, 07. R. Cimino 30