Recent Experimental Results on Amorphous Carbon Coatings for Electron Cloud Mitigation

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1 Recent Experimental Results on Amorphous Carbon Coatings for Electron Cloud Mitigation ECLOUD 10, Cornell University, Ithaca, New York USA Christina Yin Vallgren S. Calatroni, P. Chiggiato, P. Costa Pinto, H. Neupert, M. Taborelli, W. Vollenberg Vacuum, Surfaces and Coatings Group (VSC), TE-department SPS-U team: E.Shaposhnikova, G. Arduini, J. Bauche, F. Caspers, K. Cornelis, S. Federmann, E. Mahner, E. Metral, G. Rumolo, B. Salvant, F. Zimmermann CERN, CH-1211, Geneva, Switzerland October 8-12, 2010

2 Outline Motivation 1 Motivation SPS-U: Super Proton Synchrotron Upgrade New solution Amorphous Carbon Coating 2 in the lab 3 Conclusions Outlook 2 / 42

3 Outline Motivation SPS-U: Super Proton Synchrotron Upgrade New solution Amorphous Carbon Coating 1 Motivation SPS-U: Super Proton Synchrotron Upgrade New solution Amorphous Carbon Coating 2 in the lab 3 Conclusions Outlook 3 / 42

4 The goal of this work Motivation SPS-U: Super Proton Synchrotron Upgrade New solution Amorphous Carbon Coating SPS-U: make the SPS able to deliver the above nominal beams to LHC and reach maximum luminosity. Find a solution to eliminate e-cloud in the SPS, which can be implemented in the present SPS-dipoles without aperture reduction does not require bake-out is robust against air venting (maintenance, installation...) has a long life time The condition for the secondary electron yield to avoid e-cloud in SPS dipoles with nominal LHC beam is (G.Rumolo et al.) δ max < / 42

5 SPS-U: Super Proton Synchrotron Upgrade New solution Amorphous Carbon Coating Possible remedies for the electron cloud in the beam pipe: Low Secondary Electron Yield (SEY) thin-film coatings surface conditioning clearing electrodes chamber with grooves or slots Ti-Zr-V film coating (implemented in straight sections of LHC) have δ max = 1.1 after activation at temperature higher than 180 C (24h). But they cannot be applied to the SPS because the SPS magnet vacuum chambers are not bakeable. TiN works well under the effect of photon conditioning in situ. But no photons in the SPS. 5 / 42

6 Which material to start with: SPS-U: Super Proton Synchrotron Upgrade New solution Amorphous Carbon Coating Known facts For air exposed stainless steel, Cu and Alδ max > 2. In the periodic system, elements with fewer electrons (on the left side) => lower SEY. Beam scrubbed surfaces are covered by more carbon (at least Cu and StSt). Try Carbon, which has few electrons SEY of graphite is much lower than diamond, so try to make graphite-like coatings. Graphite is not very reactive, should be less affected by air exposure. Graphite-like Amorphous Carbon (a-c) Thin Film Coating. 6 / 42

7 Which material to start with: SPS-U: Super Proton Synchrotron Upgrade New solution Amorphous Carbon Coating Known facts For air exposed stainless steel, Cu and Alδ max > 2. In the periodic system, elements with fewer electrons (on the left side) => lower SEY. Beam scrubbed surfaces are covered by more carbon (at least Cu and StSt). Try Carbon, which has few electrons SEY of graphite is much lower than diamond, so try to make graphite-like coatings. Graphite is not very reactive, should be less affected by air exposure. Graphite-like Amorphous Carbon (a-c) Thin Film Coating. 7 / 42

8 Outline Motivation in the lab 1 Motivation SPS-U: Super Proton Synchrotron Upgrade New solution Amorphous Carbon Coating 2 in the lab 3 Conclusions Outlook 8 / 42

9 in the lab - DC magnetron sputtering Different coating configurations were used: Cylindrical tube with one graphite rod cathode (for lab samples for SEY investigation and vacuum characterization) Liner in tube with 4 graphite rods (Lab samples, liner for e-cloud monitors) MBB magnet chamber in-situ (chamber in the dipole) with Multi-electrode geometry (Version I: coating in-situ in SPS dipoles) MBB magnet chamber stand-alone with liner configuration (Version II: coating outside SPS dipoles) Different discharge gases (Ne, Kr, Ar) and different coating parameters (Temperature of substrate, discharge gas pressure, power) can be used. 9 / 42

10 Cylindrical tube configuration Lab samples for SEY and vacuum characterizations in the lab 10 / 42

11 Liner in tube with 4 graphite rods Lab samples, liner for e-cloud monitors in the lab The coating chambers were inserted in a solenoid and the magnetic field is parallel to the cathodes and chamber axis. The surface temperature can rise to 250 C. Four graphite rods were used to avoid coating in-homogeneity. 11 / 42

12 Liner in tube with 4 graphite rods Lab samples, liner for e-cloud monitors in the lab The coating chambers were inserted in a solenoid and the magnetic field is parallel to the cathodes and chamber axis. The surface temperature can rise to 250 C. Four graphite rods were used to avoid coating in-homogeneity. 12 / 42

13 in the lab Coating for the Electron Cloud Monitor in the SPS 13 / 42

14 in the lab Coating for the Electron Cloud Monitor in the SPS 14 / 42

15 in the lab MBB magnet in-situ with Multi-electrode geometry Version I: coating in-situ in SPS dipoles The magnetic field of the dipole was used and was perpendicular to the cathodes and chamber axis. The power during coating was kept limited in order to avoid overheating and damaging of the coil of the dipole. Three MBBs have been coated. Disadvantage: in-homogeneity. 15 / 42

16 in the lab MBB magnet in-situ with Multi-electrode geometry Version I: coating in-situ in SPS dipoles The magnetic field of the dipole was used and was perpendicular to the cathodes and chamber axis. The power during coating was kept limited in order to avoid overheating and damaging of the coil of the dipole. Three MBBs have been coated. Disadvantage: in-homogeneity. 16 / 42

17 in the lab MBB magnet stand-alone with liner configuration Version II: coating outside SPS dipoles Use the same technique as for liner coating to coat the vacuum chamber outside the SPS magnet. Three new MBBs have been coated. Disadvantage: Cut-open SPS dipole magnet and reassembly. (Expensive process!) Advantage: Perfectly homogeneous coating for large scale production can be done in advance. 17 / 42

18 in the lab MBB magnet stand-alone with liner configuration Version II: coating outside SPS dipoles Use the same technique as for liner coating to coat the vacuum chamber outside the SPS magnet. Three new MBBs have been coated. Disadvantage: Cut-open SPS dipole magnet and reassembly. (Expensive process!) Advantage: Perfectly homogeneous coating for large scale production can be done in advance. 18 / 42

19 In the lab: The SEY as a function of PE P: power, p: pressure in the lab SEY δ high P, med p high P, high p high P, low p med P, low p med P, med p low P, med p Primary Energy (ev) Measured directly after extraction from the deposition chamber and transfer to the SEY apparatus through air. The precision of the presented SEY values is estimated to ±0.03. δ max is between 0.9 and 1.1 and E max = 300 ev. (not sensitive to coating parameters as pressure, power.) 19 / 42

20 In the lab: The SEY as a function of PE P: power, p: pressure in the lab Numbers of the coatings. Total: 90 samples δ of a C coatings max Measured directly after extraction from the deposition chamber and transfer to the SEY apparatus through air. The precision of the presented SEY values is estimated to ±0.03. δ max is between 0.9 and 1.1 and E max = 300 ev. (not sensitive to coating parameters as pressure, power.) 20 / 42

21 in the lab Electron Cloud Monitor (ECM) in the SPS Log10(IntElectronCurrent/IntFBCT) Electron cloud current normalized with beam intensity v.s time, measured by ECM in the SPS. 3-4 batches of nominal LHC beam. ( protons/bunch) Normalized e cloud from the MD runs 5 a-c nr1 tested in the SPS a-c nr2 tested in the SPS Stainless Steel Time(h) SEY δ SEY measurements in the lab. a C nr1 tested in the SPS: δ = 0.92 a C nr2 tested in the SPS: δ = 1.14 Stainless Steel: δ = Primary Energy (ev) Observe! EC signal is 10 4 higher on StSt than a-c. Low SEY Low electron current signal. 21 / 42

22 in the lab Ageing observation of a-c liner in the ECM in the SPS One a-c coated liner has been tested during 3 Machine Development (MD) Runs with 3-4 batches of nominal LHC beam accelerated to 450 GeV/c. Vertical unit: nc/10 10 protons per bunch The a-c coated liner was kept in the SPS for more than one year operation. (more than 2 months of venting, maintenance, installation...) No sign of ageing in the SPS. IntElectronCurrent/IntFBCT 5 x Normalized e cloud from the MD runs 10 4 a-c in MD1: 12 August, 2008 a-c in MD2: 6-8 October, a-c in MD3: June, Time(h) / 42

23 in the lab Ageing observation of a-c liner in the ECM in the SPS One a-c coated liner has been tested during 3 Machine Development (MD) Runs with 3-4 batches of nominal LHC beam accelerated to 450 GeV/c. Vertical unit: nc/10 10 protons per bunch The a-c coated liner was kept in the SPS for more than one year operation. (more than 2 months of venting, maintenance, installation...) No sign of ageing in the SPS. IntElectronCurrent/IntFBCT 5 x Normalized e cloud from the MD runs 10 4 a-c in MD1: 12 August, 2008 a-c in MD2: 6-8 October, a-c in MD3: June, Time(h) / 42

24 in the lab Ageing observation of a-c liner in the ECM in the SPS One a-c coated liner has been tested during 3 Machine Development (MD) Runs with 3-4 batches of nominal LHC beam accelerated to 450 GeV/c. Vertical unit: nc/10 10 protons per bunch The a-c coated liner was kept in the SPS for more than one year operation. (more than 2 months of venting, maintenance, installation...) No sign of ageing in the SPS. IntElectronCurrent/IntFBCT 5 x Normalized e cloud from the MD runs 10 4 a-c in MD1: 12 August, 2008 a-c in MD2: 6-8 October, a-c in MD3: June, Time(h) / 42

25 in the lab Inspection of FIVE liners extracted from SPS One Stainless Steel liner and four a-c coated liners Liner SPS operation δ initial StSt 1 year 2.25 (Reference) (5 MD runs) C-strip 1 year 0.92 (a-c coating of 40mm width) (5 MD runs) C-Zr 1.5 years 0.95 (a-c on rough Zr coating) (9 MD runs) CNe64 3 months 0.95 (a-c coating) (2 MD runs) CNe65 3 months 0.95 (a-c coating) (2 MD runs) 25 / 42

26 in the lab Inspection of FIVE liners extracted from SPS One Stainless Steel liner and four a-c coated liners 26 / 42

27 in the lab Inspection of FIVE liners extracted from SPS One Stainless Steel liner and four a-c coated liners 27 / 42

28 in the lab Three MBB dipoles have been coated with a-c coating in-situ dipole (Version I) inserted in the SPS Microwave transmission measurements detected e-cloud related signal in the coated and uncoated magnets. F. Caspers, S. Federmann Dynamic pressure rise used to monitor the behavior of the coated and uncoated magnets. 28 / 42

29 in the lab Three MBB dipoles have been coated with a-c coating in-situ dipole (Version I) inserted in the SPS Microwave transmission measurements detected e-cloud related signal in the coated and uncoated magnets. F. Caspers, S. Federmann Dynamic pressure rise used to monitor the behavior of the coated and uncoated magnets. 29 / 42

30 in the lab E-cloud related measurements/sey measurements in the lab Dynamic pressure rise between the coated and uncoated magnets. The nominal LHC beam: 1,2,3 and 4 batches with 72 bunches at 25 ns spacing. SEY measurements before/after insertion in the SPS MBB magnet before insertion in the SPS: δ = 1.00 MBB magnet after 1 year operation: δ = 1.33 SEY δ Primary Energy (ev) No different in pressure rise. SEY increases after extraction. 30 / 42

31 in the lab E-cloud related measurements/sey measurements in the lab Dynamic pressure rise between the coated and uncoated magnets. The nominal LHC beam: 1,2,3 and 4 batches with 72 bunches at 25 ns spacing. Non-uniform coating color indicates differences in thickness and possibly composition. Bad SEY is mostly due to the coating configuration. Coat MBB vacuum chamber stand-alone outside dipole!!! (Version II) 31 / 42

32 Outline Motivation Conclusions Outlook 1 Motivation SPS-U: Super Proton Synchrotron Upgrade New solution Amorphous Carbon Coating 2 in the lab 3 Conclusions Outlook 32 / 42

33 Conclusions Motivation Conclusions Outlook A-C thin films produced by d.c magnetron sputtering show a reliable low initial SEY (well belowδ threshold = 1.3). A complete suppression of e-cloud can be achieved by coating of liners with a-c. The coating of liners does not show ageing (increase of SEY) after more than 1 year of exposure in the SPS. Magnetron sputtered a-c film is a potential solution to eliminate e-cloud. 33 / 42

34 Conclusions Motivation Conclusions Outlook A-C thin films produced by d.c magnetron sputtering show a reliable low initial SEY (well belowδ threshold = 1.3). A complete suppression of e-cloud can be achieved by coating of liners with a-c. The coating of liners does not show ageing (increase of SEY) after more than 1 year of exposure in the SPS. Magnetron sputtered a-c film is a potential solution to eliminate e-cloud. 34 / 42

35 Conclusions Motivation Conclusions Outlook A-C thin films produced by d.c magnetron sputtering show a reliable low initial SEY (well belowδ threshold = 1.3). A complete suppression of e-cloud can be achieved by coating of liners with a-c. The coating of liners does not show ageing (increase of SEY) after more than 1 year of exposure in the SPS. Magnetron sputtered a-c film is a potential solution to eliminate e-cloud. 35 / 42

36 Conclusions Motivation Conclusions Outlook A-C thin films produced by d.c magnetron sputtering show a reliable low initial SEY (well belowδ threshold = 1.3). A complete suppression of e-cloud can be achieved by coating of liners with a-c. The coating of liners does not show ageing (increase of SEY) after more than 1 year of exposure in the SPS. Magnetron sputtered a-c film is a potential solution to eliminate e-cloud. 36 / 42

37 Outlook Motivation Conclusions Outlook The future activities will be focused on: modifying the coating system in order to find an efficient and economical solution to coat beam pipes in a large scale with the same quality of coating as in the ECMs. following the ageing development of the liners and getting a deeper understanding of a-c thin film both in the lab and in the SPS. following the ageing development of the new version of MBB coating and getting a deeper understanding of the relationship between dynamic pressure rise and e-cloud effect. The first implementation in a large scale with this type of a-c coating is now planned to be performed in the SPS magnet of total 200 m during the shutdown / 42

38 Outlook Motivation Conclusions Outlook The future activities will be focused on: modifying the coating system in order to find an efficient and economical solution to coat beam pipes in a large scale with the same quality of coating as in the ECMs. following the ageing development of the liners and getting a deeper understanding of a-c thin film both in the lab and in the SPS. following the ageing development of the new version of MBB coating and getting a deeper understanding of the relationship between dynamic pressure rise and e-cloud effect. The first implementation in a large scale with this type of a-c coating is now planned to be performed in the SPS magnet of total 200 m during the shutdown / 42

39 Outlook Motivation Conclusions Outlook The future activities will be focused on: modifying the coating system in order to find an efficient and economical solution to coat beam pipes in a large scale with the same quality of coating as in the ECMs. following the ageing development of the liners and getting a deeper understanding of a-c thin film both in the lab and in the SPS. following the ageing development of the new version of MBB coating and getting a deeper understanding of the relationship between dynamic pressure rise and e-cloud effect. The first implementation in a large scale with this type of a-c coating is now planned to be performed in the SPS magnet of total 200 m during the shutdown / 42

40 Outlook Motivation Conclusions Outlook The future activities will be focused on: modifying the coating system in order to find an efficient and economical solution to coat beam pipes in a large scale with the same quality of coating as in the ECMs. following the ageing development of the liners and getting a deeper understanding of a-c thin film both in the lab and in the SPS. following the ageing development of the new version of MBB coating and getting a deeper understanding of the relationship between dynamic pressure rise and e-cloud effect. The first implementation in a large scale with this type of a-c coating is now planned to be performed in the SPS magnet of total 200 m during the shutdown / 42

41 Outlook Motivation Conclusions Outlook The future activities will be focused on: modifying the coating system in order to find an efficient and economical solution to coat beam pipes in a large scale with the same quality of coating as in the ECMs. following the ageing development of the liners and getting a deeper understanding of a-c thin film both in the lab and in the SPS. following the ageing development of the new version of MBB coating and getting a deeper understanding of the relationship between dynamic pressure rise and e-cloud effect. The first implementation in a large scale with this type of a-c coating is now planned to be performed in the SPS magnet of total 200 m during the shutdown / 42

42 Thanks Thanks for your attention! and Questions