M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 1 Issues in the Formation and Dissipation of the Electron Cloud Miguel A. Furman, LBNL 13th ICFA Beam Dynamics Mini Workshop Beam-Induced Pressure Rise in Rings BNL, Dec. 812, 2003 Lawrence Berkeley National Laboratory My gratitude to: A. Adelmann, G. Arduini, M. Blaskiewicz, O. Brning, Y. H. Cai, R. Cimino, I. Collins, O. Grbner, K. Harkay, S. Heifets, N. Hilleret, J. M. Jimnez, R. Kirby, G. Lambertson, R. Macek, K. Ohmi, M. Pivi, G. Rumolo, F. Zimmermann. M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 2 Summary Motivation: better understand electron cloud (EC) dynamics in particular: effect of secondary electron process Tools: simulations (mostly code POSINST Furman and Pivi); other codes by Ohmi, Zimmermann, Rumolo, Blaskiewicz, Adelmann,... also take SE into account electron detectors (APS, SPS, PSR, RHIC Harkay, Jimnez, Macek, Browman, Zhang,...) EC formation primary processes: photoelectrons, residual gas ionization, beam-particle losses secondary electron emission (SEY): may lead to beam-induced multipatcing (BIM) examples: sensitivity to secondary emission yield (E 0 ) (E 0 =incident electron energy) secondary emission spectrum d /dE (E=emitted electron energy) EC dissipation focus: mostly PSR, also APS and SPS: role of (0) Scrubbing effect and conclusions Lawrence Berkeley National Laboratory M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 3 Tools Simulation detailed model for and d /dE input data: measurements by R. Kirby, N. Hilleret, R. Cimino, I. Collins and others St. St., Cu, Al, TiN electron cloud is dynamical beam is a prescribed function of time, space Electron detectors RFA (Harkay and Rosenberg, NIMPR A453, 507 (2000); PRSTAB 6, ) installed at APS, PSR, BEPC, ANL IPNS RCS measure I ew and d /dE at chamber wall (prompt electrons) sweeping detector at PSR ( Browman, Macek ) installed at PSR measure EC density in the bulk (swept electrons) strip detector at SPS, COLDEX, PUs (Jimnez et al., PAC03) strip detector in an adjustable B field Lawrence Berkeley National Laboratory (ROAB003; ROPA007) (ROAB003) (TOPC003; TPPB054) PAC03 refs. in blue M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 4 EC formation: basics Electron charge conservation in a given chamber section assuming no antechamber, no net end-losses assumes 3 primary processes: photoelectrons residual gas ionization beam-particle losses Assume: =beam line density Z=beam particle charge p=chamber x-section perimeter I ew =e flux at wall [A/m 2 ] =primary production rate [m 1 ] per beam particle Lawrence Berkeley National Laboratory (M. Blaskiewicz) M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 5 EC formation: primary e rate of creation Lawrence Berkeley National Laboratory v b = beam speed Y eff = eff. quantum efficiency (e yield per ) i = ioniz. cross-section per beam particle p vac = vac. pressure T = temperature eff = eff. e yield per (beam particle)-wall collision n' bpl = beam particle loss rate per unit length per beam particle Electron production rate per beam particle per unit length of beam trajectory: M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 6 Secondary e emission Simulation (Furman-Pivi, PRSTAB 5, ): event=one electron-wall collision instantaneous generation of n secondaries (or absorption) include E 0 and 0 dependence detailed phenomenological model for and d /dE Three main components of emitted electrons: elastics: rediffused: true secondaries: NB: d /dE is different for e, r and ts!!! Lawrence Berkeley National Laboratory M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 7 Two sample measurements of the SEY Lawrence Berkeley National Laboratory Cu St. steel caveat: samples not fully conditioned! (N. Hilleret; R. Kirby) M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 8 PSR simulation: sensitivity to max Lawrence Berkeley National Laboratory stainless steel chamber, field-free region, dominant primary process: proton losses: beam signal (arb. units) max =1.5, (0)=0.36 max =1.7, (0) = 0.4 aver. electron line density vs. time (see also RPPB035) M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 9 PSR simulation: sensitivity to max Lawrence Berkeley National Laboratory beam signal (arb. units) e flux at the wall vs. time max =1.7, (0) = 0.4 max =1.5, (0)=0.36 M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 10 PSR simulation: sensitivity to max Lawrence Berkeley National Laboratory electron-wall collision energy vs. time M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 11 PSR simulation-contd. Lawrence Berkeley National Laboratory beam potential well vs. time M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 12 Sample spectrum: d /dE Depends on material and state of conditioning St. St. sample, E 0 =300 eV, normal incidence, (Kirby-King, NIMPR A469, 1 (2001)) Lawrence Berkeley National Laboratory st. steel sample = 2.04 e = 6% r = 37% ts =57% e + r =43% Hillerets group CERN: Baglin et al, CERN-LHC-PR 472. Other measurements: Cimino and Collins, 2003) Cu sample = 2.05 e = 1% r = 9% ts =90% e + r =10% M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 13 Sensitivity to relative ratios of e, r and ts : LHC Lawrence Berkeley National Laboratory LHC simulation max fixed at 2.05; dominated by photoelectrons; electron line density vs. time (LHC arc dipole) e + r = 43% e + r = 10% e + r = 0 (Furman-Pivi EPAC02) max =2.05 (see also: TPPB054) M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 14 Sensitivity to relative ratios of e, r and ts : LHC Lawrence Berkeley National Laboratory e -wall collision energy vs. time (LHC arc dipole) e + r = 43% e + r = 10% e + r = 0 M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 15 Sensitivity to relative ratios of e, r and ts : LHC Lawrence Berkeley National Laboratory effective SEY vs. time (LHC arc dipole) e + r = 43% e + r = 10% e + r = 0 M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 16 Sensitivity to relative ratios of e, r and ts : LHC Lawrence Berkeley National Laboratory power deposition vs. time (LHC arc dipole) e + r = 10% e + r = 0 e + r = 43% M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 17 EC formation: beam-induced multipacting (BIM) Lawrence Berkeley National Laboratory train of short bunches, each of charge Q=NZe, separated by s b t = e chamber traversal time b = chamber radius (or half-height if rectangular) The parameterdefines 3 regimes: If G = 1 and eff > 1, EC can grow dramatically (O. Grbner, ISR; 1977) (also for solenoidal field if T/2=s b /c: WOAA004) M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 18 BIM in the APS Lawrence Berkeley National Laboratory (Furman, Pivi, Harkay, Rosenberg, PAC01) time-averaged e flux at wall vs. bunch spacing measured simulated e + beam, 10-bunch train, field-free region (see also: RPPG002) M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 19 BIM for long bunches: case of PSR bunch length >> t a portion the EC phase space is in resonance with the bounce frequency trailing edge multipacting (Macek; Blaskiewicz, Danilov, Alexandrov,) Lawrence Berkeley National Laboratory ED42Y electron detector signal 8 C/pulse beam 435 A/cm 2 (simulation input) electron signal measured (R. Macek) simulated (M. Pivi) ( max =2.05) (ROAB003; RPPB035) M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 20 BIM for long bunches: case of PSR-contd. head truncated bunch (nominal charge) nominal bunch tail L=150 ns simulated experiment in trailing edge multipacting: truncate bunch tail at fixed bunch charge Lawrence Berkeley National Laboratory suppresses the resonance hard to put into practice! (M. Pivi) bunch profile aver. e line density (RPPG024) M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 21 EC dissipation - simplest analysis Lawrence Berkeley National Laboratory N N 2b If not monoenergetic and not along a straight line, then beam has been extracted, or gap between bunches field-free region, or constant B field assume monoenergetic blob of electrons neglect space-charge forces where K=f(angles)1.11.2 simulations show that this formula works to within ~20% and = dissipation time M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 22 EC dissipation in PSR after beam extraction Sweeping e detector measures electrons in the bulk 200 ns eff 0.5 if E = 24 eV since eff (0), you infer (0) well supported by simulations (see next slide) (Macek and Browman) Lawrence Berkeley National Laboratory (RPPB035) M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 23 Lawrence Berkeley National Laboratory EC dissipation after beam extraction: PSR simulation NB: primary e rate is 100 x nominal input SEY: max = 1.7 (0) = 0.4 EC line density vs. time (field-free region) slope = 200 ns M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 24 EC dissipation after beam extraction: PSR simulation e -wall collision energy vs. time (field-free region) Lawrence Berkeley National Laboratory M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 25 Lawrence Berkeley National Laboratory EC dissipation after beam extraction: SPS simulation NB: p vac is >> nominal stainless steel chamber, dipole magnet, B = 0.2 T, dominant primary process: residual gas ionization; slope = 170 ns input SEY: max = 1.9 (0) = 0.5 M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 26 Lawrence Berkeley National Laboratory EC dissipation after beam extraction: SPS simulation e -wall collision energy vs. time (B-field region) M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 27 Conditioning effects: beam scrubbing Decrease of SEY by e bombardment self-conditioning effect for a storage ring: beam scrubbing SPS ECE studies (M. Jimnez; F. Zimmermann): 3+ years of dedicated EC studies with dedicated instrumentation scrubbing very efficient; favorable effects seen in: vacuum pressure in-situ SEY measurements electron flux at wall e energy distribution in good agreement with simulations above 30 eV TiZrV coating fully suppresses multipacting after activation Lawrence Berkeley National Laboratory (see also: MOPA001; TPPB054) (TOPC003) M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 28 Conditioning effects: beam scrubbing PSR prompt e signal (BIM) is subject to conditioning: (R. Macek) signal is stronger for st.st. than for TiN sensitive to location and N signal does not saturate as N increases up to ~8x10 13 conditioning: down by factor ~5 in sector 4 after few weeks (low current) PSR swept e signal is not: signal saturates beyond N~5x10 13 200 ns, independent of: N location conditioning state st. st. or TiN Tentative conclusion: beam scrubbing conditions max but leaves (0) unchanged Lawrence Berkeley National Laboratory (ROAB003; RPPB035) M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 29 Conditioning effectscontd. consistent with bench results for Cu found at CERN! the result (0)1 seems unconventional if validated, it could have a significant unfavorable effect on the EC power deposition in the LHC because electrons survive longer in between bunches Lawrence Berkeley National Laboratory (R. Cimino and I. Collins, proc. ASTEC2003, Daresbury Jan. 03) Copper SEY (CERN) M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 30 Conclusions A consistent picture of the ECE is emerging for low-energy machines (long bunch, intense beam) high-energy machines (short, well separated bunches) methodical measurements and simulation benchmarks at APS, PSR and SPS are paying off some interesting surprises along the way Quantitative predictions are becoming more reliable we are growing older but wiser Lawrence Berkeley National Laboratory M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 31 Additional material Lawrence Berkeley National Laboratory M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 32 M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 33 M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 34 Lawrence Berkeley National Laboratory M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 35 Lawrence Berkeley National Laboratory M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 36 Lawrence Berkeley National Laboratory M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 37 Lawrence Berkeley National Laboratory M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 38 Lawrence Berkeley National Laboratory NOTE: rediffused+backscattered~50% (assuming low-energy cutoff=50 eV) M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 39 NOTE: rediffused+backscattered~5% (assuming low-energy cutoff=50 eV) Lawrence Berkeley National Laboratory M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 40 Lawrence Berkeley National Laboratory M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 41 Lawrence Berkeley National Laboratory M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 42 Lawrence Berkeley National Laboratory Current parameter values from fits to data M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 43 Q: is the electron emitted spectrum Maxwellian? A: only approximately. Fits to data, however, imply p n ~1.85, depending on n and material Lawrence Berkeley National Laboratory definition of Maxwellian spectrum: M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 44 Lawrence Berkeley National Laboratory backscattered and rediffused electrons artificially suppressed (true secondaries only) M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 45 BIM for long bunches: case of PSR bunch length >> t Lawrence Berkeley National Laboratory ED02X electron detector signal 8 C/pulse beam ED42Y electron detector signal 8 C/pulse beam 145 A/cm A/cm 2 M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 46 Lawrence Berkeley National Laboratory Effect of bunch shortening (PSR simulation; M. Pivi ) truncate the bunch tail to reduce trailing-edge multipacting truncated bunch (nominal charge) nominal bunch head tail M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 47 Lawrence Berkeley National Laboratory Effect of bunch shortening (PSR simulation; M. Pivi ) contd. L=254 ns (nom..) L=200 ns L=180 ns L=150 ns M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 48 Lawrence Berkeley National Laboratory M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 49 Lawrence Berkeley National Laboratory M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 50 Lawrence Berkeley National Laboratory (detailed view for copper only) M. A. Furman, BNL, Dec. 8-12, 2003, Electron Cloud... p. 51 Lawrence Berkeley National Laboratory