Positron vs. Electron Beam Behavior PETRA III Positron vs. Electron Beam Behavior Rainer Wanzenberg ECLOUD 2018 (June 3 - 7, 2018) Italy, Elba, La Biodola Bay

Outline PETRA III operation modes Positron beam operation (2009 – 2012) Electron beam operation, since 2013

PETRA III Overview The extension halls were build in 2014 (one year shut down) Extension Hall East Ada Yonath 3 + 1 beam lines (1 free slot) Max von Laue Hall 14 beam lines Extension Hall North Paul P. Ewald 2 beam lines (3 free slots)

Extension Hall East - Ada Yonath Beamline P21: In vacuum undulator moveable water cooled Wakefield suppressor 4

PETRA III - Parameter Design Parameter PETRA III Energy / GeV 6 Circumference /m 2304 Emittance (horz. / vert.) /nm 1.3 / 0.01 Total current / mA 100 Number of bunches 960 40 Bunch population / 1010 0.5 12 Bunch separation / ns 8 192 Continues mode (960 or 480 bunches) Timing mode Damping Wigglers: B ~ 1.5 T, l = 0.2 m 2 x 10 x 4 m = 80 m ex: 5 nm  1.3 nm Dispersion correction in the wiggler sections: Dx < 18 mm, Dy < 5 mm

Hybrid Lattice: DBA and FODO Qx = 37.12, Qy = 30.27, Energy loss per turn: 5.1 MeV (1.3 MeV without wigglers) FODO Arc: 14 cells (14.4 m) 28 dipoles (28 mrad) L = 5.35 m DBA octant: 8 cells (23 m) 18 dipoles (43.3 mrad) + 5 canting dipoles ( 5 mrad) L = 1 m L = 0.3 m

Positron Operation: 2009 - 2012 DORIS was operated as a synchrotron light source until 2012 (C = 289 m, E = 4.5 GeV ex = 410 nm) positron operation (e- problems with dust) PETRA III was operated with positrons from 2009 – 2012 and is operated with electrons since 2013 PETRA II: 1988 – 2007 pre-accelator for HERA Linac II PIA DESY II

Filling schemes for positron operation Design Parameter PETRA III Energy / GeV 6 Circumference /m 2304 Emittance (horz. / vert.) /nm 1.3 / 0.01 Total current / mA 100 Number of bunches 960 40 Bunch population / 1010 0.5 12 Bunch separation / ns 8 192 User runs in 2011 and 2012 100 80 240 60 40 2.0 8.9 9.6 32 128 192 A vertical emittance growth has been observed for bunch trains with 8 ns and 16 ns bunch to bunch spacing There are “upper-sidebands” in the vert. tune spectra with a clear build-up along a bunch train. A clear conditioning effect has been observed. For user runs filling patterns with 40 x 4 and 60 x 4 bunches were used in 2010. In 2011 it was possible to fill 240 bunches with a 32 ns bunch spacing. In 2012 two dedicated scrubbing runs have improved the situation. It is possible to use 320 bunches with 24 ns bunch spacing and no significant emittance growth.

PETRA III Vacuum chamber Arc: Al, 80 mm x 40 mm IPAC 2011 Secondary Electron Yield of Al Samples from the Dipole chamber of PETRA III D.R. Grosso, M. Commisso, and R. Cimino, LNF-INFN, Frascati Italy R. Flammini, CNR-IMIP, Monterotondo, Italy R. Larciprete, CNR-ISC, Rome, Italy R. W., DESY, Hamburg, Germany (a) (b) (c) Wiggler: Al, 96 mm x 17.9 mm NEG coated Undulator: Al, 57 mm x 7 mm SEY is quite high for Al-chambers, Al “forgets” scrubbing runs

Scrubbing runs (March 2012) Vert. Emittance ~140 pm rad ( for 20 h) Than dropping to 97 pm rad Horz. Emittance Starting at 1.0 nm rad Increasing to 1.8 nm rad Green: total current (100 mA) Red: vertical emittance (scale 0 … 150 pm rad) Blue: Number of bunches (480) Black: horizontal emittance (scale 0 … 6 nm rad) Run 2: March 10 / 11, 2012 Vert. Emittance Starting at 104 pm rad Decreasing to 33 pm But Horz. Emittance increase from 2 nm rad to 4 nm rad Time scale: 4 days ~10 Ah, 1.2 x 10-2 C/mm2 Scrubbing helped, but it was never possible to run 960 (8ns) or 480 (16 ns) bunches without a significant vert. emittance increase ! but after switching to electron operation in 2013 it was possible to run the design parameters (final prove that PETRA III suffered from electron cloud effects during positron operation)

Electron Operation: since 2013 Start electron operation Feb. 2013 End of user run Feb. 3, 2014 Shut down (~ 1 year) PETRA Extension Project (300 m new) Restart with beam Feb. 2015 Design Parameter PETRA III Energy / GeV 6 Circumference /m 2304 Emittance (horz. / vert.) /nm 1.3 / 0.01 Total current / mA 100 Number of bunches 960 40 Bunch population / 1010 0.5 12 Bunch separation / ns 8 192 Feb 16 – Mar 19, 2015 80 mA 960 bunches t= 4.5 h 26 Ah Electrons Feb 3, 2014: 2208 Ah t = 15 h, 100 mA, 960 bunches

Operation with Electrons, Ion effects Filling schemes without a clearing gap in 2013 with electron operation Collective effects determine the possible filling schemes in PETRA III Design parameter ok User runs, total current 100 mA Strong Electron cloud Effects during Positron Operation (2009 – 2012) Preferred Filling Scheme during Positron Operation Electron operation Vertical emittance growth, Threshold current ~ 60 mA, feedback helps

PETRA III Emittance Diagnostics Diagnostic Beam Line (Exp. Hall) Interferometric beam size measurements (North) synchrotron light from bending magnet NL 50 visible light beampipe Reference: PETRA III G. Kube, DIPAC’07, EPAC‘08 ATF - KEK H.Hanyo et al., Proc. of PAC99 (1999), 2143 T. Naito and T. Mitsuhashi, Phys. Rev. ST Accel. Beams 9 (2006) 122802 960 electron bunches, 100 mA Vert. Emittance ~ 7 pm rad (Jan 17, 2013)

Vertical Emittance Growth, e- Operation Jan 15, 2013 240 bunches, 100 mA Jan 15, 2013 480 bunches, 100 mA 56 pm rad Jan 17, 2013 960 bunches, 100 mA lower sideband 7 pm rad vert. tune Threshold current ~ 60 mA

Ion Effects – Multi bunch spectrum Qualitative Understanding: Two stream instability, coupled ion and beam motion k = mode number (the range is set for 960 bunch operation, there is only one unstable mode) 240 Bunches Unstable Mode 8.8 MHz ~ 68 f0

Ionen Effects: Couple Bunch Motion Complex solution of the dispersion relation Mode k is instable with growth rate: Feedback (design) damping rate: 1400 Hz (93 Turns) Mode growth rate: ~ 42 kHz ( 3 Turns) Simple Model, assuming: O2 ions with a density of 20 ions / cm Total current 85 mA in 240 bunches Beam size 800 mm / 10 mm S. Matsumoto et al., Experimental Study of the Ion Trapping Phenomenon in Tristan-AR, PAC 1997 D.G. Koshkarev, P.R. Zenkevich, Part. Acc., 1972, Vol3. pp.1-9

Summary Positron operation: Collective effects determine the possible filling schemes in PETRA III Positron operation: It was not possible to run with the design filling pattern 960 bunches and 8 ns bunch to bunch spacing due to elctron cloud effects in 2011 and 2012 a filling scheme with 240 bunches was used (32 ns bunch to bunch spacing) Electron operation: All problems with 960 and 480 bunches are gone, the design filling scheme is archived But the filling scheme with 240 bunches showed problems (emittance growth) which could be understood as an ion instability. In 2017 it was possible to run 240 bunches, very likely due to improved vacuum pressure (the feedback gain had to be increased).

Thank you for your attention !