1. 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

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

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

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

5. PETRA III - Parameter Design Parameter PETRA III Energy / GeV 6
Circumference /m
2304
Emittance (horz. / vert.) /nm
1.3 /
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

6. 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

7. 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

8. Filling schemes for positron operation
Design Parameter
PETRA III
Energy / GeV 6
Circumference /m
2304
Emittance (horz. / vert.) /nm
1.3 /
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 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.

9. 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

10. 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)

11. 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 /
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: Ah
t = 15 h, 100 mA, 960 bunches

12. 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

13. 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)
960 electron bunches, 100 mA
Vert. Emittance ~ 7 pm rad (Jan 17, 2013)

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

15. 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

16. Ionen Effects: Couple Bunch Motion
Complex solution of the dispersion relation
Mode k is instable with growth rate:
Feedback (design) damping
rate: 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

17. 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).

18. Thank you for your attention !