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The Challenges of Ultra-low Emittance Damping Rings
David Rubin September 6,2011
IPAC2011 – San Sebastian, Spain
September 6, 2011 IPAC2011, San Sebastian, Spain 2
Damping Rings
• Requirements • Lattice • Emittance Dilution • Emittance Tuning
– Instrumentation – Algorithms – Results
• Collective Effects – Electron Cloud – Ions – Intra-beam scattering
• Conclusion
September 6, 2011 IPAC2011, San Sebastian, Spain 3
Requirements
• Accept hot bunches of positrons ε ~ 4.5 x 10-6 m-rad • Deliver ultra-low emittance εx~ 0.5nm-rad and εy~ 2pm-rad
positrons in trains of 1300 bunches at a repetition rate of 5 Hz
• Cool them and kick them out to the linac 200ms later, having reduced that emittance by > 4 orders of magnitude with nearly 100% transfer efficiency as the average beam power is > 200kW.
(Meanwhile, ~2MW is being radiated away as synchrotron radiation) • The 1300 bunch train consists of many smaller trains with gaps for
ions to clear in the electron ring and the electron cloud to clear in the positron ring.
• The bunches are plucked one at a time in a 3MHz burst. • For every low emittance bunch that is extracted into a transfer line, a
hot bunch is accepted from the source.
Requirements
• Meanwhile the 2MW of synchrotron radiation photons strikes the walls of the vacuum chamber, emitting photo electrons
• The electrons are accelerated by the positron beam across the chamber and into the walls again where secondaries are emitted.
• The accumulating cloud of electrons is trapped in the potential well of the positron beam.
• The electron cloud – focuses the positrons, shifting tunes – Couples motion of the leading to the trailing bunches and – And the head of the bunch to the tail – Destabilizing the train and diluting the emittance.
September 6, 2011 IPAC2011, San Sebastian, Spain 4
September 6, 2011 IPAC2011, San Sebastian, Spain 5
Lattice
• The compression of the train is limited in the end by – Our ability to extract cold and inject hot bunches
without disturbing the other bunches in the circulating trains
– The total current in the ring, likely limited by instabilities or emittance dilution
• We consider the ILC baseline as a point of reference, nominally 3.2 km, with 1300 bunches and 6.2ns spacing within the mini-trains
September 6, 2011 IPAC2011, San Sebastian, Spain 6
Optics Second level
evel Fourth level Fifth level
• Positrons emerging from converter have large emittance, 9mm-mrad equivalent.
• But we require equilibrium horizontal emittance of 0.5 nm-rad. • Typically a low emittance optics is strong focusing, with a large natural
chromaticity, strong sextupoles and small dynamic aperture. • Usually this is not a problem as the emittance, and therefore the required
acceptance shrinks along with the dynamic aperture. • Acceptance required for the DR does not shrink along with the dynamic
aperture. • Acceptance is determined by phase space volume of the incoming beam. • The other requirement is that the beam emittance approach its equilibrium
value in 200ms, necessarily about 8 damping times => τx≈ 24ms. • Relatively large circumference, the necessity for expansive dynamic
aperture, short damping time (~ 2000 turns), and low equilibrium emittance • => Use wigglers to augment the radiation damping – little impact on dynamic aperture.
Layout
• Periodicity – A high degree of symmetry enhances dynamic aperture, as it reduces
the number of systematic resonances. – But not so convenient for facilities.
• Racetrack puts all of the cryogenics for RF and wigglers in a single straight
• Injection and extraction in another so that transfer lines can share a tunnel.
• Conventional facilities dictate a racetrack, and in the baseline design the circumference is evenly divided between straight and arc.
• There is zero dispersion in the straights so they generate nothing but chromaticity, that is left to the arc sextupoles to correct.
September 6, 2011 IPAC2011, San Sebastian, Spain 7
Parameters
• Another consideration is the momentum compaction – Small enough to ensure that 6mm bunch length can
be achieved with reasonable RF voltage – Large enough for reasonable threshold for single
bunch instabilities.
September 6, 2011 IPAC2011, San Sebastian, Spain 8
Damping Ring Layout
PhaseTrombone
RF
WigglersChicane
Injection
Extraction
Parameter Value Circumference[km] 3.242 Energy[GeV] 5 Τx[ms] 24 Wiggler length [m] 104 Bwiggler[T] 1.5 RF[MHz] 650 RF[MV] 14 ΔE/turn[MeV] 4.5 ϒεx [µm] 5.4 I[A] 0.4 σz[ [mm] 6 σδ [%] 0.11 αp 3.3 x10-4
Wigglers
• Wigglers decrease damping time from 135ms to 24ms
• Decrease emittance from 2.5x10-9 to 5.2x10-10
– Effective as they do significant damping but relatively little excitation
• Increase synchrotron radiated power from 320kW to nearly 2MW
September 6, 2011 IPAC2011, San Sebastian, Spain 10
Vertical emittance
• Due almost exclusively to misalignments and field errors • In perfectly aligned machine vertical emittance is more than an
order of magnitude smaller than 2pm target. • Vertically offset quadrupoles and rolled dipoles generate
vertical kicks and vertical dispersion and emittance • Tilted quadrupoles and offset sextupoles couple horizontal
dispersion into vertical • Survey and alignment – what would it take?
September 6, 2011 IPAC2011, San Sebastian, Spain 11
Quadrupole vertical offset[µm] 30 Quadrupole tilt [µm] 30 Dipole roll [µm] 30 Sextupole vertical offset [µm] 30 Wiggler tilt [µm] 30
⇒ 50% seeds, εx> 4pm-rad (95% < 14pm-rad) Need to do much better
Emittance tuning
• Measure and correct – Given enough correctors (steerings and skew quads everywhere) and
quality measurements, emittance diluting errors can be corrected – If we measure the dispersion with enough precision, and fit a machine
model using all of those correctors, load into the machine, done
• Machine physicists at light sources have been very successful cleaning up lattice errors and achieving very low emittance, indeed in some cases exceeding the ILC damping ring spec.
• In a damping ring this will have to be done routinely and necessarily with some efficiency
September 6, 2011 IPAC2011, San Sebastian, Spain 12
• ATF and CesrTA have developed tuning procedures. – Tested on the respective machines and evaluated in simulation – We can predict with some confidence extrapolation to 3.2km and 2pm
• To achieve and maintain very low emittance – Periodic survey and alignment of guide field magnets – Precision beam position monitors and beam based calibration of position
monitor offsets, tilts, button gains so that sources of emittance dilution can be identified
– Algorithms for compensating the misalignments with corrector magnets.
September 6, 2011 IPAC2011, San Sebastian, Spain 13
ATF Damping Ring
September 6, 2011 IPAC2011, San Sebastian, Spain 14
Parameter Circumference[m] 138.6 Energy[GeV] 1.3 Lattice type FOBO (18 cells /arc) Symmetry Racetrack Horizontal steerings 48 Vertical steerings 50 Skew quadrupoles 68 Horizontal emittance[nm] 1.1 Beam detectors 96 BPM diff resolution[µm] <1
ATF low emittance tuning
• Measure and correct closed orbit distortion with all steerings • Measure orbit and dispersion. Simultaneously correct a
weighted average of dispersion and orbit errors using vertical steerings – Dispersion is the difference of orbits with 1% energy differential Few pm-rad vertical emittance requires residual vertical dispersion < 5mm, corresponds to orbit difference of 50µm (insensitive to BPM offsets)
• Measure coupling and minimize with skew quads. – Coupling is defined as the change in vertical orbit due to the effect of two
nondegenerate horizontal steerings.
September 6, 2011 IPAC2011, San Sebastian, Spain 15
ATF Low Emittance Tuning
Effectiveness depends on the BPM offset error and BPM resolution. Calibration of BPM offsets is essential. With 20µm BPM resolution and no BPM alignment
5.8mm residual dispersion and measure >10pm vertical emittance with laser wire With improved beam position monitors, 5µm resolution and BPM alignment 1.7mm residual dispersion and 3.5-5pm emittance with laser wire. Consistent with simulations which furthermore indicates that with σBPM < 1µm, will reach εy< 2pm
September 6, 2011 IPAC2011, San Sebastian, Spain 16
ATF emittance tuning
September 6, 2011 IPAC2011, San Sebastian, Spain 17
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Proceedings of APAC 2004, Gyeongju, Korea
535
Laser wire measurement of emittance after tuning
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Proceedings of APAC 2004, Gyeongju, Korea
535
βv~ 7.5m βh~ 4.5m
Some evidence for IBS emittance growth
CesrTA
September 6, 2011 IPAC2011, San Sebastian, Spain 18
Parameter Circumference[m] 768.4 Energy[GeV] 2.1 (1.8-5.3) Lattice type FODO Symmetry ≈ mirror Horizontal steerings 55 Vertical steerings 58 Skew quadrupoles 25 Horizontal emittance[nm] 2.6 Damping wigglers [m] 19 (90% of synchrotron radiation) Wiggler Bmax [T] 1.9 Beam detectors 100 BPM diff resolution[µm] 10
CesrTA low emittance tuning
• Measure and correct closed orbit distortion with all steerings • Measure betatron amplitudes, phase advance and transverse
coupling. Use all 100 quadrupoles and 25 skew quads to fit the machine model to the measurement, and load correction – (Phase and coupling derives from turn by turn position data of a resonantly
excited beam)
September 6, 2011 IPAC2011, San Sebastian, Spain 19
3840511-246
15
05
–05–15
15
05
–05
–15
Phas
e.y
(deg
) P
hase
.x (d
eg)
0 10 20 30 40 50 60 70 80 90 100BPM Index
(a)
(b)
3840511-2400.10
0.05
0.00
–0.05
–0.100 10 20 30 40 50 60 70 80 90 100
BP
char
12
M Index
Betatron phase advance
horizontal
vertical
coupling
CesrTA low emittance tuning
• Re-measure closed orbit, phase and coupling, and dispersion. Simultaneously minimize a weighted sum of orbit, dispersion, and coupling using vertical steerings and skew quads. – Dispersion is determined by driving the beam at the synchrotron tune
and measuring transverse amplitudes and phases at each BPM
Typically then measure < 10pm with xray beam size monitor
September 6, 2011 IPAC2011, San Sebastian, Spain 20
3840511-2360.10
0.05
0.00
–0.05
–0.10
ac_e
ta.y
(m)
0 10 20 30 40 50 60 70 80 90 100BPM Index
Low emittance tuning - modeling
• Introduce misalignments
• BPM parameters
September 6, 2011 IPAC2011, San Sebastian, Spain 22
Element Misalignment
Quadrupole vertical offset [µm] 250
Quadrupole tilt [µrad] 300
Dipole roll [µrad] 300
Sextupole vertical offset [µm] 250
Wiggler tilt [µrad] 200
BPM precision Absolute [µm] 200 Differential [µm] 10 Tilt [mrad] 22
Emittance Tuning Simulation
September 6, 2011 IPAC2011, San Sebastian, Spain 23
- Create 1000 models - Apply tuning procedure Emittance distribution after each step
0
50
100
150
200
250
0 10 20 30 40 50
Num
ber o
f see
ds
emittance [pm]
no correction correct closed orbit ( y) correct C12 correct y, C12 & v
Low Emittance Tuning
September 6, 2011 IPAC2011, San Sebastian, Spain 24
The same simulation predicts 95% seeds are tuned to <2pm if BPM - Offsets < 100µm - Button to button gain variation < 1% - Differential resolution < 4 µm (1 µm for ATF lattice) - BPM tilt < 10mrad • We have beam based techniques for calibrating gain variation
based on turn by turn position data • Determining tilt from coupling measurements • We are exploring a tuning scheme that depends on measurements
of the normal modes of the dispersion rather than the horizontal and vertical and that is inherently insensitive to BPM button gain variations and BPM tilts.
Low Emittance Tuning
September 6, 2011 IPAC2011, San Sebastian, Spain 25
Successful low emittance tuning is all about the beam position monitors Ideally the BPMs have bandwidth to measure individual bunches - so that a witness bunch can be used to monitor orbit,β, coupling and η
Note that for both ATF and CesrTA the number and placement of correctors is more than adequate.
Electron cloud effects
• Bunch dependent coherent tune shift - measure of local cloud density • Cloud evolution depends on: Peak SEY Photon reflectivity Quantum efficiency Rediffused yield Elastic yield Peak secondary energy Fit model of cloud development to measurements of bunch by bunch tune shift to determine parameters
September 6, 2011 IPAC2011, San Sebas0an, Spain 26
Witness Bunch Study at 2GeV
September 6, 2011 IPAC2011, San Sebas0an, Spain 27
- 21 bunch train,14ns spacing - witness bunch at varied delay - 0.8×1010 particles/bunch - Data (black)
SEY=2.0
SEY=1.8
SEY=2.2 Train
Witnesses
Peak SEY Scan Coherent Tune Shifts (1 kHz ~ 0.0025), vs. Bunch Number
Tune shift modeled with synrad3d
September 6, 2011 IPAC2011, San Sebastian, Spain 28
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WEP108 Proceedings of 2011 Particle Accelerator Conference, New York, NY, USA
2 Beam Dynamics and EM Fields
Improved model of radiation distribution
Better fit to horizontal tune shift
Electron cloud effects
September 6, 2011 IPAC2011, San Sebastian, Spain 29
3840511-126Head-tail instability
Self excited power spectrum in each bunch of a 30 bunch train
Electron cloud effects
September 6, 2011 IPAC2011, San Sebastian, Spain 30
Emittance dilution
Minimum vertical emittance ~ 20pm
Bunch by bunch and turn by turn vertical emittance is measured with xray beam size monitor
Retarding Field Analyzer
September 6, 2011 IPAC2011, San Sebastian, Spain 31
View of from outside vacuum chamber of diple style RFA with 9 independent collectors. The fine mesh wire grid is in place (but transparent)
Measures the time average cloud density and energy spectrum
Electron cloud - RFA
September 6, 2011 IPAC2011, San Sebastian, Spain 32
0 50 100 150 20010 4
10 3
10 2
10 1
100
101
102
Beam current (mA)
Ave
rage
col
lect
or c
urre
nt d
ensi
ty (n
A/m
m2 )
1x20 e+, 5.3 GeV, 14ns, 5.3 GeV, SLAC Dipole RFAs
Bare AluminumTiN CoatingTiN + Grooves
Mitigation in a dipole field
140 Chapter 4. Electron Cloud Growth and Mitigation
which the NEG was activated again), the signal rose somewhat, but it processed back down toits minimum value after a few months of beam time. The other two detectors showed a similartrend.
0 50 100 150 2000
1
2
3
4
5
6
7
8
Beam current (mA)
co
llecto
r cu
rren
t d
en
sit
y (
nA
/mm
2)
4/25/2010 (before activation)
4/29/2010 (after activation)
7/20/2010 (after processing)
9/4/2010 (after CESR down)
12/7/2010 (after re!processing)
Figure 4.18: NEG RFA comparison, 1x20 e+, 5.3GeV, 14ns
Dipole Data Most of our dipole RFA measurements were done using a chicane of four magnetsbuilt at SLAC [? ]. The field in these magnets is variable, but most of our measurements weredone in a nominal dipole field of 810G. Of the four chicane chambers, one is bare Aluminum, twoare TiN coated, and one is both grooved and TiN coated. The grooves are triangular with a depthof 5.6mm and an angle of 20◦. A retarding voltage scan, done in the Aluminum chamber and withthe same beam conditions as Fig. 4.15, can be seen in Fig. 4.19. Here one can see a strong centralmultipacting spike.
Figure 4.19: Typical Al dipole RFA measurement: 1x45x1.25mA e+, 5.3GeV, 14ns
Fig. 4.20 shows a comparison between three of the chicane RFAs. We found the difference betweenuncoated and coated chambers to be even stronger than in a drift region. At high beam current, theTiN coated chamber shows a signal smaller by two orders of magnitude than the bare Al chamber,while the coated and grooved chamber performs better still.
Dipole RFA data with characteristic central peak
Aluminum chamber 45 bunches, 1.25mA/bunch 14ns spacing 5.3GeV
Electron cloud - RFA
September 6, 2011 IPAC2011, San Sebastian, Spain 33
0 10 20 30 40 50 60 70 80 900
2
4
6
8
10
12
14
16
18
Beam current (mA)
Ave
rage
col
lect
or c
urre
nt d
ensi
ty (n
A/m
m2 )
Wiggler Center Pole Comparison: 1x45 e+, 2.1 GeV, 14ns
Wig1W 5/2/10 (Cu)Wig2B 1/31/09 (TiN)Wig2B 12/5/09 (Grooved)Wig2B 5/2/10 (Electrode)
Electron cloud mitigations in damping wiggler
Electron cloud - RFA
e+ e-
• Mitigation in field free region – Electron cloud from positron and electron beams – 20 bunches – 14ns spacing – 5.3 GeV
September 6, 2011 34 IPAC2011, San Sebastian, Spain
Surface Characterization & Mitigation Tests
Drift Quad Dipole Wiggler VC Fab Al ü ü ü CU, SLAC
Cu ü ü CU, KEK, LBNL, SLAC
TiN on Al ü ü ü CU, SLAC
TiN on Cu ü ü CU, KEK, LBNL, SLAC
Amorphous C on Al ü CERN, CU
Diamond-like C on Al ü CU,KEK
NEG on SS ü CU
Solenoid Windings ü CU
Fins w/TiN on Al ü SLAC
Triangular Grooves on Cu ü CU, KEK, LBNL, SLAC
Triangular Grooves w/TiN on Al ü CU, SLAC
Triangular Grooves w/TiN on Cu ü CU, KEK, LBNL, SLAC
Clearing Electrode ü CU, KEK, LBNL, SLAC
September 6, 2011 IPAC2011, San Sebastian, Spain
Time Resolved Measurements
September 6, 2011 IPAC2011, San Sebastian, Spain 36
Shielded pickup
• Overlay of 15 two bunch measurements each with different delay of second bunch
• First bunch initiates cloud • Second bunch kicks electrons from the bottom
of the chamber into the pickup • Yielding time resolved development and decay
of cloud
40ns/div
Shielded pickup- elastic yield
September 6, 2011 IPAC2011, San Sebastian, Spain 37
Uncoated aluminum chamber. Eleven two-bunch scope traces are superposed with witness bunch delayed from 12 to 100ns. The magnitudes of the modeled signals at large witness bunch delay clearly show the dependence on the elastic yield parameter δ0 as it is varied from 0.05 to 0.95. Best fit to the measured signals is given by a value of δ0 =0.75
Shielded pickup – elastic yield
September 6, 2011 IPAC2011, San Sebastian, Spain 38
Titanium-nitride-coated aluminum chamber - Witness bunch delay ranges from 14 to 84ns - Best fit for elastic yield parameter is δ0 = 0.05
CesrTA IBS
September 6, 2011 IPAC2011, San Sebastian, Spain 39
• Horizontal beam size measured with interferometer • Calculation assumes 9pm-rad zero current vertical emittance and
80% from dispersion
ATF - Fast Ion Instability
September 6, 2011 IPAC2011, San Sebastian, Spain 40
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R/)1(J# O&/)# R/88191/(9# A%26%%(# A%*)# G*&21R8%9# *(0#
&%910'*8#J*9#)/8%R'8%9# R/'G8%#2/# 2@%#)/21/(#/O# 2@%#A%*)#
*(0#8%*0#2/#*#A%*)#91V%#A8/6>'G#*(0#%)122*(R%#J&/62@"#B(#
J%(%&*8,# 26/#51(09#/O# 1/(#%OO%R2#R*(#*OO%R2# 2@%#)*R@1(%_9#
G%&O/&)*(R%"#?(%#19#R*88%0#1/(#2&*GG1(J#1(#6@1R@#2@%#1/(9#
*&%#2'&(#AM#2'&(#2&*GG%0#AM#2@%#A%*)#G/2%(21*8"#$@19#%OO%R2#
R*(#A%#R'&%0#AM#*#9'OO1R1%(2#(')A%&#/O#%)G2M#XT#A'R5%29,#
6@1R@# *88/6# 2@%# 1/(9# 2/# R8%*&"# $@19# &%)%0M# @*9# A%%(#
*GG81%0#1(#9%Q%&*8#%P1921(J#)*R@1(%9"#N(/2@%3(0#/O#1/(#
%OO%R2#19#*#2&*(91%(2#%OO%R2,#2@%#9/>R*88%0#O*92#1/(#1(92*A1812M#
1(#6@1R@#R*9%#2@%#1/(9#R/)%#O&/)#*#91(J8%#G*99*J%#/O#2@%#
A'(R@# 2&*1(# ]:,# C^"# T/&# @1J@# 1(2%(912M# *(0# 8/6# %)122*(R%#
92/&*J%#&1(J9,#O/&#%P*)G8%,#2@%#BZ[#%8%R2&/(#0*)G1(J#&1(J,#
2@%# 1/(9# G&/0'R%0# AM# 91(J8%# G*99*J%# /O# 2@%# A%*)# R*(#
*RR')'8*2%# *(0# 8%*0# 2/# *0Q%&9%# %OO%R29# 2/# 2@%#)*R@1(%_9#
G%&O/&)*(R%"#
####$@%#&%R%(2#%PG%&1)%(2*8#92'01%9#/O#O*92#1/(#1(92*A1812M#1(#
2@%# =7=# N$T# 0*)G1(J# &1(J# ]`^# *&%# G&%9%(2%0# 1(# 2@19#
G*G%&"#?'&#)/21Q*21/(# 19# 2/# 9%%# 1(#6@*2#A%*)# R/(0121/(9#
*(0#Q*R'')#G&%99'&%9#R*(#2&1JJ%	'R@#51(0#/O#1(92*A1812M"##
2))&"'("!)*"$%-&
####T/&# 2@%# O1&92# 2&1*8,# 2@%# 1/(# G')G9# 6%&%# 2'&(%0# /OO# 1(#
9%Q%&*8# 8/R*21/(9# *&/'(0# 2@%# 0*)G1(J# &1(J# *9# 9@/6(# 1(#
T1J"#+# *(0# &%9'821(J# Q*R'')#G&%99'&%9#6%&%# 9'))*&1V%0#
1(#$*A8%#+"#$@%M#*&%#&*19%0#AM#/(%#/&0%&#/O#)*J(12'0%"#
####NO2%&# G&/G%&# 2'(1(J# S1(R8'01(J# 019G%&91/(# R/&&%R21/(#
*(0#R/'G81(J#R/&&%R21/(U,#*#91(J8%#A'(R@#@*9#A%%(#1(a%R2%0#
1(2/#2@%#0*)G1(J#&1(J"#$@%#91V%9#/O#2@%#%8%R2&/(#A%*)#*(0#
/O# 2@%# A%2*# O'(R21/(# *2# 2@%# 8*9%&# 61&%# 8/R*21/(# 6%&%#
)%*9'&%0"# $@%#Q%&21R*8# %)122*(R%# R*(#A%#%921)*2%0# 2/#A%#
*A/'2#+`#G)#O/&#V%&/#R'&&%(2#/G%&*21/("#
#
#Figure 1: Location of switched ion pumps and of laserwire.
Table 1: Vacuum Pressure in the Measurement1/(#G')G#92*2'9# E#)N# +D#)N# :D#)N#
(/&)*8#/G%&*21/(# `"K7>L#\*# E"b7>L#\*# +"D7>K#\*#
9/'2@#92&*1J@29#/OO# :"D7>K#\*# :"L7>K#\*# E"E7>K#\*#
A/2@#*&R9#Y#9/'2@#92&*1J@2#/OO# C"`7>K#\*# E":7>K#\*# #
#
T/&# )'821>A'(R@# /G%&*21/(,# 2@%# A%*)# 91V%# /O# %*R@#
A'(R@#6*9#)%*9'&%0#1(# 2@%#8*9%=&%#9R*("#N#A%*)#91V%#
A8/6'G# 6*9# (/2# *GG*&%(2# %Q%(# *2# @1J@# A%*)# 1(2%(912M"#
T1J"#:# 9@/69# 2@%# )%*9'&%0# Q%&21R*8# A%*)# 91V%# O/&# )'821#
A'(R@# /G%&*21/(# *2# :D)Nc:D# A'(R@%9"# 491(J# 2@%#
)%*9'&%0# A%*)# 91V%# 0*2*,# 2@%# Q%&21R*8# %)122*(R%# 6*9#
R*8R'8*2%0#*(0#19#9@/6(# 1(#T1J"#C"#B2#R*(#A%#9%%(# 2@*2# 2@%#
Q%&21R*8# %)122*(R%# 0/%9# (/2# R@*(J%# 91J(1O1R*(28M# 1(# 2@19#
R*9%"# [/)G*&%0# 2/# 2@%# 0*2*# 2*5%(# 1(# :DD`,#6%# 9G%R'8*2%#
2@*2#2@19#19#0'%#2/#2@%#A1JJ%&#Q%&21R*8#%)122*(R%"#
6
8
10
12
14
16
18
20
0 5 10 15 20
IP-ON: 1.0e-6PaIP-OFF: 5.5e-6Pa
Mea
sure
d Si
ze [u
m]
Bunch Number
Proj
ecte
d
####Figure 2: Measured size of multi-bunch at 20mA/20 bunches.
#
#
0
10
20
30
40
50
60
70
0 5 10 15 20
Emittance: IP-ON 1.0e-6PaEmittance: IP-OFF 5.5e-6Pa
Emitt
ance
[pm
]
Bunch Number
Proj
ecte
d
#Figure.3: Emittance of multi-bunch at 20mA/20 bunches.
Proceedings of EPAC08, Genoa, Italy MOPP066
03 Linear Colliders, Lepton Accelerators and New Acceleration Techniques A10 Damping Rings
697
Threshold depends on pressure and vertical emittance
Vacuum spoiled by turning off pumps Vertical emittance measured with laser wire
Single bunch emittance ~10pm Single bunch emittance 20pm
ATF - Fast Extraction Kicker
September 6, 2011 IPAC2011, San Sebastian, Spain 41
Extraction kicker pulse measured with timing scan 0.44mrad kick with 30cm strip line at ±10 kV Fast Ionization Dynistor (FID) pulser
Distribution of measured kick angle. Δθ/θ ~ 0.035%
The End
September 6, 2011 IPAC2011, San Sebastian, Spain 42
Many thanks to all of the many collaborators of the ATF and CesrTA projects who have contributed so much to our understanding of damping ring phenomena.
MOOCA03 - Susanna Guiducci: Damping rings design MOPS083 - Joe Calvey: Electron Cloud Mitigation Studies at CesrTA MOPS084 - Mike Billing: Electron Cloud Dynamics Measurements at CESR-TA MOPS088 - Kiran Sonnad: Simulation of Electron Cloud Beam Dynamics for CesrTA TUPC024 – M.Palmer: Review of the CESR Test Accelerator Program and Future Plans TUPC030 - Mauro Pivi: Mitigations of the Electron Cloud Instability in the ILC TUPC052 - Andy Wolski: Normal Mode BPM Calibration for Ultralow-Emittance Tuning TUPC170 - John Sikora: TE Wave Measurements of Electron Cloud Densities at CesrTA WEPC135 – J. Crittenden: Modeling Time-resolved Measurements of E-Cloud Buildup at CESRTA WEYB01 – John Flanagan: Diagnostics for Ultra-Low Emittance Beams
Quadrupole Measurements
• Left: 20 bunch train e+ • Right: 45 bunch train e+ • Currents higher than expected from “single turn” simulations
– Turn-to-turn cloud buildup – Issue also being studied in wigglers
Clear improvement with TiN
September 6, 2011 44 IPAC2011, San Sebastian, Spain
TUPD023 TUPEC077
Wiggler Clearing Electrode
• 20 bunch train, 2.8 mA/bunch – 14ns bunch spacing – Ebeam = 4 GeV with wigglers ON
• Effective cloud suppression – Less effective for collector 1
which is not fully covered by electrode
IPAC2011, San Sebastian, Spain 45
Electrode Scan 0 to 400V
RFA Voltage Scan, Electrode @ 0V RFA Voltage Scan,
Electrode @ 400V
September 6, 2011
September 6, 2011 IPAC2011, San Sebastian, Spain 46
TE Wave & RFA Measurements in L0
45-‐bunch train (14 ns) 1 mrad ≈ 5�1010 e-‐/m3 Sensi@vity: 1�109 e-‐/m3 (SNR)
2E-2W (CLEO STRAIGHT)
Processed Cu Pole center
TiN Pole Center
45 bunches 14ns spacing
2.2×1010/bunch After extended
scrubbing
Similar performance
observed MOPE088 MOPE091 TUPD022 TUPD023
See this afternoon’s posters for a discussion of RFA modeling
September 6, 2011 IPAC2011, San Sebastian, Spain 47
0 10 20 30 40
0
1
2
3
4
5
Bunch number
�Q�kHz�
Coherent tune shift vs. bunch number
September 6, 2011 IPAC2011, San Sebastian, Spain 48
0 10 20 30 40
0.00
0.05
0.10
0.15
Bunch number
�Q�kHz�
Horizontal Coherent tune shift vs. bunch number
September 6, 2011 IPAC2011, San Sebastian, Spain 50
0 5 10 15 200.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
Bunch number
�Q�kHz�
Coherent tune shift vs. bunch number
Beam Size • Measure Bunch-by-Bunch Beam Size
Same current scan as on preceding page – Beam size enhanced at head and tail of train
Source of blow-up at head requires further investigation (resonance? other?). Beam lifetimes (Touschek) consistent with center of train having smallest size.
– Beam size measured around bunch 15 is consistent with εy ~ 20pm-rad (σy=11.0±0.2 µm, βsource=5.8m)
September 6, 2011 IPAC2011, San Sebastian, Spain 51
MOPE007 MOPE090
0.8×1010 e+/bunch
1.6×1010 e+/bunch
Single Turn Fit Bunch 15
Consistent with onset of instability
Needs further investigation
Consistent with
20 pm-rad
September 6, 2011 IPAC2011, San Sebastian, Spain 52
3840511-284
BPM Index
Vert
ical O
rbit (
mm
)
6
4
2
0
–2
–4
–60 10 20 30 40 50 60 70 80 90 100
September 6, 2011 IPAC2011, San Sebastian, Spain 53
3840511-2400.10
0.05
0.00
–0.05
–0.100 10 20 30 40 50 60 70 80 90 100
BP
char
12
M Index
ac_eta dc_eta
3840511-235
0.10
0.05
0.00
–0.05
–0.10Dis
pers
ion
(m)
0 10 20 30 40 50 60 70 80 90 100BPM Index
September 6, 2011 IPAC2011, San Sebastian, Spain 54
0.10
0.05
0.00
–0.05
–0.10Dis
pers
ion
(m)
0 10 20 30 40 50 60 70 80 90 100BPM Index
3840511-234
3840511-2360.10
0.05
0.00
–0.05
–0.10
ac_e
ta.y
(m)
0 10 20 30 40 50 60 70 80 90 100BPM Index
Mitigation Performance in Dipoles (e+ & e-)
• 1x20 e+, 5.3 GeV, 14ns – 810 Gauss dipole field – Signals summed over all
collectors – Al signals ÷40
September 6, 2011 IPAC2011, San Sebastian, Spain 55
e+ e-
Longitudinally grooved surfaces offer significant promise for EC mitigation in the dipole regions of the damping rings