the challenges of ultra-low emittance damping rings · the challenges of ultra-low emittance...

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


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.



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


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.


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.


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


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?


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


•  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.


ATF Damping Ring


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.


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


ATF emittance tuning


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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


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)


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


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

Xray beam size monitor


Low emittance tuning - modeling

•  Introduce misalignments

•  BPM parameters


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


- 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


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


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


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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



3840511-126Head-tail instability

Self excited power spectrum in each bunch of a 30 bunch train



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


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


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



0 10 20 30 40 50 60 70 80 900

2

4

6

8

10

12

14

16

18

Beam current (mA)

Ave

rage

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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


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


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


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


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


•  Horizontal beam size measured with interferometer •  Calculation assumes 9pm-rad zero current vertical emittance and

80% from dispersion

ATF - Fast Ion Instability


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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@%&#51(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%&#9'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%&#61&%#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


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


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

•  Extra slides


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


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


0 10 20 30 40

0

1

2

3

4

5

Bunch number

�Q�kHz�

Coherent tune shift vs. bunch number


0 10 20 30 40

0.00

0.05

0.10

0.15

Bunch number

�Q�kHz�

Horizontal Coherent tune shift vs. bunch number


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)


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


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


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


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


e+ e-

Longitudinally grooved surfaces offer significant promise for EC mitigation in the dipole regions of the damping rings


3840511-233

Lattice - Energy

•  Higher energy – Higher threshold for collective effects, intrabeam

scattering – Emittance of injected beam reduced by adiabatic

damping •  Lower energy

– Lower cost (RF, magnets) – Lower equilibrium emittance Compromise is 5 GeV


the challenges of ultra-low emittance damping rings · the challenges of ultra-low emittance...

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