Upload
amos
View
59
Download
0
Tags:
Embed Size (px)
DESCRIPTION
Status of ATF Damping Ring low vertical emittance studies. 2009.10. K. Kubo. ATF Damping Ring (KEK). Extraction and Final Focus Test Beam Line. Test Facility for LC Test of Low emittance beam tuning Deliver low emittance beam, e.g. for final focus test (ATF2) - PowerPoint PPT Presentation
Citation preview
Status of ATF Damping Ring low vertical emittance studies
2009.10.K. Kubo
Required or target of low vertical emittanceOriginal design: 12 pmAssumption in ATF2 design: 12 pmILC damping ring design: 2 pm
Extraction and Final Focus Test Beam Line
Injector Linac
Circumference: 139 mEnergy: 1.3 GeV
Test Facility for LC•Test of Low emittance beam tuning•Deliver low emittance beam, e.g. for final focus test (ATF2)•R & D of instrumentations, etc.
ATF Damping Ring (KEK)
Low Emittance Tuning
Three consecutive corrections• COD correction• Vertical COD-dispersion correction• Coupling correctionMonitor:
BPM (Beam Position Monitors) (total 96)
Corrector:
Steering magnets (47 horizontal and 51 vertical)
Skew Qauds (trim coils of sextupole magnets, total 68)
Skew correctors - trim coils of sextupole magnets
+ I
+ I
- I /2
- I /2- I /2
- I /2
The trim windings of all 68 sextupole magnets have been arranged to produce skew quadrupole fields, used as correctors.
Currents of the top and the bottom poles are the same. Currents of other poles are one half.
Skew Quad Field by Sextupole Magnet
(Suggested by T. Raubenheimer)
Low Emittance Tuning(a) COD correction: using steering magnets,
minimize BPM reading
and , :x(y): horizontal (vertical) BPM reading.
(b) V-COD-dispersion correction: using steering magnets,
minimize dispersion and orbit y: measured vertical dispersion.
r : weight factor = 0.05
(c) Coupling correction: using skew quads,
minimize vertical response to horizontal steering
x(y): horizontal (vertical) position change at BPM due to excitation of a horizontal steering magnet.
Two horizontal steering magnets were used (Nsteer=2). About (n+1/2)p phase advance between the two.
x2
BPM
BPM
2y
y2
BPM
r2 y2
BPM
Cxy y2
BPM
x2
BPM
H steers
Nsteer
Old History of low emittance in ATF DRBy 2004, we confirmed very low emittance beam, around 4 pm.Since then, pursuit of low emittance had not been a major study item. The emittance deteriorated. Over the past year, renewed efforts have been made for low emittance.
10-12
10-11
10-10
10-9
8/1/97 8/1/98 8/1/99 8/1/00 8/1/01 8/1/02 8/1/03 8/1/04
Single bunch emittance history
Y emittance (EXT wire, SR)Y emittance (LW)
Y e
mit
tanc
e [r
ad.m
]
Date
RF
gun
2µm
BP
M
210m
A l
imit
DR
Ion
Pu
mp
20µ
m B
PMEX
T l
ine
MB
op
erat
ion
star
t M
Bra
d.
shie
ld
rad
. sh
ield
X e
mi
con
firm
ed
GL
CT
A
rad
. sh
ield
refine beam tuning by H. Hayano
Recent efforts for low emittance
Re-Alignment of magnets
Related to beam measurement• BBA (Beam Based Alignment) measurement• Optics matching (Beta-beat correction)
• ORM (Orbit Response Matrix) analysis
Effectiveness of each still needs to be understood.
DR Magnet Level Measurement
M. Takano
3
0/2cos
nnn LsnC
Smooth curves fromfitting
No data for SF, SD and QF1R in the first three measurements.
Deviation from smooth curve
RMS(DY) [mm] MAR08: 0.086 APR08: 0.084 OCT08: 0.076 NOV08: 0.057 FEB09: 0.056
Improved?
M. Takano
Beam Based AlignmentSimulation of the tuning showed importance of BPM - magnet center offset error
Emittance vs. BPM offset error with respect to the nearest magnet
Beam Based Alignment - Method
1. Make vertical local bump at the Magnet-BPM.2. Change Magnet strength.3. Measure the orbit difference for all the BPMs.
Normal Quads: Vertical, Skew Quads: Horizontal
4. Estimate the minimum orbit difference point.
BPMBPMs BPMs
Magnet (quad or skew quad)
Trim winding of sextupole magnets
T. Okugi
Beam Based Alignment - results
0
5
10
15
20
25
30
35
40
-1500 -1000 -500 0 500 1000 1500
Ver
tica
l Orb
it D
iffe
renc
e (
m)
Veritical Position (m)
0
10
20
30
40
50
60
70
80
-1500 -1000 -500 0 500 1000 1500Hor
izon
tal O
rbit
Dif
fere
nce
(m
)
Veritical Position at BPM2 (m)
RMS of beam position change at all (except for noisy) BPMs vs. local bump amplitude.Fitted as 22 )( aycbRMS
ExamplesBump at Quad Bump at Skew Quad (Sextupole)
offsetMagnet -BPM :a
Typical error of offset: ~ 30 m for Quad ~ 80 m for Skew Quad
T. Okugi
Optics matching (Beta-beat Correction)
0
5
10
15
20
25
0 20 40 60 80 100 120 140 y (
m)
arc arcarc
0
5
10
15
20
0 20 40 60 80 100 120 140
y (m
)
s (m)
Calculated vertical beta functions of two different optics matching conditions.
December 1999, when we observed small vertical emittance (about 5pm).
May 2008, when we could not achieve low emittance.
Beta-beat can increase emittance sensitivity to errors.
Optics matching (Beta-beat Correction)• Start from setting a “design” optics. (2008 fall)• Measure beta-function at every quadrupole magnet
– Beta-beat was observed.
Correction based fully on the model– We tried three (?) times. Results were different from the
calculations.– Our model was not good enough for this methods. (?)
Partially rely on model, partially empirical method Concentrate on vertical beta-function at QF1Rs (vertical beta-beat in
arc sections) – Look for quadrupole magnets whose change would partly
correct the beta-beat at QF1Rs from optics model. – Some improvement
Optics matching (Beta-beat Correction)
0
5
10
15
20
0 5 10 15 20 25 30
Before correctionCorrected
y (m
)
Quad QF1R
West arc
East arc
Vertical beta-function at all quadrupole magnet of one family in the arc sections. (Should be flat for matched optics.)
Before and after a beat correction. (Example)
Not completely satisfactory. Need more study for better modeling.But condition was improved.
ORM Analysis• Measure changes in the closed orbit with
respect to changes in strength of a number of orbit correctors
• Fits a machine model to the data, by adjusting:– Quadrupole strengths, – BPM gains and couplings,– Corrector magnet strengths and tilts.
Need more studies for understanding how to use information from ORM.
Coupling correction using ORM Analysis
ORM analysis effectively projects the betatron coupling sources onto the skew quadrupolesDetermination of skew quadrupole strengths required to cancel the coupling sources
Possible limitations• Present analysis do not include orbit distortion
– which can affect predictions of effects of correctors– will be tried after BBA and more accurate orbit corrections
• Degeneracy between errors causing apparent coupling
ORM AnalysisCorrelation between • Changes in skew quadrupole strengths determined from ORM analysis, and • Known changes in currents applied to correctors
Deviations from the straight line indicate error of present model.
Recent history of emittance in ATF DR
Vertical emittance < 10 pm (from Laser Wire measurement)Smaller than limits of other monitors?
0
10
20
30
40
50
60
Nov/1/2007 Mar/1/2008 Jul/1/2008 Nov/1/2008 Mar/1/2009 Jul/1/2009
y (pm) X-SR
SR-ILW
y (p
m)
S. Kuroda and N. Terunuma
Example of DR Laser Wire measurement
s = 8.6 m(convolution of beam size andlaser size)
H. Shimizu
Summary and Future Plans • Low emittance tuning and efforts for improving DR emittance
– Re-alignment– BBA (BPM - Magnet offset measurement)– Optics matching (Beta-beat correction)– ORM (Orbit Response Matrix) analysis
• The emittance performance has been recovered.– y < 10 pm in April and May 2009. Good enough for FF test.– Effectiveness of each item for this recovery is not clear yet.
• Plans for smaller emittance (2 pm is ILC DR design.), – More simulation studies on the tuning procedure– Analysis of beam measurement, e.g. ORM.– Upgrade of all BPM electronics (20 out of 96 BPMs were already
upgraded) – Re-alignment of magnets.
Backup Slides
DR Magnet Level Measurement
Average of 100 seeds 90% CL (90th among 100 seeds)
0
2 10-11
4 10-11
6 10-11
8 10-11
1 10-10
1.2 10-10
1.4 10-10
0 0.1 0.2 0.3 0.4 0.5 0.6
Alignment 2008 Feb.Alignment 1999
90%
y (
m)
BPM offset w.r.t. magnet (mm)
0
2 10-11
4 10-11
6 10-11
8 10-11
1 10-10
0 0.1 0.2 0.3 0.4 0.5 0.6
Alignment 2008 Feb.Alignment 1999
Mea
n
y (m
)
BPM offset w.r.t. magnet (mm)
Emittance vs. BPM offset w.r.t. nearest magnet
with two different magnet misalignment
1999 data and 2008 data used different measurement methods.Measurement error may be dominant in2008 data. Can not tell change of alignment conditions from these data.
Result of tuning simulation, 3 optics Number of random seeds giving resultsEmittance vs. BPM-Magnet offset error
0
5 10-12
1 10-11
1.5 10-11
2 10-11
2.5 10-11
3 10-11
0 0.1 0.2 0.3 0.4 0.5
optics1999Dec
optics2008May
opticsBad
< y>
(m
)
BPM-Quad misalignment (mm)
For some random seeds, SAD cannot find closed orbit, betafunctions, etc.The left figure shows number of seeds out of 100, which give results.The reason was not well studied and how to treat these results is not clear.
0
20
40
60
80
100
0 0.1 0.2 0.3 0.4 0.5
optics1999Decoptics2008MayopticsBad
Solv
ed n
umbe
r of
see
ds
BPM-Quad misalignment (mm)
Beam Based Alignment
-30
-20
-10
0
10
20
30
-500 0 500 1 103 1.5 103 2 103 2.5 103
BBA for Skew Quad
Maget Trim I = -1 AMaget Trim I = +1 A
BP
M60
X [m
]
BPM41 Y [m]
-30
-20
-10
0
10
20
30
40
-1.5 103 -1 103 -500 0 500 1 103 1.5 103
BBA for Quad
Magnet Trim = -1 AMagnet Trim = +1 A
BP
M4
Y [m
]
BPM1 Y [m]
Position at BPM outside local bump vs. amplitude of bump
Bump at Quad Bump at Skew Quad
Examples
Example of data from coupling correction
Changes in vertical orbit response to a horizontal steering.Measurement and prediction from present model.
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
0 20 40 60 80 100 120 140
ZH1RMeasuredModel
s (m)
Change of Response at all BPM to one horizontal steering magnet.
Measured April 10, 2009
ORM AnalysisResponse of all BPMs to all horizontal steering magnets (But omitted if error<0.03)
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
-0.15 -0.1 -0.05 0 0.05 0.1 0.15
Mea
sure
d r
espo
nse
chan
ge (
m/r
ad)
Model response change (m/rad)
Measured April 10, 2009