august 11, 2004spear3 chicane lattice review lifetime and injection efficiency vs. dynamic and...
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August 11, 2004 SPEAR3 Chicane Lattice Review
Lifetime and injection efficiency vs.
Dynamic and physical aperture;Measurement & simulation
August 11, 2004 SPEAR3 Chicane Lattice Review
Touschek and brehmsstrahlung lifetime reduction
For 0.04 % decrease in <energy acceptance>
• Bremsstrahlung lifetime decreases by 0.5 %; ~ln(p/p).
• Touschek lifetime decreases by 4 %; ~(p/p)3.
• Bremsstrahlung & Touschek decreases by ~2 %.
-4 -2 0 2 40
5
10
15
20
25
p/p (%)
x (
mm
)
Baseline optics
2.38 %
dynamic aperture
rf acceptance
-4 -2 0 2 40
5
10
15
20
25
p/p (%)
x (
mm
)
Chicane optics
rf acceptance
dynamic aperture
2.21 %
August 11, 2004 SPEAR3 Chicane Lattice Review
Dynamic aperture simulations
Baseline optics Chicane optics
-0.02 -0.01 0 0.01 0.020
1
2
3
4
5
6x 10
-3
x [m]
y [m
]
Baseline Optics :DA + 5mm PA
On Energy3%
-0.02 -0.01 0 0.01 0.020
1
2
3
4
5
6x 10
-3 Double Waist Asymmetric Chicane Optics :DA + 5mm PA
x [m]
y [m
]
On Energy3%
Plots show median over many error seeds.
August 11, 2004 SPEAR3 Chicane Lattice Review
Measured dynamic aperture
-4 -2 0 2 40
5
10
15
20
25
p/p (%)x
(m
m)
IDs closed
dynamic apertureRF aperturex(p/p)
-4 -2 0 2 40
5
10
15
20
25
p/p (%)
x (
mm
)
IDs open
dynamic apertureTrackingRF aperturex(p/p)
Measured dynamic aperture better than median tracking on energy, and worse off energy.
August 11, 2004 SPEAR3 Chicane Lattice Review
Kicker calibration• Simulations indicate injection efficiency should drop off, if beam
is kicked ~1 mm closer to septum.• Measurements show expected drop off.• This indicates injection bump is indeed kicking beam to 22 mm
(3 mm from septum). • Kicker calibration from this measurement within 6% of design.
-2 -1 0 1 2 3 4 50
10
20
30
40
50
60
70
80
90
100
% in
ject
ion
effi
cie
ncy
horizontal orbit at septum (mm)
Injection efficiency vs. septum closed orbit
blue: septum bump scan red: 2S bump scan, for comparison dashed blue: average of septum bump scans
0 0.5 1 1.5 2 2.5 30
10
20
30
40
50
60
70
80
90
100
110
stored beam to septum chamber (mm)
% in
ject
ion
eff
icie
ncy
500 mA stored, 40 mA/min BTS beam
Kickers are designed to kick the beam to 3 mm from septum chamber.
Stored beam starts scraping if beam is pushed ~1 mm closer to septum.
simulation measurement
August 11, 2004 SPEAR3 Chicane Lattice Review
Kicker calibration, 2
• Decking, Portmann calibration.
• Kicker amplitude to loose stored beam on septum vs. septum closed orbit.
• Calibration within 5 % of previous method.
August 11, 2004 SPEAR3 Chicane Lattice Review
Measured energy aperture
• Lifetime vs. Vgap
• 8 mA, single bunch – Touschek regime 1/3 ~ rf
acceptance• 2 % energy aperture
(agrees w/ measured dynamic aperture).
ID gaps closed
August 11, 2004 SPEAR3 Chicane Lattice Review
Coulomb scattering; BL12 gap
• BL9 aperture scans– Lifetime vs. vertical orbit– Lifetime ~ constant over 4 mm– Systematic errors– Re-measure with scrapers,
11/2004
• BL12 gap, conservative– 12 – 2 = 10 mm at BL9– Scales to 6.2 mm at BL12
• BL12 gap, aggressive– 12 – 4 = 8 mm at BL9– Scales to 5.0 mm at BL12
-5 -4 -3 -2 -1 0 1 2 3 4 50
5
10
15
20
25
30
35
40
45
50
Beam Bump Position [mm]
Life
time
[Hou
rs]
BL 9, Vertical Bump, 18.0 mA, 24 Bunches, Ion Pumps On, 4/20/04
Orbit bump at BL9 12 mm aperture.
August 11, 2004 SPEAR3 Chicane Lattice Review
Aperture scans, systematic errors• Bump increases coupling
(optimistic gap)– Included coupling
correction in bump– Filled low current/bunch
• Bump degrades vacuum (pessimistic gap)– Lifetime vs. bump in other
straights also drops off.– Scans with low current,
turned off ion pumps
• Need scrapers
-5 -4 -3 -2 -1 0 1 2 3 4 50
5
10
15
20
25
30
35
40
45
Beam Bump Position [mm]
Life
time
[Hou
rs]
BL 9, Vertical Parallel Bump, 18.0 mA, 24 Bunches, Ion Pumps On
Global Coupling Corrected & Local Correction On
Global Coupling Corrected & Local Correction Off
Sub-Optimal Global Coupling Corrected & Local Correction Off
0 1 2 3 4 50
10
20
30
40
50
60
70
Vertical beam bump [mm]
Life
time
[Hou
rs]
14S, Vertical Parallel Bump, 18.0 mA, 24 Bunches
August 11, 2004 SPEAR3 Chicane Lattice Review
Aperture scans, conclusions
• BL9 gap from 12 mm to 10 mm very likely OK.– 12 mm to 8 mm may be OK.– Further reduction not out of the question
• Aperture scans plagued with systematic errors.• Scraper measurements this fall.
August 11, 2004 SPEAR3 Chicane Lattice Review
Dynamic aperture required for injection
Baseline optics (IDs closed)
20 mm dynamic aperture should be more than enough for injection.
Should still get good injection with a 5 mm reduction in dynamic aperture.
sept
um m
agne
t iro
nse
ptum
mag
net i
ron
Stored beam Injected beam
August 11, 2004 SPEAR3 Chicane Lattice Review
Measured injection efficiency
-2 -1 0 1 2 3 4 50
10
20
30
40
50
60
70
80
90
100
% in
ject
ion
effic
ienc
y
horizontal orbit at septum (mm)
Injection efficiency vs. septum closed orbit
blue: septum bump scanred: 2S bump scan, for comparisondashed blue: average of septum bump scans
with furtheroptimization
• Simulate dynamic aperture reduction with closed orbit bump at septum.
• Efficiency decreases sooner than expected.– Poor control/understanding of
BTS optics.
– Optics distortion from bump.
– Possible obstacle.
• Nonetheless, expected ~1 mm decrease in dynamic aperture is OK.
-8 -6 -4 -2 0 2 4 6 80
10
20
30
40
50
60
70
80
90
100
% in
ject
ion
effic
ienc
y
horizontal orbit at septum (mm)
blue: septum bump scandashed blue: average of septum bump scansred: 2S bump scan, for comparisondotted red: 2S scans taken on previous day
Red = control study
August 11, 2004 SPEAR3 Chicane Lattice Review
Possible obstacle?
sept
um m
agne
t iro
n
• Mirror plate – Downstream of septum
and phosphor screen– Upstream of window– Same x-section as
septum– Last minute addition– Was not aligned
August 11, 2004 SPEAR3 Chicane Lattice Review
Injection with reduced y-aperture
• Tracking says not a problem.
• Measurement shows efficiency reduction.
• Need scraper!
-0.02 -0.01 0 0.01 0.020
1
2
3
4
5
6x 10
-3 Double Waist Asymmetric Chicane Optics :DA + 5mm PA
x [m]
y [m
]
On Energy3%
Injection rate vs. BL9 y-bump
August 11, 2004 SPEAR3 Chicane Lattice Review
Conclusions
• Chicane lattice dynamic aperture meets requirements– Sufficient for injection– Minimal reduction in beam lifetime
• Measurements show simulations (mostly) accurately predict optics performance
• BL12 gap– Expect small lifetime and injection reduction.– Needs further measurements with scraper.