Lifetime and injection efficiency vs. Dynamic and physical aperture; Measurement & simulation

August 11, 2004 SPEAR3 Chicane Lattice Review

Lifetime and injection efficiency vs.

Dynamic and physical aperture;Measurement & simulation


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 %


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.


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.


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


Kicker calibration, 2

• Decking, Portmann calibration.

• Kicker amplitude to loose stored beam on septum vs. septum closed orbit.

• Calibration within 5 % of previous method.


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


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.


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


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.


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


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


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


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


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


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


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.

Lifetime and injection efficiency vs. Dynamic and physical aperture; Measurement & simulation

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