Low alpha mode for SPEAR3 and a potential THz beamline

X. HuangFor the SSRL Accelerator Team

3/4/20103/4/2010

Future Light Source Workshop 2010 --- X. Huang

Outline• The low alpha mode for SPEAR3• The low-alpha mode for SPEAR3• Potential for a THz beamline

– Chicane THz source– THz power calculation

Parameter For SPEAR3Circumference 234 mBeam energy 3 GeVEmittance 18 nm (achromat)

10 nm (low emitx)Momentum spread 0.001Momentum compaction factor

0.0016 (low emitx)0 0012 (achromat)compaction factor 0.0012 (achromat)

Rf frequency 476.3 MHzRf voltage 3.2 MVB t 200 A ( 500 A)

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Beam current 200 mA (500mA)

Reasons to go low-alphah t X l

Shorter bunchesshort X-ray pulsesCSR in THz regime

Bunch length 4/12

022

2/1 12

/UVeh

Ef

E

rfrev

ET

2/1

42

3

2

II

ICE q

E

0rfrev

Ways to get short bunches:(1) Reduce beam energy(2) Increase rf voltage(3) Increase rf frequecy(4) Reduce momentum compaction factor - alpha(4) Reduce momentum compaction factor - alpha

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SPEAR3 low alpha optics

0 2

0.4

0.6

m)

achromatlow emittancelow alpha dsD

Cx

0

11

First and second order momentum compaction factors:

0 2 4 6 8 10 12

-0.2

0

0.2

S ( )

Dx (m

p

dsDD

Cxx

2'1 2

012

S (m)

15

The need to control :

1 , QFC , QF

5

10 x,

y (m)

The need to control 2:

heightbucket 2

1 to maintain normal rf

buckets2/3

12 1000 is required for SPEAR30 2 4 6 8 10 12

0

S (m)

12 1000 is required for SPEAR3

17208050C

Response matrix for chromaticities

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)SD()SF(

33.10805.32

10207.010247.1314.1144.1

172.0805.0

332

II

CC

y

x

We have to run with a negative Cx

Implementation of the low alpha optics

Sextupole SF is set to minimize 2Chromaticity [-2 x, 0.5 y] 2.5x 10-5

Two calibrated low alpha lattice:1.5

2

1p/21,/59,Adjust QFC to get lower alpha

0 20 40 60 800

0.5

1

1=2.0739e-005+-2.0345e-004 QFC [A]

After LOCO measurement and then orbit correction.

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Injection is more sensitive to rf frequency and injected beam timing error.

0 20 40 60 80 QFC (mA)

Measurements of alpha2x 10-6 ISF = 0

10x 10-9 ISF

= 0

1. Synchrotron tune measurements

1

1.5

2

nus4 (

2 E

/heV

cos

s)2

4

6

8

u s4 (2

E/h

eVco

s s)2

alpha0alpha0/21

Nadji et al, NIMA (1996)-0.02 -0.01 0 0.01 0.020.5

frf (MHz)

n

-1 -0.5 0 0.5 1x 10-3

2

frf (MHz)

nu alpha0/21

Longitudinal motion driven by rf

2. Orbit offset from rf frequency change.

g ynoise, not an intentional excitation.

2. Orbit offset from rf frequency change.

ignore2

3

4

modelmeas

2i

DDx ii <D2D1>/<D1^2>=1.50 for low

alpha lattice, delta<0.006.

Fit for -1

0

1

2

x (m

m)

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Fit for 1 ,2

0 50 100 150 200 250-2

-1

spos (m)

Short bunches observed

10

rms]

2 16 kHz

3.16 kHz3.95 kHz

10.0 kHz

1

bunc

h le

ngth

[ps

, r

0.50 kHz

1.50 kHz

2.16 kHz

0.0001 0.001 0.01 0.1 1 100.1

single bunch current [ma]

b

g [ ]

7.1

1

4

,

4

1

II

ff

os

s

I1 =3.8mA, 1 = 16.8ps,fs0=10.8 kHz

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Streak camera measurement by J. Corbett, et al

Orbit stabilityB tt l it di l hBetter longitudinal phase stability in low alpha mode

Horizontal orbit stability is worse, but can be kept under control by fast orbit feedback.

4 mm

FOFB on

FOFB on for /340 lattice

FOFB on

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0 mm

Lifetime

Lifetime is 30 hrs at 100 mA, alpha/21, dominated by Touschek lifetime.

A positive 3 (=0.05) helps stabilize the beam (Y. Shoji, NewSUBARU).

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User interests in low alpha mode• Timing experiment• Timing experiment

– 1 ps rms beam for a user group in several experimental sessions.

• THz?

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Plan for a THz beamlineParameter Value•Edge radiation or dipole radiation? Parameter ValueBending radius 45 mBending angle 66.7 mradA t 52 52 d2

Edge radiation or dipole radiation?•The chicane dipole source•Incoherent synchrotron radiation flux

Aperture 52 x 52 mrad2

Source point

0.3 mm

Consideration for bending radiusConsideration for bending radius•Opening angle of SR•Shielding of vacuum chamber•THz flux•Horizontal size of first mirror

hh2cutoff

3/1flux •Horizontal size of first mirror•cost

We need to optimize the design (not done yet)

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Calculated with SRW

Calculation of THz powerC id tiConsiderations:•Incoherent THz flux•CSR amplification factor

Single bunch current limit 3/7]ps[0094.0]mA[ I

Current – bunch length scaling law (for SPEAR3):

F. Sannibale model with 2/5 g

Equilibrium distribution•Vacuum chamber shielding at the port 354.2]ps[005.0]mA[ I

2/5

J. Corbett measurement

Hassinski eq. with free space CSRF(k=0.29)=3.3 (FSSR)

2SPEAR3, sigma0=1 ps, 0.005 mA

108SPEAR3, sigma0=1 ps, 0.005 mA

1

1.5

orm

aliz

ed

FSSRPPSR

103104105106107

g(

) FSSRPPSR

6 4 2 0 2 4 60

0.5y=I(s

) no

0 2 0 4 0 6 0 8 1 1 2 1 6 2 2 5 3 3 5

10010110210N

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-6 -4 -2 0 2 4 6x=s/z

0.2 0.4 0.6 0.8 1 1.2 1.6 2 2.5 3 3.51/ (mm-1)

Shielding SPEAR3, sigma0=1.7 ps, 0.017 mA 108

SPEAR3, sigma0=1.7 ps, 0.017 mA

1.5

2

mal

ized

g p

FSSRPPSR

310410510610710

g(

)

0.5

1

y=I(s

) nor

m

100101102103

N g

FSSRPPSR

-6 -4 -2 0 2 4 60

x=s/z

0.2 0.4 0.6 0.8 1 1.2 1.6 2 2.5 33.51/ (mm-1)

Assume chamber height 52 mm

R.A. Bosch, NIMA 482 (2002)

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THz power100 flux, PPSR total power, PPSR

10-4

10-2

10

cm-1

)

10-1

att)

10-8

10-6

10

flux

(Wat

ts/c

1 ps 10-2

Pow

er (W

a

1 ps

100 10210-10

10

wavenumber (1/mm)

1.7 ps2.4 ps

100 101

wavenumber (1/mm)

1 ps1.7 ps2.4 ps

T t l th h th tFlux through a 52 x 52 mrad2 aperture Total power through the aperture

The measured current-bunch length scaling law is used.

Integration is numerically over data points shown on the left plot..

The measured current bunch length scaling law is used.Parallel plate shielding model is used to calculate bunch shape deformation.

The total THz power is 144 mW for the 1ps mode, mainly from wavelengths between 3 mm and 0 5 mm The power can reach 300 mW for longer bunch

14

between 3 mm and 0.5 mm. The power can reach 300 mW for longer bunch modes, but concentrated in longer wavelengths.

3/4/2010 Future Light Source Workshop 2010 --- X. Huang

Summary• Low alpha mode for SPEAR3 was developed and is• Low alpha mode for SPEAR3 was developed and is

deliverable to users.• A plan for a THz beamline is in its early stage.p y g• Questions:

– Scaling lawSi l b h t li it b 2 4 ti hi h th d– Single bunch current limit – may be 2-4 times higher than assumed.

– CSR impedance with shielding

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