[PPT] - A Simulation Study of E-driven ILC Positron Source Masao KURIKI PowerPoint Presentation

SLIDE 1

A Simulation Study

f E-driven ILC Positron Source

Masao KURIKI (Hiroshima University)

SLIDE 2

24 August 2017 Cost Review of E-driven

Introduction

The design of the ILC positron source based on off-the-shelf

components has been established.

Further optimization was made to improve the performance and
ptimize the cost-effective system by,

– Small beam size on target for better yield. (3.5

2.0 mm rms)

– Lower drive beam energy for less cost. (4.8

3.0 GeV)

– Consider only the nominal parameter.

Booster conf i

guration (lattice) is modif i ed to make the consistency.

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24 August 2017 Cost Review of E-driven

E-driven ILC Positron Source

3.0 GeV S-band NC 5.0 GeV L-band + S-band NC

20 of 0.48us pulses are handled with NC linacs operated in 300Hz.
100 of 300 pulses are actually fired.

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24 August 2017 Cost Review of E-driven

The beam handling and format

Damping Ring

Positron Booster

tp=480 ns 197 ns 81.6 ns 33 bunches Tb = 6.15 n sec

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24 August 2017 Cost Review of E-driven

Electron Driver

3.0 GeV Electron beam with 2.0 mm RMS beam size at the target.
2.4 nC bunch charge is giving 0.39 A beam loading.
S-band Photo-cathode RF gun for the beam generation.
80 MW klystron-modulator drives 2 structures.
The effective input power for each tube is 36 MW. 50 MV/tube.

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24 August 2017 Cost Review of E-driven

60 + 4 (spare) of 3m S-band TW structures for the acceleration. The

energy is 3.2 GeV.

The lattice design was based on ATF linac, 4Q + 2RF(S) up to 600

MeV, 4Q+4RF(S) for other.

The total length is 235.2 + 20 m (RF gun + matching section).

Lattice # of cell Cell length(m) Section length(m) 4Q+2S 6 8.0 48.0 4Q+4S 13 14.4 172.8

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24 August 2017 Cost Review of E-driven

Positron Capture Linac

36 L-band SW structures designed by J. Wang (SLAC) for the

undulator capture section is employed.

Two structures are driven by one 50 MW klystron.
Surrounded by 0.5 T solenoid f i

eld.

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24 August 2017 Cost Review of E-driven

T

h e f e f e l d i e l d i n S W a n S W a c c e l c c e l e r a e r a t

r
r
T

h e v

l

t e v

l

t a g e b e c

m

e b e c

me

s e s c

n

s c

n

s t a n t i n t i f V (t)=2√β P0r L 1+β (1−e

− t T 0)− rIL

1+β

(1−e

−t−t b T 0 )

RF Beam Loading T 0= 2Q ω(1+β) t b=−T 0ln( I 2√ rL β P0) V 0= 2√β P0r L 1+β

(1− I

2√ rL β P0)

Beam Loading in SW Linac Single Cell Model : Simple, but not realistic

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24 August 2017 Cost Review of E-driven

Multi-Cell Model : More realistic

Power loss Power flow to next cells Power flow from next cells Input Power WG loss Beam loading Time differential of the energy of the center cell,

SLIDE 10

24 August 2017 Cost Review of E-driven Time differential of the voltage For the intermediate cells, For the end cells,

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24 August 2017 Cost Review of E-driven

1 1 l i n e a r s i mu l t a n e

u

s d i f e r e n t i a l e q u a t i

n

s

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24 August 2017 Cost Review of E-driven

A can be diagonalized with a orthgonal matrix R as Because B is diagonal, the equations for V' are 11 independent linear differential equations,

SLIDE 13

24 August 2017 Cost Review of E-driven The solution for V' is The solution for V is expressed as a linear sum of the solution for V'

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24 August 2017 Cost Review of E-driven

Acceleration Field

L=1.27 m (11 cells, L-band SW)
R=34e+6 Ohm/m
P0=22.5 MW (50MW at klystron, 5MW wave guide loss).
10.36 MV/tube with beta=6.0.

Single cell Multi-cell

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24 August 2017 Cost Review of E-driven

R F Mo d e a n d B e a m L

a

d i n g Mo d e

The total acceleration voltage is given as sum of the RF mode and the

Beam-loading mode.

They are not identical, but the dominant mode is common (tau=1.22 us).
The RF mode has the second dominant mode, but nothing for BL. This

gives the imperfection on the BL compensation, but the effect is not large.

RF mode BL mode

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24 August 2017 Cost Review of E-driven

Beam Loading Compensation

No big difference on the no-load voltage, but 30 % less on the heavyly loaded voltage, The beam loading compensation works well. Flatness is less than 0.1%.

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24 August 2017 Cost Review of E-driven

Capture Simulation

1000 electrons on target by GEANT 4.
The positron is decelerated and bunched at

the acceleration phase by phase-slipping.

Positrons with a large z (longitudinal

position) are not captured by the final

acceptance. This is not the case for δ.

57.4 57.5 57.6 57.7 57.8 57.9 58.0 58.1 58.2 58.3

G P T

z

100 200 300 400 500 600 700 800

G

Positron Electron

0.02
0.01

0.00 0.01 0.02

G P T

x

0.025
0.020
0.015
0.010
0.005

0.000 0.005 0.010 0.015 0.020 0.025 y

x y Capture Linac exit Chicane exit Target downstream Δx=254 um Δy=238 um N=17115(7292) Captured Positron z d s

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24 August 2017 Cost Review of E-driven

Booster

A f i

rst half is implemented by L-band acc. and the last half is by S-band.

50MW L-band Klystron drives two L-band acc. (2a = 34 mm).
80MW S-band Klystron drives two S-band acc. (2a = 20 mm).
The gradient at 0.78 A (4.8nC/bunch) beam loading is assumed.
The beam loading compensation and its accuracy determine the accelerator

gradient.

SLIDE 19

Beam-loading in TW Linac

Transient beam-loading is compensated by Amplitude Modulation.
Acceleration voltage by a f l

at RF,

RF Pulse loading

V(no beam) V(beam loading) V(with beam)

RF Pulse

SLIDE 20

B e a m L

a

d i n g C

mp

e n s a t i

n

w i t h A M

Laplace transformation of TW accelerator voltage V(s) is where E(s) is the Laplace transformation of applied voltage (power). E(s) is determined to cancel s (t) dependence of V(s or t).

E(s)

SLIDE 21

S t e p Mo d u l a t i

n

Imperfection

SLIDE 22

S a w Mo d u l a t i

n

E(t)=E 0U (t)+E1U(t−t f )+ E2 t f (t−t f )U (t−t f ) E(s)= E 0 s + E1 s e

−st f+ E2

t f s

2 e −st f

SLIDE 23

A c t u a l C

mp

e n s a t i

n

( T r a d e

f

)

S

a w mo d u l a t i

n

i s i d e a l , b u t i t r e q u i r e s a h i g h p e a k p

w

e r .

S

t e p mo d u l a t i

n

i s a r e p l a c e me n t , b u t i t h a s a n i mp e r f e c t i

n

( e n e r g y s p r e a d ) .

I

f t

p

< < t

f

, a n

p

t i mi z a t i

n

f

r

P g i v e s s ma l l e r e n e r g y s p r e a d .

SLIDE 24

2 m L

b

a n d T W s t r u c t u r e ( P

s

i t r

n

B

s

t e r )

2

m L

b

a n d ( 1 2 9 8 MH z ) d e s i g n e d f

r

K E K B i n j e c t

r

.

S

a w mo d u l a t i

n

: 2 2 . 5 MW i n p u t w i t h . 7 8 A B L g i v e s 1 4 . 4 1 MV / t u b e ( 2 m)

T

h e e n e r g y s p r e a d i s z e r

(

i d e a l ) , b u t t h e v

l

t a g e i s v e r y l i mi t e d .

22.5 MW

SLIDE 25

S t e p Mo d u l a t i

n

22.5 MW

S

t e p mo d u l a t i

n

: 1 9 . 5 4 ± . 5 1 MV .

I

f P i s

p

t i mi z e d ( l

w

e r e d ) f

r

l

w

e r e n e r g y s p r e a d , 1 7 . 3 8 ± 0 . 1 7 MV .

T

h e g r a d i e n t d e p e n d s

n

a c c e p t a b l e e n e r g y s p r e a d a n d w e t

k

1 7 . 3 8 MV a s

u

r w

r

k i n g a s s u mp t i

n

. 1 9 . 5 4 ± . 5 1 MV . 1 7 . 3 8 ± 0 . 1 7 MV

SLIDE 26

S

b

a n d T W a c c e l e r a t

r

( P

s

i t r

n

B

s

t e r )

2

m S

b

a n d ( 2 8 5 6 MH z ) a c c e l e r a t

r

d e s i g n e d f

r

K E K B i n j e c t

r

.

S

a w mo d u l a t i

n

: 2 2 . 5 MW i n p u t w i t h . 7 8 A B L g i v e s 2 3 . 3 MV / t u b e ( 2 m)

S

t e p mo d u l a t i

n

g i v e s 2 9 . 4 2 ± . 6 9 MV .

36 MW

SLIDE 27

O p t i mi z a t i

n
Step modulation gives 29.42 ± 0.69 MV.
P0 optimization does not work, because tf~tp.
Instead, semi-Step-saw modulation was made

with the peak power which is less than that for the perfect compensation.

The accelerator voltage is determined

by the acceptable energy spread.

36 MW

25.49 ± 0.23 MV.

SLIDE 28

Wh a t i s t h e a c c e p t a b l e e n e r g y s p r e a d ?

z
d

p h a s e s p a c e d i s t r i b u t i

n

a f t e r b

s

t e r h a s a l a r g e r e n e r g y s p r e a d b y R F c u r v a t u r e .

I

mp e r f e c t i

n
f

t h e c

mp

e n s a t i

n

g i v e s a d d i t i

n

a l e n e r g y s p r e a d .

T

h e e f e c t i s n

t

e x p e c t e d l a r g e , b e c a u s e t h e e n e r g y s p r e a d i s c

mp

e n s a t e d b y E C S f u r t h e r .

A

s

u

r w

r

k i n g a s s u mp t i

n

, 1 % a d d i t i

n

a l e n e r g y s p r e a d d

e

s n

t

a f e c t t h e y i e l d .

I

f l a r g e r e n e r g y s p r e a d i s a c c e p t a b l e , t h e a c c e l e r a t

r

v

l

t a g e i s g a i n e d .

1%

SLIDE 29

B

s

t e r C

n

f g u r a t i

n
L

a t t i c e d e s i g n w a s ma d e b y Y . S e i mi y a , b u t t h e a c c e l e r a t

r

v

l

t a g e w a s l a r g e r t h a n

u

r a s s u mp t i

n

s .

We

c h a n g e t h e c e l l n u mb e r f

r

e a c h s e c t i

n

g i v i n g a c l

s

e e n e r g y a t t h e s e c t i

n

e n d .

Seimiya's design Scaled design

SLIDE 30

B

s

t e r C

n

f g u r a t i

n

( l a r g e d E )

I f 3 % e n e r g y s p r e a d i s a c c e p t a b l e ( n

s

i g n i f c a n t i mp a c t

n

y i e l d ) , t h e c

n

f g u r a t i

n

i s

SLIDE 31

24 August 2017 Cost Review of E-driven

ECS Section

ECS design R56=1.2m and R65=-

0.8.

Required voltage is 122 MeV, 3

tubes are enough.

Beam-loading (phase-shift) can be

compensated by an artif i cial phase- shift of drive RF.

If it does not work, we need an

additional RF for compensate the phase shift., 4 tubes.

ECS optimization

SLIDE 32

I mp a c t

f

L a t t i c e Mo d i f c a t i

n
T

h e b

s

t e r c

n

f g u r a t i

n

( a c c e l e r a t i

n

f e l d a n d l a t t i c e ) a r e mo d i f e d .

T

h e y i e l d i s r e

e

v a u l a t e d w i t h t h e mo d i f e d b

s

t e r c

n

f g u r a t i

n

. Seimiya New # of RF (L-band) 62 144 # of RF (S-band) 56 92 Voltage (L-Band) 40(MV/tube) 17.38(MV/tube) Voltage (S-Band) 40(MV/tube) 25.49(MV/tube) Booster Length 323.6(m) 653.6 (m)

SLIDE 33

100 200 300 400 500 600 1 2 3 4

Twiss パラメータ β の比較

清宮さんの設計今回変更した設計

PTEP Positron capture simulation for the ILC electron-driven positron source Yuji Seimiya P7 より引用

SLIDE 34

100 200 300 400 500 600 1 2 3 4

Twiss Parameter Seimiya's New

PTEP Positron capture simulation for the ILC electron-driven positron source Yuji Seimiya P7 より引用

SLIDE 35

Imapct on Yield

変更前変更後 Yield 2.1 2.0 Total Energy 5.0070(GeV) 5.0917(GeV)

Yield is decreased by 5%.
The reason is now under investigation, but it might be a

pseudo effect.

The aperture is set at the end of tubes. The low gradient

and the long booster increased the density of checkpoints.

The total energy is increased. (We set the margin)

SLIDE 36

T h e G

s

p e l ?

Seimiya New # of positrons

The yield is decreased by 5%, but the number of positrons

in booster is decreased by 10% giving a low beam loading.

Further optimization might be possible.

SLIDE 37

S u mma r y

E
d

r i v e n I L C p

s

i t r

n

s

u

r c e i s

p

t i mi z e d f

r

n

mi

n a l p a r a me t e r ( s t a g i n g ) .

R

F c

n

f g u r a t i

n

i s mo d i f e d b a s e d

n

a r e a l i s t i c R F s

u

r c e d e s i g n .

T

h e b e a m l

a

d i n g c

mp

e n s a t i

n

f

r

S W a n d T W w e r e s t u d i e d .

F
r

S W, i t w

r

k s e f e c t i v e l y w e l l .

F
r

T W, s e mi

p

e r f e c t me t h

d

s f

r

L

b

a n d a n d S

b

a n d a r e c

n

s i d e r e d .

L

a t t i c e i s r e

d

e s i g n e d g i v i n g 2 . y i e l d . T h e c h a n g e i s n

t

c

n

s i d e r e d r e a l .

SLIDE 38

24 August 2017 Cost Review of E-driven

T

t

a

t

a l l L e n g L e n g t h t h

T a r g r g e t e t C a C a p t u p t u r e L r e L i n a n a c C h C h i c a c a n e n e 5 9 m E l e c t l e c t r

n

r

n

D r i v e r 2 5 5 . 2 m m P

s
s

i t r

n

r

n

B

s

t e t e r 6 5 8 ( 5 ( 5 7 4 m) ) E C S C S 7 5 . 2 m

T

t

a

t