coupler kick

Coupler Kick

Igor Zagorodnov and Martin Dohlus

DESY, BDM,

2 April, 2007

x

y

x

y

x

y

downstream couplersupstream coupler

Resonator für TESLA TEST Facility(asymmetrisch/mit DESY-HOM-Koopler)0 93 2214/0.000

150o35o

115o

( ) Gaussian bunch with rms widths

( ) ( ) kick factork W W s s ds

Notation and Definitions

0.520.5rms 2( ) ( ) ( ) rms kick factork W k W s k s ds

It gives an estimation for the head-tail difference in the kick (banana shape)

The picture from R. Wanzenberg,Review of beam dynamics …,Linac Conference, 1996

-2 0 2-3

-2

-1

0

1

2

3

0.0069 3.2 1.1 [m] kV( , )

0.0094 1.1 1.0 [m] nC

xx y

y

k

x

y

x

y

x

y

x

y

0.0142 1.02 1.15 [m] kV( , )

0.0095 1.15 0.07 [m] nC

xx y

y

k

-2 0 2-3

-2

-1

0

1

2

3( , )x yk

[mm]x

[mm]y

downstream couplers upstream coupler

Wake kick near to the axis

( , )x yk

[mm]x

[mm]y

x

y

x

y

0.021 4.3 0.07 [m] kV( , )

0.019 0.03 0.9 [m] nC

xx y

y

k

x

y

x

y

5.3mm

21.3

cr

min

kV5 5

nCe k

+Wake kick near to the axis

[mm]x

[mm]y k

x

y

x

y

x

y

x

y

2

2

x

y

x

y

x

y

x

y

old

new

How to compensate the wake kick on the axis?

We have rotated by 90 degree, but 92.5 is possible better.

0.021 4.3 0.07 [m] kV( , )

0.019 0.03 0.9 [m] nC

xx y

y

k

5.3mm

21.3

cr

min

kV5 5

nCe k

x

y

x

y

x

y

x

y

+ x

y

x

y

x

y

x

y

0.0025 2.33 0.04 [m] kV( , )

0.0002 0.02 1.1 [m] nC

xx y

y

k

1.1mm

0.2

cr

min

kV8 5

nCe k

Wake kick for the new orientation

[mm]x

[mm]yk

[mm]x

[mm]yk

x

y

x

y

x

y

x

y

+ x

y

x

y

x

y

x

y

-0.5 0 0.5-0.04

-0.03

-0.02

-0.01

0

0.01

-0.5 0 0.5-0.05

-0.04

-0.03

-0.02

-0.01

0

0.01

kV(0,0)

nCxW

kV(0,0)

nCyW

old

new

old

new

[cm]s [cm]s

Wake kick for the new orientation

RF kickdownstream coupler,new, zpen/mm=6, forwardx/mm =… y/mm=…

x

y

x

y

RF kick

upstream couplerx/mm =… y/mm=…

x

y

x

y

TESLA Cavity in Cryomodule

Zagorodnov I., Weiland T., The Short-Range Transverse Wakefields in TESLA Accelerating Structure// Proceedings of PAC 2003 Conference, USA, 2003.

2400 μm

120 μm

25 μm

European XFEL Project

http://www.desy.de/xfel-beam/index.html

2400 μm

5*8=40 couplers

Injector

Coupler RF kick is the most important. It can be reduced by alternative direction orientation of couplers.

0 1 2 3 4 50

20

40

60

80

100

120

V

nC*cavityrmsk

[mm]r

coupler wake

coupler RF kick

cavity wake

120 μm

12*8=96 couplers

Bunch Compressor

Coupler wake is the most important. It can be reduced with the new orientation of HOM couplers.

0 1 2 3 4 50

5

10

15

20

25

30

V

nC*cavityrmsk

[mm]r

coupler wake

coupler RF kick

cavity wake

100*8=800 couplers

25 μm

Main Linac

Coupler wake is the most important. It can be reduced with the new orientation of HOM couplers.

0 1 2 3 4 50

5

10

15

20

25

30

V

nC*cavityrmsk

[mm]r

coupler wake

coupler RF kick

cavity wake

2400 μm 120 μm 25 μm

Injector Bunch Compressor Main Linac

Effect of new HOM couplers orientation

Coupler wake kick is the most important. It can be reduced with the new orientation of HOM couplers.

Coupler RF kick is the most important. It can be reduced by alternative direction orientation of couplers.

0 1 2 3 4 50

20

40

60

80

100

120

V

nC*cavityrmsk

[mm]r

coupler wake

coupler RF kick

cavity wake

0 1 2 3 4 50

5

10

15

20

25

30

V

nC*cavityrmsk

[mm]r

coupler wake

coupler RF kick

cavity wake

0 1 2 3 4 50

5

10

15

20

25

30

V

nC*cavityrmsk

[mm]r

coupler wake

RMS bunch length,

m

Coupler wake Coupler RF field Cavity wake

2400

Design= 2.5

New= 1.3

2.7 21.6

120 0.14 3.5

25 0.03 0.77

0, 1,rms rms rmsk k k r

1,

* *rms V

knC mm cavity

RMS bunch length,m

Coupler wake Coupler RF field Cavity tilt by

1 mrad

(on crest / 10 grad)

Cavity wake

2400

Design= 16.4

New=1.4

58 23 / 88

0120 2.9 0.06 / 4

25 0.6 0.002 / 0.9

0,

*rms V

knC cavity

Head-Tail Kick (rms kick)

Head-Tail Kick (rms kick)

1. Transverse Coupler Wake is capacitive (integral from bunch shape)

0 1 k k k r 0, 01

3rmsk k 1, 11

3rmsk k

2. RF Coupler Kick (on crest)

( ) Re( )iksx zV s Vx V e 15MVzV

1.3GHz2k

c

0, Im( )rmsk Vx k

3. Cavity tilt by angle

0( )( ) Re(0.5 )i kszV s V e

1/ 220, Re ( ) Re ( ) ( )rmsk V s V s s ds

Conclusion

Coupler RF kick is a main effect in the injector. It can be compensated by an alternative direction orientation of couplers.

Coupler wake kick is a main effect after the 1st bunch compressor. Rotation of the HOM couplers by 90 degree allows to reduce the kick by factor 12.

0 1 2 3 4 50

20

40

60

80

100

120

V

nC*cavityrmsk

[mm]r

coupler wake

coupler RF kick

cavity wake

0 1 2 3 4 50

5

10

15

20

25

30

V

nC*cavityrmsk

[mm]r

coupler wake

coupler RF kick

cavity wake

0 1 2 3 4 50

5

10

15

20

25

30

V

nC*cavityrmsk

[mm]r

coupler wake