Electron cloud in the wigglers of ILC Damping Rings L. Wang SLAC ILC Damping Rings R&D Workshop -...

Electron cloud in the wigglers of ILC Damping Rings

L. Wang

SLAC

ILC Damping Rings R&D Workshop - ILCDR06 September 26-28, 2006

Cornell University

ILC Damping Rings R&D Workshop, Cornell, Sep. 27

Outline• Introduction• Simulation• Aperture effect• Trapping effect• Bunch train effect • Groove surface• Clearing Electrode • Comparison with dipole field• Summary


Ecloud in DAFNE wiggler?

• Fast Horizontal instability (larger Horizontal tune shift, 0.01 at 600mA) was found after modification of the wiggler

• No Vertical instability…

• KEKB, CESR DAFNE: C. Vaccarezza,etc. ecloud04


CLOUDLAND 3D PIC code for e-cloud (PRST-AB 124402)

Simulation Key parameters(beam,ring,SEY,electrode, …) Mesh Generator

Magnetic and electric fields input

Space charge solverCharge meshUpdate particle positions

Advance particle positions using the new beam and e-cloud space charge fields

Preliminary electron generator when beam passing

Secondary electron generator

Preliminary electron generator

Wake field Instability code

Future plan --Parallelize for consistent instability study


Space charge potential solver -FEM

Mesh of chamber

Three dimensional irregular mesh to better represent the general chamber geometry

handle accuracy with high order elements.

0QNQ ii 1i

iN

20 node element

Adaptive mesh for beam/ecloud.


Sample II: Electron cloud with two beams Two beams

Whole section (12m), without magnets, bunch length 10nsModel :

Copper ion N=1109; bunchspacing=1 RFbucket, Copper ion N=6109;

bunchspacing=6 RFbucket,

Z

RHIC


Optics of New 6km ring

0 500 1000 1500 2000 2500 3000 3500 4000-20

0

20

40

60

80

100

S (m)

x

y (

m)

x

y

Dx*100


CESR-c wiggler


Wiggler Field in simulation

kzykxkBk

kB

kzykxkBB

kzykxkBk

kB

yxy

z

yxy

yxy

xx

sinsin)cosh(

,coscosh)cosh(

cossinh)sinh(

0

0

0

0 20 40 60 80 100-1.5

-1

-0.5

0

0.5

1

1.5

Z

Bz

Br

2222 2

kkk yx

),,,,,(,...,3,1

, , zyxnkkkfBBNn

nxnxnn

B0=1.68Tesla

Period =0.4m

Kx=0


Simulation in wiggler 3D program is required in wiggler (3D field)

Some electrons can effectively move in longitudinal direction (beam direction) and the electron cloud is not uniform in longitudinal direction (different from dipole magnet). the modeling of beam kick, electron motion and space charge field should consider the 3D effects.


Parameters

• 2767 Bunches: 6 ns bunch spacing with a gap about 43ns, Bunch intensity 2E10, 22 bunches/train

• 5782 Bunches; 3 ns bunch spacing with a train gap about 38ns; bunch intensity 1E10; 49bunches/train

• Peak SEY1.75 at 330eV

• Pipe aperture 44mm


Train gap effect (2767bunches)

-200 -100 0 100 20010

8

109

1010

1011

1012

1013

Z (mm)

(

m-3

)

Bunch Train gaps reduce the electron cloud density by a factor of 10

0 20 40 60 80 100 12010

9

1010

1011

1012

Bunch ID

e (

m-3

)

average densitycentral density

0 20 40 60 80 100 12010

9

1010

1011

1012

1013

1014

Bunch ID

e (

m-3

)

One train

Short train


Effect of pipe aperture, 2767bunches

0 20 40 60 80 100 12010

9

1010

1011

1012

Bunch ID

e (

m-3

)


0 50 100 150 200 250 30010

8

109

1010

1011

1012

1013

1014

Bunch ID

e (

m-3

)

R=22mm R=8mm

-10 -5 0 5 100

0.5

1

1.5

2

2.5

3x 10

13

X (mm)

(m-3

)

-10 -5 0 5 100

0.5

1

1.5

2

2.5

3x 10

13

X (mm)

Ecloud density increases by a factor of 10 when I.D. reduce from 44mm to 16mm


Mirror field trapping

kzykxkBk

kB

kzykxkBB

kzykxkBk

kB

yxy

z

yxy

yxy

xx

sinsin)cosh(

,coscosh)cosh(

cossinh)sinh(

0

0

0

No mirror field trapping was found

0 20 40 60 80 100 12010

9

1010

1011

1012

Bunch ID

e (

m-3

)


Mirror field


Beam filling pattern effect

0 20 40 60 80 100 12010

9

1010

1011

1012

Bunch ID

e (

m-3

)

average density, 2767 bunchescentral density, 2767 bunchesaverage density, 5782 bunchescentral density, 5782bunches

Low Q beam pattern(5782bunches) has lower electron cloud density (I.D.=22mm)


Comparison with dipole

0 20 40 60 80 10010

9

1010

1011

1012

1013

1014

Bunch ID

e (

m-3

)


0 20 40 60 80 100 12010

9

1010

1011

1012

Bunch ID

e (

m-3

)


Dipole, B=0.194TWiggler

There is a lower electron density in Wigglers (one order)! (assuming the same initial electrons rate )


Comparison with dipole

-30 -20 -10 0 10 20 300

1

2

3

4

5

6x 10

13

X (mm)

(m-3

)-10 -5 0 5 100

0.5

1

1.5

2

2.5

3x 10

13

X (mm)

Wiggler Dipole, B=0.194T

The multipacting strips of electron cloud in the wigglers is more close to the beam


Clearing Electrode

0 20 40 60 80 100 12010

9

1010

1011

1012

1013

1014

Bunch ID

e (

m-3

)

average density, long traincentral density, long trainaverage density, bunch train, -100Vcentral density, bunch train, -100Vaverage density, bunch train, 200Vcentral density, bunch train, 200V

stripline position

Strip-line typeWire type

Strip-line type Wire type

Calculation of the impedance ( Cho, Lanfa)

Design & test of impedance is under the way, test in PEPII Dipole & CESR Wiggler

Submitted to PRSTAB

Suetsugu’s talk


Geometry of Grooved surface

(a) Triangular surface

(b) Sawtooth surface

(c) Overhanging surface


Collection of the stripped electron at injection (SNS)

Foil center(40,23,307)

Magnetic field at foil center=( -3.6, 2504,-547.9) Gauss; =210mrad

Energy of stripped electrons =522keV, =11.98mm, T=0.289ns, v=2.6e8m/s, =0.866

Catcher shape: =25, =65Z

Y

0.34% Carbon9.2 % Copper

L. Wang,et al. PRSTAB 094201(2005)


Triangular grooved surface in wiggler

Effective SEY of an isosceles triangular surface with rounded tip. max=1.74, max=330eV, B0=0.2Tesla, Rtip=0.2mm, W=4.52mm.

)

W

0 100 200 300 400 500 600 7000

0.2

0.4

0.6

0.8

1

1.2

1.4

Energy (eV)

SE

Y

=65o, =50o

=70o, =40o

=75o, =30o

=80o, =20o

Effective SEY from an isosceles triangular surface in a dipole magnetic field. max=1.74, max=330eV, B0=1.6Tesla and W=1.89mm

0 100 200 300 400 500 600 700

0.2

0.4

0.6

0.8

1

1.2

Energy (eV)

SE

Y

=70o

=75o

=80o

To reduce the impedance

The effective SEY of triangular grooved surface has very weak dependence on the size W and magnetic field.

L wang, T. Raubenheimer, G. Stupakov, (slac-pub-12001)

Experiment in PEPII Dipole & CESR Wiggler


Impedance of triangular groove

-20 -10 0 10 20

-20

-15

-10

-5

0

5

10

15

20

X (

mm

)

Y (mm)

Magnetic field lines penetrating in a groove (a half a period of a groove is shown).

The enhancement factor as a function of angle.

Gennady

Calculation of impedance with rounded tips is under the way

(Gennady, Karl and Lanfa)

Machining and extrusion

Copper-coated

Impedance increases 15%(alfa=70), it will be lower when round tips are used


Summary Bunch train can effectively reduce the build-up of ecloud in

wiggler ( a factor of 10!)

Low Q beam pattern has lower ecloud density

No mirror field trapping was found

Ecloud in wiggler also has two strips, but it is more closer to the beam comparing ecloud in the dipole magnet.

Electron cloud density in wiggler is lower than that in dipole.

Electrodes works in wiggler. (Heat & impedance is the main concerns, Exp. in PEPII and CESR )

Triangular Grooved surface likely works in wiggler, but it would be important to check with realistic field. (Impedance optimization, manufacture) (exp. At SLAC and CESR)


Acknowledgement

Thanks to all colleagues in the damping ring study, especially thanks to K.L.F. Bane, Y. Cai, T. Raubenheimer, G. Stupakov, A.Wolski, J. Gao, S. Guiducci, M. Zisman, M. Palmer, M. Pivi, F. Zimmermann, H. Fukuma, K. Ohmi, E. Kirby, Y. Suetsugu, S. Mark, R. Schlueter, D. Plate, …….

Electron cloud in the wigglers of ILC Damping Rings L. Wang SLAC ILC Damping Rings R&D Workshop -...

Documents

Transcript of Electron cloud in the wigglers of ILC Damping Rings L. Wang SLAC ILC Damping Rings R&D Workshop -...