Quasi  Traveling  Wave  Side  Couple  RF  Gun  for  SuperKEKB

TAKUYA  NATSUI,  MITSUHIRO  YOSHIDA,    XIANGYU  ZHOU,  YUJIRO  OGAWA,

 HIGH  ENERGY  ACCELERATOR  RESEARCH  ORGANIZATION  (KEK) 1-­‐1  Oho,  Tsukuba,  Ibaraki  Japan

Contents

•  IntroducRon  •  Disk  and  Washer(DAW)  type  RF  gun  •  Quasi-­‐traveling  wave  RF  gun  •  Cavity  calculaRon  and  design  of  Quasi-­‐traveling  wave  RF  gun  

•  Conclusion  

  KEKB  obtained  (e+  /  e-­‐)

SuperKEKB  required  　(e+  /  e-­‐)

Energy 3.5  GeV  /  8.0  GeV 4.0  GeV  /  7.0  GeV

Charge e-­‐      　  e+    /      e-­‐  10    1.0  nC  /  1.0  nC

e-­‐        e+    /      e-­‐  10    4.0  nC  /  5.0  nC

EmiFance      [mm-­‐mrad] 2100    /  300   6    /  20  

e-

e+J-linac

HER7 GeV

LER4 GeV

SuperKEKB

AR6.5 GeV

PF2.5~3.0 GeV

A-1 RF gun

3-2 RF gun

A sectorB sector

C sector 1 sector 2 sector 3 sector 4 sector 5 sector

J arc

SuperKEKB  Upgrade  and  RF  gun  development

Contents

•  IntroducRon  •  Disk  and  Washer(DAW)  type  RF  gun  •  Quasi-­‐traveling  wave  RF  gun  •  Cavity  calculaRon  and  design  of  Quasi-­‐traveling  wave  RF  gun  

•  Conclusion  

Why we need advanced RF gun?

Normal  RF  gun  does  not  have  focusing  E-­‐field.  5  nC  beam  charge  has  much  higher  space  charge.  We  need  advanced  RF  gun.

Normal RF gun

5  nC  beam  tracking  simulaRon.  Beam  size  will  be  too  large  for  our  use.

DAW  type  RF  gun  DAW  (Disk  and  Washer)  RF  gun  development

Strong  focus  field

Electric  field  focus   Large  coupling   Low  electric  field  

Emi[ance 6  mm-­‐mrad

Size    (σ)   1.2  mm

Bunch  length 8  psec

Energy 3.2  MeV

Beam  tracking  simulaRon  result  

DAW  (Disk  and  Washer)  RF  gun

RF gun

RF gun beam line

We already installed RF gun into KEK linac beam line and tested.

DAW type RF gun beam study result

4.8 nC beam generation 4.4 nC beam transport to linac end.

Beam has divergence angle in the gun. (calculation)

Focusing field is NOT enough. Low beam energy: 3 MeV

BPM signal. (Beam transport study)

This gun has no margin (5 nC is maximum output.).

We need a new advanced RF gun

Contents

•  IntroducRon  •  Disk  and  Washer(DAW)  type  RF  gun  •  Quasi-­‐traveling  wave  RF  gun  •  Cavity  calculaRon  and  design  of  Quasi-­‐traveling  wave  RF  gun  

•  Conclusion  

Quasi traveling wave side coupled cavities Normal side coupled cavities

Structure of the quasi traveling wave cavity

The close nose makes focus field. Our DAW RF gun is using this focus field. Side coupled cavity also can be made the close nose. But, long drift space is problem. One solution is to use tow standing wave cavity.

Quasi traveling wave side coupled cavities

Normal side coupled cavities

1st  Cavity  Design  (cathode  cell)

To  avoid  beam  defocussing,  emi[ance  growth  and  field  concentraRon,    a  lot  of  parameters  were  searched  for  design.

0 100 200 300 400 500 600 700 800 900 1000GPT z

0

1

2

3

4

5

rxy

Beam  tracking

Field  calculaRon

Feedback  to  cavity  parameters

obtain  beam  parameter  

AutomaRc  opRmizaRon  by  using  downhill  simplex  method

We  need  strong  focus  field.      But  strong  focus  field  may  cause  emi[ance  growth.  We  must avoid the electric field concentration.

Cathode

Maximum  E-­‐field  at  surface:  120  MV/m  （DAW  type  :  150  MV/m）  

1st  Cavity  Design  (cathode  cell)

Finally, we gat optimum cavity shape.

Emi[ance:  5.5  mm-­‐mrad  @  5  nC  

This  RF  gun  can  generate  10  nC  beam  

Whole  caviRes  design

This RF gun has total of seven acceleration cavities. These are divided into two standing wave structure of 3 and 4 side coupled cavities respecRvely.

Maximum  E-­‐field  at  surface:  100  MV/m  Maximum  E-­‐field  at  surface:  120  MV/m  

Beam  tracking  simulaRon  result  （5  nC）

time=2.48098e-009

728 729 730 731 732 733GPT z

11.3

11.4

11.5

11.6

11.7

Ener

gy [M

eV]

5  nC  11.5  MeV  parallel  beam

Emi[ance  5.5  mm-­‐mrad

Size  0.4  mm

Energy  spread  0.6%

Bunch  shape Gun Exit

Beam  tracking  simulaRon  result  （10  nC）

This RF gun can generate 10 nC beam.

Contents

•  IntroducRon  •  Disk  and  Washer(DAW)  type  RF  gun  •  Quasi-­‐traveling  wave  RF  gun  •  3D  cavity  calculaRon  and  design  of  quasi-­‐traveling  wave  RF  gun  

•  Conclusion  

0 p �2p �4 p �22.7

2.8

2.9

3.0

3.10 p �2p �4 p �2

Phase shift �cell @radDFrequency

@GHzD k : 3.0 %

3D  cavity  calculaRon

Acceleration mode

Coupling mode Regular  cell

3D  cavity  calculaRon

1st cavity calculation

Coupler calculation

2 types coupler

coupling  caviRes acceleraRng  cavity

cathode

Whole  cavity  shape

Cavity  shape

Mechanical  design  and  manufacturing  

Conclusion •  We  are  developing  a  photo  cathode  S-­‐band  RF  gun  for  SuperKEKB.  

•  DAW  type  RF  gun  generated  4.8  nC.  We  confirmed  electric  field  focus  in  the  caviRes.  

•  However  DAW  type  RF  gun  is  not  enough  to  our  SuperKEKB  operaRon.    

•  A  new  quasi-­‐traveling  wave  RF  gun  have  developed.  It is suitable for the high charge low emittance beam  generaRon.  

•  The  quasi-­‐traveling  wave  RF  gun  will  be  tested  soon.