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	  SuperKEKB	  Upgrade	  and	  RF	  gun	  development	
KEKB	  obtained	  (e+	  /	  e-­‐)SuperKEKB	  required	  (e+	  /	  e-­‐)Energy	

3.5	  GeV	  /	  8.0	  GeV

4.0	  GeV	  /	  7.0	  GeVCharge	e-­‐	  	  	   	  e+	  	  /	  	  	  e-­‐	  10	  	  1.0	  nC	  /	  1.0	  nCe-­‐	  	  	  	  e+	  	  /	  	  	  e-­‐	  10	  	  4.0	  nC	  /	  5.0	  nCEmiFance	  	  	  [mm-­‐mrad]

2100	  	  /	  300	  6	  	  /	  20	  	  ee+J-lina
cHER
7 GeV

LER
4 GeV

3-2 RF gun

C sector

1 sector

2 sector

3 sector

SuperKEKBAR
6.5 GeV

B sector A sector A-1 RF gun

J arc

PF
2.5~3.0 GeV

4 sector

5 sector

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

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

DAW	  (Disk	  and	  Washer)	  RF	  gun	  development	

DAW	  type	  RF	  gun	  Beam	  tracking	  simulaRon	  result	  Emi[ance	6	  mm-­‐mrad	

Size	  	  (σ)	  	1.2	  mm	Bunch	  length	

8	  psec	

Energy	3.2	  MeV	Electric	  ﬁeld	  focus	  Large	  coupling	  Strong	  focus	  ﬁeld	

Low	  electric	  ﬁeld	  DAW	  (Disk	  and	  Washer)	  RF	  gun	RF gun	RF gun beam line	We already installed RF gun into KEK linac beamline and tested.

DAW type RF gun beam study result	
4.8 nC beam generation
4.4 nC beam transport to linac end. 	

BPM signal.
(Beam transport study)	

Beam has divergence angle in thegun. (calculation)

Focusing field is NOT enough. Low beam energy: 3 MeV	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	  Structure of the quasi traveling wave cavity	

Normal side coupled cavities	

Quasi traveling wave side coupled cavities	

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

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

5obtain	  beam	  parameter	  	4

rxy

3

2

10Feedback	  to	  cavity	  parameters	

GPT

0100

200

300

400

500

600

700

800

900

1000z

AutomaRc	  opRmizaRon	  by	  using	  downhill	  simplex	  method	1st	  Cavity	  Design	  (cathode	  cell)	
Finally, we gat optimum cavity shape.	

Maximum	  E-­‐ﬁeld	  at	  surface:	  120	  MV/m	  （DAW	  type	  :	  150	  MV/m）	  Cathode	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:	  120	  MV/m	  Maximum	  E-­‐ﬁeld	  at	  surface:	  100	  MV/m	  Emi[ance:	  5.5	  mm-­‐mrad	  @	  5	  nC	  This	  RF	  gun	  can	  generate	  10	  nC	  beam	  Beam	  tracking	  simulaRon	  result	  （5	  nC）	Emi[ance	  5.5	  mm-­‐mrad	

time=2.48098e-009

Energy [MeV]11.7

Gun Exit	

11.6
11.5
11.4

Bunch	  shape	

11.3

Size	  0.4	  mm	728
GPT

Energy	  spread	  0.6%	

729730731732z5	  nC	  11.5	  MeV	  parallel	  beam	733

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	  3D	  cavity	  calculaRon	
Regular	  cell	

Coupling mode	

03.1

3.0



p 4

p 2

Acceleration mode	Frequency GHz@ D

k : 3.0 %	

2.9

2.82.70 @ Dp 4

Phase shift cell radp 2

3D	  cavity	  calculaRon	

2 types coupler	1st cavity calculation	
Coupler calculation	Whole	  cavity	  shape	

coupling	  caviRes	

acceleraRng	  cavity	

Cavity	  shape	cathode	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.