quasi&traveling&wave&side&couple& rf&gun&for&superkekb · quasi...
TRANSCRIPT
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.
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
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
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.