1. Hua Shi, Jinhui Chen, Lei Wang, Na Wang, Lihua Huo, Peng Liu, Yan Li
Progress on the fast pulsed kicker for the HEPS
Hua Shi, Jinhui Chen, Lei Wang, Na Wang, Lihua Huo, Peng Liu, Yan Li
LER 2016, October 26-28, 2016

2. Conceptual design of HEPS storage ring on-axial injection system
Outline
HEPS
Conceptual design of HEPS storage ring on-axial injection system
750mm-long stripline kicker design
Design consideration
3-D and beam impedance simulation, mechanical design
Simulation work for assessing the fabrication technique
The geometric tolerance
Assessing the fabrication technique of blade and vacuum tank
Prototype of blade and vacuum tank
300mm-long Compact kicker consideration
Summary 2

3. High Energy Photon Source (HEPS)
A future project in China before 2022
6GeV/60pm·rad/1296m LER
1 Y. Jiao. Lattice design and beam dynamics studies for HEPS. This workshop.
2 Z. Duan. Top-up injection schemes for HEPS . This workshop.
Parameters
Unit
HEPS
Lattice -
7BA
Beam Energy
GeV 6
Beam Current mA
200
Horizontal Emmitance
pm·rad 60
Circumference of Storage Ring m
1296
Number of Sections 48
Length of Straight Section for Injection & Extraction
6×2
RF Frequency
MHz
500
Bucket Spacing ns 2
6/2
Total Number of Buckets
2160
720/2160
Number of Injected Bunch(in Single Bunch Filling Mode)
432 (1/5)
720
Minimum Bunch Spacing 10 3

4. HEPS storage ring on-axial injection system
Baseline: transverse on-axial swap-out injection Or
Future goal: Longitudinal on-axial accumulation injection
1296m, 6GeV, 60pm·rad
Storage Ring 4

5. On-axial Injection system layout
HEPS
7BA Curved Section
SR injection system layout
SR extraction/MP system layout
It includes two 6m-long straight section
Number of kickers for injection system: 10300mm long
Number of kickers for extraction system(transverse swap-out injection) or machine protection(MP) system(longitudinal accumulation injection): 4750mm long. For transverse injection, the 4 kickers are used for beam extraction; for longitudinal injection, they are used for machine protection(MP) 5

6. Pulse time structure and bunch filling mode
HEPS
Transverse on-axial swap-out injection: single RF system, the minimum bunch spacing is 10ns, so the pulse setting: rise time(tr)+flat-top time(ttop)+fall time(tf)=4+5+4=13ns
Longitudinal on-axial accumulation injection: single RF system, the minimum bunch spacing is 6ns, but the bunch must be injected between the stored bunches, so the pulse setting: tr+ttop+tf= =3.5ns
The width of stripline kicker decided by: length(L) of stripline blade (L/c) + pulse width. Transverse injection: 750mm or 300mm long kicker. Longitudinal injection: 300mm long kicker. The 300mm long kicker is adopted
Single
Single
Stripline kicker pulse width
in transverse on-axial swap-out injection
Stripline kicker pulse width
in longitudinal on-axial accumulation injection 6

7. 750mm Stripline kicker design in HEPS-TF
750mm-long kicker will be fabricated to investigate the cold extrusion, CNC machining, EDM, welding and other fabrication techniques
Reference the APS-U stripline kicker design
2 “D” shape electrodes place in an ellipse cavity. Vanes design is used to decoupled 2 close stripline blades, but a deeper vane is accepted to achieve lower even-mode impedance (<60.5 )
Parameters
Unit
HEPS
APS-U
Blade length of single kicker mm
750
720
Number of kickers - 4
42
Gap between the two blades 10 9
Good field region
±2.3(x),
±1.0(y)
Field uniformity 2%
The minimum bunch spacing ns
11.4
Rise and fall time
4.5
Flat top 5
5.9
High voltage of the Pulser kV
±15
Odd-mode impedance 
50±0.5
Even-mode impedance
60±0.5 7

8. Half shell of outer body consists of 2 half ellipses that defined by:
2-D geometry
HEPS
a, b are axes of the center ellipse of the 2 blades. Vane width is defined by vane (<b)
Half shell of outer body consists of 2 half ellipses that defined by:
Center half: Xc, a0, b0
Outer half: Xc, a00, b0
2gap=10mm
blade=3mm 8

9. 3-D results 650mm main body with 250mm taper part
HEPS
Thanks for CST service of IMP, CAS
Main body (black)
Taper part (red)
Zodd / 
49.79
50.24
Zeven / 
60.36
59.68
Emax / (MV/m)
6.46
6.61
Y (5mm)
1.70
4.01
X (2.3mm)
1.44
2.99
650mm main body with 250mm taper part
Optimizing the cross section of main body and end of taper part 9

10. Z-TDR and S11 comparison of different-vane kickers
HEPS
Z-TDR
vane<b
vane=b
S11-dB
After optimization
vane<b: Zodd=49.8, Zeven=60.1
vane=b: Zodd=49.9, Zeven=64.3
S11 in 1GHz
vane<b: S11<-40dB
vane=b: S11<-30dB 10

11. Beam impedance comparison in different-vane kickers
HEPS
Longitudinal wake potential (σz=3mm)
Kicker including 4 feedthrough(FID), beam pipe and steel vacuum tank
Excitation: Gaussian beam σz=3mm
Loss factor
vane<b: 0.893V/pC, vane=b: 1.042V/pC
The loss dissipation in vane<b kicker is about 15% lower than that in vane=b
Real part of the longitudinal impedance
vane<b 11

12. Flange connection of adjacent kickers
750mm kicker mechanical design
HEPS
Adjustable support
Flange connection of adjacent kickers 12

13. Simulation work for assessing the fabrication technique
HEPS
The geometric tolerance
Comparison of the fabrication technique of blades
Assess the uniform-section stainless steel blade with Cold Extrusion technique
Simulating the kicker made of different material
Simulating the kicker without taper
Determine the fabrication technique of vacuum tank
Comparison of different welding method of the vacuum tank
WEC and welding of vacuum tank
Assess the effect of copper-blade deflection to kicker RF performance
Simulating kicker with deflection of different material

14. The geometric tolerance
HEPS
The geometric tolerance of x-direction, y-direction , rotation of single blade, scaling tolerance of single blade and vacuum tank were given
x-direction: -0.5~0.5 mm
y-direction: -0.15~0.05 mm
Rotation: 1
Scaling factor of single blade: 0.97~1.06
Scaling factor of vacuum tank: 0.989~1.012 14

15. Comparison of the fabrication technique of blades
HEPS
Material: 316L stainless steel
Method: Cold Extrusion
Flatness: 0.05~0.06mm
r’: (after heat treatment)
Material: oxygen-free copper
Method: Computer Numerical Control (CNC) machining  
Flatness: 0.05~0.1mm
The deformation of blades made by Cold Extrusion is smaller, and the cost of the Cold Extrusion is much cheaper than that of CNC machining
CNC machining can fabricate the blade with taper part, but Cold Extrusion technique can only fabricate uniform blades 15

16. Longitudinal wake potential (sigz=3mm)
Simulation of kicker-w/o taper part
HEPS
S11-dB
The dimension of kicker is same as the main part of vane<b kicker, but without the two taper parts
The simulation results show the S11 and beam loss factor are almost same in kickers with or without taper part
Longitudinal wake potential (sigz=3mm) 16

17. Simulation of kickers made of different material
HEPS
S11-dB
steel/copper vacuum tank
steel/copper blades
4 assembled kickers with steel(316L)/copper vacuum tank and blades
The reflection of the 4 kickers is almost same. The difference of insertion loss is less than 4%
The Cold Extrusion technique is considered, but we need further investigation
Insertion loss (mag) 17

18. Comparison of different welding methods of the vacuum tank
HEPS
1 Transverse welding
2 Vertical welding
3 Horizontal welding
There might be air gap, 0.1mm (thick) *0.5mm(height), inside the vacuum tank because it’s difficult for the tin solder to penetrate the weld fully
The welding between main body and tapers are same. The weld seams are cutting in different direction. The simulating results showed the air gap wouldn’t affect the RF feature
It’s very hard to control the weld seam precision of the very long vertical and horizontal weld
Zodd
()
Zeven
Emax
(MV/m) Y
(±5mm) X
(±2.3mm)
Kicker
50.07
59.54
7.45
1.82%
1.52%
1 Tran.
50.06
2 Ver.
7.44
3 Hori.
59.52
7.43
1.51%
The transverse welding and Electrical Discharge Machining are considered 18

19. The EDM of vacuum tank Material
HEPS
Material
Main part: oxygen-free copper
Taper part: stainless steel
Method: Electrical discharge machining (EDM)
The 750mm vacuum tank should be separated with three main and two taper parts for EDM, and then the five parts would be welded in the Hydrogen Furnace
Problem: For the 50mm transition parts, the local taper is too small for the 0.25mm-thick cutting wire. So the model had to change a little to fit the EDM, but the deviation reached 0.2mm. We need to improve the technique further 19

20. Assembled vacuum tank of kicker before welding
The welding of vacuum tank
HEPS
Solder wire
Copper main part
Steel transition part
Assembled vacuum tank of kicker before welding
Hydrogen Furnace
Three copper main parts and two 50mm-long steel transition parts are connected together with fixture tools
The welding in the hydrogen furnace have been finished this week. The mechanical test and analysis will be carried out soon 20

21. Simulating kicker with deflection of different material
HEPS
According to APS-U beam loss simulation, the power dissipation of copper blades is very low, so the cooling might not be considered
For vertical placed blades, copper blades has a large deflection
copper blade: 0.4mm
steel blade: 0.2mm
S-parameters, impedance and horizontal field uniformity changed a little.
The vertical field uniformity is 2.92%(steel blade) and 4.34%(copper blade), and doesn’t satisfy the requirement(2%). But the uniformity may be improved in horizontal injection Ey 21

22. 300mm-long compact kicker consideration
HEPS
100mm
In original design, the gap between adjacent kickers is 100mm, and the total length of 10300mm kickers will be 3.9m(>3.2m). So only 8 not 10 kickers can be placed in the straight section
A new compact design have been considered. The feedthroughs of two adjacent kickers being placed back to back, and one kicker only occupies the 300mm. The simulation work will be carried out later 22

23. Mechanical fabrication
Summary
HEPS
HEPS now consider on-axial injection. The kickers design satisfied both injection schemes
Injection section: 10300mm kickers
Another straight section: 4750mm kickers
750mm-long stripline kicker design have been done, but need further optimization
Mechanical fabrication
Copper blades may be considered for very low heat loss(w/o cooling). But the precision of CNC machining should be improved
For vacuum tank, the fabrication technique of EDM and hydrogen furnace welding will be investigated
The horizontal injection may improve the bad vertical field uniformity caused by deflection of copper blades
300mm-long compact kicker design will be investigated later 23

24. Thanks for your attention！