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

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

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 500 166.7+499.8 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

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

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

Pulse time structure and bunch filling mode HEPS Transverse on-axial swap-out injection: single bunch@500MHz 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 bunch @166.7+499.8MHz 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=1.5+1+1=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 bunch @500MHz Single bunch @166.7+499.8MHz Stripline kicker pulse width in transverse on-axial swap-out injection Stripline kicker pulse width in longitudinal on-axial accumulation injection 6

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

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

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

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

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

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

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

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

Comparison of the fabrication technique of blades HEPS Material: 316L stainless steel Method: Cold Extrusion Flatness: 0.05~0.06mm r’: 1.003 (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

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

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

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

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

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

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

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

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

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