Preliminary design on the 5 MeV injector and 500 kv DC gun in IHEP

1 Preliminary design on the 5 MeV injector and 500 kv DC gun in IHEP Shengguang Liu on behalf of our group Yunlong Chi, Guangwei Wang, Jinqiang Xu Zusheng Zhou, Xiaoping Li Shuhong Wang 2~3, Dec. 2010

2 Outline 1. Introduction 2. Preliminary Design on the 5 MeV Injector 3. Design on the 500 kv DC Gun 4. Summary

3 Introduction 1. Size: Loop s circumference ~ 50 m; Square area : ~ 50 m x 12 m = 600 m 2 2. Beam energy is 35MeV 3. Beam energy out of the injector is 5MeV,10mA 3

4 Introduction Our technological strategy The first option: Photocathode DC gun The backup option: 217MHz photocathode RF gun

5 Preliminary Design on the 5 MeV Injector DC Gun + solenoid1+nrf buncher+solenoid2 + two 2-cell SRF cavity as energy booster Normal ERL mode: 77pC 1. 500KV 2. 300KV

6 Preliminary Design on the 5 MeV Injector 1.3GHz NRF buncher Solenoid Q:25411.5; We set the maximum field gradient along z axis to 5MV/m, the required CW RF power is about 15KW. Taking account of the 10mA beam energy gain 230KV in the buncher, 2.3KW is needed. The total RF power for buncher is about 17.3KW.

7 Preliminary Design on the 5 MeV Injector 3 HOM dampers 4 Main couplers 2 2-cell cavities 2 Gate valves 2.3984 m 450 mm 649.2 mm 200 mm 649.2 mm 450 mm

8 Preliminary Design on the 5 MeV Injector E-Field B-Field Emittance Bunch length Beam size Energy 500KV 77pC

9 Preliminary Design on the 5 MeV Injector Simulation conditions: (1)Charge/bunch 77pC; (2)Laser RMS beam size 1.2mm; flat top laser, flat top 20ps,rise time 2ps; (3)initial kinetic energy is assumed to 0.2eV (GaAs cathode driven by 532nm); (4)High voltage of the DC gun 500kV, maximum field gradient on z-axie is 6.45MV/m; maximum field gradient on the cathode surface 5.48MV/m; (5)Maximum B-field of solenoid 1 is 430Gauss; Maximum B-field of solenoid 2 is 400Gauss; (6)Buncher 1.3GHz, Maximum e-field is 5MV/m; (7)two 2-cell SRF cavity,maximum e-field is 20MV/m ; Simulation results: Beam energy is 5MeV,RMS energy spread is 0.72%, RMS normalized emittance is 1.49mm.mrad, RMS bunch length is 0.67mm. 500KV 77pC

10 Preliminary Design on the 5 MeV Injector Simulation conditions: (1)Charge/bunch 77pC; (2)Laser RMS beam size 1.6mm; flat top laser, flat top 30ps,rise time 2ps; (3)initial kinetic energy is assumed to 0.2eV; (4)High voltage of the DC gun 300kV, maximum field gradient on z-axie is 6.45*0.6MV/m; maximum field gradient on the cathode surface 5.48 * 0.6MV/m; (5)Maximum B-field of solenoid 1 is 320Gauss; Maximum B-field of solenoid 2 is 320Gauss; (6)Normal conducting buncher 1.3GHz, Maximum e-field is 5MV/m; (7)two 2-cell SRF cavity,maximum e-field is 20MV/m ; Simulation results: Beam energy is 5.0MeV,RMS energy spread is 24KeV, RMS normalized emittance is 2.3mm.mrad, RMS bunch length is 0.8mm. 300KV 77pC

11 Preliminary Design on the 5 MeV Injector ERL photo-injector based on 217MHz NRF Gun

Preliminary Design on the 5 MeV Injector Superfish model CST model Model Code Frequency (MHz) Q P_total (kw) Pd_max (w/cm^2) R (Mohm) R/Q Stored energy (J) Vc (kv) Model1 Superfish 216.49 29989 41.96 13.65 5.96 198.7 0.93 500 MWS 216.42 29622 42.4 14.75 5.90 199.1 0.92 500 Model2 Superfish 216.06 27888 48.67 16.56 5.14 184.2 1.00 500 MWS 215.96 27602 49.65 18.60 5.03 182.4 1.01 500 1300MHz 6 = 216.7MHz

Preliminary Design on the 5 MeV Injector 3D simple RF model 3D complicated RF model Code Frequency Q0 Total loss R R/Q Vc Max power Total energy (MHz) (kw) (MOhm) (kv) density(w/cm^2) (J) Superfish (1) 216.49 29989 41.96 5.96 198.7 500 13.7 0.925 MWS-simple (2) 216.42 29622 42.39 5.90 199.1 500 14.7 0.923 MWS- complicated (3) 216.64 30379 35.54 7.03 231.5 500 18.1 0.793 500KV 38KW RF power 750KV 85KW RF power

14 Preliminary Design on the 5 MeV Injector E-Field B-Field

15 Preliminary Design on the 5 MeV Injector Emittance Beam size Energy Energy spread

16 Preliminary Design on the 5 MeV Injector Simulation conditions: (1)Charge/bunch 77pC; (2)Laser RMS beam size 0.6mm; flat top laser, flat top 20ps,rise time 2ps; (3)initial kinetic energy is assumed to 0.2eV; (4)In the gun, maximum field gradient on z-axie is 13MV/m(~500kV); (5)Maximum B-field of solenoid 1 is 430Gauss; Maximum B-field of solenoid 2 is 400Gauss; (6) Buncher 1.3GHz, Maximum e-field is 5MV/m; (7)two 2-cell SRF cavity,maximum e-field is 20MV/m ; Simulation results: Beam energy is 5.1MeV,RMS energy spread is 0.45%, RMS normalized emittance is 0.85mm.mrad, RMS bunch length is 0.73mm

17 Design on the 500 kv DC Gun 500 KeV DC gun for JLAMP VUV/Soft X-ray User Facility JLAB Gun (Older version) Jlab has good records on DC Gun: Demonstrated ~ 10 ma CW operation, Has operated 3 years Good vacuum condition ~10-11 torr Long cathode life time: (30 hours operation at 5 ma CW) JLAB Gun (new version) Large electrode area to reduce surface gradient, higher operating voltage Niobium electrodes (take advantage of SRF processing techniques) Bulk resistivity ceramic Load lock (various cathode types) Massive pumping for good vacuum Focusing geometry Light-box free operation Isolated anode for bias

18 Design on the 500 kv DC Gun 500-kV gun with a segmented insulator guard ring against field emission HV terminal support rod field emission guard ring 500 kv for 8 hours without any discharge ceramic cathode gun chamber anode Segmented insulator with guard rings e-beam segmented insulator

19 Design on the 500 kv DC Gun Cornell[8] JLab-FEL[9] KEK/JAEA[10-11] IHEP HV 750kV 350kV 500kV 500kV cathode GaAs:Cs GaAs:Cs GaAs:Cs GaAs:Cs QE 12-15%( initial ) 1% 5-7%(initial) 1% 5-7%( initial ) 1% lifetime 100h 30h 20h 20h 5-7%( initial ) 1% laser 20W, 520 nm 4W,526.5nm 1.5W-15W,530nm 2.3W,530nm Repetition rate Transverse emit. Bunch charge Average current 1.3GHz 74.85MHz 130MHz-1.3GHz 130MHz, 1.3GHz* 0.3mm.mrad 7.0mm.mrad 1.0mm.mrad 0.1mm.mrad (7.7pC) 77pC 150pC 77pC 77pC 100mA 9.1mA 10-100mA 10mA < 2.0mm.mrad 0.1mm.mrad (7.7pC) * Two operation modes:(1)130mhz,10ma,77pc;(2)1300mhz,10ma,7.7pc

20 Design on the 500 kv DC Gun Multiple activated photocathode preservations Stock chamber 10-10 Pa < 10-10 Pa Gun chamber Long-term gun operation is uaranteed by multiple plug system. Installation of Plug Quick exchanges of Plug 10-8 Pa 10-9 Pa Cs & O 2 Preparation Chamber Loading Chamber Multiple cathode cleaning Multiple NEA-surfaces are formed simultaneously. 20

21 Design on the 500 kv DC Gun 由进样室 制备室 储存室组成, 利用磁力传递杆将样品在各个真空室之间传递 一 进样室 : 1 真空获得:200L/S 的 SAES 泵 ( 意大利 )+200L/S 的离子泵 ( 三井 +Hipace700 全无油分子泵机组 ( 德国普发, 四个真空室共用 ) 2 真空测量: 数显复合冷阴极规 ( 真空计 TPG262, 高真空规 IKR270, 低真空规 TPR280; 德国普发 ) 3 极限真空:2x10-9Torr 4 系统真空检漏漏率: 5.0x10-8 Pa.l/S 5 真空室: 材料为无磁不锈钢, 表面喷丸后电解处理 ; 内部尺寸 :Ø100 H210(mm), 二个 CF35 法兰 ( 接规管和全金属角阀 ), 二个 CF100 法兰 ( 一个接 CF100 封接观察窗, 一个接离子泵口过渡接管 ), 一个 CF16 法兰 ( 接放气阀 ), 二个 CF63 法兰 ( 一个接 CF63 进口闸板阀, 一个接进口磁力传递杆 800mm) 6 样品库: 可放置 4 个样品 7 磁力送样杆:1 套 二 制备室 1 真空获得:1300L/S 的 SAES 泵 ( 意大利 )+400L/S 的离子泵 ( 三井 )+Hipace700 全无油分子泵机组 ( 德国普发, 四个真空室共用 ) 2 真空测量: 数显复合冷阴极规 ( 真空计 TPG262, 高真空规 IKR270, 低真空规 TPR280; 德国普发 ) 3 极限真空:2x10-10Torr 4 系统真空检漏漏率: 5.0x10-8 Pa.l/S 5 真空室: 材料为无磁不锈钢, 表面喷丸后电解处理 ; 内部尺寸 :Ø200 H410(mm), 三个 CF35 法兰 ( 接规管 銫源 氧气源 ), 一个 CF35 法兰 ( 接全金属角阀 ), 四个 CF63 法兰 ( 一个接进口磁力传递 400mm, 一个 CF63 观察窗, 二个 CF63 进口闸板阀 ), 三个 CF100 法兰 ( 接普通封接观察窗 加热炉 吸附泵口 ); 一个 CF150 法兰 ( 接离子泵 ); 二个 CF200 法兰 { 后端的 CF200 法兰上加一个 CF35 石英封接观察窗 ( 透紫外线 ), 二个 CF16 单心陶封高压电极 (1000V) 连接收集极 ; 前端的 CF200 法兰加 CF63 过渡, 接进口磁力传递杆 } 6 銫源: 需要用户提供銫条, 通过 CF35 法兰连接 ; 四套 氧气源管路 : 抽气管路一个三通 + 一套波纹管路 + 一个过渡接头 ; 氧气需通过管路输送到接近銫源的位置 ; 氧气管路需要单独抽真空 7 氧源: 具有一路充氧气气体管路 ( 管路漏率 <10-6Pa.L/S), 手动微调阀调节气体流量 ; 8 样品台: 加热体温度 :800, 可控可调 ; 三 存储室 : 1 真空获得:400L/S 的 SAES 泵 ( 意大利 )+200L/S 的离子泵 ( 三井 )+Hipace700 全无油分子泵机组 ( 德国普发, 四个真空室共用 ) 2 真空测量: 数显复合冷阴极规 ( 真空计 TPG262, 高真空规 IKR270, 低真空规 TPR280; 德国普发 ) 3 极限真空:2x10-11torr 4 系统真空检漏漏率: 5.0x10-8 Pa.l/S 5 真空室: Ø150 H330(mm), 二个 CF35 法兰 ( 接规管和 CD-J35 全金属角阀 ), 四个 CF63 法兰 ( 接进口磁力传递 800mm 进口磁力传递 1200mm, 进口 CF63 闸板阀 CF63 盲板 ), 一个 CF100 法兰 ( 吸附泵口 ), 二个 CF150 法兰 ( 上端 CF150 法兰封接 Φ100 普通玻璃观察窗, 下端 CF150 法兰接离子泵 ) 二个 CF63--CF35 过渡波纹管 ( 用于连接磁力传递杆和进样室 ) 6 样品库: 可放置 4 个样品. 7 磁力送样杆:2 套四 安装台架 : 优质方钢型材 (50mmX50mmX4mm) 焊接成, 快卸围板表面喷塑处理 ; 机台表面用不锈钢蒙皮装饰 ; 四只脚轮, 可固定, 可移动 ;

22 Design on the 500 kv DC Gun We design the gun cavity and do some simulations on the field distribution, based on KEK DC gun.

23 Design on the 500 kv DC Gun Field distribution of the 500-kV gun This is the field distribution nearby the support rod without the cathode ball by Poission. The result is the almost same as calculation result given by KEK This is the field distribution in the gun cavity simulated by CST, the maximum field is at the edge of the cathode.

24 Design on the 500 kv DC Gun Ceramic insulator breaking (punch-through problem due to the field emission from the surface of the support rod and the cathode ball). (1) to design the cavity and cathode ball and the electronic anode. Try to decrease the field gradient when the HV is fixed. (2) try to use the special material at those points of the maximum field. For example, Mo or Ni, try to decrease the electron number from these points due to the field emission (3) to use the guard-ring to block the electrons from the support rod and cathode surface and to protect the Ceramic insulator Extreme high vacuum (<1E-10Pa) in the gun. Cathode lifetime depends on the vacuum. In order to operate the DC gun stable in a long term, we should (1) the gun cavity and fringes would be made of special material to decrease outgassing rate. titanium or titanium alloy (2) to apply the inseam welding art and sealed nipples to decrease the leak rate. (3) Combination of NEG pumps and a bakeable pump to increase the pumping ability.

25 Design on the 500 kv DC Gun 2. 3. 6. 7. 4. 5. 1. A After The 1060nm An By pulse two high 1.3GHz insertion transverse compressor cascaded laser speed active lose is waveguide focused and polarization of mode-locked then longitudinal to compressor modulator an SHG maintenance laser shaping, laser crystal is oscillator can too pulses pick high, with beer-can optical up from (optical I so type one 12ps optical to match shaped pulse amplifiers, clock about from to amplifier pulses 2ps get every pritel) the for 530nm can laser the has ten be is pulse green used power to pulses transmitted be staking to light used can to produce decrease after be downstream. on up it. 12ps the to rep. 20w photocathode pulse rate into 1060nm 130MHz wavelength.

26 Design on the 500 kv DC Gun Key technologies on the drive laser system should be pre-researched 1. 1.3GHz active mode-locked laser oscillator, pulse rep. rate is 1.3GHz. 2. Two cascaded polarization maintenance fiber amplifiers, the laser power be amplified to 20W 3. 1060nm laser is focused on an SHG crystal with type1 match-mode to generate green light @530nm 4. Laser pulse shaping, including the transverse and longitudinal shaping. In the end,laser pulse with the beer-can shape transmit to the photocathode surface

27 Design on the 500 kv DC Gun Requirements on HV power system: 1. Output HV 550kV 10mA, Operate at 500kV stably for a long time. 2. HV ripple is better than 1.0 10-4 Cockcroft-Walton HV technology is mature technology, some companies in china can produce the HV power system. using LC filter circuit to suppress the ripple.

28 Summary 1. ERL test facility is proposed in IHEP. The task at the first step is to build the photo-injector with 5MeV energy and 10mA average current. 2. We have done the preliminary design on the photo-injector, including DC gun injector and 217MHz VHF gun injector. We designed all components of the injector system and optimized the beam dynamics. 3. We focus our efforts on the photocathode DC gun. We have finished the design of all the subsystem of the gun: preparation system of the GaAs:Cs cathode, driving laser system, gun and HV system. 4. We are trying to get funding and begin to build the DC gun in the next year. 5. We hope to collaborate with the experienced Lab on the DC gun issues

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30 Design on the 500 kv DC Gun