DC-SRF photocathode injector at Peking University · 2010/12/3. IHIP, Peking University, China. 5....

2010/12/3 IHIP, Peking University, China 1

DC-SRF photocathode injector at Peking University

Zhu Feng

Institute of Heavy Ion Physics Peking University


Outline

1. Background2. Design of the 3.5cell superconducting

cavity DC-SRF photo-injector 3. Key parts of the DC-SRF injector4. Status of the DC-SRF photo-injector


1. Background

Superconducting technology applied in large accelerator facility

LaserBunch

Compressorbypass

UndulatorsCollimator

Bunch Compresso

r

RF gun

5 MeV 127 MeV 370 MeV 700 MeV

Accelerating StructuresDiagnostics

CEBAF（6GeV->12 GeV) SNS(1GeV)

FLASH

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プレゼンテーションのノート

超导腔主要用于射频超导加速器中


In 2004, international committee of futureaccelerator (ICFA ） suggest ILC using RFsuperconducting technology.

Background

To take advantage of superconducting accelerators, injectors whichcan provide high average current, high brightness, and lowemmittance electron beam are required.


SRF gun is a novel method to achieve high quality high average current electron beam.

PKU DC-SRF photocathode injector

BNL Nb superconducting photocathode SRF gun

FZR normal conducting photocathode superconducting cavity SRF gun

Background

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2004年国际未来加速器发展委员会（ICFA）指出ILC应采用射频超导技术。但是适应超导加速器CW运行优势的注入器却亟待发展。高亮度电子枪已经发展到激光驱动光阴极技术，相比于美、德、日等先进国家，我国的技术水平还有较大差距。

Developed by PKU SRF group

Compatibility of photocathode and SC cavity

Compact structure

Could be operated at CW mode

Could handle high average current (1∼10mA)

High beam quality

DC-SRF Photo-injector


Up:

4.5KW Solid State

Power Amplifier

Left:Electron Beam spot after RF acceleration.

Prototype injector with a pierce gun and a 1.5cell superconducting cavity succeeded in accelerating electron beams at 4K.energy gain ~1MeV，emittance~5µm。

Experiments prove the feasibility of DC-SRF injector

SRF-2009 9

Upgrade of DC-SRF injector

100 KV Pierce DC gun with Cs2Te cathode matched with SRF cavity

Operating at 2K with tuner and screened LN

Providing 3-5 MeV ~70 pc superfast pulse beam with low emmittance

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After the successful commissioning of the 1.5 cell prototype DC-SRF gun. It was upgraded to a 3.5cell dc-sc photo-injector. And the cryomodule is shown here. There is a DC gun with high voltage ceramics, 3.5cell superconducting cavity, tuner, liquid helium vessel, Liquid Nitrogen screen ---and so on..


2. Design of the 3.5cell super-conducting cavity photo-injector


PKU-ERL-FEL facility

A proposal on the construction of an ERL Test Facility in China was initiated by PKU

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结合北京大学ERL-FEL加速器实验平台提出3.5cell超导光阴极注入器的设计，注入器工作两种模式，一种是束团压缩模式，用于产生THz，另一种用于ERL。

Design of the DC-SRF photoinjector

Layout of the DC-SRF photo-injector

Dynamics simulation by using software POSSION、SUPERFISH、PARMELA、ASTRA etc along DC gun & 3.5cell SRF cavity，to obtain emmittance, energy spread, bunch length and output energy of the beam



Pulse shape, beam spot and the transverse phase space of the output beam

Left: THz mode, right: IR FEL or ERL based FEL mode

SRF-2009 14

Possible steps in implementing PKU-ETF

THz facility

PKU-ERL based CBS

DC-SRF injector may provide high average electron beam with low emmittance.

THz source may provide 400-1200 µm wide range quasi-chromatic radiation

ERL CBS may produce high flux x-ray(10E8 photons/sec. @ CW mode)

ERL IR FEL provides high brightness 4-8 µm radiation with minimum consumption

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Power≈W, wave length 400μm ~ 1200μm（0.25~0.75T）adjustable in wide range Quasi-chromatic（带宽5%）优越的光脉冲时间结构 CBS @ 1A 10E8 photons delta lambta =0.4%


Drive laser

Pulse length（FWHM） 8ps

laser spot（ FWHM） 3.0mm

Repetition rate 81.25MHz

Bunch shape uniform transverse distribution, Gaussian longitudinaldistribution

Injector ERL mode THz mode

gradient 13 MV/m 15MV/m

Bunch charge 100 pc 20pc

energy 5MeV ~5MeV

Transverse emittance (rms) 1.2mm·mrad 2.1 mm·mrad

Longitudinal emittance (rms) 15 deg－KeV 3.0deg－KeV

Bunch length（rms） 3ps 0.55ps

Rms beam spot 0.3mm 1.7mm

Energy spread ～0.5% 0.55%

Parameters of the DC-SRF injector（DC voltage 90KV）


3. Key parts of the DC-SRF injector


Key parts of the DC-SRF injector

parts:

1、DC-gun+3.5cell cavity

2、HOM couplers

3、on-line tuner

4、main coupler

5、cryostat

6、photocathode fabrication system

7、drive laser system

High voltage, 2K temperature, low temperature tuner,ultrahigh vacuum, dust free, vibration defense 、protection from terrestrial magnetism 、 alignment 、interlock problems

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这台注入器是北京大学提出来的，在国际上受到高度关注。它的设计与研制由我来负责。其核心部件为一个直流皮尔斯电子枪和3。5cell超导腔，在完成了其物理设计之后，需要对整台器进行设计。主要部件为右侧所列的，设计中需要重点考虑的方面：100kV高压、从高压电源到光阴极经过三种不同的气体状态（大气、高真空、超高真空）的绝缘与密封，温度从室温到77K再到2K的温度变化，在有限的空间内具体的实现具有相当的难度；2K，这是国内首次可以运行在2K下的超导注入器或加速器，2K恒温器的热损是设计的重要指标，为了减小热损增加了77KLN冷屏。2K热损小于10W，超导腔运行下2K下对氦气压的波动、液氦面的波动，根据波动要求完成了LHe管道的设计；2K低温在线调谐器。


DC-gun：pierce structure

Injector cavity：3.5cell superconducting cavity

3.1DC-gun + 3.5-cell superconducting cavity

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腔型：3.5cell，其中3个单元采用TESLA的设计参数。超导腔腔型的优化设计需要综合考虑DC高压段（首腔上含有皮尔斯枪的阳极）、超导腔的物理性能和机械性能、与直流枪的匹配问题、高阶模衰减和主耦合器馈入功率等问题，优化的重点为3.5cell的首腔和端腔组件。太高，体积小，束孔小，束流引起的尾场效应严重，表面电阻较高；频率太低，腔体体积太大，恒温器、液氦规模均增大，不经济。综合考虑到低温系统的配置、微波系统、加速器的大小等诸多因素，对于超导电子直线加速器的工作频率一般在为1到2GHz之间进行优化选择。1.3GHz是微波功率源的一个重要标准频率。

structure of DC-gun Electric field distribution of the DC-gun


DC pierce gun


RF design

HOMs

DC structure end groups3.5cell cavity

Lhe pipes tuner

Mutipacting

Mechanical properties

Beam dynamics

Design process of the 3.5cell superconducting cavity


プレゼンター


3.5cell超导腔是为了适用北京大学注入器而自行设计的超导腔，设计时需要考虑 3.5cell超导腔的设计与结构以及皮尔斯电极的设计


Electric field distribution of the 3.5cell cavity

Freq. 1301MHz R/Q (Ω):417 Bp/Eacc:4.95 Ep/Eacc:2.12


SRF-2009 22

Geometrical parameters

Mid half cell

Left sideof 1st half cell

Right side of the 1st half cell

Last cell

Requator(mm)

103.3 105.3 105.3 103.3

Riris (mm) 35 6 35 39

Rc(mm) 42.0 17.14 17.14 40.3

a (mm) 12 3 12 10

b (mm) 19 3 20 13.5

length（mm) 57.7 35.19 37.72 56.0

Main physical & geometrical parameters of 3.5cell cavity

Mode TM010,π-mode

Working frequency 1300 MHzQ0 1×1010

Eacc 13 MV/mEffective Length 0.417 mG-factor 242 ΩShunt Impedencer/Q

417 Ω

Epeak/Eacc 2.12Bpeak/Eacc 4.95

mT/(MV/m)


SRF-2009 23

Simulation on Multipacting

Simulated result by program MultiPac

Result from FishPact

No serious multipacting with reasonable geometrical parameters


2010/12/3 ERL Workshop 24

Stiffer ring Position (distance from the axis) /mm

1 38

2 85

3 50

4 80

5, 6, 7 53.5

position of the stiffing rings of the 3+1/2 cell cavity

Lorentz force detuning coefficient

tuning range of the cavity

Frequency change by 0.1mm cavity deformation

Force on the cavity with 0.1mm cavity deformation

Flatness change after tuning ±0.4mm

1.2Hz/(MV/m)2 ±200kHz 70kHz 1000N <3%


Mechanical properties of the 3+1/2 cell cavity


Fabrication of the 3.5cell large grain niobium cavity

deep drawn，precise machining，high vacuum electron beam welding



Room temperature RF measurement and adjustment of the 3.5-cell cavity

multi-cell cavity tuning facility at PKU

Modes spectrum

Field flatness of the pi mode

94%


SRF-2009 27

Large grain 3.5 cell Nb cavity of 23.5 MV/m @ Q0 >1E10 after BCP, HPR and baking 2 hrs at 8000c by Dr. R. Geng at J-Lab

Simulation results on MP


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Field gradient limited by the 1st half cell of the cavity

3.2 high order mode couplers

Test of the HOM couplers on the 3.5cell cavity


HOMC on the 3.5cell superconducting cavity

Peking University 29

f（MHz） ode 0.5mm 1mm 1.5mm 2mm 2.3mm1652.406 TE111（1） 1.94x106 9.55x105 1.07x106 1.45x106 2.49x106

1695.484 TE111（2） 1.17x107 5.82x106 峰重叠 7.64x106 1.21x107

1757.300 TE111（3） 2.72x106 峰重叠 1.61x106 2.06x106 1.52x106

1797.265 TM110（1） 2.15x106 1.66x106 1.99x106 2.72x106 3.26x106

1864.4925 TM110（2） 2.97x107 1.89x107 2.12x107 1.83x107 1.38x107

1876.990 TM110（3） 1.66x107 1.06x107 1.15x107 9.99x106 4.30x106

1882.496 TM110（4） 5.35x106 3.45x106 3.91x106 3.63x106 3.01x106

2374.582 TE111（4） 3.41x106 4.69x106 1.57x106 7.78x106 2.42x106

2412.774 TM011（1） 6.44x105 7.46x105 9.55x105 1.25x106 1.58x106

2429.367 TM011（2） 1.98x105 2.27x105 2.86x105 3.91x105 5.09x105

2462.537 TM011（3） 7.21x105 7.26x105 9.22x105 1.28x106 1.68x106

2678.580 TM020（1） 1.80x105 1.57x105 1.33x105 1.75x105 2.25x105

2703.662 TM020（2） 2.23x104 1.6x104 1.70x104 2.29x104 3.40x104

2732.066 TM020（3） 2.29x104 1.50x104 1.57x104 1.92x104 2.95x104

2769.828 TM020（4） 1.49x105 8.93x104 8.82x104 1.01x105 1.56x105

2010/12/3

The HOM coupler can absorb the dangerous HOMs and keep cutoff for the fundmental mode

The distance between the antenna and the F part is 1mm

for fundmental mode, Qext=1013

for high order modes, Qext≈104～106

3.2 high order mode couplers

3.3 on-line tuner

Design of the tuner

Test of the 3.5cell cavity tuner

Tuning range±200kHz

Little change of the field flatness within the tuning range

120

130

140

150

160

170

180

0 50 100 150 200 250 300 350 400

位置/mm

场强

/相对

单位

原始场平调谐+200Hz场平调谐-200Hz场平

3.3 tuner

3.4 Main coupler

• Capacitive coupling structure referred to KEK proposed coupler structure in 2005

• Four parts connected by flanges

• Disk ceramic window, without contacting inner conductor

characteristics：1. Simple window structure, easy to

fabricate2. Inner conductor at low temperature,

heat load small3. Stress on ceramic window not strong4. Convenient for assembly and

maintenance

3.4 Main coupler

At 1.3GHz, SWR=1.07，

The bandwidth is 30MHz when SWR is smaller than 1.1

RF test of the coupler


3.5 cryostat

1: photocathode transportation line ； 2：Lhe buffer and two phase tube；3：LIN buffer and LIN thermal shield ；4： DC part；5：suspending structure；6：vacuum vessel；7：3+1/2cell superconducting cavity, main coupler and tuner

3.5 cryostat

-40.0

-20.0

0.0

20.0

40.0

60.0

80.0

100.0

120.0

5 10 15 20 25 30

点号

B / mGs

EW分量 NS分量 UD分量绝对值

Vacuum vessel also as magnetic shielding

Vacuum vessel of the cryostat

Magnetic field distribution along the axis of the cryostat

（the cryostat is horizontal）

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恒温器外筒由纯铁制成，外镀镍，防止生锈，外筒一方面提供超导腔真空绝热环境，另一方面对地磁进行屏蔽

3.5 Cryostat

80K LIN thermal shielding：composed of copper pipes and copper cylinder，the highest temperature is 81K，outside of the cylinder is thermal insulator

3.5 Cryostat

LHe buffer、two phase tube and suspending structure

3.6 on-line photocathode fabrication system

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在制备光阴极过程中，通过控制加热器的温度控制Te和Cs的蒸镀速率。新的设计中增加了膜厚仪进行碲膜和铯膜厚度的测量。此膜厚仪内置一控制仪和调控议，可以通过晶片上膜厚和沉积速率信号反馈到其输出端口，从而自行调整端口信号，实现对碲膜和铯膜厚度已经沉积速率的自动控制，这样更加有利于准确控制蒸镀过程。

3.7 drive laser system

The commercial picosecond laser (Time-Bandwith GE-100) upgraded，it composed of picosecond oscillator, amplifier, frequency multiplier, electricity power, control system and cooling system

sesam seed laser FR

200Wfiber couplerdiode laser

Ç»Íâ ±¶Æµ£¨ 532nm/266nm£©

Ç»Íâ ±¶Æµ£¨ 1064nm/532nm£©

¶à ³Ì ·Å´ó µ¥Ôª

Nd£º YVO4¾§Ìå

266nm

1064nm

整体外观示意图整体外观示意图

The layout of the laser system in class 1000 room

3.7 drive laser

The laser output power: IR laser（1064nm）40W，UV light（266nm）higher than 4W


4. Status of the 3.5cell cavity DC-SRF photo-injector

20MV superconducting accelerator

4. Status of the 3.5cell cavity DC-SRF injector

Cryomodule of the DC-SRF photo-injector


Cryomodule with one 9cell superconducting cavity


2K cryogenic system at PKU


Beam loading test of the 3.5cell cavity DC-SRF injector will be done in the following months.


Thank you！


应用前景2：THz源

PKU-THz Facility Beam Parameters.

Quantity Value

Beam energy 5.38MeV

Charge per beam bunch 20pC

Bunch repetition Rate 81.25MHz

Rms energy Spread ~0.5%

Rms emittance 2.6 mm mrad

bunch length (FWHM) at undulator ~1ps

Quantity Value

Wavelength 400μm ~ 1200μm

Radiation Angel 0.04 rad

Bandwidth 5%

Peak Power ~100 kW

Average Power ~1W

Calculated Optical Parameters

15MV/m

特点：高平均功率（~W）波长400μm ~ 1200μm（0.25~0.75T）大范围可调相干性好，准单色（带宽5%）优越的光脉冲时间结构


应用前景3：基于PKU-ERL的CBS-X射线源

低发射度1um左右，高平均流强mA量级，脉冲电荷量要求并不高

入射角度 20°

光阑半径 5mm

对撞点到探测器距离 2.3m

电子束激光脉冲

能量 27MeV 波长 1064 nm

脉冲电量 77pc 脉冲能量 112 μJ

水平尺寸 191 μm (RMS) 水平尺寸 30 μ m

竖直尺寸 70 μm (RMS) 竖直尺寸 30 μ m

脉冲长度 8 ps 脉冲长度 7 ps(FWHM)

脉冲重复频率81.25 MHz,占空比5％对撞重复频率 81.25 MHz，占空比5％

归一化发射度 1 μ m

相对能散 0.13%

X光子能量 12.5KeV

探测器处光子通

量

（CW模式）1.60×108 (s-1cm-2)

（宏脉冲模式，5%占空比） 8.0×106 (s-1cm-2)

相对谱宽度 0.7%

谱亮度（CW模式）2.04×108

（宏脉冲模式，5%占空比）1.02×107

特色：电荷量要求不很高，基于SRF和ERL

准单色（谱宽度仅为0.7％)

高光子通量，比目前高104量级

波长1Å左右

发展前途：电子束能量进一步提高，硬X射线，γ射线

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介绍三种应用前景，3.5cell的成功研制为将来这些应用前景奠定基础

DC-SRF photocathode injector at Peking University · 2010/12/3. IHIP, Peking University, China. 5....

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Transcript of DC-SRF photocathode injector at Peking University · 2010/12/3. IHIP, Peking University, China. 5....