Introduction to China-ADS Han Li E-mail:han.li@physics.uu.se Nov 3rd, 2014

Contents Background of C-ADS Schematic and Roadmap of the C-ADS program Design considerations for the C-ADS accelerator Key technology R&D on the Spoke012 cavity Summary 2

Background of C-ADS(I) Rapid economy growth in China demands for energy resource. About 4 billion tons standard coal will need in 2050, and the electricity will be 2000 GWe, 20% contributed from nuclear power. 2020 70GWe ( 5% total electricity ) 2030 200GWe ( 10% total electricity ) 2050 400GWe ( 20% total electricity ) May be more than total nuclear power in the world right now ! Nuclear waste will be a bottleneck for nuclear power development.

Background of C-ADS（II） The toxicity of the nuclear wast, mainly due to ionizing radiation, will affect future generations for long into the future. The large quantity and its long-lived toxicity present significant challenges in waste management.

Background of C-ADS（III） The strategy of sustainable fission energy in China is consoled by top Chinese scientists, following are some Advanced Nuclear Energy Programs in China: Fast Reactors (FR) in Advanced Nuclear Fuel Cycles ADS for nuclear waste transmutation As a long-term program, ADS will be supported by CAS. Budgets for C-ADS (Phase 1) have been allocated by the central government. 5

Accelerator Driven sub-critical System Accelerator Driven sub-critical System (ADS) has been recognized as a good option for nuclear waste transmutation. The goals of ADS are followings: 1) With the performances of hard and wide neutron spectra, large flux, powerful transmutation ability for long-lived radiation nucleus, ADS significantly reduce the radiation life time, level and volume of minor actinide and other long-lived nuclear wastes 2) Output extra energy so as to improve the utilization of fuel

ADS project around the world ATW OMEGA EA Accelerator linac editcyclotron energy & current 0.8GeV 100mA /1.5GeV 125mA 1.5GeV 39mA 25mA 1GeV 12.5mA target Liquid Lead Solid tungsten liquid chlorine

Liquid-metal Target (IMP) Schematic of C-ADS Proton Neutron Proton Linear Accelerator (IHEP, IMP) Liquid-metal Target (IMP) Reactor (PbBi coolant ) (IPP, USTC) 8

At 2011, Chinese Academy of Sciences (CAS) started the “Strategic Priority Research Program” named “Future Advanced Nuclear Fission Energy”. As one of the two parts of this program, ADS part will strive for the self-development of the series key technology from test facility to demonstrate facility, and make greater contributions to the national energy supply and sustainable development of nuclear fission energy.

Roadmap of C-ADS program

Main specifications of the C-ADS linac Particle Proton Unit　 Energy 1.5 GeV Current 10 mA Beam power 15 MW Frequency 162.5/325/650 MHz Duty factor 100 % Beam loss <1 (or 0.3) W/m Beam trips /year <25000 <2500 <25 1s<t<10s 10s<t<5m t>5m

Design considerations for the C-ADS accelerator R&D studies for the superconducting cavities for ADS are underway (1)QWR/HWR (2)Spoke Cavity (3) Elliptical cavity 12

Layout of the C-ADS linac Main linac Two identical injectors on line, either with scheme injector-1 or with scheme injector-2

RF cavities for Injector RF cavities based on Injector Scheme-I RFQ frequency: 325 MHz Single-cell spoke cavities (three types: one in injector, two in main linac) RFQ output energy: 3.2 MeV, trade-off between RFQ and low-beta spoke cavities RF cavities in Injector Scheme-II RFQ frequency: 162.5 MHz HWR cavities to reach 10 MeV RFQ output energy: 2.1 MeV, reducing radiation and RFQ requirement (length and vane voltage)

Key technology R&D on the Spoke012 cavity PhD thesis: The design and experimental study of a very low Beta superconducting Spoke cavity for China-ADS

Challenges for very low Beta superconducting Spoke cavity Difficulty in RF design In order to find out an advance spoke cavity structure, which has a better performance in low  region, some new spoke structures have been considered. Poor mechanical properity,due to df/dp Low Beta means short Iirs-Iirs length and smaller resonat volume difficulty in manufacturing Lake of successful experience there is no successful experience for such low Beta Spoke cavity

R&D on superconducting Spoke cavity structure ——3λ/2 Spoke cavity design compare to the traditional λ/2 design， a 3λ/2 Spoke cavity could enlarge the resonat volum in order to reduce the df/dp factor. Spoke009T Spoke012 Lcav (mm) Liris T W Dcav D1 D2 Spoke012 170 74 29 89 438 81 219 Spoke009T 260 160 80 120 476 288 17

comparison researching have been done both for RF and mechanical performance Spoke012 Spoke009T f(MHz） 325 R/Q (Ω)@βopt 135 35 Ep/Eacc 3.2 9.3 Bp/Eacc (mT/MV/m） 4.6 14.6 G(Ω) 53 70 TTF 0.77 0.4 distribution of electronic field in a λ/2 Spoke cavity distribution of electronic field in a 3λ/2 Spoke cavity PS：Eacc is identified as the voltage divied by Liris length 18 curve of trasmit time

mechanical property Spoke012 Spoke009T df/dp (kHz/torr) 18 6.8 tunning sensitivity（kHz/mm） 1319 620 hardness of cavity（mm/980N） 0.58 0.44 deformation of cavity @ 1Bar（mm） 4.5 3.6 Preliminary design study shows that the new structure can significantly improve and enhance the mechanical properties of the cavity, but at the expense of poorer RF parameters. 19

R&D on superconducting Spoke cavity structure ——camber end-wall Spoke cavity design Changing shapes and dimensions of spoke base and end-wall were found to be an useful method in R&D work on enhancing RF performance. Spoke012I Spoke012II Dcav （mm） Lcav Liris T W A1 A2 D1 D2 Spoke012I 438 170 74 29 89 110 280 85 98 Spoke012II 468 180 73 22 82 94 398 90 112.5 20

（1）optimization of Spoke base shape Spoke shape round elliptical racetrack G (Ω) 51 53 70 R/Q0 (Ω) 124 135 93 Epeak/Eacc 5.1 4.8 5.6 Bpeak/Eacc (mT/(MV/m)) 7.7 6.9 6.6 (a)round (b)elliptical (c)racetrack Finally, compared with round and race-track shape, elliptical spoke base has been chosen due to a more uniform magnetic field distribution. 21

The static Lorentz coefficient （2）optimization of end wall A camber end-wall has been selected for a better RF performance and stronger structure. parameters Flat end-wall Camber end-wall Ep/Eacc 4.8 4.4 Bp/Eacc (mT/(MV/m)) 7.0 6.3 G(Ω) 53 61 R/Q（Ω） 135 140 df/dP (pipe free) Peak stress =212 MPa -18 kHz/torr =157 MPa -10.9 kHz/torr Tuning sensitivity 1.3MHz/mm 776.9 kHz/kN 1.0 MHz/mm 399.9 kHz/kN The static Lorentz coefficient (Hz/(MV/m)2) -25.8 -15.1 22

R&D on superconducting Spoke cavity structure ——sphere Spoke cavity design Participated in the R&D work on Multipacting effect (collaborate with PUK ),and give a new design (sphere spoke cavity) which has little MP in operation region. Dcav （mm） Lcav Liris T W D1 D2 Spoke012_A 468 180 73 22 82 112.5 90 Spoke012_B 459 196.6 23 78 89（91） 23

（4）An asymmetrical spoke bar is design for easier assembling In order to destroy the resonace condition, we could change the distribution of surface electromagnetic field by have different fillet radius between end wall and side wall. （3）To make an easier welding, we chang the side wall into a part of a shpere(the geometric center of cavity as the centre of this shpere ) （4）An asymmetrical spoke bar is design for easier assembling （1）enlarge the fillet radius coulde made the Multipacting High-risk areas toward the spoke base. （2）decrease the fillet radius of Spoke base also have a positive effect to reduce the Multipacting. 24

distribution of electromagnitic field Spoke012_B Spoke012_A Frequency 325MHz Geometry factor 63 Ω 61 Ω R/Q 161Ω 142 Ω Ep/Eacc 4.3 4.5 Bp/Eacc 6.5 mT/MV/m 6.4 mT/MV/m TTF 0.76 distribution of electromagnitic field Preliminary design study shows that the sphere structure has a higher R/Q factor which could make a lower surface power loss, while other paramenters are almost the same RF performance as Spoke012_A. 25

Multipacting high-risk area is around the Spoke base and coupler edge Spoke012_A Spoke012_B Multipacting high-risk vs. acceleratinggradient Spoke012_B Spoke012_A Multipacting high-risk area is around the Spoke base and coupler edge 26

mechanical perfprmance Spoke012_A Spoke012_B df/dp 3.26mm/atm -10.89kHz/torr Peak stress=157MPa 1.07mm/atm -3.42kHz/torr Peak stress=91MPa tuning sensitivity 0.38mm/100kg force 1.04MHz/mm 0.37mm/100kg force 1.12MHz/mm Sphere spoke cavity is better than a traditional spoke cavity structure both in RF and mechanical performance. But it has a high challenge for fabrication and there is now no factory could charge this structure in China. 27

Finally, we choose a camber end-wall Spoke cavity design for the first prototype superconducting Spoke012 cavity. 28

In order to maximize the shunt impedance and minimize ratio of Epeak/Eacc and Bpeak/Eacc and then get a higher accelerating gradient, the RF parameters of spoke012 with different geometrical characters then were deeply study , using the CST_MWS software. EM design for Spoke012 Cross section of spoke012 cavity RF parameters of Spoke012 Epeak/Eacc 4.5 Bpeak/Eacc 6.4 mT/(MV/m) G 63Ω R/Q 142Ω results of the simulations

The mechanicl Dsign of Spoke012 Different stifferner have been studied to improve the mechanical stability of Spoke012 cavity. 30

In order to meet the requirements of helium pressure sensitivity and lower the von stress of cavity, the structure of Spoke012 cavity is enhanced by three types of stiffeners, including two circular ribs in the end-wall outer region ,six daisy ribs in the inner region and eight circumferential ribs on the cylindrical portion of the cavity. All stiffeners are made of reactor-grade niobium. 31

deformation and von stress distribution due to cooling down Mechanical simulation for Spoke012 cavity(2) 6 types of Spoke012’s mechanical properties were discussed, including pressure sensitivity, tuning sensitivity, Lorentz force detuning , frequency shift due to cooling down , microphonics and von stress distribution. The simulation results show that stiffener design for Spoke012 has met the requirements. pressure sensitivity analysis with pre-tuning under 1atm (deformation and von stress) deformation and von stress distribution due to cooling down deformation due to microphonics

With stiffener and vessel Mechanical design for Spoke012 cavity(3) The simulation parameters are close to the measured values in HT. Test results indicate that the design of the prototype cavity is successful and may meet the requirements of China-ADS. property Spoke012 Without stiffener With stiffener and vessel df/dP(pipe free) -10.9kHz/torr Von stress=157MPa -156.41Hz/torr Von stress<40MPa df/dP(pipe fixed) -278Hz/torr Von stress=389MPa +40Hz/torr Von stress<50MPa Tuning sensitivity 1.036MHz/mm 1.034MHz/mm The static Lorentz coefficient -15.1Hz/(MV/m)2 -1.3Hz/(MV/m)2 Cooling down （300Kto 4.2K） ______ 463kHz

Fabrication of prototype Spoke012 cavity In collaborations with PKU and HIT universities, two prototype of Spoke012 cavity has been fabricated since 2012. 34

Post-processing of Spoke012 During Buffered Chemical Polishing(BCP), a total etching (~170μm) is obtained with the temperature controlled under 20℃. After BCP, Spoke012-02# was moved to a class 100 clean room for HPR. The cavity was left to dry in the clean room overnight and assembled with other components the next day. The cavity had a 120℃ baking for the next 48 hours.

procedure of calebration

Procedure of vertical test locking the cavity frequency calebration for cables at a low temperature adjust the penetrate length of input atenna to approach VSWR=1 measure the dacay time→ calculate for QL detect the coupling factor (Qe)of every port in a low power condition and get the first Q0 factor check the dacay time and Eacc by different pick up signal increas the input power and measure the Q0 curve vs. Eacc Conditioning（if necessary） measure the highest Eacc of the cavity

Vertical test stand for Spoke012 Vertical test stand for Spoke012 at IHEP include an LLRF control system, vertical cryostat, cryonic system, radiation detection and protection system. Pt Pr signal decay time （ms） Pt 180 Pr 174 spoke012 with hanger 39

VT result of Spoke012 After post processing, the Spoke012-2# prototype cavity without helium vessel was vertical-tested successfully at IHEP.

80K experiment for horizontal test Before horizontal test, room temperature and 80K experiments have been done to make sure the Spoke012-2# prototype cavity and tuner work . Some key parameters of cavity were got, measured value of tuning sensitivity is consist to the design value 1kHz/μm. room temperature experiment 80k experiment

Equipments for Spoke012 Horizental test at IHEP

Development of High power coupler at IHEP

Horizontal test for Spoke012 Spoke012-2# cavity with helium vessel was horizontally tested in the beginning of September 2013 at IHEP. In this test, a serious Multipacting effect played a critical role in the limitation of increasing the accelerating gradient. MP region is consist to the simulation. the maximum accelerating gradient under CW reached 6.5MV/m, and at this gradient, Q0 of the cavity is 2.2×108. 44

Frequency control of Spoke012 at IHEP Some important measured values got from the horizontally test. It’s a very useful guiding design for the frequency control of next Spoke012 cavities. Up to now,Spoke012-3# cavity’s frequency is consist with our expectation.

Development of cryomodule for Spoke cavity at IHEP

Development of RFQ at IHEP A 3 MeV - 10 mA CW RFQ was constructed and commissioned at IHEP. ADS RFQ Frequency 325MHz Energy 3MeV Duty Factor CW Operating Long time

Development of 5-cell elliptical SC cavity at IHEP Two elliptical cavity sections (Ellip063 and Ellip082) to cover energy from 150-180 MeV to 1.5 GeV

Summary Sustainable nuclear energy has high priority in China. The C-ADS program has been officially started under the coordination of CAS, and is led by three CAS institutes. The R&D phase for the driver linac is to build a SC linac with a CW beam of 50-MeV and 10-mA, and relevant infrastructure. It is a great challenge to build a high-performance CW proton linac. Strong collaboration with international leading laboratories is very important. This is not only an important step towards the ADS but also a contribution to the accelerator community. 49

Reference [1]OECD/NEA,Actinide and Fission Product Partitioning and Transmutation,25-29 September 2006 [2]OECD/NEA，Nuclear Energy Data，OECD 2013NEA No. 7162 ，2013 [3]Accelerator-driven Systems (ADS)and Fast Reactors (FR) in Advanced Nuclear Fuel Cycles，OECD 2002， P47-48 [4]Accelerator-driven Systems (ADS)and Fast Reactors (FR) in Advanced Nuclear Fuel Cycles，OECD 2002， P47-48 [5]Y. He et al.，SRF cavity for ADS project in China，Proceedings of SRF2013, 2013, Paris [6]Han Li, doctoral degree thesis in the Graduate School of Chinese Academy of Sciences, 2014

Thanks for your attention！ 51