Fast-bunching design of compact heavy ion RFQ linac

Fast-bunching design of compact heavy ion RFQ linac 1 2 3 first-author 1 1 3 corresp Corresponding author, yinxj@impcas.ac.cn Corresponding author, yinxj@impcas.ac.cn yinxj@impcas.ac.cn 1 1 3 1 3 1 3 1 2 3 1 2 3 1 2 3 1 3 Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China University of Chinese Academy of Sciences, Beijing 100049, China University of Chinese Academy of Sciences, Beijing 100049, China Huizhou Research Center of Ion Science, Huizhou 516003, China Huizhou Research Center of Ion Science, Huizhou 516003, China We propose the construction of a compact linac as the injector of a cancer therapy facility at the Institute of Modern Physics (IMP) of the Chinese Academy of Sciences (CAS). Based on a traditional setup, a new compact fast-bunching design is first introduced to optimize the 600 keV/u RFQ with a 0.05 pmA 12 C 4+ beam. This shortens the RFQ structure length from the standard design value of 272–230 cm, while effectively regulating the particle loss and emittance growth. In addition, a detailed error analysis was performed after the optimization process. The error sources cover input beam parameters errors, machining errors and alignment errors. The simulation results show that the beam loss and emittance growth of the RFQ are acceptable and within typical ranges of error. Linac RFQ Beam dynamics design Fast-bunching. 1 Introduction 1 The RFQ is an essential component of the linac and has a significant advantage with respect to the acceleration of beams with low velocity in the typical range of approximately 0.01–0.06 times the speed of light [ 1 1 ]. In recent years, many compact accelerators have utilized RFQ as injectors in many fields such as cancer therapy research and other radiation-based applications. For instance, hardon radiotherapy has gradually been developed in clinics, and many facilities have been built around the world such as in Germany [ 2 2 ], Japan [ 3 3 , 4 4 ] and China [ 5 5 , 6 6 ]. The injection and extraction energy parameters of some of these RFQ injectors are listed in Table 1 Table 1 [ 7 7 ]. 1 1 Institute/Hospital 1 1 Name of facility 1 1 Location Country 1 1 Injection energy (keV/u) 1 1 Extraction energy (keV/u) 1 1 Heidelberg 1 1 HICAT 1 1 Germany 1 1 8 1 1 400 1 1 CCLRC 1 1 PARMELA 1 1 Warrington 1 1 8 1 1 382 1 1 CNAO 1 1 CNAO 1 1 Italy 1 1 8 1 1 400 1 1 NIRS 1 1 HIMAC 1 1 Japan 1 1 8 1 1 600 1 1 Gunma Univ. 1 1 GHMC 1 1 Japan 1 1 10 1 1 400 Recently, a new linac injector for the carbon ion therapy facility was proposed and designed by IMP. It consists of an ECR ion source, a 162.5 MHz RFQ, a compact Inter-digital H-mode Drift-Tube-Linac (IH-DTL), and beam transport lines. The layout of the linac is shown in Fig. 1 Fig. 1 .The RFQ operates at 0.1% duty factor, and accelerates a 12 C 4+ beam from 8 keV/u to 600 keV/u with a peak current of 0.05 pmA(0.2 emA). In the design process, the peak current is set to 0.1 pmA to maintain current tolerance. The dynamics design of the RFQ, which is mainly directed against space-charge effects, has been extensively investigated worldwide over many years [ 8 8 - 12 12 8-12 ]. However, the requirement of a compact structure is considered to be more important in most radiotherapy facilities than the suppression of the space-charge effect. In such facilities, the structure size impacts cost and can pose construction challenges. In this report, the optimization of the RFQ design will be investigated based on the Gentle-bunching (GB) section of the Four-section design. A new fast-bunching section is introduced to replace the GB section. This results in a compact design of the RFQ while keeping particle loss and emittance growth well-controlled. 2 Dynamics design 1 The dynamics design of the RFQ can be performed using the code PARMTEQM [ 13 13 ] which is widely used [ 14 14 , 15 15 ] and important parameters such as the input energy and the inter-vane voltage should be defined in advance. In the design process, a high input energy results in a long RFQ cavity due to the cell length and the effect of the bunching process, which generally leads to a decrease of the accelerating gradient of the RFQ. The ion source extraction voltage is usually chosen to be 20 to 30 kV for the C 4+ ions as shown in Table. 2 Table. 2 [ 7 7 ]. The extraction voltage of this source should be chosen to match two conditions: one is an adequate beam intensity with a relatively good quality and the other is a reduction of the sparking risk. A suitable inter-vane voltage is required in an RFQ to effectively maintain the radial focusing strength and accelerating gradient. However, this value is restricted by the maximum surface field of the electrode. Finally, the intervane voltage is chosen in the range of 70 to 80 kV. 1 1 Name of facility 1 1 Charge state of C ions 1 1 Extraction voltage (kV) 1 1 HIMAC 1 1 2+/4+ 1 1 48/24 1 1 HIBMC 1 1 4+ 1 1 25 1 1 HIRFL-CSR 1 1 4+ 1 1 20 1 1 HIT 1 1 4+ 1 1 24 1 1 GHMC 1 1 4+ 1 1 30 1 1 CNAO 1 1 4+ 1 1 24 1 1 PTC-Marburg 1 1 4+ 1 1 24 1 1 NRoCK 1 1 4+ 1 1 24 A basic dynamics design of the proposed RFQ was performed by PARMTEQM after reiterating the important parameters previously mentioned. However, a few problems were encountered. For example, the beam size could not be well controlled when it entered the GB section as shown as in Fig. 6 Fig. 6 , which impacts the transmission efficiency and the beam quality due to abrupt changes in certain parameters and phase advance resonances. On the other hand, the length of the electrode is 2.7 m. The fabrication of such an electrode in one segment will be difficult in standard machining environments. Thus, the best approach is to reduce the length or separate the electrodes into segments for machining. The optimization procedure was repeated to achieve an optimal design with a maximum transmission efficiency, and a minimum emittance growth and structure length. Some specifications and constraints are listed as follows: 1. For the proposed RFQ operating with 0.1% duty factor, the maximum surface field is constrained to lower than 27.2 MV/m. This corresponds to a Kilpatrick factor [ 16 16 ] of less than 2.0 at 162.5 MHz. 2. The structure length should be less than 2.5 m to minimize construction costs and power requirement. 3. Beam transmission efficiency should be as high as possible. 4. Phase advance resonances should be avoided. Parametric resonance and coupling between the transverse and the longitudinal phase space are avoided by changing the focusing factor B along the cells. The B changes with the transverse RF defocusing force to maintain the transverse beam movement in dynamic balance [ 10 10 , 20 20 ]. In addition, abrupt changes of parameters at the junctions are smoothed to improve the transmission efficiency [ 8 8 ]. The traditional RFQ dynamics design is based on Kapchinsky’s adiabatic bunching condition [ 22 22 ]. Under this condition, the geometric length of the separatrix is almost constant in spite of the increase in the velocity of particles, which can reduce the impact of the space charge effect. In a traditional design, the RFQ is divided into four sections: radial matching, shaping, gentle bunching(GB), and accelerating sections. The GB-section where the Kapchinsky’s condition is applied could be further divided into pre-bunching (small m and slow m ramping) and bunching (fast m ramping) sections [ 23 23 ]. The space-charge effect is not strong in the proposed RFQ for a compact linac design, and the GB-section can be shortened to preserve length for the accelerating section. A short fast-bunching section is introduced to substitute for the long adiabatic pre-bunching section. The parameter S which is almost proportional to the separatrix area is used for optimization of the fast-bunching section. S is defined as [ 23 23 ]: <math display="block" id="M1"><mrow><mi>S</mi><mo>=</mo><msqrt><mrow><mrow><mo>|</mo><mi>Δ</mi><mo>|</mo></mrow></mrow></msqrt><msup><mi>β</mi><mn>2</mn></msup><msup><mi>γ</mi><mn>3</mn></msup><mi>g</mi><mo stretchy="false">(</mo><msub><mi>ϕ</mi><mtext>s</mtext></msub><mo stretchy="false">)</mo><mn>,</mn></mrow></math> where, <math display="block" id="M2"><mrow><mi>Δ</mi><mo>=</mo><mfrac><mrow><msup><mi>π</mi><mn>2</mn></msup><mi>q</mi><mi>A</mi><mi>V</mi><mi>sin</mi><mo stretchy="false">(</mo><msub><mi>ϕ</mi><mtext>s</mtext></msub><mo stretchy="false">)</mo></mrow><mrow><mn>2</mn><mi>m</mi><msup><mi>c</mi><mn>2</mn></msup><msup><mi>β</mi><mn>2</mn></msup></mrow></mfrac><mn>,</mn></mrow></math> <math display="block" id="M3"><mrow><mi>g</mi><mo stretchy="false">(</mo><msub><mi>ϕ</mi><mtext>s</mtext></msub><mo stretchy="false">)</mo><mo>=</mo><mo stretchy="false">(</mo><mi>ψ</mi><mo>/</mo><mn>2</mn><mi>π</mi><mo stretchy="false">)</mo><msqrt><mrow><mn>1</mn><mo>−</mo><msub><mi>ϕ</mi><mtext>s</mtext></msub><mi>cot</mi><mo stretchy="false">(</mo><msub><mi>ϕ</mi><mtext>s</mtext></msub><mo stretchy="false">)</mo></mrow></msqrt><mn>,</mn></mrow></math> A is the accelerating efficiency, V is the inter-vane voltage, ϕ s is the synchronous phase angle, ψ is the phase width, β is the synchronous velocity, γ is the Lorentz factor, q is the charge, and m is the rest mass of the ion. An increase in S is important in forming a good beam bunch under the influence of a strong space-charge force. However, for low-current dynamics, this parameter could be kept at a constant, which facilitates faster beam bunching with sufficiently high transmission [ 23 23 ]. The parameter S can be kept almost constant in the fast-bunching section through optimization of the modulation factor m and the synchronous phase angle ϕ s . The modulation factor grows faster compared to the case of a traditional design. Fig. 2 Fig. 2 shows the optimized parameter curves of the fast-bunching section. When the optimized m factor of the fast-bunching is compared with a traditional m factor, the platform at the pre-bunching section almost vanishes. Moreover, the entire length of the RFQ is shortened based on the premise of ensuring particle transport, and the RFQ acceleration efficiency is increased. Additionally, the shaping section is optimized to allow the beam to transmit effectively during the fast-bunching process. In this section, the m factor is optimized to a relatively low value, which decreases the separatrix height in the RFQ entrance and maintains a sufficient acceptance for the input beam. Fast-bunching is used to create a more compact structure by ignoring the space-charge effect. As the beam current is increased, the fast-bunching process terminates, therefore, the current limits the application range of the fast-bunching design. Fig. 3 Fig. 3 shows the impact of an increase of the current in the fast-bunching process. The beam experiences dispersion in the longitudinal phase space, since the longitudinal phase advance, decreases as the space charge effect increases. This impacts the beam transmission and quality in the bunching process. The current should be lower than 1.0 pmA in the design of the 162.5 MHz RFQ. This can be realized by analyzing the influence of the current increase on the fast-bunching process. Fig. 4 Fig. 4 and Table. 3 Table. 3 show the parameters of the 162.5 MHz RFQ dynamics design after optimization. The final Kilpatrick factor of the design is 1.83. In the case of the fast-bunching design, phase advance resonances are avoided, the transmission efficiency is increased, and the structure length is shortened. A transmission efficiency of 99.3% is obtained with an RFQ length of 230 cm. 1 1 Parameter 1 1 Traditional 1 1 Fast-buncher 1 1   1 1 design 1 1 design 1 1 Frequency (MHz) 1 1 162.5 1 1 162.5 1 1 Beam current (euA) 1 1 200 1 1 200 1 1 Input energy (keV/u) 1 1 8 1 1 8 1 1 Output energy (keV/u) 1 1 601.93 1 1 601.45 1 1 Duty factor (%) 1 1 1 1 1 1 1 1 Kilpatrick factor 1 1 1.82 1 1 1.83 1 1 Minimum aperture (a) (cm) 1 1 0.28 1 1 0.3 1 1 Average aperture (r0) (cm) 1 1 0.42 1 1 0.45 1 1 Input trans. emit. ( π mm ⋅ mrad) 1 1 0.200 1 1 0.200 1 1 Output trans. emit. ( π mm ⋅ mrad) 1 1 0.200 1 1 0.199 1 1 Output longitudinal emit. ( π MeV ⋅ deg) 1 1 0.434 1 1 0.242 1 1 Length of the vane (cm) 1 1 272.89 1 1 230.14 1 1 Transmission efficiency (%) 1 1 95.5 1 1 99.3 The simulation results of the PARMTEQM are shown in the Fig. 5 Fig. 5 and Fig. 6 Fig. 6 . The number of particles in the simulation is 10000. The particles are judged to be lost when their energy deviates from that of the synchrotron particle by more than 5%. The sum of the lost particles and transverse emittance is clearly reduced in the optimized design as shown in Fig. 7 Fig. 7 . It is observed that the loss peak in the optimization design occurs at approximately cell-180, because the fast-bunching process causes the separatrix to shrink quickly. The particles at the edge of the separatrix will be lost longitudinally when the beam enters the accelerating section. 3 Error analysis 1 The tolerance of the RFQ for a non-ideal input beam directly influenced the beam stability and quality. Both the operating stability of the ion source and the ripple of the LEBT power supplies impact the beam parameters at the RFQ entrance [ 17 17 , 18 18 - 19 19 18-19 ]. It is difficult to adjust the parameters of the beam to satisfy dynamics design during actual operation. Consequently, it is necessary to perform the error analysis at the entrance of the RFQ. The results are shown in Fig. 8 Fig. 8 . The design values of the beam parameters at the entrance of the RFQ are ε t =0.2 π mm ⋅ mrad (Norm. RMS), the beam current of 0.1 pmA, and the energy of 8 keV/u with zero energy spread and 360° phase width. The controlling variables method was used during the simulation. One of the parameters such as the emittance, current or energy spread of the input beams is adjusted while the other parameters are kept constant in the simulations. The Fig. 8 Fig. 8 shows the relationship between some input beam parameters and the transmission efficiency. A large emittance which is indicative of a large beam size and divergence, will decrease the transmission efficiency. The transmission efficiency is approximately 95% with 6% energy spread when the emittance is 0.35 π mm ⋅ mrad. This energy spread is much greater than that produced by the LEBT. When the beam current is 0.8 pmA, the transmission efficiency is maintained at 96%. This current tolerance satisfies the requirement of the accelerator and provides a large space for subsequent upgrading. Except for the impact of a non-ideal input beam on the RFQ, there are some errors which result from fabrication, assembling, and operation. Some of these errors may adversely affect the beam transmission in the RFQ. As such, it is necessary to perform an error analysis of the RFQ. In this regard, we performed 1000 simulations using the TraceWin code. The error setting includes five items as shown in Table. 4 Table. 4 . The errors are uniformly distributed in the ranges listed in Table 4 Table 4 . 1 1 Parameters 1 1 Range 1 1 Distribution 1 1 Uniformly 1 1 dR (mm) 1 1 ±0.1 1 1 d (mm) 1 1 ±0.1 1 1 ϕ (°) 1 1 ±1 1 1 Δ T (mm) 1 1 ±0.2 1 1 Δ L (mm) 1 1 ±0.2 The dR value refers to the error of the electrode pole radius, and the d refers to the error of the depth of the modulation curve. Both of these values are set to 0.1 mm based on prior experience with SSC-Linac fabrication. The ϕ refers to the error of the RF phase, which is determined by the precision of the RF phase control system. The Δ T and Δ L are the cavity position offsets produced during installing, which are set by the precision of the collimation. Based on the analysis of 1000 sets of errors, the probability distribution of the beam loss is determined using TraceWin simulations as shown in the Fig. 9 Fig. 9 . The calculated transmission efficiency is slightly higher than that of PARMTEQM, because the electric field and the beam loss criteria are different [ 24 24 ]. As shown in Fig. 9(a) Fig. 9(a) , it is 70% more likely to maintain the transmission efficiency above 97% when the fabrication and operation errors are considered. In Fig. 9(b) Fig. 9(b) , an emittance growth of less than 15% is highly feasible. This value will exceed not 30% when the RFQ error is taken into account. The emittance growth satisfies the operational requirement, and therefore, this dynamics design could be used for fabrication. 4 Summary 1 A new RFQ design method which uses a fast-bunching section instead of the traditional GB section is developed for a compact, low-intensity linac. The design is constrained by the condition that the S parameter could be kept almost constant when the space-charge effect is not strong. In the case of IMP cancer therapy RFQ, very low beam loss is achieved using a fast longitudinal bunching process. Finally, bunching design is adopted to meet the strict requirements of a short length. This proposed method could benefit the next generation of RFQs for medical and nuclear physics applications where the current is relatively low, and the space-charge is not important. References T. Wangler , RF Linear Accelerators ( 2008 ),p.46. RF Linear Accelerators H. Eickhoff , R. Bar , A. Dolinskii , et al ., HICAT - the German hospital-based light ion cancer therapy project . Paper presented at Particle Accelerator Conference , 2003 . PAC 2003 . HICAT - the German hospital-based light ion cancer therapy project K. Kawachi , T. Kanai , M. Endo , et al ., Radiation oncological facilities of the HIMAC . J Jpn Soc Ther Radiol Oncol , 1 , 19 - 29 ( 1989 ).. Radiation oncological facilities of the HIMAC T. Ohno , T. Kanai , S. Yamada , et al ., Carbon Ion Radiotherapy at the Gunma University Heavy Ion Medical Center: New Facility Set-up . Cancers , 3 ( 4 ), 4046 - 4060 ( 2011 ). doi: 10.3390/cancers3044046 http://doi.org/10.3390/cancers3044046 Carbon Ion Radiotherapy at the Gunma University Heavy Ion Medical Center: New Facility Set-up T. Ohno , Particle radiotherapy with carbon ion beams . The Epma Journal , 4 ( 1 ), 9 - 9 ( 2013 ). doi: 10.1186/1878-5085-4-9 http://doi.org/10.1186/1878-5085-4-9 Particle radiotherapy with carbon ion beams J.C. Yang , J. Shi , W.P. Chai , et al ., Design of a compact structure cancer therapy synchrotron . Nuclear Inst Methods in Physics Research A , 756 ( 16 ): 19 - 22 ( 2014 ). doi: 10.1016/j.nima.2014.04.050 http://doi.org/10.1016/j.nima.2014.04.050 Design of a compact structure cancer therapy synchrotron A. Kitagawa , T. Fujita , M. Muramatsu , et al ., Review on heavy ion radiotherapy facilities and related ion sources . Review of Scientific Instruments , 81 ( 2 ): 295 ( 2010 ). doi: 10.1063/1.3268510 http://doi.org/10.1063/1.3268510 Review on heavy ion radiotherapy facilities and related ion sources G. Liu , Y.R. Lu , Y. He , et al ., Design of a CW high charge state heavy ion RFQ for SSC-LINAC . Nuclear Instruments Methods in Physics Research Section A Accelerators Spectrometers Detectors Associated Equipment , 701 ( 3 ): 186 - 193 ( 2013 ). doi: 10.1016/j.nima.2012.11.017 http://doi.org/10.1016/j.nima.2012.11.017 Design of a CW high charge state heavy ion RFQ for SSC-LINAC C. Li , Sun. L , Y. He , et al ., Conceptual design of LEBT and RFQ for the HIAF linac . Nuclear Instruments Methods in Physics Research Section A Accelerators Spectrometers Detectors Associated Equipment , 2013 : 426 - 433 . doi: 10.1016/j.nima.2013.06.019 http://doi.org/10.1016/j.nima.2013.06.019 Conceptual design of LEBT and RFQ for the HIAF linac C. Zhang , Z.Y. Guo , A. Schempp , et al ., Low-beam-loss design of a compact, high-current deuteron radio frequency quadrupole accelerator , Physical Review Special Topics - Accelerators and Beams , 7 ( 10 ): 100101 ( 2004 ). doi: 10.1103/PhysRevSTAB.7.100101 http://doi.org/10.1103/PhysRevSTAB.7.100101 Low-beam-loss design of a compact, high-current deuteron radio frequency quadrupole accelerator R. Gaur , P. Shrivastava . Beam Dynamics and Electromagnetic Design Studies of 3 MeV RFQ for SNS Programme , Journal of Electromagnetic Analysis and Applications , 2010 , 02 ( 09 ): 519 - 528 . doi: 10.4236/jemaa.2010.29068 http://doi.org/10.4236/jemaa.2010.29068 Beam Dynamics and Electromagnetic Design Studies of 3 MeV RFQ for SNS Programme C. Xiao , Y. He , et al ., Particle-In-Cell Simulation of RFQ in SSC - Linac ., arXiv: Accelerator Physics , 2010 . Particle-In-Cell Simulation of RFQ in SSC - Linac K.R. Crandall , T.P. Wangler , L.M. Young , et al ., RFQ Design Codes, LA-UR-96-1836 . RFQ Design Codes, LA-UR-96-1836 Y.S. Cho , Design of a 200-MHz RFQ for 3-MeV He beam irradiation . Journal of the Korean Physical Society , 63 ( 7 ): 1327 - 1331 ( 2013 ). doi: 10.3938/jkps.63.1327 http://doi.org/10.3938/jkps.63.1327 Design of a 200-MHz RFQ for 3-MeV He beam irradiation X. Yan , K. Zhu , Y. Lu , et al ., Design of RFQ Accelerator Facility of PKUNIFTY , Physics Procedia , 26 , 79 - 87 ( 2012 ). doi: 10.1016/j.nima.2010.12.028 http://doi.org/10.1016/j.nima.2010.12.028 Design of RFQ Accelerator Facility of PKUNIFTY R.A. Jameson , NEW LINAC TECHNOLOGY -FOR SSC, AND BEYOND? * Paper presented at International Conference on High-Energy Accelerators , Fermi National Accelerator Laboratory , Batavia, Il . August. 2011 . NEW LINAC TECHNOLOGY -FOR SSC, AND BEYOND? * X.H. ZHANG , Y.J. Yuan , J.W. Xia , et al ., Instability Research of 53.667 MHz Heavy Ion RFQ , J.Atomic Energy Science and Technology , 49 ( 5 ): 951 - 954 . doi: 10.7538/yzk.2015.49.0500951 http://doi.org/10.7538/yzk.2015.49.0500951 Instability Research of 53.667 MHz Heavy Ion RFQ T. Sen , M.J. Syphers . Effect of power supply ripple on emittance growth in the collider, Particle Accelerator Conference, 1993 . Proceedings of the . IEEE , 1993 : 146 - 148 vol. 1 . Effect of power supply ripple on emittance growth in the collider, Particle Accelerator Conference, 1993 Y. Cao , J. Li , L T. Sun , et al . An all permanent magnet electron cyclotron resonance ion source for heavy ion therapy . [J]. Review of Scientific Instruments , 2014 , 85 ( 2 ). doi: 10.1063/1.4852335 http://doi.org/10.1063/1.4852335 An all permanent magnet electron cyclotron resonance ion source for heavy ion therapy X.H. Zhang , Y.J. Yuan , J.W. Xia , et al ., Conceptional design of a heavy ion linac injector for HIRFL-CSRm . China physics C:English , 38 ( 6 ): 74 - 81 ( 2014 ). doi: 10.1088/1674-1137/38/10/107002 http://doi.org/10.1088/1674-1137/38/10/107002 Conceptional design of a heavy ion linac injector for HIRFL-CSRm X.Q. Yan , J.X. Fang , Z.Y. Guo , et al ., The beam mismatches in the RFQ dynamics design . Nuclear Instruments Methods in Physics Research , 554 ( 1-3 ): 132 - 137 ( 2005 ). doi: 10.1016/j.nima.2005.08.067 http://doi.org/10.1016/j.nima.2005.08.067 The beam mismatches in the RFQ dynamics design M. Weiss , Radio-frequency quadrupole . Language , 1995 . Radio-frequency quadrupole S. Yamada . Buncher section optimization of heavy ion RFQ linacs [J]. 1981 : 316 - 318 . Buncher section optimization of heavy ion RFQ linacs K. Zhu , Y. R. Lu , X. J. Yin , et al . The beam commissioning of a CW high charge state heavy ion RFQ , J. Nuclear Instruments Methods in Physics Research , 2015 , 794 ( 3 ): 113 - 121 . doi: 10.1016/j.nima.2015.05.012 http://doi.org/10.1016/j.nima.2015.05.012 The beam commissioning of a CW high charge state heavy ion RFQ The authors would like to give special thanks to Prof. Yuan-Rong Lu at Peking University for his helpful suggestions, and to several other individuals of the Institute of Modern Physics, CAS, for their help and support. 10.1007/s41365-018-0514-x This work was supported by the National Natural Science Foundation of China (No.11375243) and the Guangdong Innovative and Entrepreneurial Research Team Program (No. 2016ZT06G373). 2018-04-11 2018-05-28 2018-06-23 2018-11-23 2018-12-01 2021-12-20 © China Science Publishing & Media Ltd. (Science Press), Shanghai Institute of Applied Physics, the Chinese Academy of Sciences, ChineseNuclear Society and Springer Nature Singapore Pte Ltd. 2018 This is a post-peer-review, pre-copyedit version of an article published in Nuclear Science and Techniques. The final authenticated version is available online at: http://dx.doi.org/10.1007/s41365-018-0514-x http://dx.doi.org/10.1007/s41365-018-0514-x . 2018 Nuclear Science and Techniques 12 29