Design and commissioning of B_rav measurement system for SC200 superconducting cyclotron

Design and commissioning of B rav measurement system for SC200 superconducting cyclotron 1 first-author 2 2 corresp Corresponding author, chengen@ipp.ac.cn Corresponding author, chengen@ipp.ac.cn chengen@ipp.ac.cn 2 2 3 3 2 School of Mechanical and Automotive Engineering, Anhui Polytechnic University, Wuhu 241000, China School of Mechanical and Automotive Engineering, Anhui Polytechnic University, Wuhu 241000, China Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230026, China Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230026, China Hefei CAS Ion Medical and Technical Devices Co., Ltd, Hefei 230088, China Hefei CAS Ion Medical and Technical Devices Co., Ltd, Hefei 230088, China The SC200 proton therapy superconducting cyclotron was developed by ASIPP (Hefei, China) and JINR (Dubna, Russia). A measurement system was designed to assess the average radial component of the magnetic field ( B rav ) with 15 search coils in the median plane. The winding differences of the search coils affect the measurement accuracy of the B rav . Based on the electromagnetic induction principle, to measure the B rav accurately, this paper focuses on the design and commissioning of the B rav measurement system. The preliminary results confirm that the system design is reasonable and suitable. After testing the search coil at different speeds, the optimal speed was determined as 2.5 mm/s. The relative error was approximately 0.1% under the maximum radial component of the magnetic field B r of 7 G. The measurement precision was up to 1.0×10 -3 , which can provide the required measurement tolerance of 3–7 G for B r in the median plane. The commissioning of the B rav measurement system is an important step for B r measurement. It can check and adjust the asymmetry of the superconducting coils (SCs). Superconducting cyclotron Magnetic field Measurement system Commissioning 1 INTRODUCTION 1 The SC200 proton therapy superconducting cyclotron will be able to accelerate protons to an energy of 200 MeV with a maximum beam intensity of 1 μA. The average magnetic field of the cyclotron is up to 3.6 T [ 1 1 - 2 2 1-2 ]. As a key component of the cyclotron, the superconducting magnet provides the isochronous magnetic field with a strong focusing force to restrict beam movement. However, the asymmetry of sectors and the superconducting coils (SCs) generates a radial component, B r , of the magnetic field in the median plane, directly affecting the vertical deviation of the beam orbit from the median plane [ 3 3 - 6 6 3-6 ]. A number of measurement methods have been proposed to measure the average radial component of the magnetic field ( B rav ), including nuclear magnetic resonance (NMR) [ 7 7 ], hall probes [ 8 8 - 10 10 8-10 ], and flux measurements with search coils [ 3 3 ][ 11 11 - 14 14 11-14 ]. To design such a measurement system, the field strength, homogeneity, variation in time, and required accuracy should be considered 8 . Search coils are highly sensitive and less strongly influenced by the vertical component of the magnetic field ( B z ), which is more accurate than the hall probes for magnetic field measurement. The use of a variety of search coils is the most-often used tool for characterizing field qualities in cyclotrons [ 15 15 - 18 18 15-18 ]. For SC200, the B rav measurement system was designed to measure the B rav of the magnetic field by using search coils with a high testing accuracy. The B rav measurement system mainly includes a drive system, control system, and data acquisition system. In particular, based on the electromagnetic induction principle, there are 15 search coils moving in the magnetic field to measure the B rav . The minimum and maximum measurement radii were 30 mm and 620 mm, respectively. The search coils are made of copper and covered with an insulating varnish. Owing to the quality differences in the winding process, it is necessary to perform the commissioning of the search coil outside of the SC200 cyclotron. In this study, we present develop a detailed design and investigate the required commissioning work to improve B rav measurement accuracy. This paper describes the B rav tolerance analysis, the commissioning platform design, and research. The analysis and results are of great significance for the B r measurement of the SC200 proton therapy superconducting cyclotron. 2 B _rav TOLERANCES FOR SC200 SUPERCONDUCTING CYCLOTRON 1 Owing to the asymmetry of sectors and SCs, the B rav existing in the Azimuth-Varied Field cyclotron, which causes the effective median plane (EMP) of the magnetic system, does not coincide with the median plane of the cyclotron. The EMP was formulated by J. I. M. Botman and H. L. Hagedorn for the cyclotron work region [ 3 3 ]. Thus, the tolerances for the B rav of the magnetic field should be estimated. When the magnetic system symmetry is broken, stable vertical oscillations exist near the EMP. The horizontal field component exists in the median plane. To separately identify the tolerances for the horizontal field components from the permitted vertical beam offset, the B rav can be written as <math display="block" id="M1"><mrow><msub><mi>B</mi><mrow><mtext>rav</mtext></mrow></msub><mo> </mo><mo>=</mo><msub><mi>Z</mi><mrow><mtext>eff</mtext></mrow></msub><msub><mi>B</mi><mrow><mtext>zav</mtext></mrow></msub><msub><mi>Q</mi><mtext>z</mtext></msub><msup><mrow/><mn>2</mn></msup><mo>/</mo><mi>R</mi><mo>,</mo></mrow></math> where Z eff is the vertical position of the EMP, B zav is the average vertical component of the magnetic field at radius R , Q z represents the vertical betatron frequency, and R is the magnetic field radius. The SC200 superconducting cyclotron has been proposed and designed [ 17 17 , 19 19 - 21 21 19-21 ]. The isochronous field B zav distribution is shown in Fig.1(a) Fig.1(a) , and the maximum magnetic field was approximately 3.54 T [ 20 20 , 22 22 ]. From the computed vertical betatron frequency Q z in Fig.1(b) Fig.1(b) , Eq. (1) shows the tolerance distribution of B rav for the acceptable vertical offset of the beam of 1 mm shown in FIG.2 FIG.2 . With the frequency Q z close to 0.32 in the extraction region, the isochronous field B zav was approximately 3.54 T. The B rav tolerance in the median plane was approximately 3–7 G, shown in Fig.2 Fig.2 . Consequently, the testing resolution of the B rav measurement system should be smaller than 1 G. 3 COMMISSIONING PLATFORM DESIGN 1 3.1 TESTING PRINCIPLE 2 The magnetic flux distribution produced by the test coil had an excitation current of 2 A, as shown in Fig.3 Fig.3 . It generates a magnetic field of 3–7 G, the same as the magnetic field B rav tolerance of SC200 superconducting cyclotron. A commissioning diagram comprising a test coil and 15 concentric search coils is shown in Fig.4 Fig.4 . According to the electromagnetic induction principle, when the search coils move in the magnetic field, the induced voltage U is generated, which can be integrated by the fluxmeter. The testing flux change △ Φ t can be written as <math display="block" id="M2"><mrow><mtext>Δ</mtext><msub><mi>Φ</mi><mtext>t</mtext></msub><mo>=</mo><mstyle displaystyle="true"><mrow><mo>∫</mo><mi>U</mi></mrow></mstyle><mtext>d</mtext><mi>t</mi><mo>.</mo></mrow></math> The radial component change △ B r can be calculated using <math display="block" id="M3"><mrow><mi>Δ</mi><msub><mi>B</mi><mtext>r</mtext></msub><mo>=</mo><mi>Δ</mi><msub><mtext>Φ</mtext><mtext>t</mtext></msub><mo>/</mo><mi>A</mi><mo>.</mo></mrow></math> The effective sensitive area of the search coil A is <math display="block" id="M4"><mrow><mi>A</mi><mo>=</mo><mi>N</mi><mo>⋅</mo><mn>2</mn><mi>π</mi><mi>R</mi><mo>⋅</mo><mn>2</mn><mi>Δ</mi><mi>Z</mi><mo>.</mo></mrow></math> where N is the number of search coil turns, R is the coil radius, and Δ Z is the distance shift from the median plane. The search coil was first connected to the fluxmeter, which was shifted from its initial position of –Δ z to a terminal position of +Δ z . The fluxmeter acquired the magnetic flux generated by the coil. Subsequently, the other coils were changed to connect to the fluxmeter, and the previous steps were repeated. 3.2 PLATFORM DESIGN 2 Based on the testing principle, the search coils must be a priority during design. The search coils comprised copper wire, with a diameter of 0.3 mm, covered with insulating varnish. The search coils were numbered from C1 to C15. Each coil could be connected to the LINKJOIN LZ840 fluxmeter by a coil selector. Then, the coil parameters, including the radius, the number of turns, and the coil resistance, were sent to the fluxmeter. The distribution of the search coils on the disk is shown in FIG.5 FIG.5 . The input coil parameters are shown in Table I Table I . 1 1 Coil No. 1 1 C1 1 1 C2 1 1 C3 1 1 C4 1 1 C5 1 1 C6 1 1 C7 1 1 C8 1 1 C9 1 1 C10 1 1 C11 1 1 C12 1 1 C13 1 1 C14 1 1 C15 1 1 Radius R (mm) 1 1 30 1 1 55 1 1 80 1 1 105 1 1 130 1 1 155 1 1 180 1 1 205 1 1 230 1 1 255 1 1 280 1 1 305 1 1 330 1 1 355 1 1 380 1 1 Number of turns N 1 1 34 1 1 26 1 1 20 1 1 16 1 1 10 1 1 10 1 1 8 1 1 8 1 1 8 1 1 6 1 1 6 1 1 6 1 1 6 1 1 6 1 1 6 1 1 Coil resistance（Ω） 1 1 7.705 1 1 7.822 1 1 8.038 1 1 7.847 1 1 7.914 1 1 8.15 1 1 8.051 1 1 8.236 1 1 8.547 1 1 7.91 1 1 8.108 1 1 8.237 1 1 8.53 1 1 8.622 1 1 8.855 The commissioning platform of the B rav measurement system was designed with a drive system, control system, and data acquisition system, as shown in Fig.6 Fig.6 . The self-aligning system includes two groups of cross screws and linear guide structures. These institutions can adjust the disk center coinciding with the geometric center of the superconducting cyclotron. The drive system can drive the search coils to move along the vertical axis of the cyclotron. The control system comprises the parameter settings area, the data and status display area, and the logic control area. The data acquisition system is responsible for collecting the measurement signals. The LINKJOIN LZ840 fluxmeter collects the flux signal with high sensitivity, which should be warmed for five minutes and done zero setting and drift setting before using. To avoid the magnetic field influence from B z , it is necessary to adjust and confirm the relative position between the test coil and search coil. An angular error of 1 mrad will produce an approximately tenfold error in the B r value. Therefore, the parallelism of the search coil and test coil must be less than 0.4 mm, and that of the concentricity must be less than 0.5 mm. In this way, the B r value will not be influenced by the B z value. 4 COMMISSIONING AND DISCUSSION 1 To confirm that the B rav measurement system operates well, based on the testing principle above, system commissioning should be conducted outside the cyclotron. The drive system made the search coils move from their initial position of -10 mm to the terminal position of +10 mm. The fluxmeter acquired the first flux Φ 1 generated by the first search coil C1. Subsequently, the second flux Φ '1 was generated when the disk moved in reverse. Following this, C2 was switched to connect to the fluxmeter, and the previous steps were repeated. This was performed sequentially until coil C15, and all the measurement data were collected for further analysis. We found that the coil speed affects the B rav results. Thus, the testing was conducted with five different speeds in the range of ±10 mm. The collected flux was fitted by the least square method. The B rav was calculated using Eq.3 in FIG.7 FIG.7 , and the trend of the B rav curves are consistent. The theoretical value ( B rth )was provided by the TOSCA software. The B rav was closer to the B rth as the coil speed increased from 1 mm/s to 2.5 mm/s. There were no obvious relative error changes between the 2.5 mm/s and 3 mm/s speeds. Compared with B rth , the relative error of B rav was calculated and is shown in FIG.8 FIG.8 . The relative error of B rav with a speed of 2.5 mm/s was the smallest. The relative error of the curves is greater in two edge radius ranges. When increasing the coil speed, the flux variation within a unit time will increase correspondingly. Thus, the signal-to-noise ratio will be promoted. For the fluxmeter, the disturbance caused by noise will comprise a smaller proportion and the measurement results will be more accurate at the points where the value of the signal-to-noise ratio is larger. Otherwise, owing to the structure parameters of the fluxmeter, the original right signal completely becomes the interfering signal. In the case of a severe signal drift, the effective signal is often submerged. Therefore, 2.5 mm/s is considered to be the optimal speed for the search coil. Following this, the search coils were shifted four times with a speed of 2.5 mm/s. The B rav distributions were deduced and are shown in Fig.9 Fig.9 . The B rth and B rav curves are consistent, as shown in Fig.10 Fig.10 . The B rav denotes the average measured value from four B rav values. As shown in Fig.11 Fig.11 , the relative error curve first increases then decreases with the radius increase. The minimum error occurred at R = 205 mm, corresponding to C8. The minimum relative error was 0.09513% with a B rav of 7 G, which continued increasing to approximately 12.37% for B rav of 1 G at the edge point. In addition, the smallest absolute error and biggest absolute error of △ B rav were 0.006857 G and 0.05402 G, respectively, both less than 1 G. The measurement accuracy of the B rav changed with the radial location. For the radial range of 0-205 mm, the magnetic field intensity increased together with the measuring accuracy. For the radial range of 205-380 mm, the measuring accuracy decreased. There is a low intensity at both ends of the B r distribution curve as the measurement accuracy is susceptible to interference. The measurement accuracy was high under the high intensity field in the middle radial position. 5 CONCLUSION 1 In summary, this paper presents the detailed design and commissioning for a B rav measurement system. The commissioning platform was designed to verify the measurement precision based on the electromagnetic induction principle. Under the testing magnetic field, the coil speed of 2.5 mm/s is considered to be the optimal speed for the search coil. The relative error was approximately 0.1% under the maximum B r of 7 G. The measurement precision reached 1.0×10 -3 , which satisfies the measurement requirements. The analysis and results are of great significance for the B r measurement of the SC200 proton therapy superconducting cyclotron. However, the measurement error of the system exceeds 10% in edge radius ranges; thus, in future, we must improve the measurement precision by optimizing the system structure or researching a reasonable optimization method. Reference G. A. Karamysheva , O. V. Karamyshev , N. A. Morozov et al ., Magnetic system for SC200 superconducting cyclotron for proton therapy , Proceedings of Cyclotrons 2016 , Zurich, Switzerland , Cyclotrons , 353 - 355 ( 2016 ). doi: 10.18429/JACoW-Cyclotrons2016-THC03 http://doi.org/10.18429/JACoW-Cyclotrons2016-THC03 Magnetic system for SC200 superconducting cyclotron for proton therapy M. M. Xu , Y. T. Song . Conceptual Design of Scanning Magnets for Superconducting Proton Therapy Facility [J]. IEEE Transactions on Applied Superconductivity , 27 , 1 - 8 ( 2017 ). doi: 10.1109/TASC.2017.2698201 http://doi.org/10.1109/TASC.2017.2698201 Conceptual Design of Scanning Magnets for Superconducting Proton Therapy Facility J.I.M. Botman , H. L. Hagedoorn , Median plane effects in the Eindhoven AVF cyclotron . IEEE Trans. On Nucl. Sci . 28 , 2128 - 2130 ( 1981 ). doi: 10.1109/TNS.1981.4331613 http://doi.org/10.1109/TNS.1981.4331613 Median plane effects in the Eindhoven AVF cyclotron S. Brandenburg , W.K. van Asselt , M.A. Hofstee , et al ., Vertical beam motion in the AGOR cyclotron . Proc. of EPAC 2004 , Switzerland , 1384 ( 2004 ). http://accelconf.web.cern.ch/AccelConf/e04/PAPERS/TUPLT098.PDF http://accelconf.web.cern.ch/AccelConf/e04/PAPERS/TUPLT098.PDF Vertical beam motion in the AGOR cyclotron J. Stursa , V. Bejeovec , A. Borkovzi et al ., The axial injection system of the isochronous cyclotron [J]. 1513 - 1515 ( 1992 ). http://accelconf.web.cern.ch/AccelConf/e92/PDF/EPAC1992_1513.PDF http://accelconf.web.cern.ch/AccelConf/e92/PDF/EPAC1992_1513.PDF The axial injection system of the isochronous cyclotron S. Vorojtsov , N. Morozov , E Bakewicz et al ., Harmonic coil application for shaping of the magnetic field of isochronous cyclotron AIC-144 [J], ( 2000 ). http://www1.jinr.ru/Preprints/2000/P9200039.pdf http://www1.jinr.ru/Preprints/2000/P9200039.pdf Harmonic coil application for shaping of the magnetic field of isochronous cyclotron AIC-144 J. Van de Walle , W. Kleeven , C. L'Abbate , et al . Mapping of the New IBA Superconducting SYNCHROCYCLOTRON (S2C2) for Proton Therapy , Proceedings of Cyclotrons , Vancouver, BC, Canada , 272 - 274 ( 2013 ). http://accelconf.web.cern.ch/AccelConf/CYCLOTRONS2013/papers/tu4pb01.pdf http://accelconf.web.cern.ch/AccelConf/CYCLOTRONS2013/papers/tu4pb01.pdf Mapping of the New IBA Superconducting SYNCHROCYCLOTRON (S2C2) for Proton Therapy K. H. Park , Y. G. Jung , D. E. Kim , et al . Field mapping system for cyclotron magnet [J]. Nuclear Inst & Methods in Physics Research A , 545 , 533 - 541 ( 2005 ). doi: 10.1016/j.nima.2005.02.009 http://doi.org/10.1016/j.nima.2005.02.009 Field mapping system for cyclotron magnet S. Marks . Precise integration of undulator Hall probe scans [J]. IEEE Transactions on Magnetics Mag , 30 , 2435 - 2438 ( 1994 ). doi: 10.1109/20.305769 http://doi.org/10.1109/20.305769 Precise integration of undulator Hall probe scans Y. Paradis , D. Vandeplassche , W. Beeckman , et al . The Magnetic Field Mapping System for the IBA C70 Cyclotron [J]. Cyclotrons and Their Applications ( 2007 ). http://accelconf.web.cern.ch/accelconf/c07/PAPERS/78.PDF http://accelconf.web.cern.ch/accelconf/c07/PAPERS/78.PDF The Magnetic Field Mapping System for the IBA C70 Cyclotron A. K. Jain . Overview of magnetic measurement techniques, CERN Academic Training Program ( 2003 ). http://cds.cern.ch/record/610089 http://cds.cern.ch/record/610089 Overview of magnetic measurement techniques, CERN Academic Training Program M. Li , Y. L. Lv , L. Cao , et al . Field Mapping System Design for the Superconducting Cyclotron CYCIAE-230 [J]. IEEE Transactions on Applied Superconductivity , 28 , 1 - 1 ( 2018 ). doi: 10.1109/TASC.2018.2789447 http://doi.org/10.1109/TASC.2018.2789447 Field Mapping System Design for the Superconducting Cyclotron CYCIAE-230 A. K. Jain . Magnetic field measurements and mapping techniques [J]. CERN Academic Training Program ( 2003 ). http://cds.cern.ch/record/610089?ln=zh_CN. http://cds.cern.ch/record/610089?ln=zh_CN. Magnetic field measurements and mapping techniques K. N. Henrichsen . Classification of magnetic measurement methods [J], CERN, Geneva, Switzerland , 16 , 70 - 83 ( 1992 ). doi: 10.5170/CERN-1992-005.70 http://doi.org/10.5170/CERN-1992-005.70 Classification of magnetic measurement methods L.H. Harwood , J.A. Nolen , M. Fowler , et al ., Characteristics and performance of the system developed for magnetic mapping of the NSCL superconducting K800 cyclotron magnet [J], IEEE Trans. On Nucl. Sci . 32 , 3734 ( 1985 ). doi: 10.1109/tns.1985.4334485 http://doi.org/10.1109/tns.1985.4334485 Characteristics and performance of the system developed for magnetic mapping of the NSCL superconducting K800 cyclotron magnet G. A. Karamysheva , S. G. Kostromin , N. A. Morozov , et al ., Development of a method for measuring the radial component of the magnetic field in AVF cyclotrons , Accelerator Technology Main Systems: Proceedings of IPAC2014 , 1274 - 1276 ( 2014 ). doi: 10.18429/JACoW-IPAC2014-TUPRO099 http://doi.org/10.18429/JACoW-IPAC2014-TUPRO099 Development of a method for measuring the radial component of the magnetic field in AVF cyclotrons G. Karamysheva , N. Morozov , P. Shishlyannikov , Median plane effects and measurement method for radial component of magnetic field in AVF cyclotrons, Magnet and Vacuum : Proceedings of CYCLOTRONS 2010 , Lanzhou, China, Cyclotrons , 206 - 208 ( 2010 ). doi: 10.18429/JACoW-APAC2010-MOPCP077 http://doi.org/10.18429/JACoW-APAC2010-MOPCP077 Median plane effects and measurement method for radial component of magnetic field in AVF cyclotrons, Magnet and Vacuum A. Roy , T. Bhattacharjee , R. B. Bhole , et al ., Median plane magnetic field mapping for superconducting cyclotron (SCC) in VECC [J]. Accelerator Technology: APAC 2007 , Raja Ramanna Centre for Advanced Technology(RRCAT) , Indore, India , 652 - 654 ( 2007 ). doi: 10.18429/JACoW-APAC2007-THPMA016 http://doi.org/10.18429/JACoW-APAC2007-THPMA016 Median plane magnetic field mapping for superconducting cyclotron (SCC) in VECC O. V. Karamyshev , G. A. Karamysheva , N. A. Morozov , et al ., Beam tracking simulation for SC200 superconducting cyclotron [C], 1268 - 1271 ( 2016 ). doi: 10.18429/JACoW-IPAC2016-TUPMR018 http://doi.org/10.18429/JACoW-IPAC2016-TUPMR018 Beam tracking simulation for SC200 superconducting cyclotron N. A. Morozov , O. V. Karamyshev , G. A. Karamysheva , et al ., Computer modeling of magnet for SC200 superconducting cyclotron , Hadron Accelerators: Proceedings of IPAC2016 , Busan, Korea, Cyclotrons , 1265 - 1268 ( 2016 ). doi: 10.18429/JACoW-IPAC2016-TUPMR017 http://doi.org/10.18429/JACoW-IPAC2016-TUPMR017 Computer modeling of magnet for SC200 superconducting cyclotron K. Z. Ding , Y. F. Bi , G. Chen , et al ., Study of the beam extraction from superconducting cyclotron SC200 [C], Proceedings of Cyclotrons2016 , Zurich, Switzerland , Cyclotrons , 87 - 91 ( 2016 ). doi: 10.18429/JACoW-Cyclotrons2016-MOP14 http://doi.org/10.18429/JACoW-Cyclotrons2016-MOP14 Study of the beam extraction from superconducting cyclotron SC200 G. A. Karamysheva , Y. F. Bi , G. Chen , et al ., Compact superconducting cyclotron SC200 for proton therapy , Proceedings of Cyclotrons2016 , Zurich, Switzerland , Cyclotrons , 371 - 373 ( 2016 ). doi: 10.18429/JACoW-Cyclotrons2016-THC03 http://doi.org/10.18429/JACoW-Cyclotrons2016-THC03 Compact superconducting cyclotron SC200 for proton therapy 10.1007/s41365-019-0614-2 This work was supported by the Research Initiation Foundation of Anhui Polytechnic University (No. 2018YQQ001), the Pre-Research National Natural Science Foundation of China of Anhui Polytechnic University (No. 2019yyzr13), the National Natural Science Foundation of China (Nos.11575237 and 11775258), the National Magnetic Confinement Fusion Science Program (No.2015GB101001), and the International Scientific and Technological Cooperation Project of Anhui (No.1704e1002207). 2018-03-28 2018-09-30 2018-11-23 2019-05-15 2019-06-01 2021-04-10 © 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. 2019 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/s41365-019-0614-2 http://dx.doi.org/10.1007/s41365-019-0614-2 . 2019 Nuclear Science and Techniques 06 30