合肥光源数字横向逐束团反馈系统
|
摘要
合肥光源储存环200MeV注入,800MeV能量运行,横向耦合束团不稳定性导致注入过程困难,同时影响运行的稳定性。为了克服注入过程中的横向不稳定性,目前合肥光源使用八极铁帮助注入,有效地提高了注入流强,从100mA提高到250mA以上。然而八极铁的非线性效应会改变束流的动力学孔径,影响注入效率,从而限制流强的进一步提高。合肥光源的升级改造计划中,束流的发射度从目前的160nm-rad降低到30nm-rad左右,低发射度情况下不能使用八极铁,因此我们非常有必要研发一套横向逐束团反馈系统来抑制注入过程以及运行中出现的横向不稳定性。这项工作不仅是当前合肥光源运行中亟待解决的问题,而且是升级改造工程中的重要课题之一。
横向逐束团反馈系统,是目前世界上高能加速器实验室普遍应用克服横向耦合束团不稳定性的关键技术。在合肥光源模拟横向逐束团反馈系统研发的基础上,我们开发了一套数字横向反馈系统。相对于模拟系统繁杂的构造与调试分析工具的缺乏,数字系统简洁可靠,调试手段丰富,是反馈系统更高层次的平台,也正是我们将模拟系统升级为数字系统的驱动力。数字系统通过对逐圈信号的存储,应用数字信号处理技术开发高阶的滤波器来进一步提高反馈功效。对于实验调试和数据分析,专用的数字处理器的出现进一步提升了系统的灵活性和扩展性,是反馈技术新的发展方向。
合肥光源数字横向逐束团反馈系统使用TED数字处理器。考虑到合肥光源的横向的工作点参数以及45个束团数,我们修改了处理器的FPGA程序,将其6个ADC平均分配给独立的两个反馈回路,使一台处理器能够实现独立的水平方向和垂直方向反馈。数字系统应用RF直接采样前端,简化了前端电子学线路,节约了系统成本并方便了调试和维护工作。由于合肥光源横向的工作点靠近半整数频率且工作点易发生漂移,通过分析比较各种适用于逐束团反馈计算的数字滤波器算法,我们使用时域的最小二乘法设计数字FIR滤波器,并针对注入的情况进行了滤波器参数优化。
数字横向反馈系统不论在800MeV能量运行还是在200MeV能量注入的情况下,都能有效地抑制横向的不稳定性。数字系统可以有效提高注入流强,在不加八极铁的情况下,能重复稳定注入超过250mA,与八极铁同时作用,最高注入流强超过350mA。储存环升能过程中,横向的工作点发生大的漂移而导致反馈相位发生大的改变,造成束流丢失。
文章还探讨了利用横向的条带Kicker配合现有的横向数字反馈系统进行纵向反馈的可能。围绕着数字横向逐束团反馈系统的研究工作值得深入地开展下去,使之能够在未来成为储存环稳定运行必不可少的工具和手段。
Hefei Light Source (HLS) is with injection at 200MeV, operation at 800MeV, and the transverse coupled-bunch instabilities (TCBI) of the storage ring influence the injection process and steady operation. HLS now is using the octopole magnet to suppress the TCBI during injection and increases the beam current from 100mA to more than 250mA. However, the nonlinearity of the octopole magnet changes the dynamic aperture, and lowers the injection efficiency. The octopole magnet limits the further increase of the beam current during injection. According to the HLS upgrade plan, the emittance of the beam will be 30nm.rad, much smaller than 160nm.rad now, and lower emittance makes the octopole magnet impossible to be used as an operational tool to suppress TCBI. Therefore, we need to develope a transverse bunch-by-bunch feedback (TBF) system to cure TCBI during injection and operation. And this work is not only the problem which is needed to be solved in nowaday operation of HLS, but also will be an important technology for the upgrade of HLS.
TBF systems could suppress the TCBI and are developed in the accelerator labs around the world. Based on the development of the analog TBF system, we developed a digital TBF, which is simpler and more reliable than the analog one. And the digital TBF system is a better platform for feedback with ability of higher taps of digital filter, which has a better performance in feedback. The digital feedback processor has been developed with flexibility in tuning and versatile tools for diagnostics, which is new development for feedback technology. The HLS digital TBF system is based on the TED digital feedback processor. Considering the working points and harmonic number of bunches, we modify the FPGA program of the feedback processor to assign the 6 ADCs to two independent feedback loops for both horizontal and vertical feedback. The RF direct sampling scheme is used in HLS digital TBF system, and simplifies the electronics circuits and saves the cost for tuning and maintaining. The filter design is optimized for injection and time domain least square fitting meathod is used to generate the coefficients of the digital FIR filter to cure the tune shift during injection.
The HLS digital TBF system could suppress TCBI during injection and operation, and could improve the beam current during injection. Without octopole magnet, the feedback could store more than 250mA current. And with octopole magnet and feedback on, the beam current was over 350mA during injection. The beam lost during ramping due to the tune change.
Longitudinal feedback with transverse stripline kicker is also discussed in this paper. A further study of the digital TBF system is needed to make it as a necessary tool for the operation of the storage ring in HLS.
横向逐束团反馈系统,是目前世界上高能加速器实验室普遍应用克服横向耦合束团不稳定性的关键技术。在合肥光源模拟横向逐束团反馈系统研发的基础上,我们开发了一套数字横向反馈系统。相对于模拟系统繁杂的构造与调试分析工具的缺乏,数字系统简洁可靠,调试手段丰富,是反馈系统更高层次的平台,也正是我们将模拟系统升级为数字系统的驱动力。数字系统通过对逐圈信号的存储,应用数字信号处理技术开发高阶的滤波器来进一步提高反馈功效。对于实验调试和数据分析,专用的数字处理器的出现进一步提升了系统的灵活性和扩展性,是反馈技术新的发展方向。
合肥光源数字横向逐束团反馈系统使用TED数字处理器。考虑到合肥光源的横向的工作点参数以及45个束团数,我们修改了处理器的FPGA程序,将其6个ADC平均分配给独立的两个反馈回路,使一台处理器能够实现独立的水平方向和垂直方向反馈。数字系统应用RF直接采样前端,简化了前端电子学线路,节约了系统成本并方便了调试和维护工作。由于合肥光源横向的工作点靠近半整数频率且工作点易发生漂移,通过分析比较各种适用于逐束团反馈计算的数字滤波器算法,我们使用时域的最小二乘法设计数字FIR滤波器,并针对注入的情况进行了滤波器参数优化。
数字横向反馈系统不论在800MeV能量运行还是在200MeV能量注入的情况下,都能有效地抑制横向的不稳定性。数字系统可以有效提高注入流强,在不加八极铁的情况下,能重复稳定注入超过250mA,与八极铁同时作用,最高注入流强超过350mA。储存环升能过程中,横向的工作点发生大的漂移而导致反馈相位发生大的改变,造成束流丢失。
文章还探讨了利用横向的条带Kicker配合现有的横向数字反馈系统进行纵向反馈的可能。围绕着数字横向逐束团反馈系统的研究工作值得深入地开展下去,使之能够在未来成为储存环稳定运行必不可少的工具和手段。
Hefei Light Source (HLS) is with injection at 200MeV, operation at 800MeV, and the transverse coupled-bunch instabilities (TCBI) of the storage ring influence the injection process and steady operation. HLS now is using the octopole magnet to suppress the TCBI during injection and increases the beam current from 100mA to more than 250mA. However, the nonlinearity of the octopole magnet changes the dynamic aperture, and lowers the injection efficiency. The octopole magnet limits the further increase of the beam current during injection. According to the HLS upgrade plan, the emittance of the beam will be 30nm.rad, much smaller than 160nm.rad now, and lower emittance makes the octopole magnet impossible to be used as an operational tool to suppress TCBI. Therefore, we need to develope a transverse bunch-by-bunch feedback (TBF) system to cure TCBI during injection and operation. And this work is not only the problem which is needed to be solved in nowaday operation of HLS, but also will be an important technology for the upgrade of HLS.
TBF systems could suppress the TCBI and are developed in the accelerator labs around the world. Based on the development of the analog TBF system, we developed a digital TBF, which is simpler and more reliable than the analog one. And the digital TBF system is a better platform for feedback with ability of higher taps of digital filter, which has a better performance in feedback. The digital feedback processor has been developed with flexibility in tuning and versatile tools for diagnostics, which is new development for feedback technology. The HLS digital TBF system is based on the TED digital feedback processor. Considering the working points and harmonic number of bunches, we modify the FPGA program of the feedback processor to assign the 6 ADCs to two independent feedback loops for both horizontal and vertical feedback. The RF direct sampling scheme is used in HLS digital TBF system, and simplifies the electronics circuits and saves the cost for tuning and maintaining. The filter design is optimized for injection and time domain least square fitting meathod is used to generate the coefficients of the digital FIR filter to cure the tune shift during injection.
The HLS digital TBF system could suppress TCBI during injection and operation, and could improve the beam current during injection. Without octopole magnet, the feedback could store more than 250mA current. And with octopole magnet and feedback on, the beam current was over 350mA during injection. The beam lost during ramping due to the tune change.
Longitudinal feedback with transverse stripline kicker is also discussed in this paper. A further study of the digital TBF system is needed to make it as a necessary tool for the operation of the storage ring in HLS.
引文
[1] K H Hu, Demi Lee, S Y Hsu, et al, Operation Experiences of the Bunch-by-bunch Feedback System of TLS, Proceedings of PAC07, Albuquerque, New Mexico, USA.
[2] Weixing Cheng, Takashi Obina, Tohru Honda, et al, Bunch-by-bunch Feedback for the Photon Factory Storage Ring, Proceedings of EPAC 2006, Edinburgh, Scotland.
[3] M. Lonza, D. Bulfone, C. Gamba, Digital Processing Electronics for the ELETTRA Transverse Multi-bunch Feedback System, ICALEPCS 1999, Trieste, Italy.
[4] R Nagaoka, L Cassinari, J C Denard, et al, Transverse Feedback Development at Soleil, Proceedings of DIPAC 2007, Venice, Italy.
[5] Alessandro Drago, John Fox, Dmitry Teytelman, et al, Commissioning of the IGP Feedback System at DAФNE, Proceedings of EPAC08, Genoa, Italy.
[6] R Takai, M Tobiyama, T Obina, et al, Bunch by Bunch Feedback System Using iGp at KEK-PF, Proceedings of DIPAC09, Basel, Switzerland.
[7] V Poucki, P Lemut, M Oblak, et al, Combating Multi-bunch instabilities with the Libera Bunch-by-bunch Unit, Proceedings of EPAC08, Genoa, Italy.
[8] M Sands, The Physics of Electron Storage Rings, An Introduction, SLAC-121, UC-28(ACC), May 1979.
[9]陈佳洱,1993.加速器物理基础.北京:原子能出版社.
[10] Marco Lonza, Multi-bunch Feedback systems, CAS, Beam Diagnostics. Dourdan, France, 28 May– 6 June 2008.
[11]夏德钎,自动控制理论.北京:机械工业出版社.
[12] J D Fox and E Kikutani, Bunch Feedback Systems and Signal Processing, Invited tutorial at t the US-CERN-Japan-Russia School on Beam Measurements, Montreaux, Switzerland May 1998.
[13] G A Voss, Single Beam Collective Phenomena in Electron Storage Rings, Diagnosis and Cures. CERN 77-13: p265.
[14]刘建宏,HLS Bunch-by-bunch测量系统研制及束流不稳定性的初步研究,博士论文,中国科学技术大学.
[15]郑凯,合肥光源逐束团测量和模拟反馈系统,博士论文,中国科学技术大学.
[16]王世一,数字信号处理,北京:北京理工大学出版社.
[17] Proakis J G, Manolakis D G. Introduction to Digital Signal Processing. New York: Macmillan Publishiing Company, 1988.
[18] Tretter S A. Introduction to Discrete-Time Signal Processing. New York: John Wiley and Sons, 1976.
[19] T Nakamura, S Date, K Kobayashi, et al, Transverse Bunch-by-bunch Feedback System for the SPring-8 Storage Ring, Proceedings of EPAC 2004, Lucerne, Switzerland.
[20] H Hindi, N Eisen, J Fox, Analysis of DSP-Based longitudinal Feedback System: Trials at SPEAR and ALS,Proceedings of the 1993 IEEE Particle Accelerator Conference. 17-20 May 1993, Washington, DC.
[21] T Nakamura, K Kobayashi, FPGA Based Bunch-by-Bunch Feedback Signal Processor, 10th ICALEPCS 2005, Geneva, Switzerland.
[22]王筠华,刘建宏,郑凯等,合肥光源逐束团测量和横向束流反馈系统设计,强激光与粒子束,2006,18(2),291-296.
[23]杨永良,合肥光源束流不稳定性测量和横向模拟反馈,博士论文,中国科学技术大学。
[24] http://www.minicircuits.com/pages/pdfs/an60038.pdf.
[25]戴蓓蒨,线性电子线路.合肥:中国科学技术大学出版社.
[26] Datasheet of AD9433. Analog Devices.
[27] J H Wang,L Ma, D K Liu, et al,Development of Transverse Feedback System and Instabilities Suppress at HLS, PAC07, 2007.6, USA.
[28]黄智伟,锁相环与频率合成器电路设计.西安:西安电子科技大学出版社.
[29]唐利孬,李凯,张杰,数字式视频瞬时AGC系统.应用科技,第33卷第12期,2006年12月.
[30] D A Goldberg, G R Lambertson, Dynamic Devices: A Primer on Pickups and Kickers, LBL-31664, November 1991.
[31] G Lambertson, Dynamic Devices: Pickups and Pickers. Lawrence Berkeley National Laboratory. Paper LBL-22085.
[32]刘祖平,同步辐射光源物理引论.合肥:中国科学技术大学出版社.
[33]孙葆根,合肥光源工作点测量系统,核技术,Vol.24,No.1,2004年1月.
[34] T Nakamura, Chromoticity for energy spread measurement and for cure of transverse multi-bunch instability in the SPring-8 storage ring, Proceedings of the PAC, Chicago, 2001.
[35]徐宏亮,合肥储存环注入状态下的高频系统研究,强激光与粒子束,第16卷第一期,2004年1月.
[36]王筠华,刘建宏,孙葆根等,逐圈测量系统定标和新近实验结果,强激光与粒子束, 2004,16(5):672-6.
[2] Weixing Cheng, Takashi Obina, Tohru Honda, et al, Bunch-by-bunch Feedback for the Photon Factory Storage Ring, Proceedings of EPAC 2006, Edinburgh, Scotland.
[3] M. Lonza, D. Bulfone, C. Gamba, Digital Processing Electronics for the ELETTRA Transverse Multi-bunch Feedback System, ICALEPCS 1999, Trieste, Italy.
[4] R Nagaoka, L Cassinari, J C Denard, et al, Transverse Feedback Development at Soleil, Proceedings of DIPAC 2007, Venice, Italy.
[5] Alessandro Drago, John Fox, Dmitry Teytelman, et al, Commissioning of the IGP Feedback System at DAФNE, Proceedings of EPAC08, Genoa, Italy.
[6] R Takai, M Tobiyama, T Obina, et al, Bunch by Bunch Feedback System Using iGp at KEK-PF, Proceedings of DIPAC09, Basel, Switzerland.
[7] V Poucki, P Lemut, M Oblak, et al, Combating Multi-bunch instabilities with the Libera Bunch-by-bunch Unit, Proceedings of EPAC08, Genoa, Italy.
[8] M Sands, The Physics of Electron Storage Rings, An Introduction, SLAC-121, UC-28(ACC), May 1979.
[9]陈佳洱,1993.加速器物理基础.北京:原子能出版社.
[10] Marco Lonza, Multi-bunch Feedback systems, CAS, Beam Diagnostics. Dourdan, France, 28 May– 6 June 2008.
[11]夏德钎,自动控制理论.北京:机械工业出版社.
[12] J D Fox and E Kikutani, Bunch Feedback Systems and Signal Processing, Invited tutorial at t the US-CERN-Japan-Russia School on Beam Measurements, Montreaux, Switzerland May 1998.
[13] G A Voss, Single Beam Collective Phenomena in Electron Storage Rings, Diagnosis and Cures. CERN 77-13: p265.
[14]刘建宏,HLS Bunch-by-bunch测量系统研制及束流不稳定性的初步研究,博士论文,中国科学技术大学.
[15]郑凯,合肥光源逐束团测量和模拟反馈系统,博士论文,中国科学技术大学.
[16]王世一,数字信号处理,北京:北京理工大学出版社.
[17] Proakis J G, Manolakis D G. Introduction to Digital Signal Processing. New York: Macmillan Publishiing Company, 1988.
[18] Tretter S A. Introduction to Discrete-Time Signal Processing. New York: John Wiley and Sons, 1976.
[19] T Nakamura, S Date, K Kobayashi, et al, Transverse Bunch-by-bunch Feedback System for the SPring-8 Storage Ring, Proceedings of EPAC 2004, Lucerne, Switzerland.
[20] H Hindi, N Eisen, J Fox, Analysis of DSP-Based longitudinal Feedback System: Trials at SPEAR and ALS,Proceedings of the 1993 IEEE Particle Accelerator Conference. 17-20 May 1993, Washington, DC.
[21] T Nakamura, K Kobayashi, FPGA Based Bunch-by-Bunch Feedback Signal Processor, 10th ICALEPCS 2005, Geneva, Switzerland.
[22]王筠华,刘建宏,郑凯等,合肥光源逐束团测量和横向束流反馈系统设计,强激光与粒子束,2006,18(2),291-296.
[23]杨永良,合肥光源束流不稳定性测量和横向模拟反馈,博士论文,中国科学技术大学。
[24] http://www.minicircuits.com/pages/pdfs/an60038.pdf.
[25]戴蓓蒨,线性电子线路.合肥:中国科学技术大学出版社.
[26] Datasheet of AD9433. Analog Devices.
[27] J H Wang,L Ma, D K Liu, et al,Development of Transverse Feedback System and Instabilities Suppress at HLS, PAC07, 2007.6, USA.
[28]黄智伟,锁相环与频率合成器电路设计.西安:西安电子科技大学出版社.
[29]唐利孬,李凯,张杰,数字式视频瞬时AGC系统.应用科技,第33卷第12期,2006年12月.
[30] D A Goldberg, G R Lambertson, Dynamic Devices: A Primer on Pickups and Kickers, LBL-31664, November 1991.
[31] G Lambertson, Dynamic Devices: Pickups and Pickers. Lawrence Berkeley National Laboratory. Paper LBL-22085.
[32]刘祖平,同步辐射光源物理引论.合肥:中国科学技术大学出版社.
[33]孙葆根,合肥光源工作点测量系统,核技术,Vol.24,No.1,2004年1月.
[34] T Nakamura, Chromoticity for energy spread measurement and for cure of transverse multi-bunch instability in the SPring-8 storage ring, Proceedings of the PAC, Chicago, 2001.
[35]徐宏亮,合肥储存环注入状态下的高频系统研究,强激光与粒子束,第16卷第一期,2004年1月.
[36]王筠华,刘建宏,孙葆根等,逐圈测量系统定标和新近实验结果,强激光与粒子束, 2004,16(5):672-6.