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Longitudinal phase-space diagnostics using a stripline-type beam-timing monitor at the KEKB injector linac
Nuclear Inst. and Methods in Physics Research, A 949 (2020) 162922
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Longitudinal phase-space diagnostics using a stripline-type beam-timing monitor at the KEKB injector linac T. Suwada β Accelerator Laboratory, High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan Department of Accelerator Science, Graduate University for Advanced Studies (SOKENDAI), 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan
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Keywords: Beam-timing diagnostic instrumentations Beam-timing monitors Longitudinal phase spaces Linear accelerator
ABSTRACT A new beam-timing monitor (BTM) has been developed to analyze the longitudinal beam dynamics and bunching characteristics at the pre-injector of the KEKB injector linear accelerator (linac). The BTM is a conventional stripline-type beam monitor with two pickup electrodes. It measures the relative time delay between the arrival time of the beam signal and 1st-zero-cross time of the fundamental accelerating radio frequency (rf) signal (2856 MHz) immediately after the detection of the beam signal. The beam tests were performed to evaluate the performance and characteristics of the BTM for primary single-bunched electron beams with high bunch charges of βΌ8 nC for positron production. It was found that the results show that the resolution in the delay-time measurement is π βΌ1.2 ps in one standard deviation. This report describes the basic design of the BTM system, the beam tests, and results in detail, to investigate the sensitivity and stability of the beam timing based on the longitudinal phase-space parameters at the pre-injector and location A1 of the injector linac, along with the calibration method in the pulse-height variation of the BTM signal.
1. Introduction It is important to diagnose not only the transverse, but also the longitudinal phase-spaces of the charged particle beams with as high accuracy as possible, to stably accelerate and transport them, and to maintain the beam qualities along the entire long sections in highenergy accelerator complexes. Although many diagnostic instrumentation techniques such as beam position monitors [1] and wire scanners [2] are available in transverse diagnostics, only a few instrumentation techniques are available for the longitudinal direction. A beam-timing monitor (BTM) is one of the longitudinal diagnostic instrumentation techniques, using which the arrival time of the charged particle beams can be measured with respect to a fundamental accelerating radio frequency (rf) wave. Based on the BTM instrumentation, non-destructive diagnostics in the longitudinal direction may become available, through which the longitudinal beam optics and bunching characteristics can be investigated, especially at the pre-injector section, in real-time in accelerator operation. The Super KEK B-factory (SKEKB) [3] is a next-generation B-factory that is currently in operation at KEK, after the KEK B-factory (KEKB) [4] was discontinued in 2010. The SKEKB is an electron/positron collider with asymmetric energies; it comprises 4 GeV positron (LER) and 7 GeV electron (HER) rings in which the designed stored beam currents are 3.6 A and 2.6 A, respectively. The target luminosity (8 Γ 1035 cmβ2 sβ1 )
of the SKEKB is 40 times the peak luminosity of the KEKB. The highenergy flavor particle physics experiments, considering the CP violation in B mesons [5], is the main driver behind this study. The KEKB injector linac [6] is an electron/positron linear accelerator for both the SKEKB rings and two light sources: the Photon Factory (PF) and Photon Factory-Advanced Ring for pulse X-rays (PF-AR). The injector linac was drastically upgraded for the SKEKB [7]. The BTM is one of essential diagnostic instruments to perform a nondestructive diagnosis of the beam optics in the longitudinal direction along the entire injector linac based on the measurements of the arrival time of charged beams. In this study, the basic design, developments, and experimental results of the new BTM employed in large accelerator complexes are reported in detail. 2. Overview of the pre-injector system The main function of the pre-injector of the injector linac is briefly described here. The pre-injector can produce a high-intensity and single-bunched beam of proper beam characteristics with charges of 10 nC, a bunch length of 4.2 ps in one standard deviation, and a normalized emittance well below 0.1 mm in one standard deviation. The generation of such a high-intensity electron beam is required as primary electrons for positron generation. A conventional triode-type
β Correspondence to: Accelerator Laboratory, High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan. E-mail address: [email protected].
https://doi.org/10.1016/j.nima.2019.162922 Received 5 August 2019; Received in revised form 10 September 2019; Accepted 4 October 2019 Available online 9 October 2019 0168-9002/Β© 2019 Elsevier B.V. All rights reserved.
T. Suwada
Nuclear Inst. and Methods in Physics Research, A 949 (2020) 162922
Fig. 1. Mechanical drawings of the BTM, (π) front view, (π) side view, and (π) a photograph of the BTM installed at location A44. The length is indicated in millimeters.
possible, so that the signal can be picked-up with short rise time and high peak voltage without any signal degradation. The inner diameter (28.6 mm) between the electrodes and the angular width (50β¦ ) of the electrode were chosen to comprise a 50 Ξ© transmission line. Quick-release flange couplings (NW40, standard KF flange [9]) were used at both ends of the monitor for easy installation in the beam line.
thermionic gun and a high-speed grid pulser were employed to achieve high current intensities. A high voltage of 180 kV is applied to the gun, and a maximum charge of 15 nC is applied for the pulse width of less than 2 ns. The grid pulser controls the beam repetition (maximum 50 Hz) as well as the beam intensity, depending on the beam modes by changing the output voltage. A two-subharmonic-buncher system (SHB1 at 114 MHz and SHB2 at 571 MHz) is introduced after the electron gun, allowing for smooth pulse compression in the following bunching section. After the two SHBs, the S-band (2856 MHz) prebuncher (PB) and buncher (B) systems are installed to realize the high-intensity and single-bunched beam at the optimized acceleration voltages in PB and B (1.3 MV/m and 20 MV/m, respectively). A solenoid-focusing field (maximum 0.2 T) in the pre-injector is optimized to maintain the Brillouin flow to minimize the emittance increase due to space-charge forces. The nominal beam energy is estimated to be πΈ βΌ 25 MeV at the exit of the pre-injector. More detailed descriptions of the pre-injector can be found in detail elsewhere [8].
3.2. Design of the instrumentation system A typical pickup signal is generated from one channel of the BTM, which shows a bipolar signal wave, while another channel of the BTM is simply terminated by a 50 Ξ© terminator. The pickup signal is directly sent to a real-time oscilloscope (Tektronix, DPO70404C, BW4 GHz, 25 GS/s [10]) through an rf coaxial cable of length 30 m (WF-H50-4S, Mitsubishi Cable Industries, Inc. [11]). The minimal time resolution of the oscilloscope is specified as 200 fs. A fundamental accelerating rf signal (2856 MHz) is sent to another channel of the oscilloscope, which was divided from the rf monitor line by an rf coaxial cable of length 20 m (S04272B, HUBER+SUHNER, Ltd. [12]). The oscilloscope measures the delay-time using its internal function, in which the start time is triggered by the front edge of the BTM signal, and the stop time is determined by the 1st zero-cross of the accelerating rf signal. The BTM was installed at location A44 in sector A during summer shutdown in 2018. A44 is located 50 m downstream of the thermionic electron gun, where the electron energy is πΈ βΌ 530 MeV. The purpose of the BTM is to non-destructively diagnose the bunching characteristics at the pre-injector, the beam optics, and stability in the longitudinal direction after the pre-injector.
3. Beam-timing monitor system 3.1. Mechanical design Mechanical drawings of the BTM, (π) front view, (π) side view, and (π) a photograph of the BTM installed at location A44, are shown in Fig. 1. It is a conventional stripline-type monitor made of stainless steel (SUS304) with two pickups (SMA-vacuum-feedthrough) upstream in the vertical direction, while the downstream ends are short-circuited to a pipe to simplify the manufacturing process. The total length (πΏ = 500 mm) was chosen as the stripline length (πΏπ = 448 mm) as long as 2
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Nuclear Inst. and Methods in Physics Research, A 949 (2020) 162922
Fig. 2. (π) Typical BTM signal with 12 dB fixed attenuators, and (π) similar BTM and accelerating rf signals measured for the primary electron beams. The image is an enlarged view of (π).
4. Beam tests 4.1. Signal response of the BTM The signal responses of the BTM were measured by using primary electron beams for positron production. The beam charges of the electron beam were typically βΌ8.2 nC/bunch during this experiment. The typical signal waveform is shown in Fig. 2(π). 12 dB fixed attenuators were inserted to the signal input channel in order to adjust the input signal intensity to the dynamic range of the oscilloscope. The typical pulse height (ππ ) was βΌ1.9 V with the fixed attenuators for typical primary electron beams. The time interval between the bipolar signal peaks is 3 ns, which corresponds to the turnaround time of the signal propagation along the stripline electrode. Such a long time interval may be sufficient to obtain a clear front edge of the bipolar signal without any distortion and attenuation. This is the reason why such a long time period was applied to the stripline electrode of the BTM. It can be seen that the fast rise time (ππ ) of the front edge of the bipolar signal is ππ βΌ 120 ps. Fig. 2(π) shows the typical signal waveform along with the fundamental accelerating rf signal, for which the horizontal time axis and vertical range are expanded and set as 40 ps/div and 500 mV/div. The fast front edge of the bipolar signal was used to trigger the oscilloscope, and the trigger threshold level (πth ) was set to be a fixed value, πth = β1 V. The threshold level corresponds to the pulse height of βΌ53% to the typical BTM signal for the primary electron beams. The time at which the front edge of the BTM signal across the trigger threshold level, gives the start time π0 , and the stop time π1 , may be obtained using the time at which the first falling edge of the accelerating rf signal zero-crosses in the delay-time measurement. Thus, the measured delay-time (ππ ) is simply defined by, ππ = π1 β π0 ,
Fig. 3. Time traces of the delay-time (ππ ) and pulse height (ππ ) in the delay-time measurement in typical operation of the injector linac for the LER injection in one day.
Fig. 3, in which SHB1π and PX/PYA1M indicate the phase tuning of SHB1 and the current tuning applied to the horizontal (π) and vertical (π ) pulsed steering magnets installed at location A1M, which are located βΌ16 m downstream of the thermionic electron gun. 4.3. Pulse-height calibration procedure in the delay-time measurement The measured delay-time depends, in principle, on the pulse height of the BTM signal as shown in Fig. 2, because the trigger threshold level is set to be constant, and the start time in the delay-time measurement varies according to the pulse height. Thus, the measured delay-time should be properly corrected to prevent any pulse-height dependence. Fig. 4 shows the variation in the delay-time measurement as a function of the attenuation value with fixed attenuators (1 dB step) in the calibration measurement applied to the primary electron beams. The fixed attenuators were inserted at the input channel of the fundamental accelerating rf signal in order to measure the variation in the electrical length of the fixed attenuators, and the delay-times were measured as a function of the attenuation values. The number of data points for each attenuator value is 1000; a data point is given by a set of average and standard errors. The result clearly shows a linear relation between the attenuation values and the measured delay-times. Further, it is seen that the delay-time per 1 dB (π₯ππ ) is π₯ππ = 88.3 Β± 0.6 ps/dB. Fig. 5 shows the variation in the delay-time measurement as a function of the pulse height of the BTM signal with fixed attenuators (1
(1)
and it can be easily measured using the internal function of the oscilloscope. 4.2. Time traces in the delay-time measurement Fig. 3 shows the time traces of the delay-time and the pulse height obtained in the delay-time measurements without any corrections for the signal waveforms in typical operation of the injector linac for the LER injection in one day. It can be seen that the time trace of the delay-time varies with the pulse height. While some step-like variations can be seen in the time traces, they are otherwise relatively stable. The occurrence of such steplike variations was due to various beam tunings by operators during the nominal operation for the LER injection. Several beam tunings were recorded in the operation log files of the injector linac. The typical parameters in beam tunings during the measurements are shown in 3
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Nuclear Inst. and Methods in Physics Research, A 949 (2020) 162922
Fig. 4. Variation (π₯ππ ) in the delay-time measurement as a function of the attenuation values with fixed attenuators (1 dB step) in the calibration measurement applied to the primary electron beams.
Fig. 6. Distribution plot of the delay-times after the pulse-height correction procedure in the measurement for the primary electron beams, and β¨πππ β© shows the mean value of πππ .
delay-time πππ is simply given by πππ = ππ + π₯ππ .
(3)
Fig. 6 shows the distribution plot of the delay-times after the pulse-height correction procedure measured for the primary electron beams, where β¨πππ β© indicates the mean value of πππ . Here, the distribution plot was plotted using the data between 9:04 and 10:42 am on 27/Feb/2019, as shown in Fig. 3; the number of data was 3681. One standard deviation was obtained as π β 1.2 ps based on the fitting procedure with a Gaussian function. This value limits the oneshot measurement to the delay-time because of the limitations of the oscilloscope in noise floor level, while the averaging operation could further decrease the statistical error in the delay-time measurement. 5. Test results 5.1. Delay-time response measurements for the pre-injector parameters By adopting typical parameters at the pre-injector and location A1, the delay-time responses of the BTM were measured as a function of these parameters. The typical parameters at the pre-injector are the phases of the SHB1 and SHB2, the phases of the B and PB, and those are the phase of the accelerating structure and the field strength of steering magnets at location A1. Here, it should be noted that each phase is defined by the difference from each nominal set point. Fig. 7 shows the results of the delay-time response measurements depending on the pre-injector parameters. Fig. 7(π) and (π) show the variations in the delay-time and pulse height without any pulse-height corrections, and the variations in the delay-time both with and without the pulse-height corrections as a function of the SHB1 phase (π₯π), respectively. Fig. 7(π) and (π) show the similar results as shown in Fig. 7(π) and (π) as a function of the SHB2 phase (π₯π), respectively. Fig. 7(π) and (π ) show the similar results as a function of the B phase (π₯π). Fig. 7(π) and (β) show the similar results as a function of the PB phase (π₯π). Here, the number of each data point is 600, and each data point is given by a set of average and statistical errors based on one standard deviation. The measured delay-times were successfully corrected based on the pulse-height fitting procedure.
Fig. 5. Variation (π₯ππ ) in the delay-time measurement as a function of the pulse height of the BTM signal with fixed attenuators (1 dB step) in the calibration measurement.
dB step) in the calibration measurement. It should be noted that equal numbers of fixed attenuators (1 dB step) were inserted at both the input channels of the oscilloscope to properly compensate the variations in the electrical length of each channel due to the insertion of fixed attenuators in this delay-time measurement. The result shows that the variation in the delay-time measurement as a function of the pulse height is approximately in accordance with a parabolic fitting function. The measured delay-time should be corrected using the following fitting function, π₯ππ = 76.0ππ2 β 291.7ππ + 279.2,
(2)
based on the least-squares fitting procedure, in which the units of the pulse height and delay-time are V and ps, respectively. The corrected 4
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Nuclear Inst. and Methods in Physics Research, A 949 (2020) 162922
Fig. 7. (π) Variations in the delay-time ππ and pulse height ππ without any pulse-height correction, (π) variations in the delay-time ππ both with and without the pulse-height correction as a function of the SHB1 phase (π₯π), (π) and (π) the similar results as a function of the SHB2 phase (π₯π), (π) and (π ) the similar results as a function of the B phase (π₯π), (π) and (β) the similar results as a function of the PB phase (π₯π). The solid lines show a guide for the polynomial fitting curve (2nd- or 4th-order) in the plots with the pulse-height correction, and a guide for only the eye in the other plots.
5
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Nuclear Inst. and Methods in Physics Research, A 949 (2020) 162922
Fig. 8. (π) Variations in the delay-time ππ and pulse height ππ without any pulse-height correction, (π) variations in the delay-time ππ both with and without the pulse-height correction as a function of the Acc A1 phase (π₯π), (π) and (π) the similar results as a function of the current (πΌ) applied to PXA1M, (π) and (π ) the similar results as a function of the current (πΌ) applied to PYA1M. The solid lines are a guide for the polynomial fitting curve (linear or 2nd-order) in the plots with the pulse-height correction, but a guide for only the eye in the other plots.
magnets PXA1M and PYA1M, as shown in Fig. 8(π) and (π ), clearly indicate that the pulse-height correction procedure can be effectively conducted because the delay-time responses are sufficiently linearized within the measurement errors.
5.2. Delay-time response measurements for the A1 parameters Fig. 8 shows the results of the delay-time response measurements for the A1 parameters. Fig. 8(π) and (π) show the variations in the delaytime ππ and pulse height ππ without any pulse-height correction and the variations in the delay-time ππ both with and without the pulse-height correction as a function of the Acc A1 phase, respectively. Fig. 8(π) and (π) show the similar results as a function of the current applied to the pulsed steering magnet PXA1M, respectively. Fig. 8(π) and (π ) show the similar results as a function of the current applied to the pulsed steering magnet PYA1M, respectively. Here, the number of each data point is 600, and each data point is given by a set of average and statistical errors based on one standard deviation. The measured delay-times were successfully corrected based on the pulse-height fitting procedure. The results for the pulsed steering
5.3. Analysis in the sensitive region for the longitudinal phase-space parameters The maximum correction for the measured delay-time is βΌ3 ps, excluding the cases with a relatively large beam loss. It can be seen that clear and stable correlations are available for the averaged delaytimes depending on the longitudinal phase-space parameters, although detecting the variation of the delay-time on a pulse-by-pulse basis is difficult, due to beam-intensity fluctuation. 6
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Nuclear Inst. and Methods in Physics Research, A 949 (2020) 162922
Table 1 Summary table of the derivatives of the delay-time πππ obtained at each nominal set point in the longitudinal phase-space parameters after the calibration correction procedure at the pre-injector and A1.
Parameter
Sensitivity [ps/deg.]
Sensitive region [deg.]
Fitting procedure (πππ. ππππππ )
SHB1 phase π₯π SHB2 phase π₯π Buncher phase π₯π PB phase π₯π Acc A1 phase π₯π
β2.2 Β± 0.3 β0.69 Β± 0.04 β1.88 Β± 0.06 β0.09 Β± 0.02 1.07 Β± 0.03
Β±0.55 Β± 0.06 Β±2.0 Β± 0.1 Β±0.64 Β± 0.02 Β±14 Β± 3 Β±1.12 Β± 0.03
4 2 4 4 2
Acknowledgments The authors would like to thank Mr. H. Saotome of Kanto Information Service Co., Ltd. for his help in coding the data-acquisition system software. This study was fully supported by Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan. References [1] T. Suwada, N. Kamikubota, H. Fukuma, N. Akasaka, H. Kobayashi, Nucl. Instrum. Methods 440 (2000) 307. [2] N. Iida, Y. Funakoshi, M. Kikuchi, K. Satoh, T. Suwada, T. Kawamoto, in: Proc. the 1999 Particle Accelerator Conference, PACβ99, New York City, U.S.A., 1999, pp. 2108, March 29-April 2. [3] Y. Ohnishi, T. Abe, T. Adachi, K. Akai, Y. Arimoto, K. Ebihara, K. Egawa, J. Flanagan, H. Fukuma, Y. Funakoshi, K. Furukawa, T. Furuya, N. Iida, H. Iinuma, H. Ikeda, T. Ishibashi, M. Iwasaki, T. Kageyama, S. Kamada, T. Kamitani, K. Kanazawa, M. Kikuchi, H. Koiso, M. Masuzawa, T. Mimashi, T. Miura, T. Mori, A. Morita, T. Nakamura, K. Nakanishi, H. Nakayama, M. Nishiwaki, Y. Ogawa, K. Ohmi, N. Ohuchi, K. Oide, T. Oki, M. Ono, M. Satoh, K. Shibata, M. Suetake, Y. Suetsugu, R. Sugahara, H. Sugimoto, T. Suwada, M. Tawada, M. Tobiyama, N. Tokuda, K. Tsuchiya, H. Yamaoka, Y. Yano, M. Yoshida, S. Yoshimoto, D. Zhou, Z. Zong, Prog. Theor. Exp. Phys. 2013, 03A011. [4] T. Abe, K. Akai, N. Akasaka, M. Akemoto, A. Akiyama, M. Arinaga, Y. Cai, K. Ebihara, K. Egawa, A. Enomoto, E. Ezura, J. Flanagan, S. Fukuda, H. Fukuma, Y. Funakoshi, K. Furukawa, T. Furuya, J. Haba, K. Hara, T. Higo, S. Hiramatsu, H. Hisamatsu, H. Honma, T. Honma, K. Hosoyama, T. Ieiri, N. Iida, H. Ikeda, M. Ikeda, S. Inagaki, S. Isagawa, H. Ishii, A. Kabe, E. Kadokura, T. Kageyama, K. Kakihara, E. Kako, S. Kamada, T. Kamitani, K. Kanazawa, H. Katagiri, S. Kato, T. Kawamoto, S. Kazakov, M. Kikuchi, E. Kikutani, K. Kitagawa, H. Koiso, Y. Kojima, I. Komada, T. Kubo, K. Kudo, S. Kurokawa, K. Marutsuka, M. Masuzawa, S. Matsumoto, T. Matsumoto, S. Michizono, K. Mikawa, T. Mimashi, T. Mitsuhashi, S. Mitsunobu, T. Miura, K. Mori, A. Morita, Y. Morita, H. Nakai, H. Nakajima, T.T. Nakamura, H. Nakanishi, K. Nakanishi, K. Nakao, H. Nakayama, M. Nishiwaki, Y. Ogawa, K. Ohmi, Y. Ohnishi, S. Ohsawa, Y. Ohsawa, N. Ohuchi, K. Oide, T. Oki, M. Ono, T. Ozaki, E. Perevedentsev, H. Sakai, Y. Sakamoto, M. Sato, K. Satoh, M. Satoh, Y. Seimiya, K. Shibata, T. Shidara, M. Shimada, S. Stanic, M. Shirai, A. Shirakawa, T. Sueno, M. Suetake, Y. Suetsugu, R. Sugahara, T. Sugimura, T. Suwada, O. Tajima, S. Takano, S. Takasaki, T. Takenaka, Y. Takeuchi, Y. Takeuchi, M. Tawada, M. Tejima, M. Tobiyama, N. Tokuda, K. Tsuchiya, S. Uehara, S. Uno, Y. Wu, N. Yamamoto, Y. Yamamoto, Y. Yano, K. Yokoyama, Ma. Yoshida, Mi. Yoshida, S. Yoshimoto, K. Yoshino, M. Yoshioka, D. Zhou, F. Zimmermann, Z. Zong, Prog. Theor. Exp. Phys 2013, 03A001. [5] T. Abe, et al., in: Z. DoleΕΎal, S. Uno (Eds.), KEK Report 2010-1, 2010. [6] M. Akemoto, D. Arakawa, A. Enomoto, S. Fukuda, Y. Funakoshi, K. Furukawa, T. Higo, T. Honda, H. Honma, N. Iida, M. Ikeda, K. Kakihara, T. Kamitani, T. Kasuga, H. Katagiri, S. Kazakov, M. Kikuchi, Y. Kobayashi, H. Koiso, N. Kudou, M. Kurashina, H. Matsushita, T. Matsumoto, S. Matsumoto, S. Michizono, T. Mimashi, T. Mitsuhashi, T. Miura, T. Miyajima, S. Nagahashi, H. Nakajima, K. Nakao, T. Obina, Y. Ogawa, Y. Ohnishi, S. Ohsawa, K. Oide, T. Oogoe, M. Satoh, T. Shidara, A. Shirakawa, M. Suetake, T. Sugimura, T. Suwada, M. Tadano, T. Takenaka, M. Tawada, A. Ueda, Y. Yano, K. Yokoyama, M. Yoshida, Prog. Theor. Exp. Phys. 2013, 03A002. [7] K. Furukawa, et al., in: Proceedings of the 3rd International Particle Accelerator Conference, IPACβ13, Shanghai, China, 2013, pp. 1583β1585. [8] I. Abe, N. Akasaka, M. Akemoto, S. Anami, A. Enomoto, J. Flanagan, S. Fukuda, H. Fukuma, Y. Funakoshi, K. Furukawa, H. Hanaki, H. Honma, N. Iida, M. Ikeda, K. Kakihara, N. Kamikubota, T. Kamitani, H. Katagiri, T. Kawamoto, M. Kikuchi, H. Kobayashi, H. Koiso, T. Matsumoto, S. Michizono, K. Nakahara, H. Nakajima, K. Nakao, Y. Ogawa, Y. Ohnishi, S. Ohsawa, K. Oide, T. Oogoe, Y. Otake, I. Sato, K. Satoh, T. Shidara, A. Shirakawa, M. Suetake, T. Suwada, T. Urano, S. Yamaguchi, Y. Yano, Nucl. Instrum. Methods Phys. Res. 499 (2003) 167. [9] https://evacvacuum.com. [10] https://www.tek.com. [11] http://www.mitsubishi-cable.co.jp/en/. [12] https://www.hubersuhner.com/en.
The derivatives of the delay-time πππ (sensitivity) obtained at each nominal set point in the longitudinal phase-space parameters after the calibration correction procedure at the pre-injector and A1 are listed in Table 1. The derivatives of the delay-time response were obtained using the fitting curves with polynomial functions. A sensitive region for the measured delay-time can be calculated at each nominal set point. The sensitive region is defined by the phase region corresponding to one standard deviation in the delay-time measurement, while the averaging operation can further reduce statistical errors. It can be seen that the most sensitive parameter in the delay-time measurement is the SHB1 phase, whose sensitivity is β2.2 Β± 0.3 ps/deg.; the sensitive region is Β±0.55 Β± 0.06 deg. in variation of the SHB1 phase. Meanwhile, the least sensitive parameter is the PB phase, whose sensitivity is β0.09 Β± 0.02 ps/deg.; the sensitive region is Β±14 Β± 3 deg. in variation of the PB phase. Thus, analyses of multi-dimensional longitudinal phase spaces based on simultaneous multi-dimensional measurements using the longitudinal phase-space parameters can help study the longitudinal physical parameters of the charged beams in real-time in nominal accelerator operation. 6. Conclusions In this research, we successfully developed and tested a new beamtiming monitor to non-destructively diagnose the longitudinal phasespace parameters of single-bunched electron beams with high-bunch charges in the KEKB injector linac. The resolution in the delay-time measurement was found to be βΌ1.2 ps in one standard deviation based on a pulse-by-pulse basis measurement. The responses of the delay-time were also successfully measured as a function of the longitudinal phase-space parameters at the preinjector and location A1, and the sensitive regions for one-shot measurement were obtained for each parameter. Although the obtained results were sufficient for non-destructive monitoring of the variations in the beam-timing measurements in real-time at the injector linac, another technique with a zero-crossing discriminator may improve the resolution in the delay-time measurement and broaden the dynamic range on the beam charges. The developed BTM can be applied to complex longitudinal phase-space instrumentations in large accelerator complexes.
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Longitudinal phase-space diagnostics using a stripline-type beam-timing monitor at the KEKB injector linac T. Suwada β Accelerator Laboratory, High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan Department of Accelerator Science, Graduate University for Advanced Studies (SOKENDAI), 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan
ARTICLE
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Keywords: Beam-timing diagnostic instrumentations Beam-timing monitors Longitudinal phase spaces Linear accelerator
ABSTRACT A new beam-timing monitor (BTM) has been developed to analyze the longitudinal beam dynamics and bunching characteristics at the pre-injector of the KEKB injector linear accelerator (linac). The BTM is a conventional stripline-type beam monitor with two pickup electrodes. It measures the relative time delay between the arrival time of the beam signal and 1st-zero-cross time of the fundamental accelerating radio frequency (rf) signal (2856 MHz) immediately after the detection of the beam signal. The beam tests were performed to evaluate the performance and characteristics of the BTM for primary single-bunched electron beams with high bunch charges of βΌ8 nC for positron production. It was found that the results show that the resolution in the delay-time measurement is π βΌ1.2 ps in one standard deviation. This report describes the basic design of the BTM system, the beam tests, and results in detail, to investigate the sensitivity and stability of the beam timing based on the longitudinal phase-space parameters at the pre-injector and location A1 of the injector linac, along with the calibration method in the pulse-height variation of the BTM signal.
1. Introduction It is important to diagnose not only the transverse, but also the longitudinal phase-spaces of the charged particle beams with as high accuracy as possible, to stably accelerate and transport them, and to maintain the beam qualities along the entire long sections in highenergy accelerator complexes. Although many diagnostic instrumentation techniques such as beam position monitors [1] and wire scanners [2] are available in transverse diagnostics, only a few instrumentation techniques are available for the longitudinal direction. A beam-timing monitor (BTM) is one of the longitudinal diagnostic instrumentation techniques, using which the arrival time of the charged particle beams can be measured with respect to a fundamental accelerating radio frequency (rf) wave. Based on the BTM instrumentation, non-destructive diagnostics in the longitudinal direction may become available, through which the longitudinal beam optics and bunching characteristics can be investigated, especially at the pre-injector section, in real-time in accelerator operation. The Super KEK B-factory (SKEKB) [3] is a next-generation B-factory that is currently in operation at KEK, after the KEK B-factory (KEKB) [4] was discontinued in 2010. The SKEKB is an electron/positron collider with asymmetric energies; it comprises 4 GeV positron (LER) and 7 GeV electron (HER) rings in which the designed stored beam currents are 3.6 A and 2.6 A, respectively. The target luminosity (8 Γ 1035 cmβ2 sβ1 )
of the SKEKB is 40 times the peak luminosity of the KEKB. The highenergy flavor particle physics experiments, considering the CP violation in B mesons [5], is the main driver behind this study. The KEKB injector linac [6] is an electron/positron linear accelerator for both the SKEKB rings and two light sources: the Photon Factory (PF) and Photon Factory-Advanced Ring for pulse X-rays (PF-AR). The injector linac was drastically upgraded for the SKEKB [7]. The BTM is one of essential diagnostic instruments to perform a nondestructive diagnosis of the beam optics in the longitudinal direction along the entire injector linac based on the measurements of the arrival time of charged beams. In this study, the basic design, developments, and experimental results of the new BTM employed in large accelerator complexes are reported in detail. 2. Overview of the pre-injector system The main function of the pre-injector of the injector linac is briefly described here. The pre-injector can produce a high-intensity and single-bunched beam of proper beam characteristics with charges of 10 nC, a bunch length of 4.2 ps in one standard deviation, and a normalized emittance well below 0.1 mm in one standard deviation. The generation of such a high-intensity electron beam is required as primary electrons for positron generation. A conventional triode-type
β Correspondence to: Accelerator Laboratory, High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan. E-mail address: [email protected].
https://doi.org/10.1016/j.nima.2019.162922 Received 5 August 2019; Received in revised form 10 September 2019; Accepted 4 October 2019 Available online 9 October 2019 0168-9002/Β© 2019 Elsevier B.V. All rights reserved.
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Nuclear Inst. and Methods in Physics Research, A 949 (2020) 162922
Fig. 1. Mechanical drawings of the BTM, (π) front view, (π) side view, and (π) a photograph of the BTM installed at location A44. The length is indicated in millimeters.
possible, so that the signal can be picked-up with short rise time and high peak voltage without any signal degradation. The inner diameter (28.6 mm) between the electrodes and the angular width (50β¦ ) of the electrode were chosen to comprise a 50 Ξ© transmission line. Quick-release flange couplings (NW40, standard KF flange [9]) were used at both ends of the monitor for easy installation in the beam line.
thermionic gun and a high-speed grid pulser were employed to achieve high current intensities. A high voltage of 180 kV is applied to the gun, and a maximum charge of 15 nC is applied for the pulse width of less than 2 ns. The grid pulser controls the beam repetition (maximum 50 Hz) as well as the beam intensity, depending on the beam modes by changing the output voltage. A two-subharmonic-buncher system (SHB1 at 114 MHz and SHB2 at 571 MHz) is introduced after the electron gun, allowing for smooth pulse compression in the following bunching section. After the two SHBs, the S-band (2856 MHz) prebuncher (PB) and buncher (B) systems are installed to realize the high-intensity and single-bunched beam at the optimized acceleration voltages in PB and B (1.3 MV/m and 20 MV/m, respectively). A solenoid-focusing field (maximum 0.2 T) in the pre-injector is optimized to maintain the Brillouin flow to minimize the emittance increase due to space-charge forces. The nominal beam energy is estimated to be πΈ βΌ 25 MeV at the exit of the pre-injector. More detailed descriptions of the pre-injector can be found in detail elsewhere [8].
3.2. Design of the instrumentation system A typical pickup signal is generated from one channel of the BTM, which shows a bipolar signal wave, while another channel of the BTM is simply terminated by a 50 Ξ© terminator. The pickup signal is directly sent to a real-time oscilloscope (Tektronix, DPO70404C, BW4 GHz, 25 GS/s [10]) through an rf coaxial cable of length 30 m (WF-H50-4S, Mitsubishi Cable Industries, Inc. [11]). The minimal time resolution of the oscilloscope is specified as 200 fs. A fundamental accelerating rf signal (2856 MHz) is sent to another channel of the oscilloscope, which was divided from the rf monitor line by an rf coaxial cable of length 20 m (S04272B, HUBER+SUHNER, Ltd. [12]). The oscilloscope measures the delay-time using its internal function, in which the start time is triggered by the front edge of the BTM signal, and the stop time is determined by the 1st zero-cross of the accelerating rf signal. The BTM was installed at location A44 in sector A during summer shutdown in 2018. A44 is located 50 m downstream of the thermionic electron gun, where the electron energy is πΈ βΌ 530 MeV. The purpose of the BTM is to non-destructively diagnose the bunching characteristics at the pre-injector, the beam optics, and stability in the longitudinal direction after the pre-injector.
3. Beam-timing monitor system 3.1. Mechanical design Mechanical drawings of the BTM, (π) front view, (π) side view, and (π) a photograph of the BTM installed at location A44, are shown in Fig. 1. It is a conventional stripline-type monitor made of stainless steel (SUS304) with two pickups (SMA-vacuum-feedthrough) upstream in the vertical direction, while the downstream ends are short-circuited to a pipe to simplify the manufacturing process. The total length (πΏ = 500 mm) was chosen as the stripline length (πΏπ = 448 mm) as long as 2
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Nuclear Inst. and Methods in Physics Research, A 949 (2020) 162922
Fig. 2. (π) Typical BTM signal with 12 dB fixed attenuators, and (π) similar BTM and accelerating rf signals measured for the primary electron beams. The image is an enlarged view of (π).
4. Beam tests 4.1. Signal response of the BTM The signal responses of the BTM were measured by using primary electron beams for positron production. The beam charges of the electron beam were typically βΌ8.2 nC/bunch during this experiment. The typical signal waveform is shown in Fig. 2(π). 12 dB fixed attenuators were inserted to the signal input channel in order to adjust the input signal intensity to the dynamic range of the oscilloscope. The typical pulse height (ππ ) was βΌ1.9 V with the fixed attenuators for typical primary electron beams. The time interval between the bipolar signal peaks is 3 ns, which corresponds to the turnaround time of the signal propagation along the stripline electrode. Such a long time interval may be sufficient to obtain a clear front edge of the bipolar signal without any distortion and attenuation. This is the reason why such a long time period was applied to the stripline electrode of the BTM. It can be seen that the fast rise time (ππ ) of the front edge of the bipolar signal is ππ βΌ 120 ps. Fig. 2(π) shows the typical signal waveform along with the fundamental accelerating rf signal, for which the horizontal time axis and vertical range are expanded and set as 40 ps/div and 500 mV/div. The fast front edge of the bipolar signal was used to trigger the oscilloscope, and the trigger threshold level (πth ) was set to be a fixed value, πth = β1 V. The threshold level corresponds to the pulse height of βΌ53% to the typical BTM signal for the primary electron beams. The time at which the front edge of the BTM signal across the trigger threshold level, gives the start time π0 , and the stop time π1 , may be obtained using the time at which the first falling edge of the accelerating rf signal zero-crosses in the delay-time measurement. Thus, the measured delay-time (ππ ) is simply defined by, ππ = π1 β π0 ,
Fig. 3. Time traces of the delay-time (ππ ) and pulse height (ππ ) in the delay-time measurement in typical operation of the injector linac for the LER injection in one day.
Fig. 3, in which SHB1π and PX/PYA1M indicate the phase tuning of SHB1 and the current tuning applied to the horizontal (π) and vertical (π ) pulsed steering magnets installed at location A1M, which are located βΌ16 m downstream of the thermionic electron gun. 4.3. Pulse-height calibration procedure in the delay-time measurement The measured delay-time depends, in principle, on the pulse height of the BTM signal as shown in Fig. 2, because the trigger threshold level is set to be constant, and the start time in the delay-time measurement varies according to the pulse height. Thus, the measured delay-time should be properly corrected to prevent any pulse-height dependence. Fig. 4 shows the variation in the delay-time measurement as a function of the attenuation value with fixed attenuators (1 dB step) in the calibration measurement applied to the primary electron beams. The fixed attenuators were inserted at the input channel of the fundamental accelerating rf signal in order to measure the variation in the electrical length of the fixed attenuators, and the delay-times were measured as a function of the attenuation values. The number of data points for each attenuator value is 1000; a data point is given by a set of average and standard errors. The result clearly shows a linear relation between the attenuation values and the measured delay-times. Further, it is seen that the delay-time per 1 dB (π₯ππ ) is π₯ππ = 88.3 Β± 0.6 ps/dB. Fig. 5 shows the variation in the delay-time measurement as a function of the pulse height of the BTM signal with fixed attenuators (1
(1)
and it can be easily measured using the internal function of the oscilloscope. 4.2. Time traces in the delay-time measurement Fig. 3 shows the time traces of the delay-time and the pulse height obtained in the delay-time measurements without any corrections for the signal waveforms in typical operation of the injector linac for the LER injection in one day. It can be seen that the time trace of the delay-time varies with the pulse height. While some step-like variations can be seen in the time traces, they are otherwise relatively stable. The occurrence of such steplike variations was due to various beam tunings by operators during the nominal operation for the LER injection. Several beam tunings were recorded in the operation log files of the injector linac. The typical parameters in beam tunings during the measurements are shown in 3
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Fig. 4. Variation (π₯ππ ) in the delay-time measurement as a function of the attenuation values with fixed attenuators (1 dB step) in the calibration measurement applied to the primary electron beams.
Fig. 6. Distribution plot of the delay-times after the pulse-height correction procedure in the measurement for the primary electron beams, and β¨πππ β© shows the mean value of πππ .
delay-time πππ is simply given by πππ = ππ + π₯ππ .
(3)
Fig. 6 shows the distribution plot of the delay-times after the pulse-height correction procedure measured for the primary electron beams, where β¨πππ β© indicates the mean value of πππ . Here, the distribution plot was plotted using the data between 9:04 and 10:42 am on 27/Feb/2019, as shown in Fig. 3; the number of data was 3681. One standard deviation was obtained as π β 1.2 ps based on the fitting procedure with a Gaussian function. This value limits the oneshot measurement to the delay-time because of the limitations of the oscilloscope in noise floor level, while the averaging operation could further decrease the statistical error in the delay-time measurement. 5. Test results 5.1. Delay-time response measurements for the pre-injector parameters By adopting typical parameters at the pre-injector and location A1, the delay-time responses of the BTM were measured as a function of these parameters. The typical parameters at the pre-injector are the phases of the SHB1 and SHB2, the phases of the B and PB, and those are the phase of the accelerating structure and the field strength of steering magnets at location A1. Here, it should be noted that each phase is defined by the difference from each nominal set point. Fig. 7 shows the results of the delay-time response measurements depending on the pre-injector parameters. Fig. 7(π) and (π) show the variations in the delay-time and pulse height without any pulse-height corrections, and the variations in the delay-time both with and without the pulse-height corrections as a function of the SHB1 phase (π₯π), respectively. Fig. 7(π) and (π) show the similar results as shown in Fig. 7(π) and (π) as a function of the SHB2 phase (π₯π), respectively. Fig. 7(π) and (π ) show the similar results as a function of the B phase (π₯π). Fig. 7(π) and (β) show the similar results as a function of the PB phase (π₯π). Here, the number of each data point is 600, and each data point is given by a set of average and statistical errors based on one standard deviation. The measured delay-times were successfully corrected based on the pulse-height fitting procedure.
Fig. 5. Variation (π₯ππ ) in the delay-time measurement as a function of the pulse height of the BTM signal with fixed attenuators (1 dB step) in the calibration measurement.
dB step) in the calibration measurement. It should be noted that equal numbers of fixed attenuators (1 dB step) were inserted at both the input channels of the oscilloscope to properly compensate the variations in the electrical length of each channel due to the insertion of fixed attenuators in this delay-time measurement. The result shows that the variation in the delay-time measurement as a function of the pulse height is approximately in accordance with a parabolic fitting function. The measured delay-time should be corrected using the following fitting function, π₯ππ = 76.0ππ2 β 291.7ππ + 279.2,
(2)
based on the least-squares fitting procedure, in which the units of the pulse height and delay-time are V and ps, respectively. The corrected 4
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Nuclear Inst. and Methods in Physics Research, A 949 (2020) 162922
Fig. 7. (π) Variations in the delay-time ππ and pulse height ππ without any pulse-height correction, (π) variations in the delay-time ππ both with and without the pulse-height correction as a function of the SHB1 phase (π₯π), (π) and (π) the similar results as a function of the SHB2 phase (π₯π), (π) and (π ) the similar results as a function of the B phase (π₯π), (π) and (β) the similar results as a function of the PB phase (π₯π). The solid lines show a guide for the polynomial fitting curve (2nd- or 4th-order) in the plots with the pulse-height correction, and a guide for only the eye in the other plots.
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Nuclear Inst. and Methods in Physics Research, A 949 (2020) 162922
Fig. 8. (π) Variations in the delay-time ππ and pulse height ππ without any pulse-height correction, (π) variations in the delay-time ππ both with and without the pulse-height correction as a function of the Acc A1 phase (π₯π), (π) and (π) the similar results as a function of the current (πΌ) applied to PXA1M, (π) and (π ) the similar results as a function of the current (πΌ) applied to PYA1M. The solid lines are a guide for the polynomial fitting curve (linear or 2nd-order) in the plots with the pulse-height correction, but a guide for only the eye in the other plots.
magnets PXA1M and PYA1M, as shown in Fig. 8(π) and (π ), clearly indicate that the pulse-height correction procedure can be effectively conducted because the delay-time responses are sufficiently linearized within the measurement errors.
5.2. Delay-time response measurements for the A1 parameters Fig. 8 shows the results of the delay-time response measurements for the A1 parameters. Fig. 8(π) and (π) show the variations in the delaytime ππ and pulse height ππ without any pulse-height correction and the variations in the delay-time ππ both with and without the pulse-height correction as a function of the Acc A1 phase, respectively. Fig. 8(π) and (π) show the similar results as a function of the current applied to the pulsed steering magnet PXA1M, respectively. Fig. 8(π) and (π ) show the similar results as a function of the current applied to the pulsed steering magnet PYA1M, respectively. Here, the number of each data point is 600, and each data point is given by a set of average and statistical errors based on one standard deviation. The measured delay-times were successfully corrected based on the pulse-height fitting procedure. The results for the pulsed steering
5.3. Analysis in the sensitive region for the longitudinal phase-space parameters The maximum correction for the measured delay-time is βΌ3 ps, excluding the cases with a relatively large beam loss. It can be seen that clear and stable correlations are available for the averaged delaytimes depending on the longitudinal phase-space parameters, although detecting the variation of the delay-time on a pulse-by-pulse basis is difficult, due to beam-intensity fluctuation. 6
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Nuclear Inst. and Methods in Physics Research, A 949 (2020) 162922
Table 1 Summary table of the derivatives of the delay-time πππ obtained at each nominal set point in the longitudinal phase-space parameters after the calibration correction procedure at the pre-injector and A1.
Parameter
Sensitivity [ps/deg.]
Sensitive region [deg.]
Fitting procedure (πππ. ππππππ )
SHB1 phase π₯π SHB2 phase π₯π Buncher phase π₯π PB phase π₯π Acc A1 phase π₯π
β2.2 Β± 0.3 β0.69 Β± 0.04 β1.88 Β± 0.06 β0.09 Β± 0.02 1.07 Β± 0.03
Β±0.55 Β± 0.06 Β±2.0 Β± 0.1 Β±0.64 Β± 0.02 Β±14 Β± 3 Β±1.12 Β± 0.03
4 2 4 4 2
Acknowledgments The authors would like to thank Mr. H. Saotome of Kanto Information Service Co., Ltd. for his help in coding the data-acquisition system software. This study was fully supported by Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan. References [1] T. Suwada, N. Kamikubota, H. Fukuma, N. Akasaka, H. Kobayashi, Nucl. Instrum. Methods 440 (2000) 307. [2] N. Iida, Y. Funakoshi, M. Kikuchi, K. Satoh, T. Suwada, T. Kawamoto, in: Proc. the 1999 Particle Accelerator Conference, PACβ99, New York City, U.S.A., 1999, pp. 2108, March 29-April 2. [3] Y. Ohnishi, T. Abe, T. Adachi, K. Akai, Y. Arimoto, K. Ebihara, K. Egawa, J. Flanagan, H. Fukuma, Y. Funakoshi, K. Furukawa, T. Furuya, N. Iida, H. Iinuma, H. Ikeda, T. Ishibashi, M. Iwasaki, T. Kageyama, S. Kamada, T. Kamitani, K. Kanazawa, M. Kikuchi, H. Koiso, M. Masuzawa, T. Mimashi, T. Miura, T. Mori, A. Morita, T. Nakamura, K. Nakanishi, H. Nakayama, M. Nishiwaki, Y. Ogawa, K. Ohmi, N. Ohuchi, K. Oide, T. Oki, M. Ono, M. Satoh, K. Shibata, M. Suetake, Y. Suetsugu, R. Sugahara, H. Sugimoto, T. Suwada, M. Tawada, M. Tobiyama, N. Tokuda, K. Tsuchiya, H. Yamaoka, Y. Yano, M. Yoshida, S. Yoshimoto, D. Zhou, Z. Zong, Prog. Theor. Exp. Phys. 2013, 03A011. [4] T. Abe, K. Akai, N. Akasaka, M. Akemoto, A. Akiyama, M. Arinaga, Y. Cai, K. Ebihara, K. Egawa, A. Enomoto, E. Ezura, J. Flanagan, S. Fukuda, H. Fukuma, Y. Funakoshi, K. Furukawa, T. Furuya, J. Haba, K. Hara, T. Higo, S. Hiramatsu, H. Hisamatsu, H. Honma, T. Honma, K. Hosoyama, T. Ieiri, N. Iida, H. Ikeda, M. Ikeda, S. Inagaki, S. Isagawa, H. Ishii, A. Kabe, E. Kadokura, T. Kageyama, K. Kakihara, E. Kako, S. Kamada, T. Kamitani, K. Kanazawa, H. Katagiri, S. Kato, T. Kawamoto, S. Kazakov, M. Kikuchi, E. Kikutani, K. Kitagawa, H. Koiso, Y. Kojima, I. Komada, T. Kubo, K. Kudo, S. Kurokawa, K. Marutsuka, M. Masuzawa, S. Matsumoto, T. Matsumoto, S. Michizono, K. Mikawa, T. Mimashi, T. Mitsuhashi, S. Mitsunobu, T. Miura, K. Mori, A. Morita, Y. Morita, H. Nakai, H. Nakajima, T.T. Nakamura, H. Nakanishi, K. Nakanishi, K. Nakao, H. Nakayama, M. Nishiwaki, Y. Ogawa, K. Ohmi, Y. Ohnishi, S. Ohsawa, Y. Ohsawa, N. Ohuchi, K. Oide, T. Oki, M. Ono, T. Ozaki, E. Perevedentsev, H. Sakai, Y. Sakamoto, M. Sato, K. Satoh, M. Satoh, Y. Seimiya, K. Shibata, T. Shidara, M. Shimada, S. Stanic, M. Shirai, A. Shirakawa, T. Sueno, M. Suetake, Y. Suetsugu, R. Sugahara, T. Sugimura, T. Suwada, O. Tajima, S. Takano, S. Takasaki, T. Takenaka, Y. Takeuchi, Y. Takeuchi, M. Tawada, M. Tejima, M. Tobiyama, N. Tokuda, K. Tsuchiya, S. Uehara, S. Uno, Y. Wu, N. Yamamoto, Y. Yamamoto, Y. Yano, K. Yokoyama, Ma. Yoshida, Mi. Yoshida, S. Yoshimoto, K. Yoshino, M. Yoshioka, D. Zhou, F. Zimmermann, Z. Zong, Prog. Theor. Exp. Phys 2013, 03A001. [5] T. Abe, et al., in: Z. DoleΕΎal, S. Uno (Eds.), KEK Report 2010-1, 2010. [6] M. Akemoto, D. Arakawa, A. Enomoto, S. Fukuda, Y. Funakoshi, K. Furukawa, T. Higo, T. Honda, H. Honma, N. Iida, M. Ikeda, K. Kakihara, T. Kamitani, T. Kasuga, H. Katagiri, S. Kazakov, M. Kikuchi, Y. Kobayashi, H. Koiso, N. Kudou, M. Kurashina, H. Matsushita, T. Matsumoto, S. Matsumoto, S. Michizono, T. Mimashi, T. Mitsuhashi, T. Miura, T. Miyajima, S. Nagahashi, H. Nakajima, K. Nakao, T. Obina, Y. Ogawa, Y. Ohnishi, S. Ohsawa, K. Oide, T. Oogoe, M. Satoh, T. Shidara, A. Shirakawa, M. Suetake, T. Sugimura, T. Suwada, M. Tadano, T. Takenaka, M. Tawada, A. Ueda, Y. Yano, K. Yokoyama, M. Yoshida, Prog. Theor. Exp. Phys. 2013, 03A002. [7] K. Furukawa, et al., in: Proceedings of the 3rd International Particle Accelerator Conference, IPACβ13, Shanghai, China, 2013, pp. 1583β1585. [8] I. Abe, N. Akasaka, M. Akemoto, S. Anami, A. Enomoto, J. Flanagan, S. Fukuda, H. Fukuma, Y. Funakoshi, K. Furukawa, H. Hanaki, H. Honma, N. Iida, M. Ikeda, K. Kakihara, N. Kamikubota, T. Kamitani, H. Katagiri, T. Kawamoto, M. Kikuchi, H. Kobayashi, H. Koiso, T. Matsumoto, S. Michizono, K. Nakahara, H. Nakajima, K. Nakao, Y. Ogawa, Y. Ohnishi, S. Ohsawa, K. Oide, T. Oogoe, Y. Otake, I. Sato, K. Satoh, T. Shidara, A. Shirakawa, M. Suetake, T. Suwada, T. Urano, S. Yamaguchi, Y. Yano, Nucl. Instrum. Methods Phys. Res. 499 (2003) 167. [9] https://evacvacuum.com. [10] https://www.tek.com. [11] http://www.mitsubishi-cable.co.jp/en/. [12] https://www.hubersuhner.com/en.
The derivatives of the delay-time πππ (sensitivity) obtained at each nominal set point in the longitudinal phase-space parameters after the calibration correction procedure at the pre-injector and A1 are listed in Table 1. The derivatives of the delay-time response were obtained using the fitting curves with polynomial functions. A sensitive region for the measured delay-time can be calculated at each nominal set point. The sensitive region is defined by the phase region corresponding to one standard deviation in the delay-time measurement, while the averaging operation can further reduce statistical errors. It can be seen that the most sensitive parameter in the delay-time measurement is the SHB1 phase, whose sensitivity is β2.2 Β± 0.3 ps/deg.; the sensitive region is Β±0.55 Β± 0.06 deg. in variation of the SHB1 phase. Meanwhile, the least sensitive parameter is the PB phase, whose sensitivity is β0.09 Β± 0.02 ps/deg.; the sensitive region is Β±14 Β± 3 deg. in variation of the PB phase. Thus, analyses of multi-dimensional longitudinal phase spaces based on simultaneous multi-dimensional measurements using the longitudinal phase-space parameters can help study the longitudinal physical parameters of the charged beams in real-time in nominal accelerator operation. 6. Conclusions In this research, we successfully developed and tested a new beamtiming monitor to non-destructively diagnose the longitudinal phasespace parameters of single-bunched electron beams with high-bunch charges in the KEKB injector linac. The resolution in the delay-time measurement was found to be βΌ1.2 ps in one standard deviation based on a pulse-by-pulse basis measurement. The responses of the delay-time were also successfully measured as a function of the longitudinal phase-space parameters at the preinjector and location A1, and the sensitive regions for one-shot measurement were obtained for each parameter. Although the obtained results were sufficient for non-destructive monitoring of the variations in the beam-timing measurements in real-time at the injector linac, another technique with a zero-crossing discriminator may improve the resolution in the delay-time measurement and broaden the dynamic range on the beam charges. The developed BTM can be applied to complex longitudinal phase-space instrumentations in large accelerator complexes.
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