TPS Fast Orbit Feedback Upgrade

The orbit feedback system for the Taiwan Photon Source (TPS) was delivered in 2014. With the installation of an increasing number of insertion devices, a variety of wide-band disturbances are produced. In 2019, a proposal was put forth to enhance the stability of the orbit through the implementation of the fast orbit feedback (FOFB) system upgrade. The upgrade plan encompasses the revision of the power supply controller and an increase in the feedback computation rate from 10 kHz to 30 kHz. Following the upgrade, the bandwidth of the TPS fast orbit feedback system has been expanded from 250 Hz to 400 Hz in the vertical plane and from 200 Hz to 250 Hz in the horizontal plane. The integrated power spectrum density of the orbit could be reduced by approximately 20% with effective measures.


Introduction
These guidelines, written in the style of a submission to J. Phys.: Conf.Ser., show the best layout for your paper using Microsoft Word.If you don't wish to use the Word template provided, please use the following page setup measurements.The TPS is a 3-GeV synchrotron radiation facility that has been in operation since 2016.It is comprised of a 150 MeV S-band linac, a linac to booster transfer line (LTB), a booster synchrotron, booster to storage ring transfer line (BTS), and a storage ring with a circumference of 518.4 m [1].The TPS, a synchrotron machine with low emittance and ultra-high photon brightness, necessitates a stable beam orbit for optimal performance.In order to maintain orbit stability at a level below 1/10 of the beam size, the Fast Orbit Feedback (FOFB) system was implemented and made available to users in September 2016, shortly after the official opening of the TPS [2].
The TPS FOFB system comprises three primary subsystems, namely the Beam Position Monitoring (BPM), orbit feedback computation unit, and corrector power supply controller.The electrical system of TPS BPM utilizes I-TECH Brilliance+ [3] and the feedback computation is also employed its gigabit data exchange module (GDX).The power supply controller is the customer designed product called Corrector Power Supply Controller (CPSC), which has been contracted to D-tacq [4].
The FOFB system can be considered delicate and vulnerable.Only one little component of the system crashed or perturbed or malfunctioned could be fatal.The degradation of FOFB performance is negligible.The most severe scenario involves the activation of the orbit interlock, resulting in a beam trip.During the initial years of operation, it was observed that the failure of the FOFB system could be attributed to three primary factors: the malfunctioning of BPM electronics, data loss in GDX BPM grouping, and direct-current current transformer (DCCT) malfunction in the power supply.In order to enhance the reliability of the FOFB system, we have implemented multiple upgrades to the BPM system, both in terms of hardware and software.These upgrades have resulted in a significant decrease in the system's crash rate, thereby improving its overall performance.For the issue of data loss in BPM grouping, we have implemented a monitoring system and modified our exception-checking process to mitigate its potential impact.The malfunction of the DCCT of power supply is predominantly observed in instances where the setting values are set to zero.Following the removal of slow corrector power supplies that were not utilized for DC orbit correction, there has been a significant reduction in power supply surges caused by DCCT malfunction.
In addition to proposing a plan to improve the reliability of FOFB, we have also suggested an upgrade plan to enhance its performance.It was previously anticipated that the TPS beamlines phase II would be completed within the current year, with phase III to be implemented shortly thereafter.With the installation of an increasing number of insertion devices, it is anticipated that there will be a corresponding increase in the diversity of orbit disturbances induced.In particular, certain beamline proposals, such as the twin EPU66 fast switching or electromagnetic undulator [5], have the potential to generate high frequency noise.The upgrade plan was implemented in 2019 as a result.
The performance of the FOFB is primarily determined by the bandwidth of the FOFB, which is constrained by the bandwidth of subsystems such as the corrector, power supply, and vacuum chamber, as well as various latencies.To address this issue, TPS has implemented dedicated fast correctors for the FOFB system, which have been installed above the bellows site.Based on our estimations, it appears that the bandwidth of our subsystem is nearly sufficient.The potential cause of the bottleneck may be attributed to the latency.As a result, the upgrade plan has been determined to increase the updating frequency from 10 kHz to 30 kHz.Following the increase in update rate, a reduction in latency time for BPM, computation, and power supply setting is anticipated.The proposed upgrade plan entails the upgrading of both the BPM firmware and the power supply controller from CPSC to CPSC2.The CPSC2 had replaced the original CPSC in 2021, and its reliability has been verified.A firmware upgrade for BPM proceeded later in 2022.This report aims to provide a summary of the upgrade details for the BPM and corrector power supply, as well as a comparison of the FOFB performance before and after the upgrade.

Corrector power supply controller and BPM upgrade
The TPS initial CPSC has been developed to cater to various small power supply requirements for TPS SR/BR/LTB/BTS correctors, fast correctors, skews, trims, and other related applications.The device offers a wide range of functionalities, including synchronous setting, pre-and post-trigger waveform readings, arbitrary waveform play and fast setting for FOFB.The newly developed CPSC2 has been specifically designed for fast correctors.The necessity for high resolution of analogue input is reduced due to the smaller kick strength, and the long-term stability is not deemed critical.Hence, it is possible to opt for a more economical alternative that comes with an 18-bit DAC and 16-channel ADC (as opposed to CPSC's 20-bit DAC and 32-channel ADC) but lacks a thermal stabilizer.Nevertheless, all functionalities of CPSC2 are identical to those of CPSC.In order to ensure a smooth migration process, the CPSC2 has been designed to support both the original FOFB with a 10 kHz updating rate and the new FOFB with a 30 kHz updating rate.This is particularly important given the limited machine study and maintenance time available, and the fact that TPS has been operating normally.In 2020, the replacement of CPSC online running for FOFB with CPSC2 was observed for a period of time to confirm its reliability.Subsequently, each CPSC was replaced by CPSC2 in the following year, one by one.
The TPS BPM electronics were commissioned alongside the TPS beam commissioning in 2014 [6].The system comprises four distinct modules, namely the timing module, BPM modules, the interconnection board (ICB) module, and the GDX (Gigabit data exchange) module, which is responsible for FA data grouping and FOFB computation.This firmware upgrade pertains to both the BPM and GDX modules.The streaming data rate of the BPM has been enhanced from 10 kHz to 30 kHz.The reduction of BPM latency time and increase in the bandwidth of FOFB can effectively suppress orbit disturbance.The GDX modules have undergone revision to address the issue of grouping loss exception, which may otherwise disrupt the FOFB computation process.The initial frequency was 10 kHz.Following the upgrade, the frequency has been elevated to 30 kHz.The GDX modules are capable of obtaining comprehensive orbit data through their grouping mechanism.The feedback correction is computed and subsequently transmitted to the power supply controller within the corresponding cell.The FOFB system presents a multiple input and multiple output (MIMO) control problem, in which each sensor (BPM) and actuator (corrector) can be regarded as a linear map.Singular Value Decomposition (SVD) is a commonly employed method for obtaining a reliable and accurate approximation solution [7][8] [9].The blue line represents the original system, while the red line represents the upgraded system with a 30 kHz updating rate.Both horizontal and vertical bandwidth have been extended.The bandwidth for the horizontal plane has been increased from 200 Hz to 250 Hz.In the context of the vertical plane, it is noteworthy that the bandwidth has been observed to increase from 250 Hz to 400 Hz.The vertical bandwidth is more extended than the horizontal bandwidth.It is possible that the open loop bandwidth of the vertical plane exceeds that of the horizontal plane.The bottleneck in the bandwidth of the FOFB for the horizontal plane is determined by the correctors/vacuum chamber bandwidth, rather than the updating rate or latency time.

FOFB performance after upgrade with 30 kHz updating rate
Figure 2: The bandwidth comparison of FOFB before and after upgrade.Blue line is presented as the original system; red line is as the new ones after upgrade.The left plot is for horizontal plane; the right plot is for vertical plane 3.2.Short-term orbit stability comparison when FOFB on and off Figure 3 displays the spectrum of the orbit over a duration of one second.The upper subplot pertains to the horizontal plane, while the lower subplot pertains to the vertical plane.The blue line is denoted as FOFB on, while the red line is represented as FOFB off.It can be observed that the stability of the orbit is enhanced when FOFB on.The integrated power spectrum density of the vertical plane was found to be suppressed below 1 um from 1 Hz to 1 kHz, as illustrated in Figure 4.The stability of the horizontal orbit is comparatively inadequate owing to the lower bandwidth of FOFB system and the presence of high-frequency disturbances originating from the superconductive RF cavity.The upper subplot is for horizontal plane; the lower one is for the vertical plane.
3.3.Long-term orbit stability for 10 days when FOFB on Fig. 5 illustrates the long-term orbit stability of the TPS over a duration of ten days.The blue line represents the horizontal position, while the red line represents the vertical position.The vertical position fluctuation was observed to remain within a range of 0.5 microns for a period of 10 consecutive days.The horizontal fluctuation exceeds one micron by a small margin.The observed spike on the horizontal plane can be attributed to a minor seismic event.The seismic activity resulted in a temporary saturation of the FOFB system, however, it quickly recovered and did not lead to any beam trip.

Conclusions
In order to enhance the stability of the orbit, a proposed upgrade to the TPS FOFB was put forth in 2019.The proposed upgrade primarily involves increasing the updating rate from 10 kHz to 30 kHz.This will be achieved through the upgrade of the corrector power supply and the firmware revision of the BPM/FOFB.The project has been finalized and is scheduled for online operation in 2022.Following the upgrade, the bandwidth of the FOFB system in the vertical plane has been increased from 250 Hz to 400 Hz, while in the horizontal plane, it has been increased from 200 Hz to 250 Hz.With the installation of additional insertion devices and the occurrence of various orbit perturbations, the TPS has demonstrated the ability to maintain sub-micron orbit stability over both short and longterm periods.

Figure 1
illustrates the orbit feedback infrastructure, which bears resemblance to the original FOFB system.The fast streaming data of BPM is grouped by GDX extension modules.Two GDX modules 14th International Particle Accelerator Conference Journal of Physics: Conference Series 2687 (2024) 072013 IOP Publishing doi:10.1088/1742-6596/2687/7/0720133 have been installed in each cell of the BPM platforms, one for horizontal and the other for vertical.

Figure 1 :
Figure 1: FOFB infrastructure 3.1.FOFB bandwidth comparison before and after upgrade Figure 2 illustrates the comparison of bandwidth performance for FOFB before and after the upgrade.The blue line represents the original system, while the red line represents the upgraded system with a 30 kHz updating rate.Both horizontal and vertical bandwidth have been extended.The bandwidth for the horizontal plane has been increased from 200 Hz to 250 Hz.In the context of the vertical plane, it is noteworthy that the bandwidth has been observed to increase from 250 Hz to 400 Hz.The vertical bandwidth is more extended than the horizontal bandwidth.It is possible that the open loop bandwidth of the vertical plane exceeds that of the horizontal plane.The bottleneck in the bandwidth of the FOFB for the horizontal plane is determined by the correctors/vacuum chamber bandwidth, rather than the updating rate or latency time.

Figure 3 :
Figure 3: The spectrum of BPM position comparison when FOFB on and off.The upper subplot is for horizontal plane; the lower one is for the vertical plane.

Figure 4 :
Figure 4: The integrated power spectrum density of BPM position comparison when FOFB on and off.The upper subplot is for horizontal plane; the lower one is for the vertical plane.

Figure 5 :
Figure 5: The TPS long-term orbit stability for ten days.The blue is represented horizontal position;the red line is as vertical one.This horizontal spike was caused by a minor earthquake.