New controls for White Circuits power supplies for the booster synchrotron of Taiwan light source

The controls of the White Circuits for the booster synchrotron of Taiwan Light Source (TLS) were developed in the late 1990s. That design is based on various analog circuitry to detect 10 Hz magnet amplitude and phase. The existing implementation consists of analog regulation for amplitude control and digital regulation for the relative phase between magnet families. Recently, modernized White Circuits controls were implemented to prevent component obsolescence in the existing system. The upgraded system adopts digital regulation for both amplitude and phase loops. Improve performance and easy maintenance are the goals of this upgrade.


Introduction
The Taiwan Light Source (TLS) is a 1.5-GeV third generation of synchrotron light source, and it has been operated since 1993 at the National Synchrotron Radiation Research Center (NSRRC).TLS consists of a 50 MeV electron LINAC, a 1.5 GeV booster synchrotron, and a storage ring with 360 mA top-up injection.Its circumference is 120 m with a harmonic number of 200.The controls for the White Circuits [1,2] of the booster synchrotron in the TLS were developed in the late 1990s.Its design is based on various analog circuits for detecting the amplitude and phase of a 10 Hz magnet.The current implementation utilizes analog regulation for amplitude control and digital regulation for the relative phase between magnet families.The old control system [3][4][5] is being considered for redesign due to the age and difficulty of maintenance of the old system.New modernized White Circuits controls were implemented recently to avoid obsolesce of components of the existing system.Upgraded systems adopt digital regulation for amplitude and phase regulation loops.
To ensure the normal operation of the new TLS booster White Circuit control system, many systems such as the timing system, arbitrary waveform generator system, regulation system, and interlock system are required.The timing system is used to provide and transmit the trigger signals required for the operation of the system.An 8-channel Arbitrary Waveform Generator (AWG) device has been introduced in this application, which can provide adjustable pulse and waveform outputs to meet the power supply and timing control requirements.The utilization of commercially available AWG devices instead of specially designed equipment [6] can offer the advantage of improved maintainability and reduced effort.
The regulation system is used to dynamically adjust the output waveform parameters of the AWG, ensuring that the output of the power supply remains stable at the setting value during an injection operation.The interlock system functions to protect and ensure the correct operating sequence of the power supply, preventing equipment malfunctions.
On the back end of the control system, a Python script and an EPICS architecture have been integrated.On the front end, a concise user interface has been developed using the EDM tool for remote real-time parameter control and status display.The goal of this upgrade is to improve performance and ease of maintenance with a new control system.The detailed content will be summarized and presented in this paper.

System architecture 2.1. System layout
The layout of the TLS booster White Circuit control system is illustrated in Figure 1.The hardware components include an industrial computer with an ADC module, arbitrary waveform generator (AWG) device, RS232 converter, and interlock module.The control signals that pass through the interlock module are used for controlling the power supply output.The power supply is connected to the White Circuits system and the current waveform is read back through the DCCT for feedback to fine-tune the waveform parameters of the AWG.The software components consist of EPICS IOC, PID, and Python scripts.The Python scripts include control programs for the AWG, waveform fitting, and regulation PID loop.

Timing system
The old booster control system's timing relied on measuring the booster dipole current waveform to generate the booster injection point trigger, which was then synchronized with the master clock and coincidence clock.The current booster injection point is now controlled by the new TLS booster White Circuit control system.The new timing system uses a time-based 10 Hz injection point trigger, which is generated from an AWG device, to synchronize the booster ramping waveform and is predefined for booster reference injection and extraction.

Regulation system
To stable control the power supply output of the White Circuit, the regulation system is necessary, which consists of three parts: using ADC to capture the output current signal of the White Circuit, performing fitting analysis on the current signal to extract the amplitude and phase values of the waveform, and finally using PID feedback to control the amplitude and phase setting values of the AWG device.The output current waveform of the White Circuit is captured by a Hytec ADC8417 IP module with 24 bits resolution, which is installed in a MXC industry computer.A Python fitting script is used to analyze the amplitude and phase of the power supply output waveform obtained from the ADC readings.The EPICS Proportional-Integral-Derivative (PID) algorithms were implemented for real-time auto-tuning of the amplitude and phase of AWG output waveform.The overall regulation loop has a synchronous 10 Hz update frequency.

Interlock system
The working conditions of the White Circuit require a combination of a set of DC values and another set of AC waveforms.Without the DC set values, supplying only the AC waveforms would cause a failure in the unipolar capacitor within the White Circuit, and in severe cases, could result in the explosion of the capacitor.Therefore, an interlock system was designed to ensure the safe operation of the White Circuit power supply.The interlock module consists of an external hardware circuit that is installed between the AWG output and the power supply control signal input.It is used to determine whether the DC set values and AC waveforms are present simultaneously and to respond by either allowing or blocking conduction.When both DC and AC signals are present, the control signal for the power supply can be supplied smoothly.Conversely, when the DC signal is not yet ready, the interlock module will not allow the AC waveform signal to be supplied to the power supply.

AWG device
The application employs an 8-channel arbitrary waveform generator (model P350) developed by Highland Technology.The device is built with a Field Programmable Gate Array (FPGA) chip, an embedded Linux device with Gigabit Ethernet that facilitates system integration with EPICS.It provides eight independent and synchronized 16-bit waveform playback functions.The amplitude, phase, and time shift parameters of the output waveform can be continuously and instantly adjusted online.The overall architecture and functionality can meet the requirements.The AWG device uses the wavetable working mode, mainly to provide pulse timing waveform signals to the subsystem, including signals such as 10Hz, injection points, and extraction points.The selected pulse waveform file for this application is 100 microseconds in pulse width, 32768 points in length, and played back at a speed of 10 Hz.

EPICS architecture
To achieve remote control and reading of the AWG device through EPICS PV, an industrial computer (Linux 64-bit) equipped with EPICS and Python was utilized.A Python program connects to the AWG device through the Secure Shell Protocol (SSH) communication protocol for operation and reading actions.All data can be saved in the EPICS Soft IOC (Input/Output Controller) via Python and Channel Access (CA) to enable real-time remote GUI operation of the AWG device.The overall architecture is shown in Figure 2.

Channel configuration
To meet the requirements of the White Circuit control system for the TLS Booster, the output channel configuration of the AWG device is shown in Table 1.The first four channels are output pulse type waveforms for the timing system, which are read from the pre-set waveform files; the last four channels are output sine waveforms for the RF and the three main power supply systems (DACPS -Dipole AC Power Supply, FQACPS -Focusing Quadrupoles Power Supply, DQACPS -Defocusing Quadrupoles Power Supply).

Python script
This application involves writing Python programs that use the Paramiko [7] package tool to send control command strings to the AWG device via the SSH communication protocol over a network cable and to read the working status of the device.With the Paramiko package, a communication channel between the AWG device and EPICS PV can be established.The communication speed is also a key parameter in this application, so the data update frequency was measured.With the Python program continuously accessing the AWG device without interruption, the average data update frequency can reach 25 Hz, as shown in Figure 3.The decrease in update frequency is caused by the uncertainty of network communication delay between AWG equipment and the Python program.Although the update frequency may sometimes drop below 15 Hz, the basic value is still greater than 10 Hz, which is sufficient for the design and operation requirements of the TLS 10 Hz control system.

GUI development
For the present application, a GUI control interface for the AWG device was developed by using EDM tools, as shown in

Performance of new system
The stability of the injection current in the booster ring can be used to quickly evaluate whether a new White Circuit control system performs better.As shown in Figure 5, a comparison of the injection current between the old and new systems in the booster ring reveals that the current fluctuations and continuity in the old system are poorer.The new system can stabilize the injection current variations, has a higher average current, and does not experience any intermittent conditions.All of this demonstrates that the performance of the new White Circuit control system for the TLS booster has been improved.

Conclusion
In response to the upgrading needs of the Taiwan Light Source (TLS) White Circuit control system, an Arbitrary Waveform Generator (AWG) device, a new timing architecture, a redesigned interlock module, and digital regulation loops were introduced to meet the requirements.The EPICS control framework was established to enable remote real-time parameter control and status display through PV.Based on the experience of more than a year of operation on the new control system, it can be concluded that the system does meet the expected requirements and even outperforms the old system in terms of overall stability and ease of maintenance.The stability and performance of the AWG device played a key role in achieving these results.

Figure 1 .
Figure 1.Layout of White circuit control system.

Figure 4 .
Figure 4. GUI control interface of the AWG devices.

14th 6 Figure 5 .
Figure 5. Strip chart of performance evaluation of old (upper) and new (lower) White Circuit control system.

Table 1 .
Channel configuration of AWG device.