Chih-Hsien Huang

Beam loss studies at the Taiwan Photon Source

PIN-photodiodes and RadFETs are installed in the storage ring of the Taiwan Photon Source (TPS) to study beam loss distributions and mechanisms. In the highest dose area, the radiation comes mainly from hard X-rays produced by synchrotron bending magnets. During beam cleaning and after replacing a vacuum chamber, losses due to inelastic Coulomb scattering occur mostly downstream from bending magnets while elastic scattering causes electrons to get lost mainly after an elliptically polarizing undulator which has a limited vertical aperture. During the injection period, the beam loss pattern can be changed by modifying injection conditions or lattice settings. The beam loss usually happens in the injection section and small-aperture section. The injection efficiency can be improved by minimizing the detected injection loss.

Methods to detect error sources and their application at the TPS

For a low-emittance photon light source, beam stability is a very important property to attain a high-quality photon beam. While it is hard to avoid beam perturbations in a storage ring, it is more important to quickly find the source locations and to remove or eliminate the sources as soon as possible. In this report, we develop a method to identify the locations of multiple sources. For a source with a particular frequency, the relative phase between sources can also be obtained. This method has been a useful tool during TPS operation and its methodology and practical applications are described in this report.

Commissioning of the Bunch-by-Bunch Transverse Feedback System for the TPS Storage Ring

Taiwan Photon Source (TPS) finished its Phase II commissioning in December of 2015 after installation of two superconducting RF cavities and ten sets of insertion devices in mid-2015. The storage ring achieved to store beam current up to 520 mA. Intensive insertion devices commissioning were performed in the second quarter of 2016 and delivered beam for beam-line commissioning and performed pilot experiments. One horizontal stripline kicker and two vertical stripline kickers were installed in May 2015. Bunch-by-bunch feedback system were commissioning in the last quarter of 2015 and the second quarter of 2016. Commercial available feedback processors and power amplifiers were selected for the feedback system integration. Beam property and performance of the feedback system were measured. Problems and follow-up measures are also addressed. Results will be summarized in this report. INTRODUCTION The TPS is a 3 GeV synchrotron light source which was performed Phase I commissioning without insertion devices (ID) and with two 5-cell Petra cavities in the last quarter of 2004 and the first quarter of 2015 up to 100 mA stored beam [1]. Phase–II commissioning was done in the last quarter of 2015 with 10 sets of IDs and two KEKBtype superconducting RF modules and reached 520 mA stored beam maximum. Transverse coupled-bunch instability, caused by the resistive wall impedance and fast ion will deteriorate beam quality. Bunch-by-bunch feedback will suppress various transverse instabilities to ensure TPS achieve its design goals. Vertical bunch by bunch feedback loop was commissioning [2] in the first quarter of 2015 with prototype vertical kicker to test functionality includes feedback, bunch cleaning, single bunch transfer function, tune measurement. Power amplifier from AR and R&K were tested. One horizontal kicker and two vertical kickers were installed in the shutdown period of the second and the third quarter of 2015. Commissioning of both planes with insertion devices operation was started in the last quarter of 2015 and the second quarter of 2016. Threshold current for the longitudinal instability appeared at ~80 mA when using with two 5-cell Petra cavities without insertion devices. Longitudinal instability disappeared up to 500 mA stored beam current during phase-II commissioning equip with two KEK-B type superconducting cavities with 10 sets of insertion devices in the last quarter of 2015. Transverse instabilities are dominated by wall resistivity and ion in TPS storage ring. STATUS OF THE FEEDBACK SYSTEM Two vertical kickers and one horizontal kicker were installed during mid-2015 shutdown. Concept of these kickers is derives from the design of PSI/SLS [3] and adapt to fit vacuum duct of TPS at ID straight. Length of the electrode is 300 mm. Shunt impedance at low frequency is about 40 k and 25 k for vertical and horizontal kicker respectively, Perspective drawing and installation at the storage ring are shown in Fig. 1. To save space to accommodate more insertion devices, all kickers install at upstream of in-vacuum undulator (IU22) at three 7 m long straight. Three kickers are distributed at three short straight. This prevents the option to install all feedback electronics at the same site. Three in-vacuum insertion devices were install at these kickers respectively. The horizontal kicker was installed at upstream of SR03 (upstream straight of lattice cell #3), and two vertical kickers were installed at upstream cell SR11 and SR12. Feedback electronics for horizontal and vertical planes where installed at different areas in which shared RF frontend is impossible. The kicker electrodes are not well match to 50 Ohm. Measured impedance is around 75~95 Ohm between the feedthrough structure and electrode respect to the vacuum chamber. This leads to large broadband beam power picked up which prevent power amplifier work properly, high power low pass filter with cut off frequency 350 MHz were installed at each power amplifier output to block high frequency beam power to enter power amplifier output. Horizontal kicker x 1 set Vertical kicker x 2 sets Figure 1: Transverse kickers install at upstream of three 7 m short straight which in-vacuum undulators located. Feedback electronics of bunch-by-bunch equip feedback functionality, such as housing keep, filter design, timing adjustment, etc. It supports bunch oscillation data capture for analysis to deduce rich beam information, tune measurement, bunch clearing, beam excitation, etc. Features of the planned system include the latest high dynamic range ADC/DAC (12 bits), high performance FPGA, flexible signal processing chains, flexible filter design, bunch feedback, tune measurement, bunch † cheng.ys@nsrrc.org.tw WEPG02 Proceedings of IBIC2016, Barcelona, Spain ISBN 978-3-95450-177-9 612 C op yr ig ht

Design of a Hybrid Multiperiod Robinson Wiggler for TPS Light Source

A Robinson wiggler is designed to decrease the emittance within 1 nm · rad for Taiwan Photon Source. According to an analysis of the beam dynamics, decreasing the emittance with a multiperiod Robinson wiggler is more efficient than a single-period traditional Robinson wiggler. This wiggler consists of a dipole field and a strong gradient field, which creates a strong dynamic field integral multipole error. To enhance the gradient field and to have also a small dynamic field integral multipole error, a compensated side-pole design and an edge-pole shape in each pole are proposed in this paper. After optimization of the magnet, the dipole and gradient fields are 0.82 T and -37 T/m, respectively. The concept of the design of the magnetic circuit and the results of an analysis of the magnetic field are discussed herein.

Transient Orbit of Injection in Taiwan Light Source Storage Ring

Top-up operation has been started since many years ago at Taiwan Light Source Storage Ring (TLS-SR). For this operation it is important to reduce the beam injections should not excite the oscillation of stored beams. For further reduction of these oscillations, corrections with injection kicker-magnets are used.The details of the study will be reported in this paper. INTRODUCTION This study aimed to minimize injection transverse beam oscillation of the Taiwan Light Source Storage Ring (TLS-SR). Artificial neural network (ANN) design software, known as computer-aided formula engineering (CAFE) [1], was used to analyze and optimize the injection kicker-magnets parameters of the storage ring. We aimed to identify the main influential the injection kicker-magnets parameters of the storage ring and, through optimization, develop the injection kickermagnets parameters of the storage ring adjustment program that best stability and minimizes injection transverse beam oscillations. RESEARCH PROCESS Artificial Neural Network ANNs are construction methods for nonlinear models. Among which, back-propagation networks (BPNs) are currently the most representative and commonly applied of the ANN learning models [2] [3]. Data Collection The equipment that affects the injection transverse beam oscillations includes injection kicker-magnets(1~4). Each device has a tuning knob for the magnet voltage and timing settings with 8 values. The beam injection oscillations is determined by the turn-by-turn Beam Position Monitor (BPM) system data for the 40∼340 turns integral value. Using MATLAB programming to establish the effective operating range of each quality factor, we employed a random number setting every minute to intercept different settings and response values. In total, 134 pieces of data were obtained.[4] ANN Trainand -Test Analysis After calculating the ANN model construction, we obtained the “trainand -test” error convergence curve, as shown in Fig. 1. They appear to converge after approximately 60 computations. Figure 1: The “trainand -test ” error convergence curve. The “trainand -test ” scatter plots for the training and test samples are shown in Figs. 2 and 3, respectively. Figure 2: The “trainand -test ” scatter plot of the training samples. Figure 3: The “trainand -test ” scatter plot of the test samples. _____________________________________________________ # chiao@nsrrc.org.tw THPOW033 Proceedings of IPAC2016, Busan, Korea ISBN 978-3-95450-147-2 4012 C op yr ig ht

Design and Implementation of Control Interface and Timing Support of TPS Phase-I Beamlines

Taiwan Photon Source (TPS) with low emittance provides extremely bright X-rays. Seven advanced phaseI beamlines of TPS are being constructed and commissioned. The control interfaces for a beamline or experimental station and support from the accelerator control system are designed and are being implemented. The beamline control interface and supports include a beamline interlock status monitor, accelerator timing transmission, broadcast of accelerator operating status, transmission of the beam-current reading and control of insertion devices. This report summarizes the efforts in implementing the beamline EPICS IOC and support from the accelerator control system during beamline commissioning in TPS phase-I.