Weixing Cheng

Techniques for transparent lattice measurement and correction

A novel method has been successfully demonstrated at NSLS-II to characterize the lattice parameters with gated BPM turn-by-turn (TbT) capability. This method can be used at high current operation. Conventional lattice characterization and tuning are carried out at low current in dedicated machine studies which include beam-based measurement/correction of orbit, tune, dispersion, betabeat, phase advance, coupling etc. At the NSLS-II storage ring, we observed lattice drifting during beam accumulation in user operation. Coupling and lifetime change while insertion device (ID) gaps are moved. With the new method, dynamical lattice correction is possible to achieve reliable and productive operations. A bunchby-bunch feedback system excites a small fraction (~1%) of bunches and gated BPMs are aligned to see those bunch motions. The gated TbT position data are used to characterize the lattice hence correction can be applied. As there are ~1% of total charges disturbed for a short period of time (several ms), this method is transparent to general user operation. We demonstrated the effectiveness of these tools during high current user operation.

Improvements of NSLS-II X-ray Diagnostic Beamlines

There are two X-ray diagnostic beamlines (XDB) developed at NSLS-II storage ring to measure emittance, energy spread, and other machine parameters. The first beamline utilizes a soft bending magnet radiation has been in operation since 2014. The tungsten pinhole originally located in the air had corrosion issue. The beamline has been improved by extending the vacuum to the imaging system. The second X-ray pinhole beamline using three-pole wiggler (TPW) radiation has been constructed and commissioned recently. Energy spread is able to be precisely measured due to large dispersion at the source point. A gated camera is equipped with the new beamline to acquire profiles within one turn. Recent operation experience and beam measurements will be presented in this paper.

Beam position monitor gate functionality implementation and applications

Graphical abstract

Fast glitch detection of coupled bunch instabilities and orbit motions

During high current operation at NSLS-II storage ring, vertical beam size spikes have been noticed. The spikes are believed due to ion instability associates with vacuum activities localized in the ring. A new tool has been developed using gated BPM turn-by-turn (TBT) data to detect beam centroid glitches. When one turn orbit deviates outside the predefined window, a global event will be generated. This allows synchronized data acquisition of TBT beam positions around the ring. Bunch by bunch data is acquired at the same time to analyze the possible coupled bunch instabilities (CBI). Besides CBI mainly due to ion bursts, fast orbit glitches have been captured with the new tool. Sources of the glitches can be identified.

Beam measurements using visible synchrotron light at NSLS2 storage ring

Visible Synchrotron Light Monitor (SLM) diagnostic beamline has been designed and constructed at NSLS2 storage ring, to characterize the electron beam profile at various machine conditions. Due to the excellent alignment, SLM beamline was able to see the first visible light when beam was circulating the ring for the first turn. The beamline has been commissioned for the past year. Besides a normal CCD camera to monitor the beam profile, streak camera and gated camera are used to measure the longitudinal and transverse profile to understand the beam dynamics. Measurement results from these cameras will be presented in this paper. A time correlated single photon counting system (TCSPC) has also been setup to measure the single bunch purity.

NSLS-II Active Interlock System and Post-Mortem Architecture

The NSLS-II at Brookhaven National Laboratory (BNL) started the user beam service in early 2015, and is currently operating 13 of the insertion device (ID) and beamlines as well as constructing new beamlines. The fast machine protection consists of an active interlock system (AIS), beam position monitor (BPM), cell controller (CCs) and front-end (FE) systems. The AIS measures the electron beam envelop and the dumps the beam by turning off RF system, and then the diagnostic system provides the post-mortem data for an analysis of which system caused the beam dump and the machine status analysis. NSLS-II post-mortem system involves AIS, CCs, BPMs, radio frequency system (RFs), power supply systems (PSs) as well as the timing system. This paper describes the AIS architecture and PM performance for NSLS-II safe operations. INTRODUCTION NSLS-II storage ring (SR) completed commissioning in 2014 [1-2], and started operation and user beam service in 2015. In 2016, up to 16 insertion devices were installed as well as the user service with two superconducting RF cavity and 250 mA stored beam current. The active interlock system is one of the major machine protection systems from the synchrotron radiation. The main purpose of AIS is to protect the insertion device vacuum chamber and the storage ring vacuum chamber from missteered synchrotron radiations from IDs and Dipole magnets radiation. The required active interlock insertion device (AI-ID) system response time is maximum < 1 ms, because through 1 ms duration damping wiggler (DW) aluminum vacuum chamber will increase the surface temperature to 100 C at 1.5 mrad vertical angles. For the storage ring bending magnet protection, which is called the active interlock bending magnet (AI-BM), the response time is 10 ms. Allowance envelop defined for protecting the device and configured offset is xy=+/-0.5 mm, and the angle is xy=+/0.25 mrad. This paper will present the AIS hardware configuration, FPGA internal functions, global PM hardware configuration and internal timing diagrams. NSLS-II operation status and the future plan. SYSTEM DESCRIPTION NSLS-II AIS showed robust and stable performance during operation, and lots of flexibilities for implementing machine protection from the synchrotron radiation and critical machine faults. One of the benefits is the real-time offset/angle calculation, and all of the decision engines are located at the central FPGA core, which is called C31. The AIS hardware layout is shown in Fig 1, and more details of the system and each device regarding characteristics and functions are described in [1-2]. AI Database And Web interface softIO C1 softIO C2 AI FPGA Interfa ce RF Transmitter and LLRF C OPI-CSS PM Client DISK Storage EPS RF Transmitter and LLRF D Input signals from machine Ethernet cable (1 Gbps) Wire (TTL) SDI fiber network (5 Gbps) Cell 1 Cell 30 SDI CW SDI CCW Timing

Precise Beam Orbit Response Measurement with AC Excitation

Fast correctors at NSLS-II storage ring have broad frequency response (~1kHz bandwidth). Together with high accurate BPM 10kHz data, they makes the broadband fast orbit feedback realistic. Fast orbit feedback (FOFB) calculation is taking place in the cell controller where BPM 10kHz data is transferred from local BPMs in the cell and shared with other cells around the ring. With integrated numerical controlled oscillator (NCO) inside the cell controller FPGA, beam orbit response can be precisely measured while driving the electron beam with AC current. Compared to the normal DC orbit response measurement, this method eliminates the measurement errors due to orbit drift. Accurately measured orbit response matrix can be used to characterize the machine lattice. Fast corrector frequency responses have been measured using the same method, by scanning the excitation frequency. This information can be used to optimize the fast orbit feedback control loop.

NSLS-II Active Interlock System for Fast Machine Protection

At National Synchrotron Light Source-II (NSLS-II), a field-programmable gate array (FPGA) based global active interlock system (AIS) has been commissioned and used for beam operations. The main propose of AIS is to protect insertion devices (ID) and vacuum chambers from the thermal damage of high density synchrotron radiation power. This report describes the status of AIS hardware, software architectures and operation experience.