Diamond Light Source Beam Stabilization Feedback System Mark Heron, Head of Control Systems

Diamond Light Source Beam Stabilization Feedback System Mark Heron, Head of Control Systems

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## Diamond Light Source Beam Stabilization Feedback System Mark Heron, Head of Control Systems

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**Diamond Light Source Beam Stabilization Feedback SystemMark**Heron, Head of Control Systems Diamond Light Source Beam Stabilization Feedback System**Beam Stabilization Feedback System**• Describe Orbit Stabilization feedback system applied to Diamond Storage Ring • Requirements • Feedback Process • Feedback Controller • Communication Controller • Computation • Structure • Installation • Performance Diamond Light Source Beam Stabilization Feedback System**Orbit Feedback: Requirements**• Overall requirement • To stabilise the electron beam in the SR to maximise photons on the experiment sample • Detail requirements for Beam Stabilization Feedback System • For the photon beam position to be reproducible fill to fill of SR • To keep the photon beam stable on the sample • To keep the electron beam stable to better than 10% of dimensions in X and Y and 10% opening angle • Over a time scale of 10s mSec to days Diamond Light Source Beam Stabilization Feedback System**Orbit Feedback: Requirements**• There are a number of ongoing beam disturbances to suppress • Long term - Years/Months • Ground settling • Season changes • Medium - Days/Hours • Sun and Moon • Day-night variations (thermal) • Rivers, rain, water table, wind • Synchrotron radiation • Refills and start-up • Sensor motion • Drift of electronics • Local machinery • Filling patterns • Short - Minutes/Seconds • Ground vibrations • Traffic, Earth quakes • Power supplies • Injectors • Insertion devices • Air conditioning • Refrigerators/compressors • Water cooling • Beam instabilities in general Diamond Light Source Beam Stabilization Feedback System**Orbit Feedback: Feedback Process**7x X and 7 x Y per Cell (Total of 336) Corrector Magnets (Actuators) 7 x X and 7 x Y per Cell ( Total of 336) BPM Positions (Sensors) Diamond Light Source Beam Stabilization Feedback System**Orbit Feedback: Feedback Process**• Orbit feedback is an example of a cross-directional control problem • Each sensor and actuator can be reasonably assumed to have the same dynamics • The response the linear map from actuator effort to sensor position Inverse Response Matrix Vector DC Setpoints [168] Vector BPM Setpoints [168] Regulators [168] Vector of Corr Magnet Values[168] Vector of BPM Positions[168] Vector Product Σ Σ Accelerator Diamond Light Source Beam Stabilization Feedback System**Orbit Feedback: Feedback Process**• Orbit Feedback is made up of three parts • Feedback algorithm • Maintains required stability • Communication Controller • Take data from 168 x 2 BPM monitors distributed over 561m to Computation Nodes • Computation Nodes for feedback algorithm • Calculate correction values in real-time • Write correction values to the power supplies for the magnets • Realise the required performance sample rate Fs=10kHz • All of above in ~100usec Diamond Light Source Beam Stabilization Feedback System**Orbit Feedback: Feedback Controller**• Response Matrix maps from actuators ( Corrector Magnets) to monitors (BPMs) • For Feedback we need to go from monitors (BPMs) to actuators ( Corrector Magnets) • Use Signal Value Decomposition of the Response Matrix to get the pseudo Inverse Responsive Matrix • This is ill-conditioned hence increases sensitivity to BPMs noise. Apply regularization to scale the singular values in calculating the pseudo-inverse • Regularized pseudo Inverse Responsive Matrix gives a robust map from monitors ( BPMs) to actuators (Corrector Magnets) Response Matrix Inverse Response Matrix Diamond Light Source Beam Stabilization Feedback System**FOFB Latencies / Bandwidth**• Libera BPM Group delay of FIR: 148 µs • Libera BPM Group delay of 2 IIR: < 71 µs • Distribution of data around ring: 50 µs • DMA transfer to CPU: 49 µs • Conversion integer to float : 5 µs • Matrix multiplication 2*7*168: 4 µs • PID controller : 1 µs • Write into PS controller: 3 µs • Total: < 331 µs • Magnet/chamber estimated to have 500 Hz BW • Bandwidth of PS controller currently limits loop (set to 100Hz, but programmable) Diamond Light Source Beam Stabilization Feedback System**Orbit Feedback: Feedback Open Loop Response**• Measure the plant open loop characteristic • First order response plus delay • At Ts= 100usec the delay ~4 x Ts Diamond Light Source Beam Stabilization Feedback System**E**Error U Input on Process Disturbance D Y Output Σ Σ Gc Controller Gp Process R Set Point _ Internal Model Controller _ GPM Process Model Σ Orbit Feedback: Feedback Controller • Use an Internal Model Controller (IMC) which uses a process model in the feedback loop to remove process effects from the feedback loop • IMC gives a single parameter to optimise and leads to better performance and robustness than the traditional controllers (PID) on systems with a delays. • Built a model for SISO version of the system, plant model and gain controller • Optimised for stability and robustness • Determined by Gain and Phase margins Diamond Light Source Beam Stabilization Feedback System**Orbit Feedback: Communication Controller**• Requirements for communications • Move the data from 168 BPMs to the Computation nodes in deterministic time • Performance • Time budget 50usec • Reliability of data transfer • Cope with data loss, but can’t retransmit • Resilience to loss of connection(s) or node(s) • Need to recover or resume operation from loss of nodes or connections • Considered using standard product or protocols • Reflective memory • MAC/IP/TCP/UDP don’ fit well with above • Commercial solutions didn’t meet requirements hence designed the Communication Controller Diamond Light Source Beam Stabilization Feedback System**Orbit Feedback: Communication Controller**• Low latency, high reliability communication network. • Utilise the available Xilinx FPGA Rocket IO interface on Libera BPM. • Designed a packet forwarding Communication Controller in VHDL • Each Node is connected to at least 2 other Nodes • At start of frame, a Node (Libera BPM unit) forwards its data on each link • All data received on any input link forwarded once on all outputs • Same basic design used inside Libera BPM and inside Computation Node receiver Diamond Light Source Beam Stabilization Feedback System**Orbit Feedback: Communication Controller**Define communication packet 30 bytes SOP 20 Bytes data CRC32 EOP idle • Bit rate of 2.5Gbps gives link speed incl. 8b/10b = 250MB/s • Packet transmission time for 30 Byte @ 250MB/s = 120ns • Minimal total transmission time 2 planes (168 * 120nsec) = 20.16us Packet payload (20 Bytes) • 32 bit ID, time frame count, status, flags • 32 bit x-Position [nm] • 32 bit y-Position [nm] • 32 bit BPM Sum • 32 bit Time Stamp [nsec] Packet Framing (10 Bytes) • 16 bit SOP • 32 bit CRC32 • 16 bit EOP • 16 bit idle Diamond Light Source Beam Stabilization Feedback System**Communication Frame No 1**COMPUTE NODE ALL BPM DATA COMPUTE NODE ALL BPM DATA BPM 1 DATA BPM 2 DATA BPM 3 DATA BPM 4 DATA Click to start Click to finish Diamond Light Source Beam Stabilization Feedback System**Communication Frame No 2**COMPUTE NODE ALL BPM DATA COMPUTE NODE ALL BPM DATA BPM 1 DATA BPM 2 DATA BPM 3 DATA BPM 4 DATA Click to start Click to finish Diamond Light Source Beam Stabilization Feedback System**Communication Frame No 3**COMPUTE NODE ALL BPM DATA COMPUTE NODE ALL BPM DATA BPM 1 DATA BPM 2 DATA BPM 3 DATA BPM 4 DATA Click to finish Click to start Diamond Light Source Beam Stabilization Feedback System**Communication Frame No 4**COMPUTE NODE ALL BPM DATA COMPUTE NODE ALL BPM DATA BPM 1 DATA BPM 2 DATA BPM 3 DATA BPM 4 DATA Click to finish Click to start Diamond Light Source Beam Stabilization Feedback System**Orbit Feedback: Communication Controller**Computation Node BPM Monitors One Cell • Actual network is connected as Torus • Data distribution < 40usec • Robust to loss of link(s) or node(s) • With loss of links or nodes the propagation delay increases but with 50usec budget . Diamond Light Source Beam Stabilization Feedback System**Orbit Feedback: Computation**• Data move from Communication Controller interface into processor memory • Computation aspects breaks down into 3 parts • Mapping from monitor to actuator space • Matrix multiplication • Appling the IMC regulator • Realised as a 5th order IIR on each of 168 x 2 actuator inputs • Multiply accumulate • Appling rate of change limiter and bounds checking to preserve the beam and enable smooth starting and stopping • Logic and arithmetic • Data move from processor to Power Supplies. Diamond Light Source Beam Stabilization Feedback System**Orbit Feedback: Computation**• Use MVME5500 for embeded VME Systems • Features • 1GHz MHz MPC7455 PowerPC Processor • Cache 32K L1, 256K L2, 2 MB L3 • Gigabit Ethernet and Fast Ethernet Port • Two PCI 64-bit/66 MHz PMC-Sockets • To interface Communication Controller • AltiVec Coprocessor • Fixed-length vector operation • Single Instruction Multiple Data • Optimized for digital signal processing • Multiply, Multiply-accumulate • 2.2 Gigaﬂops/sec • Use VxWorks as RTOS Diamond Light Source Beam Stabilization Feedback System**Orbit Feedback: Computation**Inverse Response Matrix Correctors BPM • Using AltiVec processor • Full Response Matrix x2 multiplication take 96 usec • Partition the problem • Calculate 1/24th of the corrector values ie one Cells worth in 4usec • Regulation takes 1usec on PPC processor • But requires 24 processors boards • Fits well with the distributed nature of the problem = 168 168 * Sub Matrix of Inverse Response Matrix Correctors BPM 7 = 168 * Diamond Light Source Beam Stabilization Feedback System**Orbit Feedback: Structure (one of 24 cells)**Controls Network Event Network PS VME crate PMC Rocket IO FB Processor PSU IF PSU IF Processor Event Rx … PSU 1 PSU 14 14 Corrector PSUs eBPM eBPM eBPM eBPM eBPM eBPM eBPM Cell -n Cell +n Cell +m Cell -m Diamond Light Source Beam Stabilization Feedback System**Orbit Feedback: Installation (one of 24 cells)**Computation Node Corrector power supplies BPM Monitors Diamond Light Source Beam Stabilization Feedback System**Orbit Feedback: Controller Performance**Diamond Light Source Beam Stabilization Feedback System**Orbit Feedback: Performance**60mA Suppression of beam motion Diamond Light Source Beam Stabilization Feedback System**Orbit Feedback: Performance**Diamond Light Source Beam Stabilization Feedback System**Communications Controller Availability**• The Diamond Communication controller is now being used on Soleil, Delta and ESRF • Its available from Diamond (without support) or from ITech as an option on the Libera BPM with commercail support Diamond Light Source Beam Stabilization Feedback System**Acknowledgement**• This is the work of many people. • Including Diamond Control Systems Group, Steven Duncan (Oxford University), Leo Breuss (Super Computing Systems) and others. Diamond Light Source Beam Stabilization Feedback System**Questions?**Diamond Light Source Beam Stabilization Feedback System