22/4/2009 mark heron diamond light source beam stabilization feedback system diamond light source...

22/4/2009 Mark Heron

Diamond Light Source Beam Stabilization Feedback System


Mark Heron, Head of Control Systems



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



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

mmx 3.121231.0 radradx 4.2241.0' mmy 6.04.61.0 radrady 4.041.0'



Orbit Feedback: Requirements

• 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

• There are a number of ongoing beam disturbances to suppress



Orbit Feedback: Feedback Process

7 x X and 7 x Y per Cell ( Total of 336) BPM Positions (Sensors)

7x X and 7 x Y per Cell (Total of 336) Corrector Magnets (Actuators)



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

Regulators [168]Vector

ProductΣ Σ

Vector BPM Setpoints [168]

Vector DC Setpoints [168]

Inverse Response Matrix

Accelerator

Vector of BPM Positions[168]

Vector of Corr Magnet

Values[168]



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



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



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)



• Measure the plant open loop characteristic– First order response plus delay

• At Ts= 100usec the delay ~4 x Ts

Orbit Feedback: Feedback Open Loop Response



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

Σ

Σ

ΣGc Controller

GPM Process Model

Gp Process

Y Output

Disturbance DU Input on Process

R Set Point

E Error

Internal Model Controller

_

_



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



Orbit Feedback: Communication Controller

• 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

• 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




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]

SOP 20 Bytes data CRC32 EOP idle

Packet Framing (10 Bytes)

• 16 bit SOP

• 32 bit CRC32

• 16 bit EOP

• 16 bit idle

Define communication packet 30 bytes

• 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



Click to start Click to finish

BPM 1 DATA

COMPUTE NODEALL BPM DATA

BPM 2 DATA BPM 3 DATA BPM 4 DATA


Communication Frame No 1







BPM 1 DATA BPM 2 DATA BPM 3 DATA BPM 4 DATA




Computation Node

BPM MonitorsOne 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 .



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.



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



Orbit Feedback: Computation

168

168

CorrectorsInverse Response

Matrix BPM

= *

168

7

CorrectorsSub Matrix of Inverse

Response Matrix 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



Pro

cess

or

Controls Network

PS VME crate

eBPM eBPM eBPM eBPM eBPM eBPM eBPM

Cell -m

Cell -n Cell +n

Cell +m

Orbit Feedback: Structure (one of 24 cells)

14 Corrector PSUs

PSU 1 PSU 14

PS

U I

F

PS

U I

F…

Event Network

FB

Pro

cess

or

PM

C R

ock

et

IO

Eve

nt

Rx



Orbit Feedback: Installation (one of 24 cells)

Computation Node

Corrector power supplies

BPM Monitors



Orbit Feedback: Controller Performance



Orbit Feedback: Performance

60mA

Suppressionof beam motion



Orbit Feedback: Performance



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



Acknowledgement

• This is the work of many people. • Including Diamond Control Systems Group, Steven Duncan (Oxford

University), Leo Breuss (Super Computing Systems) and others.



Questions?

22/4/2009 mark heron diamond light source beam stabilization feedback system diamond light source...

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