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Real Time Measurement and Control at JET Overview & Status. Robert Felton 1 , and JET EFDA Contributors 1 Euratom / UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxon, OX14 3DB, UK.

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real time measurement and control at jet overview status
Real Time Measurement and Control at JETOverview & Status

Robert Felton1, and JET EFDA Contributors

1 Euratom / UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxon, OX14 3DB, UK

This work this work has been performed under the European Fusion Development Agreement. It is funded in part by the United Kingdom Engineering and Physical Sciences Research Council and by EURATOM

ICALEPCS 2005 / RTMC at JET / R.Felton

jet joint european tokamak
JET = Joint European Tokamak
  • Fusion plasmas in reactor-relevant conditions
  • Theory - Deuterium and Tritium easiest to access
    • D + D = T 1MeV + p 3MeV
    • D + T = 4He 3.5 MeV + n 14 MeV
    • temperature 100 M oC,
    • density 2-3 x 1020 m-3 (1 mg m-3)
    • confinement > 1s
      • improved confinement modes
    • complex interplay of magnetic and kinetic forces
      • internal and edge instabilities with pressure gradients
      • short and long range forces: not “classical ideal gas”
  • Practical - Toroidal Magnetic Confinement
    • magnetic confinement, shape and current
    • power loads on vessel components
    • particle fuelling and exhaust
    • impurities from plasma-wall interaction

ICALEPCS 2005 / RTMC at JET / R.Felton

jet joint european tokamak1
JET = Joint European Tokamak
  • Machine Engineering - many and varied issues
    • vessel toroidal R 3m, r 2m, 200 m3, Inconel
    • wall CFC tiles (Beryllium and Tungsten coming)
    • vacuum base 10-8 mBar (cryo), plasma 10-5 mBar
    • magnets 32 Toroidal, 9 Poloidal, ~ kV, ~ kA
    • heating NB, 20MW, RF 30MHz 8MW, 3.7GHz 10MW
    • fuelling 12 gas injectors + pellet; ~500 mBarl per pulse
    • radiological Biological shield, Tritium compatibility
    • remote-handling radioactive and toxic (Be) components
    • diagnostics magnetic, thermal, optical x-ray .. visible, neutronic ...

Pulsed ~ 10s 300MJ

ICALEPCS 2005 / RTMC at JET / R.Felton

jet joint european tokamak2
JET = Joint European Tokamak
  • Systems Engineering - many and varied
    • machine control
      • hierarchical, distributed, pulsed
      • home-grown
    • real-time communications
      • analogue, digital signals
      • data packet networks
    • operations data
      • 15000 points, 35000 pulses and growing
    • data acquisition
      • 1ns … 1s, nV .. kV,
      • VME, PCI, CAMAC, PLC
    • data analysis
      • traditionally post pulse,
      • increasingly real-time
    • remote participation
      • VRVS

ICALEPCS 2005 / RTMC at JET / R.Felton

tokamak measurement control
Tokamak Measurement & Control

Hierarchical machine control

Systems (vessel, magnets, gas, auxiliary heat & fuel, diagnostics)

Independent, with common, distributed time-base (fibre-optic + local decode)

Controlled by specific Operators

Connected by ethernet (TCP/UDP/IP; > 100 systems, miles of copper/fibre)

Operations (experiments)

Parameter sets designed by Session Leader in pulse schedule

Distributed to the Systems by Level1 Supervisor infrastructure

Checked and loaded to machine by Engineer-in-Charge, and System Operators

Distributed real-time control


Real-time, calibrated outputs (avoid device dependence)

Real-time data sent to/from a Central Controller over ATM AAL5 (~ 40 systems)

Central Controller has its own Operator (PDO)


Control algorithm - conceptualised by Scientists, realised by PDO

Event driven (step NB on n=2 mode) and feed-back (3He conc, q-profile)

High level language in pulse schedule

ICALEPCS 2005 / RTMC at JET / R.Felton

hierarchical machine control
Hierarchical Machine Control

L1 Machine Supervisors

user interface

component data

parameter data

results data

user & system logs

L2 Machine Systems

control & status

start & stop

set-up & readout

r-t signal processing

r-t physics

L3 Device Drivers

specific functions

Level 1












Level 2

NB oct4








Level 3


gas valve




ICALEPCS 2005 / RTMC at JET / R.Felton

machine operations
Machine Operations

The EIC and Operators validate the parameters (JET Operating Instructions) and load the plant.

Other users (e.g. Heating, Diagnostics) set-up their equipment.

The Plasma Duty Officer prepares and loads Real-Time Control Algorithms.

Check & Load

Pulse Schedule

EIC, Operators


Pulse Schedule


Pulse Schedule

Pulse Schedule



plant state

Run Pulse


Pulse Schedules

reference to other pulse schedules or JET pulses

convert physics parameters to control parameters.

validate parameters for consistency and safety.

non-experts use expert scenarios for otherwise tricky situations (shape)



ICALEPCS 2005 / RTMC at JET / R.Felton

the jet real time control facility basic
The JET Real-Time Control Facility - Basic

Shape & Current Control


PF Coils

Interferom Density

GAS + Pellets






Comms network analogue

ICALEPCS 2005 / RTMC at JET / R.Felton

the jet real time control facility 2005
The JET Real-Time Control Facility - 2005

Shape & Current Control (PPCC)

PF Coils


VUV impurities

GAS + Pellets


Vis Da, Brem, ELM


Neutron X-ray etc.

Vis H/D/T



ECE Te (R)


q profile


CXS Ti (R)

Flux surfaces EQX



Wall Load

MSE pitch (R)

EQX kinetic map

Simulink code

Coil Protection

X-ray Ti (0)

Pale blue = Diagnostic, Sky blue = Analysis, Red = Heating / Fuelling / Magnets & Power, Yellow = PPCC (XSC), Green = RTMC

R-T Controller

R-T Signal Server

Comms network ATM, some analogue

ICALEPCS 2005 / RTMC at JET / R.Felton

distributed process control real time

physics device independent

standard data sets

sizes : 4 to 400 float pt nos.

rates : 1 to 250 ms


fast, low latency < 0.15 ms


changes : local impact

isolation : fibre-optic

range : 1 .. 100 m


analogue messy

ATM AAL5 configurable, reliable, available

Industry standard, multi-platform, multi-vendor

Time - a seperate network

Distributed Process Control (Real-Time)

Level 2









ICALEPCS 2005 / RTMC at JET / R.Felton

diagnostics analysis
Diagnostics & Analysis

Earl Ferrers:“My Lords, what kind of thermometer reads a temperature of 140 million degrees centigrade without melting?”

Viscount Davidson:“My Lords, I should think a rather large one.”

from a debate on JET in the House of Lords (1987)

Wide range of processing techniques, and space / time resolution

Filtering and down-samplingBlack Body Bolometer 48 chan, 2ms out

Cross-calibration factorsElectron Cyclotron Emission 96 chan. 2ms

Phase tracking of modulated signals Far InfraRed Interferometry 15 chan. 2ms

Lock-in amplifiers (in software) Motional Stark Effect 25 chan. 2ms

Levenberg Marquadt spectral fitting Charge Exchange Spectr. 14 spectra, 50ms

Thomson Scattering

LIDAR laser 250ms, analysis 25 ms

Plasma magnetic boundary by Taylor expansion

“XLOC” 65 coeffs, 2ms

Finite element MHD equilibrium Grad-Shafranov

“Equinox” 500 pt mesh 25ms

Interpolation Te, Ne, q, etc on flux surfaces

“Equinox map” r/a = 0; 0.1; 1.0

The JET LIDAR Thomson scattering system

ICALEPCS 2005 / RTMC at JET / R.Felton

magnets heating fuelling
Magnets, Heating & Fuelling

Physics Inputs Outputs Rate

Shape & Current Magnetics PF currents [9] 2 msVertical Stability Fast Radial Field 0.2 ms

Gas & PelletsGIM[3] GIM[3] 10 msDensity Control Dens[3] Dens[3] 10 ms

Neutral BeamPreq[8] Pact[8] 10 ms120kV 60A 20 MW

Ion Cyclotron RFPreq[4], dFreq[4] Pact[4], dFact[4] 10 ms25..50 MHz 4MW

Lower Hybrid RFPreq[3] Pact[3] 10 ms12 GHz 4MW

Alfven EigenmodeFreq Fact 10 ms

[n] refer to Groups == flexible selection of different NB PINIs, RF oscillators, antennae, gasses, etc.

ICALEPCS 2005 / RTMC at JET / R.Felton

the real time controller
The Real-Time Controller

Preparation Level1

  • User (PDO) designs and loads the algorithm
  • High level process block / data flow language

Operation Level2

  • RTCC receives measurement data
  • RTCC evaluates the user algorithm
  • RTCC sends heat /fuel requests

Diag. Inputs




  • flexible, general purpose (not low-level code)
  • easy (for PDO) :

Event-triggered e.g. disruption avoidance, MHD

Feedback SISO e.g. b with NBI

  • difficult (even for PDO) :

MIMO control e.g. profiles

Vector, matrix calculations, state-space

Modular sub-routines



10 ms cycle

ICALEPCS 2005 / RTMC at JET / R.Felton

the real time controller matlab simulink extension
The Real-Time Controller - Matlab/Simulink extension

Preparation Matlab/Simulink & Level1

  • User designs Matlab / Simulink models
  • User generates C function, data and DLL files
  • User transfers the code and parameter files to RTMX

Operation Level2

  • RTMX receives Diagnostic data, etc.
  • RTMX sends control requests to RTCC
  • RTCC relays the Heat/Fuel requests

Diag. Inputs

Simulink model

RTMX processor



  • Flexible
  • EFDA users work on control problem at home lab
  • Use Matlab / Simulink function libraries (discrete time)
  • Responsibilities
    • PDO still loads and runs RTMX and RTCC
    • Protection stays with Local Managers



10 ms cycle

ICALEPCS 2005 / RTMC at JET / R.Felton

control design
Control Design





r(t) or R(z)



uff(t) or Uff(z)

operating point


y(t) or Y(z)sensor

u(t) or U(z) actuator

System Identification

To obtain signals Actuator : u(t) e.g. PNB and Sensor y(t) e.g. bNuse theoretical models TRANSP, JETTO, ASTRA, CRONOS, GS2, …or use experimental data.

Model the process P as a differential equation for y(t) resulting from u(t). use State-Space or Laplace transforms : Y(z) = GP(z) . U(z)

Control Design

Design a controller C which achieves a desired reference signal r(t) by driving the actuator u(t) using feedback of the measured signal y(t) within constraints (e.g. error, settling time)Check the controller C by simulation, using the process model P

U(z) = GC(z) . E(z) E(z) = R(z) - Y(z)

ICALEPCS 2005 / RTMC at JET / R.Felton

rt system engineering
RT System Engineering
  • RT systems have been developed to satisfy JET Scientific Programme
    • they work in parallel with existing measurement and control systems
    • they integrate with existing system infrastructures
  • Even so, diversity and sustainability not always balanced
    • Common Application Frameworks - HTTP protocol
      • 1 VxWorks, 2 Windows - healthy competition - should have prize-giving !
    • Common Platforms
      • VME + PowerPC + VxWorks & PCI + PC + Windows - future ?
    • Association-supplied Diagnostics “In-kind procurement”
      • Windows + Linux diverse interfaces, long-term support of internals ?
  • RT systems will evolve further
    • Need to improve functional partitioning, and data distribution
    • Model-based system engineering not yet established at JET way to go!









ICALEPCS 2005 / RTMC at JET / R.Felton

work in progress jet s ep programme
Work In Progress (JET’s EP programme)
  • Magnets / Shape and Current Control

eXtreme Shape Control Plasma Ops, CREATE, ENEA, CEA

Coil Protection System Power Supplies

  • Heating and Fuelling

xxLM upgrade to PowerPC and ATM CODAS

RF frequency control, LH position control CODAS

  • Diagnostics

Bolometer, MSE, X-ray Expts, CODAS

visible cameras, video distribution, hot spots Expts, CODAS

  • Analysis

Matlab / Simulink Plasma Ops

Equinox and Polarimetry, MSE Plasma Ops, CEA, U.Nice

Disruption Prediction Plasma Ops, U.Naples, ENEA

L-mode / H-mode Plasma Ops, & Murari

  • Databases & Communications

extend ATM network, Plasma Ops, CODAS

ICALEPCS 2005 / RTMC at JET / R.Felton

long term to do jet s ep2 programme
Long term To Do (JET’s EP2 programme)
  • Magnets / Shape and Current Control
    • Vertical Stabilsation upgrade project ~ many Associations, ~ MEu !
    • Error Field Correction Coils control ?
  • Heating and Fuelling
    • ELM info for ITER-like antenna ?
    • Pellet synch
  • Diagnostics & Analysis
    • EP2: Be / W Diagnostics, Neutron and Gamma Cameras
    • Alven Eigenmodes ?
    • RT magnetics analysis to speed up PostPulse Analysis
    • “Integrated” Analysisancient (map onto flux) and modern (pattern recog.)
  • Databases & Communications & Computers
    • try EPICS, MDSplus
    • evaluate new network technology Is there an Integrated Services Data Network (control, status, events, audio, video, time)?
    • evaluate new computer technology PCIexpress, CELL

ICALEPCS 2005 / RTMC at JET / R.Felton

Real-time Diagnostics

simplified operation and analysis :: reliable quick-look

real-time processing will be “designed in” to many new Diagnostics

limited by lines of sight, field of view, calibration dependencies

Real-time Magnets, Heating & Fuelling

improving modelling and control algorithms for shape and stability

improving power output and control

Real-time Experiment Control

SISO and MIMO demonstrated; more sophisticated tools needed

Real-time Communications

ATM ok - fast enough for most applications, flexible, reliable

Science Requirements (JET programme in support of ITER) can best be satisified by Real-Time Measurement and Control

Scientific Task Forces explore Plasma and Fusion Physics, and physics-based control concepts - either simple or complex

Real-time systems are the means to practically demonstrate the concepts.


ICALEPCS 2005 / RTMC at JET / R.Felton