1. Examples of ITER CODAC requirements for diagnostics
S. Arshad
Colloquium on ITER-CODAC Plant Control Design Handbook and EU Procurement of Control and Instrumentation for ITER
28 October 2008

2. Hot fusion plasma can be contained in a magnetic field

3. New engineering and physics challenges for measurement and control
Containment improves with size – ITER will be much larger than today’s machines
JET: World’s largest tokamak
ITER
R (m)
6.2
a (m) 2
IP (MA) 16
Bt (T)
5.3
Paux (MW)
40 – 90
Pa (MW)
80+
Q (Pfus/Pin) 10
Prad (MW) 48
tpulse (s)
400+ R a
New engineering and physics challenges for measurement and control

4. Wide range of diagnostics needed to diagnose fusion plasma
Port type
No. used
Equatorial 9
Upper 12
Lower 9
Additionally many measurements inside vessel
UPPER PORT 10
X-Ray Survey
Imaging VUV Spectroscopy
UPPER PORT 11
Edge Thomson
EQUATORIAL PORT 11
X-Ray Crystal Spectroscopy, array
Divertor VUV Spectroscopy
X-Ray Survey
Core VUV Monitor
Neutral Particle Analyser
Reflectometry
EQUATORIAL PORT 9
MSE
Toroidal Interferometer / Polarimeter
ECE
Wide Angle TV/IR
DIVERTOR PORT 10
X-point LIDAR
Divertor Thomson Scattering
H-Alpha Spectroscopy
DIVERTOR PORT 8
Divertor Reflectometry

5. The EU will supply a range of diagnostics to ITER
Ports for diagnostics & heating systems
General scheme for processing of diagnostic data
Physics studies
Analog processing
Off-line processing
ADC
Real-time processing
Controller
Machine protection & plasma control
Processed data from diagnostics (Courtesy of EFDA-JET)
About 40 diagnostic systems installed in ports and inside / outside the toroidal chamber; 13 to be supplied by the EU:
Plasma wall interaction
Plasma shape & neutron profile
Temperature & density profiles
Wide-angle viewing system
Magnetics
Radial neutron camera
Core Thomson scattering
Bolometers
Core charge exchange recombination spectrometer
Hard X-ray monitor
Plasma position reflectometer
Pressure gauges
Thermocouples
LFS collective Thomson scattering
High-resolution neutron spectrometer
Gamma-ray spectrometers

6. The magnetics diagnostic is a large system for basic plasma control, machine protection and physics studies
Purpose
Prototype magnetics sensors
Control
Protection
Physics
Determine plasma current, shape and movement
Measure thermal energy of plasma
Detect and quantify plasma instabilities
Reconstruct magnetic flux surfaces (equilibrium)
Detect and quantify any current flowing from plasma into vessel         
In-vessel pick-up coil  
In-vessel pick-up coil
Ex-vessel pick-up coil
Diagnostic comprises pick-up coils, flux loops, Rogowski coils
~1050 sensors inside the vessel (shown in figure)
~600 additional sensors outside vessel
Hall probe
External rogowski coil

7. Overview of magnetics signal processing
Event triggers
dB/dt B
Int
Off-line processing
Physics studies
ADC
Amp
Real-time processing
Control & protection
dB/dt
Around 1650 sensors in total
Digital or analogue integrators
Amplifiers
Slow (4kHz) ADCs for basic equilibrium
Fast (1 MHz) ADCs for instabilities
Typically with optical isolation
Data stored for specialist off-line studies
Real-time signals distributed to other plant systems (power amplifiers for tokamak magnets, machine protection systems)
ALL NUMBERS ARE INDICATIVE

8. Plasma current and shape (1/2)
Plasma current measured by integrating magnetic field over poloidal contour (Ampere’s law)
Plasma shape characterised by gap between plasma boundary (solid red line) and first wall
Shape controlled by changing current in tokamak coils

9. Plasma current and shape
Similar arrangement for 410 in-vessel Rogowski coils feeding vessel current reconstruction code
Event triggers
dB/dt B
Int
Off-line processing
Physics studies
ADC
Amp
Real-time processing
Control & protection
dB/dt
Around 750 sensors (of which 380 in-vessel)
Typical raw signal from 0.05m2 pick-up coil in +/-60mV range under normal operation; +/-5V at disruptions
Individual signals integrated (typical time constant 100ms; output +/-5V) and digitised separately
Integrated signal in range of 0.06Vs; frequency response ~10kHz; drift <0.35mVs after pulse of 3600s
Summing integrator for ‘hardware’ calculation of plasma current (10kA-15MA range, 1% accuracy)
Integrated signals typically sampled at 4kHz (20kHz at events)
Typically 16 bit ADC with dithering, 25 bits without)
Calibration of signals
On-line data validation checks and corrective actions (e.g. voting system with 3 toroidal positions)
Second plasma current calculation from individual signals
Plasma boundary and plasma-wall gaps determined (1-2cm accuracy) 100k FLOP/cycle (10ms cycle time  0.01GFLOPS)
Control signals generated for gap control and distributed to power amplifiers for tokamak coils
Data stored for specialist off-line studies including full equilibrium reconstruction combining data from other diagnostics (20GB per pulse)
ALL NUMBERS ARE INDICATIVE

10. High frequency instabilities – analysis & control
Event triggers
dB/dt B
Int
Off-line processing
Physics studies
ADC
Amp
Real-time processing
Control & protection
dB/dt
Around 270 high frequency sensors (with response up to 100kHz)
High frequency results in relatively strong (voltage-range) signals which can be recorded directly with low gain
Frequency response up to 300kHz
RMS signals from summing amplifiers may for rapid overview of instabilities or for event triggering
16 bit resolution likely to be adequate
Sampling rates up to 1 MHz
Event triggering to manage data quantities
Data stored for specialist off-line studies; of order 50GB per pulse
Real-time signals for feedback control (resistive-wall modes)
Additional, more specialised, event triggers
Similar arrangement for around 380 in-vessel sensors for plasma vertical speed control; 10kHz sampling; 30GB storage; 1GFLOPS
ALL NUMBERS ARE INDICATIVE

11. Overview of requirements for some diagnostics
System
Electronics
ADCs
Storage (per pulse)
Magnetics
1200 integrators
650 amplifiers
1600 slow ADC channels (20kHz)
270 fast ADC channels (1 MHz)
110GB
Bolometry
500 lock-in amplifiers (50kHz)
500 ADC channels
360MB
Charge Exchange
Read-out from up to 75 CCD cameras (100 spectra/sec. 560 pixels each)
N/A
30GB
Core LIDAR TS
150 ADC channels at 20GSa/S; 10-bit samples
100MB
ALL NUMBERS ARE INDICATIVE