1. Atomic beam diagnostics on fusion devices
Sándor Zoletnik
Department of Plasma Physics
KFKI Research Institute for Particle and Nuclear Physics
(KFKI RMKI)
Association EURATOM-HAS
KFKI-RMKI
Association - HAS

2. Fusion research
Magnetic confinement fusion research reached a state where plasma conditions are close to the ones required for a fusion reactor.
This is made possible by a huge improvement of
plasma technology in the past decades:
Magnetic configurations, improved confinement
Heating, current drive
Diagnostics and plasma control
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Atomic beam diagnostics on fusion devices

3. Plasma diagnostics
Plasma diagnostics uses a set of special and extreme physical methods using a wide range of physical phenomena and technologies:
Magnetic and electric probes
Electromagnetic wave measurements:
active and passive
from microwave to gamma ray
Particle detectors, analyzers
Particle beams ….
Probes can be inserted only
into the cold edge plasma
In the core local measurements
are possible only by intersecting two lines:
Incoming beam and observation (detection)
The only exception is a category of
microwave measurements where a critical
surface exists in the plasma
O-mode
X-mode
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Atomic beam diagnostics on fusion devices

4. External coil currents
Understanding fusion plasmas
A fusion plasma is an extremely complex system with interactions on a wide range of scales (10 micron – 100 m, 0.1 microsec – 100 sec)
Beam heating
modeling
External coil currents
MHD equilibrium
and parameters
Microwave heating
RF heating
Plasma current drive
Turbulence
Transport
Plasma edge
Fuelling
Radiation loss
Fusion reactions,
alpha heating
Impurities
Primary unstable waves
Secondary (meso)
structures
Flow
instabilities
Radial profiles
Transport
Turbulence
Plasma turbulence is an especially challenging field which self-consistently determines the plasma state:
A nonlinear system of waves, flows at multiple scales
Special turbulence diagnostics are needed: well localized and fast measurements
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Atomic beam diagnostics on fusion devices

5. Beam diagnostics
Beam diagnostics are powerful techniques for measuring several plasma parameters: density, temperature, magnetic field, potential and their fluctuations.
There are two basic possibilities:
Injecting an ion beam and detecting the same
or a secondary ion beam
Need large Larmor radius
 Heavy ions, high energies
 Heavy Ion Beam probe (HIBP)
TJ-II HIBP diagnostic (CIEMAT, Madrid)
Injecting an atomic beam and observing its line radiation
Beam Emission Spectroscopy (BES), Motional Stark Effect (MSI)
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Atomic beam diagnostics on fusion devices

6. Various beams Different beams are used for BES: Gas jet (0.1 eV)
accesses only very edge of plasma (Scrape-Off Layer)
Laser blow-off (10 eV)
Somewhat inside plasma
Pulsed beam
Alkali beams (50 keV)
Up to core plasma in small devices (measures almost directly density)
Heating beams (50 keV)
Large diameter, powerful H, D, He beams reaching core plasma
Often needs special observation gemotery
MSI uses heating beams only
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Atomic beam diagnostics on fusion devices

7. Beam Emission Spectroscopy program at KFKI RMKI
KFKI RMKI has started a multi-device BES program aiming at comparative measurements on a series of different fusion devices in the EU fusion research programme.
Wendelstein 7-AS: Quasi 2D turbulence measurement with Li-beam
(Garching, Germany )
TEXTOR-94: Li-beam diagnostic
(Jülich, Germany, 2002-)
JET: Li-beam upgrade
(Culham, UK, Li-beam (2003-)
MAST: Core turbulence measurement with
BES on heating beam (Culham, UK, 2006-)
COMPASS: Various BES schemes
(Prague, Czech Rep., 2008-)
TCV: Gas jet injection
(Lausanne, Switzerland, 2007-)
ASDEX Upgrade: Turbulence measurement in Li-beam
(Garching, Germany, 2007-)
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8. BES technology at the Hungarian fusion Association
BES needs technically challenging components, KFKI RMKI has most of them:
Simulation:
Atomic physics modelling, design of schemes
Ion source:
Solid state ion source or heating beam
Acceleration and beam control system:
Focussing, beam chopping, gas injection
Detection:
High QE, fast detectors to detect all the photons and reduce background
Data evaluation:
Statistical methods, correlation analysis
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9. Beam simulation, design of schemes
Comprehensive simulation tools enable design of BES systems
Standard BES with Li, Na, … beams
Details of light collection, smearing, …
Mixture of BES and HIBP is being studied:
injecting an atomic beam and detecting ions
Vibrating beam, quasi-2D measurement
(KFKI RMKI invention, 2000)
Beam sweeps measurement region within a few microseconds
Sweeping time is shorter than turbulence decorrelation time
Spatial location maps to time in detectors:
2D information can be extracted by time-slicing data
Li-beam simulation for COMPASS
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Atomic beam diagnostics on fusion devices

10. Ion source Ion sources for alkali beams are developed at KFKI RMKI
High temperature ( °C) ceramics materials
W or Mo filament heating, heat shields
Extraction with 5-8 kV in Pierce geometry
Limited lifetime, needs replacement after hours beam operation
(a few second/discharge in current experiments)
Extracted Li-beam
Li ion source testing at KFKI RMKI
The RMKI ion source for JET
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11. Acceleration, neutralization, beam control
Alkali beams are accelerated to keV and formed by a standard 3 electrode system
Beam position/vibration/chopping is controlled by deflection plates
Neutralizer is a Na gas cell (not provided by KFKI RMKI yet)
Beam can be checked by Faraday cup, and by imaging on metal plates
Alternative acceleration schemes are being simulated.
The TEXTOR Li-beam
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12. Light detectors
BES is limited by photon statistics, needs high Q.E. 1 MHz bandwidth and low noise
The RMKI Avalanche detector system:
Compact 8 channel array using large area
Hamamatsu APDs: 5x5 mm
State-of-the-art 3-stage low noise amplifiers
Vacuum enclosure
TEC cooled/stabilised
16 channel system being built for TEXTOR
Very close to ideal detector from 1010 photons/s
Test LEDs
Detectors
Amplifiers
Ideal detector with QED=100% and 85%
Typical PM range
Calibration
Comparable in S/N to much larger and more expensive US system
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Atomic beam diagnostics on fusion devices

13. Next generation BES detectors
The detector for the upgraded MAST BES system will use a 4x8 APD matrix
Analogue electronics from previous system
Digital electronics based on KFKI RMKI camera design:
Event Detection Intelligent CAMera (EDICAM)
Will appear as high-speed (>1 MHz) low-resolution camera
Hamamatsu S8550
EDICAM itself is a new camera concept for the next generation fusion experiments and industry:
Mpixel, x32 pixel
Digital eye concept:
Low frequency readout on 1.3 Mpixel sensor
Automatic fast readout on changing regions on interest
Ultra high-speed (10G) industry-standard interface
The EDICAM sensor head under testing
These specialised cameras will have industrial applications.
A company is being set up for this purpose.
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2D BES turbulence imaging diagnostic for MAST
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14. ITER bolometer diagnostic lines of sight as designed by KFKI RMKI
Data evaluation
Comprehensive evaluation programs and statistical analysis tools have been developed for turbulence BES over the past 12 years:
Correlation and spectral analysis with all tricks to get rid of noise and background
Special methods to detect temporal and spatial changes in measurements
Related numerical technique: tomography
At present KFKI RMKI provides all tomography
simulations for ITER:
bolometer, neutron, X-ray diagnostics
Related tool:
Tomography laboratory demonstration device:
TOMOLAB
ITER bolometer diagnostic lines of sight as designed by KFKI RMKI
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15. Results: Li-BES on Wendestein 7-AS
Density profile, temporal and spatial
correlation of fluctuations are
reconstruced from SOL to edge/core
Only rought estimate of Te and Zeff is needed
Non-perturbing diagnostic
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16. Results from 2D diagnostic
2D density profile
2D correlation (radial-poloidal) function
Poloidal velocity is determined
from shift of correlation along magnetic
surface.
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17. Results from trial core BES system on MAST
Detection limit for fluctuations is 1-2%
SOL-edge turbulence is well seen:
Fluctuation level > 10%
Autocorrelation time ~50 μs
Radial propagation
Spatial correlation determined by detection
Magnetohydrodynamic modes seen, density fluctuation correlated with
magnetic field
Detection limit in upgraded system will be ~0.2%
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18. Conclusions, outlook
Our improved and new BES systems will come on-line in the next 1-2 years:
TEXTOR, ASDEX Upgrade, JET, MAST, COMPASS, TCV
KFKI RMKI has the most up-to-date technologies for BES on fusion devices
A bunch of turbulence phenomena are detected at the plasma edge:
partly explained by theory partly not
Core turbulence measurement is marginal with alkali beams
 MAST core turbulence should provide data
Improved detectors/cameras are suitable for industrial applications.
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