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Prog WKS 2011
RFX-mod Diagnostic systems
for 2011 campaignpresented by S. Martini
Prog WKS 2011
RFX vs RFX-mod diagnostics RFX vs RFX-mod diagnostics (from RFX Prog- Workshop 2007)
Measurement RFX RFX-mod
ne CO2 interferometer CO2 interferometer20 point/ 1 pulse Thomson scattering 84 point/10 pulse Thomson scattering
12 point edge Thomson scatteringMicrowave reflectometer Microwave reflectometer
Te Multipoint Thomson scattering 84 point/ 10 pulse Thomson scatteringSi(Li)–pulse height analyser (PHA) 12 point edge Thomson scatteringSpectroscopy (line intensity ratio) Spectroscopy (line intensity ratio)SXR two-filter monitor SXR two-filter monitor (6 chords)
SXR two-filter tomography
Ti Multichannel spectrometer Multichannel spectrometerE||B neutral particle analyser (NPA) Diagnostic Neutral Beam CXRSTOF NPA
Impurities/flows Multichannel visible–UV spectrometer Multichannel visible–UV spectrometer Flat-field survey spectrometer Flat-field survey spectrometerVacuum CTV spectrometer Vacuum CTV spectrometerInterference filter array Interference filter arrayGrazing incidence spectrometer Grazing incidence spectrometerSXR–bolometric tomography SXR–bolometric tomographyMultilayer filters SXR spectrometer Multilayer filters SXR spectrometer
Solid pellet injectorDiagnostic Neutral Beam CXRSlaser Blow-Off
Prog WKS 2011
RFXRFX vs RFX-mod diagnosticsvs RFX-mod diagnosticsMeasurement RFX RFX-mod
Fluctuations & SXR monitor array SXR tomography Turbulence Electrical probe arrays Electrical probe arrays
CO2 interferometer CO2 interferometerMicrowave reflectometer Microwave reflectometerFIR polarimeter FIR polarimeter
GPI
Edge plasma Langmuir probes Triple Langmuir probeU-probeISISGundestrup probeGPIedge Te & ne from He line intensity ratio
Plasma-Wall Int. Surface collector and erosion probes Surface collector and erosion probes/influxes Interference filter array Interference filter array
CCD cameras with interference filters CCD cameras with interference filtersHmonitors Hmonitors
CMOS fast camera
Internal B Magnetic probes Magnetic probes (Fast insertable pneum.)FIR polarimeter FIR polarimeter
Solid pellet injector+ CMOS fast camera
Prog WKS 2011
Achievements 2010
• New NPA diagnostic: First Ti measurements
• FIR polarimeter: Repair & modification to operate at longer , => improved resolution
• New horizontal SXR tomography camera: Operational
• Microwave reflectometer: Routine operation of the Ka band
• Room temperature solid pellet injector: Extensively used for wall conditioning
• CXRS/DNBI: progress in the solution of the measuring problems, => produced some preliminary data.
Prog WKS 2011
Core confinement: TCore confinement: Tee & n & nee profiles profiles
Prog WKS 2011
84 scatt. volumes on equatorial diameter (-0.95<r/a<0.85)
28 filters+APD polychormators 4 spectral channels
TS signal collectedthrough 3 ports
Fiber optic delay lines multiplex (l=15m t=70ns):
3 positions/spectrometer
ND:YLF laser (=1053nm):• E ~ 5J• Pulse length ~20ns FWHM • 10 pulses @ 50 Hz
Outline of the Main Thomson Scattering
70ns 70ns
28 Digitizers @ 500MHz
Prog WKS 2011
Main Thomson Scattering
0
100
200
300
400
500
600
700
800
-0,5 -0,4 -0,3 -0,2 -0,1 0,0 0,1 0,2 0,3 0,4 0,5
ensemble av. 1 MAfit 1MA19531 OPCD t=0,095 s
Te (eV)
r (m)
Prog WKS 2011
Main Thomson scattering• New laser (100 pulses @ 100Hz, old was 10 pulses @ 40 Hz ).
• Old YLF laser to be upgraded (to use both lasers together).
=> further increase number of pulses, study of transient events.
• Beam profiler system with fast camera installed near the laser entrance window to facilitate alignment.
• Modification of the diagnostic mechanical structure for easier mounting and installation of the collecting optics.
• Automatic windows cleaning system further developed and used for TS main windows and internal mirrors of the Zeff diagnostic.
Prog WKS 2011
• Two independent modules (A&B)
• Mod. A: CO2 & He-Ne Lasers
• Mod. B: CO2 & CO Lasers
• 14 chords
• Up to 250 kHz time resolution
• Measurement error ≈2·1018 m-3
MIR Interferometer
Prog WKS 2011
RFX MIR interferometer measurements
0
5
n (1
019 m
-3)
1B
2B
6B
7B8B
t (s)
0
5n (1
019 m
-3) 1A
2A
3A
4A5A6A
7A
8A
00.20.40.60.8
1
I t (M
A )
8147
Module B chords use in vessel mirrors
Plasma current
Module A
Module B
Prog WKS 2011
The CO2 laser are old (moreover discontinued from repair by
the manufacturer) and will be replaced in 2011.
Laser replacement will improve reliability (new one will have a
higher stability).
Further improvements 2011:
– installation of a motorized sliding retro-reflector for calibration purpose
– system for remote monitoring of laser power emission.
CO2 multi-chord interferometer
Prog WKS 2011
SXR TOMOGRAPHY
• SXR Bremsstrahlung radiation detected by Si photodiodes (25m-thick Beryllium foils)
• 78 lines of sight
• bandwidth hundreds kHz
• tomographic emissivityreconstructions based on the Cormack-Bessel algorithm
Prog WKS 2011
New manipulator for SXR tomography• New horizontal manipulator
silicon photodiodes
3 Be foils with different thickness:
• selection of SXR energy ranges
• improvement of SXR tomographic diagnostic
• double-filter technique gives Te profile
high time resolution: 100-200 kHz
high space resolution:
• 65 lines of sight
• 3 poloidal sections
• toroidal overlap
Prog WKS 2011
New horizontal SXR camera
The radial profiles of Te from Thomson
Scattering (black points) and from the
SXR data (red triangles) at the same
time for a MH pulse.
The new camera has 65 photodiodes (instead of 21) in 3 arrays of 19, 27 & 19 diodes.
Each array has its own Be foil, so that the SXR tomography can be used either to reconstruct the SXR emissivity (all the arrays with same Be foil) or the Te, profile
(through the two-foil technique).
The space resolution is 2 cm and time resolution is ≥10kHz (up to 50kHz).
A significant effort devoted to reduce EMI by the toroidal windings.
Prog WKS 2011
SXR multifilter
• New multifilter designed and built in 2009.
• 8 channels for accurate time evolution of
Te(0) with 5 kHz resolution.
• Different Be foils installed => up to 6
independent Te(0) measurements.
Prog WKS 2011
Comparison beween temperatures calculated by SXR multifilter
Black line =>Te(0) from ratio of C/B signals, green line =>Te(0)
obtained from the ratio D/A. The two Te are basically the same,
showing the cooling of the plasma when the pellet is ablated.
Time resolution 5 kHz.
Thickness of Be foils also
shown.
pellet
Prog WKS 2011
Ion temperature: NPA and Ion temperature: NPA and CXRS/DNBICXRS/DNBI
Prog WKS 2011
First Ti data from NPA Diagnostic
11-channel NPA on loan from IPP fully
commissioned in 2010 :
Measurementes show “two slopes”
neutral particle fluxes energy
distribution. Low energy population
(E<2.5 keV) presumably associated to
the bulk Maxwellian.
Preliminary Ti from low energy fluxes
gives Ti/Te≥0.5 and time behaviour
which, at high ne correlates well with Te
from SXR multifilter.
During reconnection events, fast ions
generation (E>5 kEV) also seen.
a)
“Bulk”
High energy ‘tail’
b)
a)
“Bulk”
High energy ‘tail’
b)
Prog WKS 2011
Ti measurement from NPA
During 2011 further optimization will be performed: – Improved shielding of the external magnetic field
– Remote control (from SIGMA) of the applied voltages.
– Detailed interpretation of the spectra using the Nené Monte Carlo code.
Prog WKS 2011
Diagnostic Neutral Beam
• In 2009 it was seen the beam was
stopped in the duct connecting the
injector to RFX.
• In 2010 pumping improved adding
two cryopumps and the duct cross
section increased, form 10 to 15 -
20 cm
• In one day of operation before the
shutdown hints of charge exchange
signal showed up in the spectrum
Comparison of two spectra with and without beam. The difference corresponds to the active signal.
The new duct with two 2000 l/s criopumps
Prog WKS 2011
Edge Confinement and TurbulenceEdge Confinement and Turbulence
Prog WKS 2011
Spherical mirrorPlane mirror
Vacuum window
Lens
To spectrometer for Te, ne profile measurements
He cloud
GPI
10 cm
Edge ne & Te profiles (THB) and Gas Puffing Imaging
• Edge radial profile of ne and Te by the line intensity ratio method
• Spatial resolution of 5mm in the outer 35mm of the radius for the turbulent structure measurements by the GPI system
Prog WKS 2011
Thermal Helium Beam (THB)
3 emission lines of He atomic beam injected into plasma observed. Light
collected from 8 different radial positions, 0 to 35 mm with a spatial
resolution of 5 mm:
– Now measure evolution of edge profiles of Te, ne and Pe (0.94<r/a<1)
with time resolution of 0.5 ms.
Measurements routinely available for all RFX-mod discharges.
Prog WKS 2011
Thermal Helium Beam (THB)
Using conditional average technique, it is also possible to study high
frequency fluctuations, and characterise the edge structures (“blobs”)
Coherent structures seen as peaks in density and pressure.
Prog WKS 2011
Edge Thomson Scattering• Single pulse ruby laser (7J @ 694nm, 30ns at FWHM) focused on a 3mm pin-hole in vacuum.
• Sapphire lens & prism deflect beam by 30° and image the pin-hole in vacuum vessel.
• A camera lens (f=83mm / F#1.2) collects light at ~150° from 16 positions over =1mm fibers:
12 scattering volumes for Te, ∼10mm resolution;
4 measuring points for detecting background plasma light.
• The entrance port hosts the input system & the collection window stable alignment.
• Fibers are arranged in a 4x4 pattern and fed into a 4 spectral channels spectrometer.
• An Intensified CCD (ICCD) acquires the Thomson and the Background signal
Prog WKS 2011
microwave frequency modulation pattern
Reflectometer system on RFX-mod
• When the linear profile constraint, a narrow band system gives a good estimate of the cut-off layer position
• Narrow band system can be extremely fast: – reliable measurements even in presence of strong density
fluctuations
Narrow band system (4 GHz span in 1 μs)
Reflectometer vs Edge TS
27 – 31 GHz ne ~ 1019 m-3
2 μs
f
• Full Abel reconstruction of an unknown profile requires a wide band system• But.. in many cases real profiles can be assumed linear
Prog WKS 2011
Microwave Reflectometer
Radial position of the cut-off layer as a function of the global electron density ne and of the parameter ne/nG
The system with one IMPATT source has been routinely operating on RFX-mod in 2010. This allowed to perform extensive analyses over a large discharge database, as shown below:
Radial position of the cut-off layer as a function of the electron density ne for standard and post-litization pulses
Prog WKS 2011
27 – 31 GHz ne ~ 1019 m-3
3 simultaneous narrow band systems (4 GHz span in 250 ns)
42 – 46 GHz ne ~ 2.4 1019 m-3
56 – 60 GHz ne ~ 4.2 1019 m-3
Reflectometer upgrade
• 3 point measurement:– better profile reconstruction– turbulence radial correlation measurements
• Increase of the modulation frequency:– better time resolved measurement of ne fluctuations
– direct measurement of the radial propagation – compensation of errors due to Doppler shift
microwave frequency modulation pattern0.5 μs
f
Prog WKS 2011
Fast Reciprocating Manipulator (FARM)
The FARM design has been completed in 2010.
In 2011 the manipulator and a new edge probe with
multiple measurements capability will be built.
The aims of the new diagnostic are the reconstruction of
edge ne, Te and flow profiles in all RFX-mod plasma
conditions, the investigation of turbulence and current
filaments at high Ip, and the measurement of the average
edge current density.
This latter measurement should clarify the crucial issue
of ohmic constraint satisfaction in Single Helicity
equilibria.
Prog WKS 2011
FaRM: foreseen measurements
• Radial profile of current density (useful information for plasma modeling: boundary condition input for calculation of helical equilibrium; study of power lost in the edge region)
• Current density turbulent structures
• Radial profiles of different quantities
– Pressure (ne and Te)
– Flow (parallel and perpendicular)
– Electric fields
– Vorticity
– Reynolds stress …
r
The Fast Reciprocating Manipulator (FaRM) is suitable for installation of different probe heads and can host up to one hundred signals. Maximum fast insertion is 100 mm
The f probe head will be equipped with arrays of both magnetic and electrostatic sensors
The concepts used in the U-probe head and Gundestrup head will be exploited
Prog WKS 2011
Impurities: ZImpurities: Zeff eff DiagnosticsDiagnostics
Prog WKS 2011
Previously too high Zeff values measured along a vertical
diameter due to strong contamination of the Bremsstrahlung
radiation.
Detailed inspection of the spectrum and measurements at
different , identified molecules produced close to the wall as
the contaminating source (molecular pseudo-continuum)
Solution: => A new Zeff diagnostics is under development
measuring along a toroidal path to maximize plasma
contribution relative to contaminated edge region.
Zeff from continuum Bremsstrahlung in visible range
Prog WKS 2011
Zeff diagnostic : new layout
• A mirror used to get toroidal LOS affected by reduction due to C ,B deposits.
• Improvements: –mirror face in counter-
current direction–an instertable mirror+
calibrated source allows to measure the reflectivity variation
LOS
Instertable mirror with a
calibrated lamp to
measure reflectivity of
mirror 1
Observation mirror
Telescope
RFX-mod
Previuos position of observation mirror affected by PWI
Ip
• Promising preliminar measurements in 2010
Prog WKS 2011
Internal Magnetic FieldInternal Magnetic Field
Prog WKS 2011
FIR Polarimeter summary
Main actions during 2010 :
• Recommission CO2 laser damaged by fire in 2009;
• New pre-amplifier boards for the detectors
reduced sensitivity to stray B & improved S/N ratio;
• Modifications to operate with FIR laser at 184 m
(instead of 119 m) for chords #3, 4, 6 with impact
parameters respectively -0.06, +0.06, +0.31 ,
=> factor 2.4 improved measuring resolution
(Faraday rotation angle
Prog WKS 2011
FIR polarimeter chord layout6 vertical chords (5 active)
chord name
h [m]
ch1 -0.35
ch2 -0.25
ch3 -0.06
ch4 +0.06
ch5 +0.22
ch6 +0.31
FIR radiation: =118.8 m
ch2 ch3 ch4 ch5 ch6ch1
Prog WKS 2011
FIR polarimeter new measurements
Polarimeter measurements with =184 m
Polarimeter switched to 184 m for 3 chords (#3, 4, 6)
Advantage clearly seen for chords #3 & 4, which measure small angles: at 119 m the relative error would be >100%.
Measuring error (from zero-line before/after pulse) is now 1-2°, even in the worst condition at 2 MA
Prog WKS 2011
Safety factor from pellet ablation Safety factor from pellet ablation cloudcloud
Prog WKS 2011
Magnetic field diagnostic
(r)B
(r)B
R
rq(r)
p
t
))(tan(
1)(
rR
rrq
Magnetic field profile in a RFP Relationship between pitch of the magnetic field w(r) and safety factor q(r)
@ reversal Bt=0 => vertical ablation cloud
@ magnetic axis Bp=0 => horizontal ablation cloud
Prog WKS 2011
Cryogenic pellet injector + Fast CMOS camera
Looking at the pellet from behind, the fast CMOS camera follows the time evolution of the pellet ablation cloud.
Sensor: CMOS with 17μm pixel
Shutter: electronic shutter from 16.7ms to 1.5μs independent of frame rate
Frame rate: up to 109500 fps
Max resolution: from 1024x1024 pixels up to 1000 fps to 128x16 pixels at 109500 fps
Prog WKS 2011
Ablation cloud time evolutionpenetration of the pellet inside the plasma looked with the fast CMOS camera
Prog WKS 2011
Pellet trajectory diagnostics
212
12 L
II
IIx
xx
xx
Two-Dimensional Position Sensitive Device (2D-PSD)
212
12 L
II
IIy
yy
yy
• A PN junction between two layers of resistors highly homogeneous.
• The junction is photo sensitive : electrons produced by incident photons are collected at the electrodes.
• The current collected at each electrode is proportional to the distance of the light source from the electrode itself.
Prog WKS 2011
The second PSD
x
y
z
H
K
2
Fs1
Fs2
PSDl1
PSDl2
• Pellet position is calculated considering the projected position on two PSD sensors.
• Because of errors, the projections of the two positions do not intersect .
• The assumed position of the pellet is the midpoint of the segment perpendicular to both lines.
• Only a small part of the trajectory can be reconstructed.
Area covered by the
horizontal PSD
Area covered by the vertical
PSD
Prog WKS 2011
Pellet ablation rate
Ablation rate measured by PSD
Hot zone
Pellet trajectory
Prog WKS 2011
Comparison measurement-theoryUsing 2 PSD instead of 1 the error is corrected
Prog WKS 2011
Plasma-wall interaction monitor Plasma-wall interaction monitor with CMOS camerawith CMOS camera
Prog WKS 2011
Plasma-wall interaction studiesFast CMOS camera can look at the Hα emission due to the plasma-wall interaction
ports
keys of the tiles
interaction
Prog WKS 2011
Warping
Using the keys of the tiles a map of the
viewing area can be reconstructed
This area can be warped with a fitting code
The maximum position error is ± 2°
Prog WKS 2011
Comparison with LCFS
theoretical reconstruction of the plasma LCFS radius from
magnetic measurements
Good agreement with the images of
the fast camera with two conditions:
modes m=0 are negligible if the
reversal parameter is shallow (F > 0.07)
modes with n>24 are negligible
Prog WKS 2011
• RFX-mod is equipped of rich and powerful set of diagnostics with high temporal and spatial resolution.
• New diagnostics/upgrades are expected during 2011, which will further enhance the measuring capability and the effectiveness of the next experimental campaigns.
Conclusions
Prog WKS 2011
Microwave Reflectometer
In 2010 the fast driver routinely operated for a single microwave IMPATT oscillator on the Ka band giving good measurements of edge ne and showing good agreement with THB and edge Thomson
Scattering.
– During 2011 two new bands will be set-up and commissioned, building new drivers around existing microwave equipment. The reflectometer will thus measure the displacement of plasma layers at 3 given densities, allowing detailed studies of the edge region.
– In parallel to this the old IMPATT microwave sources, which are no longer available on the market, will be substituted with sources implementing new technology.
Prog WKS 2011
Reflectometry Principle of operation
rc
rc
Reflectometer measures the phase delay:
Cut-off position from Abel inversion:
O-mode wave equation:
Wave reflection (cut-off)at plasma frequency:
Refraction index:
group delay
Higher frequency wavesare reflected more inside
Prog WKS 2011
Thermal Helium Beam (THB)A He atomic beam injected into plasma and 3 of its emission lines (at 667.8, 706.5 and 728.1 nm ) observed. Light collected from 8 different radial positions, 0 to 35 mm with a spatial resolution of 5 mm. A spectrograph is used as polychromator. The lines can be observed by:
• a CCD with a time resolution of ~100 µs,
• 3 multianode PMTs for a resolution up to 10 µs.