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

END

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.