RFX-mod Diagnostic Status and Plans S.Martini on behalf of the RFX Team

RFX-mod Programme Workshop 2009 – 20-22 January 2009

RFX-mod Diagnostic Status and Plans

S.Martini

on behalf of the RFX Team


• IntroductionIntroduction

• 2008 “new entries”2008 “new entries”

• 2009 plans2009 plans

• Conclusions Conclusions


RFX Achievements 2008

• FIR polarimeter operational and providing data

• New measurements:

• edge Te and ne from He lines intensity ratio,

• impurity injection by laser Blow-off,

• q-profile from H pellets ablation cloud

• desorption diagnostic

• edge Thomson scattering


ScopeReconstuction of BΘ profile by

measurements of faraday angle.

Details• 5 + 1 channels• FIR radiation at 118.8 μm• Measurements range between 5° and

10°• Time resolution 1÷3 ms• Measure Faraday angles with error <

10%

Future plans• Installation completed during spring

2008• Measure of the magnetic axis position • BΘ profile computed by Abel inversion• Equilibrium computed using

polarimetric measurements as constraints

First polarimeter measurement in RFX-modF. Auriemma, M. Brombin, A. Canton, E. Zilli


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


Sample polarimeter measurementshigh current & density #25570

MODEL: &p

ne$ [1-(r/a)15]

measurements


Polarimeter summary

first faraday rotation measurements on 5 calibrated chords in high current RFX-mod discharges

...to do:

residual oscillations at the end of the pulse

automatic calibration procedure

enhancing and stabilizing FIR laser output power

1 broken beam splitting grid new beam splitting system with quartz plates better beams alignment

installation chord #1


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.


Thermal Helium Beam (THB)

An example of results obtained using

THB with CCD cameras: time evolution

of edge radial profiles of Te, ne and Pe.

At the end of 2008 PMTs have been

installed. After calibration and tests, first

plasma signals have been collected.


Laser Blow-Off (LBO) Same laser used for edge Thomson scattering and LBO,

with a beam splitter allowing the simultaneous activation. First injections carried out ablating a Ni target, a well-

suited impurity for transport studies in RFX-mod plasma. Different target thickness and optic configurations tested

to optimize the Ni ablation.


Sample: LBO inside QSH Island

Shot #24073 at 1.2 MA. Top: line integrated SXR brightness. Centre: Te by double filter diagnostic. Bottom: dominant mode m=1,n=-7 and

secondary mode m=1,n=-11

-> Ni entered inside hot structure.

LBO provide Ni source inside QSH island,

allowing the study of impurity transport.

Lines Ni XVII and Ni XVIII (249 & 292 Å)

observed, together with SXR emissivity increase


q profile from pellet ablation cloud

Using new fast CMOS camera, first safety

factor profile, q(r), measurements in RFX-

mod by observing ablation cloud of H pellets.

Cloud angle has been

measured


q profile from pellet ablation cloud

First measurements prove the

possibility to measure q(r).

Spatial resolution and accuracy

to improve with Li pellet injector

thanks to lower pellet speed

and more elongated cloud.

profiles agree with toroidal equilibrium model


DESOrption diagnostic

To seek better density control during operation, new diagnostic, DESO, implemented

A series of dummy openings before each RFX-mod shot improves piezo valves flow reproducibility.

By processing time evolution of in-vessel pressure, DESO computes both total number of particles supplied by the valve system and total number of particles outgassed from wall and extracted by pumping system.


DESOrption diagnostic DESO measurements, coupled to other diagnostics data

(masses of injected pellets, mass spectrometer measurements of particles removed from wall during He GDC’s), allows to compute 3 parameters : Des% Desorption Factor -> ratio between particles extracted after

pulse end and total ones fuelled. DeltaPart Number of particles left in the wall after each shot ->

difference between total fuelled particles and outgassed ones (in case of He GDC extracted particles are subtracted),

TotPart -> total number of particles stored in the wall since last baking or boronization procedure, computed as sum of DeltaPart for all shots since last wall conditioning.


DESOrption diagnostic

Des% describes wall capability to absorb particles in each shot. Correlates to I/N values more than TotPart: a non-absorbing wall (Des%>100%) forces I/N to 210-14Am, corresponding to

maximum sustainable ne.

Conversely, DeltaPart behavior shows that more particles are stored in the wall at each shot, i.e. an effective way to prevent wall particle accumulation has not yet been found.


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


Edge Thomson Scattering

Example of measureRed: edge TsBlue : closest main Ts profile#25119,n 8E19

Done: acquisition has shifted from CCD camera to fast APDStatus: able to measure for n> 3 x 1019

Fiber coupling and optics rearrange should shift limit to 1 x 1019

To reach lower limits a mechanical modification needed (to overcome vignetting of external channels)


2009 plans

• Acquiring new diagnostics in order to :• Improve fundamental data set (NPA)

• Supplement operation of NBI on loan from TPE-RX (FILD).

• Enhance analysis capability at high current (Li NB diagnostic)

• Completion / development 2008 activities


A Neutral Particle Analyser (NPA), based on re-ionization and magnetic deflection has been borrowed from the Max Planck Institute in Greifswald

22 channels analyse the ion (H,D) distribution function in the 0.2-30 keV energy range.

Ti measurement from NPA


Ti measurement from NPA

the 11 (H) channels of NPA system will be used to

measure Ti and detect fast ion tails.

Fast data acquisition will allow 50s count windows.

Data will be analyzed using Monte Carlo codes

simulating neutrals production inside the plasma:

utilize modified Nené code, originally developed to

reconstruct particle source term in transport simulations.


Fast Ion Losses Diagnostic (FILD)

To supplement high power NBI injector on loan

from TPE-RX, a fast-ion diagnostic will study

losses due to instabilities.

2009 dedicated to a feasibility study to identify

the best solution between: Magnetic collimator spectrometer

Faraday cup collector


FILD

Top and side view of collimator. Gyroradius (energy) of the particle determines how far

from the aperture it strikes the scintillator (left). Pitch angle determines where it strikes along the

orthogonal dimension (right).


FILD

FILD realized with a Faraday cup collector:

Charged particles penetrate through a stack of conducting foils, separated by insulating foils.

Depending on their energy, they pass a number of foils before being stopped, thus causing a current signal.


Lithium neutral beam diagnostic

A 35 keV Li beam with current of 1 mA will penetrate the plasma up to ne ~2·1019 m-3.

ne profile obtained from intensity of selected spectral Li

lines measured by a CCD camera and an array of 16 avalanche detectors

1. ne profile with high spatial resolution and bandwidth of 100 Hz

2. ne fluctuation at 16 radial positions up to 500 kHz.


Collection optics (left) and poloidal section (right) for TEXTOR Lithium beam diagnostic

Lithium neutral beam diagnostic


Completion / further development 2008 activities

Upgrade of the Diagnostic Neutral Beam Injector

CXRS affected by high background due to natural charge exchange processes, particularly in outer plasma region.

Maximization of optical throughput in 2008 did not increase signal enough to disentangle active CX component from dominating passive one.

=>To increase the active CX emission, an upgrade of the beam performance is called for.

Best solution is to decrease beam divergence with new extraction and acceleration grids. This will increase the beam current density, and favor both MSE and CXRS measurements.


Diagnostic Neutral Beam: Ti measurements

Increased optical etendue insufficient: CX signal still dominated by passive component.

Simulations (Von Hellermann code) suggested looking at O VIII rather than C VI. Yet monitoring O VIII line @ 6068 Å with highly luminous high resolution spectrometer yielded no active CX signal.

Passive O VIII core plasma emission provided Ti evaluation, although

uncertainties on transport coefficients and measurement geometry do not permit to exactly define radial measuring position: at high density Ti~Te , at

intermediate ne Ti ~ 50% Te,, while at low ne O emission too low for Doppler

broadening evaluations. MST experience suggests using UV emission lines (larger effective CX

cross sections) -> Calculation of such lines added in simulations and new diagnostic layout being designed, to compensate for optical fibers losses.


Diagnostic Neutral Beam: Bt measurements

Hα measurements provided a weak beam emission signal that will be used for a first attempt to estimate Bt in the center.

However the weakness of the signal confirms need to restore injector current at least to original value( 2.5 equivalent A) and that smaller beam divergence should be sought for, possibly by changing the extraction grids.


Completion/further development 2008 activities

Microwave reflectometer

After successfull commissioning of first band, installation of the other 4 bands planned for 2009.

Soft X-Ray (SXR) diagnostics

New horizontal SXR camera

Various mechanical parts have been built and will be completed in 2009. Most electronics purchased and tested. The diagnostic will be installed on RFX in the first part of 2009.

SXR Multifilter

Supplies the core Te by two-foil technique. Planned to upgrade from 4 to 6 channels with an improved chord layout.

Tomography vacuum and control system

The new vacuum system and control computer will be installed in the first shutdown of 2009.



Edge measurements

Temperature and density profile from thermal He beam

A first set-up, consisting of a spectrometer coupled to a CCD camera, gave Te and ne in with a time response of 80 ms at 3 radial positions. The spectrometer will be modified to accomodate 3 slits coupled to photomultipliers for a time response up to 2 MHz, suitable for Te and ne fluctuations measurements

Fast insertable pneumatic system for edge probes

Following the feasibility study performed during year 2008, the system will be developed in 2009.

Arcless power supply for ion saturation measurement

Following the design activity performed in year 2008, the construction and test of the new power supply will be carried out.


Microwave Reflectometer

Ka band (2640 GHz, ne: 0.92·1019m3), installed.

First measurements show strong reflection when

the ne > critical value :

(fpe2 = e2ne/(4me) > fmw

2 )

Signal post-processing to extract physical information in preparation.

Other 4 bands in 2009 to get fast time evolution of a 5-point density profile


Upgrade of triple Langmuir probe In addition to temperature, plasma density and potential

measurements added.

Measurement circuit rebuilt => range of temperature

measurement doubled.

System for protecting circuits from plasma arcs tested and

installed.

New acquisition system based on optical fibers: sampling

frequency increased to 5 MHz.

Effect of magnetizing winding currents (up to 50 kA) on optical

transmitters reduced by positioning close to vacuum vessel.


impurity pellet injector

PelletInjector characteristics

•Pellet speed: 50÷200 m/s

•Pellet size: Ø0.5÷2 mm x 1÷3 mm

•Magazine: 30 pellets

•Material: Li, C, B

Aims

• Measurement of the pitch of the magnetic field lines

• Transport studies

• First wall conditioning


Impurity pellet injector

Interface to RFX-mod designed and ordered. Important preparation activities completed:

Lithium handling and pellet preparation tools have developed

Tests done to determine vacuum pumping requirements to limit driver gas injection into RFX-mod.

Sabot loading parts re-design improved launch system reliability and reduced running manpower requirements.

Injector to be installed in early 2009.


New horizontal SXR camera

Most of the electronics (acquisition) purchased;

2 prototype amplifiers tested, defining the final version of the amplification stage.

The various parts of the diagnostic have been built but the final on RFX-mod will occur in 2009



Impurity pellet injector

Due to delay in designing injector/machine interface, injector

will be mounted in beginning of 2009.

It will be used with Lithium for wall conditioning and for

magnetic pitch angle measurements using the new fast

CMOS camera.

Impurity transport studies will be also performed.


RFX-mod diagnostics present & futureRFX-mod diagnostics present & future

Physical quantity 2008 2009ne CO2 interferometer

84 point/10 pulse Thomson scattering12 point edge T. scattering

Microwave reflectometer

Te 84 point/ 10 pulse Thomson scatteringSpectroscopy (line intensity ratio)SXR two-filter monitor (4 chords) 12 point edge Thomson scattering

SXR two-filter tomography

Ti Multichannel spectrometerDiagnostic Neutral Beam CXRS

Magnetic deflection NPA

Impurities &

flows

Multichannel visible–UV spectrometerFlat-field survey spectrometerVacuum CTV spectrometerInterference filter arrayGrazing incidence spectrometerSXR–bolometric tomographyMultilayer filters SXR spectrometerlaser Blow-Off

Solid pellet injectorDiagnostic Neutral Beam CXRS

Internal B Magnetic probes

FIR polarimeter Q profile from H pellets + CMOS fast camera

Fast insertable probbesSolid pellet injector+ CMOS fast camera


RFX-mod diagnostics present & futureRFX-mod diagnostics present & future

Physical quantity 2008 2009Fluctuations &

Turbulence

SXR tomography Electrical probe arraysCO2 interferometerGPI

Microwave reflectometerFIR polarimeter

Edge plasma Triple Langmuir probeU-probeISISGundestrup probeGPIedge Te & ne from He line intensity ratio

Plasma-Wall Int.

/influxes

Surface collector and erosion probesInterference filter arrayCCD cameras with interference filtersHmonitors CMOS fast camera


Conclusions

• Some interesting new diagnostics became fully operational in 2008

• Others made progress and should be available before summer 2009

• This makes the diagnostic data set reacher and should entice more challenging experimental proposal for the RFX-mod experimental program

• Developement work continues and “new entries” are expected also for next year

RFX-mod Diagnostic Status and Plans S.Martini on behalf of the RFX Team

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