M. Hron IAEA RCM, Beijing, China 23/10/2006

Edge plasma physics and relevant diagnostics development

on the CASTOR tokamak

Presented by M Hron

for the CASTOR team

Institute of Plasma Physics, Academy of Sciences of the Czech Republic

EURATOM Association IPP.CR, Prague, Czech Republic

and collaborators

EURATOM Associations: ENEA Padova (Padua, Italy), CEA (Cadarache, France),

Etat Belge (Ghent University, Belgium),

M. Hron IAEA RCM, Beijing, China 23/10/2006

CASTOR tokamak

1960built in Kurchatov Institute, Moscow

1977put in operation in IPP Prague

1985reconstructed (new vessel)

31.12.2006shutdown

M. Hron IAEA RCM, Beijing, China 23/10/2006

CASTOR tokamak

MAIN PARAMETERSMAIN PARAMETERS

major radius 0.4 m

minor radius 85 mm

plasma volume 0.1 m3

plasma current 10 kA

toroidal magnetic field 1.3 Tesla

pulse length 30 ms

plasma density 1-2*1019 m-3

plasma temperature 150 eV

edge plasma density 2*1018 m-3

edge plasma temperature 15 eV

Manpower 20 My

MAIN PHYSICS TOPICSMAIN PHYSICS TOPICS

Edge plasma physicsfluctuation measurements, biasing

Wave plasma interactionfast particle generation, wave propagation

Diagnostics developmentSXR spectroscopyadvanced probes

M. Hron IAEA RCM, Beijing, China 23/10/2006

Diagnostics

M. Hron IAEA RCM, Beijing, China 23/10/2006

60 mm

Poloidal array of 124 probesPoloidal resolution = 2.9 deg (3 mm)64 fast channels available - signals of one half of the ring can be monitored simultaneously.

Rake probe• Distance between the tips 2.5 mm• Total length 35 mm• Movable on the shot to shot basis• Ufloat or Isat mode of operation

Probe arrays

M. Hron IAEA RCM, Beijing, China 23/10/2006

Poloidal distributionRadial distribution at the top of the torus

Measured by the rake probe in a single shot

Measured by the poloidal ring in four shots

Floating potential profiles

M. Hron IAEA RCM, Beijing, China 23/10/2006

Ring represents the poloidal limiter

Plasma is not centered, but downshifted

Separatrix is not defined by the limiter

Tips at the top – localized in the SOLConnection length >> 2R to amaterial surface (shield)depends on the local helicity of magnetic field lines - q(a)

Tips at the bottom - Closed MagneticField Lines

Respective position of separatrix and probes

M. Hron IAEA RCM, Beijing, China 23/10/2006

Turbulence in the SOL

M. Hron IAEA RCM, Beijing, China 23/10/2006

Poloidally periodicpatterns (bipolar) propagating poloidally are evident.

Po

loid

al d

irec

tio

n

LFS

TOP

HFS

Bottom

Time 0.5 ms

Potential “valley” Potential “hill”

Ufl(, t) – raw data

M. Hron IAEA RCM, Beijing, China 23/10/2006

Po

loid

al d

irec

tio

n

Time lag [ms]

Poloidal periodicityas confirmed by cross-correlationanalysis

The reference probeis located at the top of the torus

Poloidal periodicity

M. Hron IAEA RCM, Beijing, China 23/10/2006

Dominant poloidal mode number is found to be m = 6-7 (standard discharge conditions on CASTOR)

Poloidal mode analysis

M. Hron IAEA RCM, Beijing, China 23/10/2006

The safety factor q(a) was increased in time by ramping down the plasma current. q

(a)

Time [ms]

Dominant mode number m clearly follows the evolutionof the edge safety factor q(a)

m

8

7

6

5

4

8

7

6

5

4

Poloidal mode analysis

M. Hron IAEA RCM, Beijing, China 23/10/2006

Conclusion - Turbulence in SOL

Flute-like structure elongated along the magnetic field lines

Radial dimension ~ 1 cmPoloidal dimension ~ 1 cmLifetime ~ 1-40 sPoloidal wavelength ~ 5-15 cm

Only a single (bipolar) turbulent structure exists in the SOL.

Snakes q-times around the torusm=q, n=1 mode

Starts (and ends) on the Ion (and Electron) side of the poloidal limiter

Propagates poloidally due to the local ExB drift

experimental data folded on the toroidal surface (toroidal angle = time)

M. Hron IAEA RCM, Beijing, China 23/10/2006

Biasing

M. Hron IAEA RCM, Beijing, China 23/10/2006

Motivation

Generate electric fields in the edge plasma

manipulate with ion flows via ExB drift

reduce plasma fluctuations

improve particle&heat confinement

Massive electrode is inserted

in the edge plasma and biased

with respect to the vessel

Biasing experiments

density

H_alpha

U_bias

I_bias

biasingphase

1050 15 20 25t [ms]

M. Hron IAEA RCM, Beijing, China 23/10/2006

Biased flux tube - originates at the electrode and extends upstream and downstream

Peaks - Intersection of the biased flux tube with the poloidal ring

Electrode is localized within the SOL and biased with respect to the vessel

Poloidal distribution of floating potential

SOL biasing

M. Hron IAEA RCM, Beijing, China 23/10/2006

• Terminates on the electron and ion side of the poloidal limiter at the bottom part of the torus. • Intersects q-times a poloidal cross section

• Originates at the electrode• Extends upstream and downstream along the magnetic field lines

Unfolded torusPoloidal cross section

SOL biasing

M. Hron IAEA RCM, Beijing, China 23/10/2006

EpolxBtor drift

in radial direction

IsatBias/Isat

OHEpol

Convective cells

BIAS

ohmicElectrode

A significant modificationof density profile is

observed during the SOLbiasing

M. Hron IAEA RCM, Beijing, China 23/10/2006

Er(r) during Vfl peaks

10 s

• Sudden rise of oscillating behaviour during the biasing phase

• The effect involves a wide radial region

Edge plasma biasing

M. Hron IAEA RCM, Beijing, China 23/10/2006

• More clear evidence of a periodic radial propagation of high density structures is provided by the fluctuating part of Isat signal

Ufl

Isat

Ejection of particles

M. Hron IAEA RCM, Beijing, China 23/10/2006

• Mach numbers show an equivalent behaviour with the 10 kHz • poloidal and toroidal flows swap during the relaxations.

MII

M

~100 s

0.1

0.2

0.3

0.4

0.5

11.6 11.8 12.0time [ms]

0

Modification of flows

M. Hron IAEA RCM, Beijing, China 23/10/2006

Summary - Biasing

Biasing experiments resulted in effective inducing of an improved plasma confinement, characterized by steeper gradients of density and radial electric field.

SOL biasing creation of a bised flux tube in the SOLradial drift of particles (Epol x Btor)modification of the density profile

Edge plasma biasingperiodic creation and collapse of a transport

barrier (high shear region) at 10 kHz

critical gradients achieved both on floating potential and plasma density

radial propagation of high density structuresresponse of the neutral particle influx from the

wall

M. Hron IAEA RCM, Beijing, China 23/10/2006

Summary and future plans

M. Hron IAEA RCM, Beijing, China 23/10/2006

Summary

EDGE PHYSICSEdge plasma polarization

Convective cellsRelaxation phenomenaEmissive electrode – late 2006

M. Hron et al: Detailed measurements of momentum balance during the periodic collapse of a transport barrier, 33rd EPS Plasma Physics Conference, Roma, Italy, 19-23 June, 2006 P.Devynck et al: Plasma Phys. Control. Fusion 47 (2005) 269-280 J.Stockel et al.: Plasma Phys. Control. Fusion 47 (2005) 635-643

Electro-magnetic properties of the turbulenceA Bencze et al: Observation of zonal flow-like structures using autocorrelation-width technique, Plasma Phys. Control. Fusion 48 (2006) S137-S153  P. Devynck et al: Dynamics of turbulent transport in the Scrape-off-Layer of the CASTOR tokamak, accepted for publication in Physics of Plasmas, in October 2006 

M. Hron IAEA RCM, Beijing, China 23/10/2006

Summary

Density fluctuationsFluctuations of density and turbulent particle flux

P. Peleman et al: Highly resolved measurements of periodic radial electric field and associated relaxations in edge biasing experiments, PSI Conf., Hefei China, 2006, P3-23, accepted for publication in Journal of Nuclear Materials

M. Hron IAEA RCM, Beijing, China 23/10/2006

Summary

DIAGNOSTICS DEVELOPMENTElectric probes

Further experiments and modelling:Tunnel probe for Te measurementsBall pen probeR. Dejarnac et al.: Study of SOL plasma by advanced oriented Langmuir probes on the CASTOR tokamak, to be submitted to PPCF  J. Stöckel et al: Advanced probes for edge plasma diagnostics on the CASTOR tokamak, submitted to Journal of Physics, Conference Series. 

Hydrogen absorption in metallic membranesExperiments performed in late 2005

prepared for publication M.E. Notkin et al: Measurements of the suprathermal hydrogen flux on the CASTOR tokamak, to be published in Nuclear Instruments and Methods in Physics Research Section B 2006 

M. Hron IAEA RCM, Beijing, China 23/10/2006

Summary

CORE TRANSPORT AND TURBULENCETransport of non-intrinsic impurities

Experiments performed on CASTORParticipation on T-10 experiments

V.Piffl et al: Measurements of line radiation power in the CASTOR tokamak, 33nd EPS Conference on Plasma Physics, Roma, 19/6-23/6/2006, P-2.126 V.Weinzettl et al: Snake-like structures after pellet injection in the T-10 tokamak, 33nd EPS Conference on Plasma Physics, Roma, 19/6-23/6/2006, P-4.080 

EDUCATIONExperimental training course on tokamak physics

July 2006, 16 participants from 9 countries

M. Hron IAEA RCM, Beijing, China 23/10/2006

Summary

EXPERTISE EXCHANGETurbulence and biasing experiments – a) Ghent University, Ghent, Belgiumb) RFX, ENEA Padova, Italyc) CEA Cadarache, Franced) LPMI, Nancy University, Francee) IST Lisbon, Portugalf) Nuclear Fusion Institute, Kurchatov Institute, Moscow, Russiag) ERM/KMS Brussels, Belgium

Diagnostics development and improvement – a) CEA Cadarache, Franceb) Innsbruck University, Austria

Core transport and and turbulence – a) Budker Institute of Nuclear Physics, Novosibirsk, Russia

M. Hron IAEA RCM, Beijing, China 23/10/2006

Future plans

CASTORshut down at the end of 2006negative biasing using emissive electrode

Magnetic properties of turbulence probe head prepared for TJ-II

Simulations of plasma deposition in tile gaps modelling of plasma penetration into castellated tile gaps

Educational activitiesEducation of stuents of Czech UniversitiesExperimental training course on tokamak physicsorganized by IPP Prague and KFKI Budapest