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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