Lesson II

Lesson II : Main Tokamak Scenarios and basic kinetic measurements : 

Lesson II : Main Tokamak Scenarios and basic kinetic measurements Francesco Paolo Orsitto ENEA C R Frascati

Outline : 

Outline Characteristics of main Tokamak scenarios H-Mode Hybrid mode ITB mode Introduction to kinetic measurements : Meas Te, ne, Ti, ni by Thomson Scattering

arguments : 

arguments Physics of confinement and transport of energy MHD stability Control of transport regimes Experiments with tritium

Physics of confinement: 

Physics of confinement Regimes of confinement are classified in relation to the spatial scales relevant : i) Regimes where the relevant spatial scale is the plasma dimension are named L-mode ( low confinement modes) ii) Regimes where the Larmor radius is the fundamental relevant scale are named H-modes ( High Confinement) the transition to H-mode is linked to a threshold power

Transition to H mode: 

Transition to H mode PL-H ~ C BT n0.75 R2. For example in JET PL-H ~8MW H-mode has important characteristics

Slide6: 

Example od a discharge in ELMy H-mode Internal Energy of the discharge ELMs Density Heating power ELMs ( edge localized modes) corrispond to instabilities generated when locally the beta limit is reached J Cordey et al. Conf. IAEA 2004

Slide7: 

Kadomtsev(1975) e Connor e Taylor(1977) demostrated confinement scaling laws for ELMy H-mode fit of data of confinament multi machine database Recent Experiments on JET(EU) e DIIID(Ga, USA) dimonstrated that in the range of parameters useful for a demonstrative reactor ( D McDonalds and J Cordey Conf IAEA 2004, McDonalds IAEA 2006, Valovic Nuclear Fusion 2006)

Slide9: 

operational regimes in a tokamak: correspondence of current profiles ↔ pressure profiles q~B/I pressure = nT E Joffrin and X Garbet Conf IAEA 2004, T Luce IAEA FEC Conference 2006

Slide10: 

Simulation of spatial distribution of turbolence corrisponding to two current profiles: monotonic or non-monotonic ( X Garbet e P Mantica EPS 2004)

Slide11: 

Shaping e confinement: H-mode G Saibene, P Lomas EPS 2003

internal transport barriers in Advanced Tokamak regimes ( where non-monotonic current profiles are used) : 

internal transport barriers in Advanced Tokamak regimes ( where non-monotonic current profiles are used) Density spatial profile Temperature spatial profile Campaign DT1 in JET

Formation of ITB and suppression of turbolence at JET (Measurements)( G Conway et al PRL 2002): 

Formation of ITB and suppression of turbolence at JET (Measurements) ( G Conway et al PRL 2002)

Slide14: 

Scenario ITB on FTU with Lower Hybrid e Electron Cyclotron Heating( V Pericoli, M DeBenedetti, C Sozzi et al 2004, and V Pericoli et al IAEA FEC 2006)

Slide17: 

Core MHD and fast particles Density peaking and impurity control ELMs and ELM control Material erosion, migration and deposition Summary and conclusions ITER Baseline, Hybrid and ITB scenarios Schematic of tokamak plasma profiles for various operating scenarios Pressure, temperature or density Normalised radius r/a Pa/Ploss ~ n tET f(Zeff) ~ b tE B2 g(Zeff) Performance improvement by MHD, confinement and impurity control q profile control of MHD and transport

Slide18: 

Hybrid performance similar to H-mode at high q95~4 Improved hybrid performance at low q95~3, slightly better than H-mode with b controlled in real time Characteristics of hybrid discharge at q95= 3.2 Hybrid modes at low q95~3 reach bN~3 Hybrid and H-mode in ITER-like shape Maintain q0>1 to avoid sawteeth Bootstrap current ~ e.bp q95~3 Hybrid 2006 H-mode 2006 q95~4 Figure of merit H89bN/q952 Hybrid 2003 Courtesy of E. Joffrin (2006)

Internal Transport Barriers with q95~5 and 32MW: 

Internal Transport Barriers with q95~5 and 32MW Pulse characteristics Temperature and density profiles Before ITB During ITB 2006 ITB discharges extended to lower q95~5, higher power (32MW) and high core and edge densities Time (s) r/a 1.9MA/3.1T 1.9MA/3.1T

Slide20: 

Calculated magnetic shear Control of core MHD (sawteeth) demonstrated Pulse No: 58934 Internal kink mode destabilisation requires critical shear of 0.2 for this discharge Critical shear exceeded near q=1 with -900 ICCD phasing (counter-current), explaining observed sawtooth destabilisation Criterion for sawtooth crash Sq=1 > Sq=1 critical dW / (Sq=1 tA) < w*I / 2 Increase shear near q=1 Sawteeth can destabilise Neoclassical Tearing Modes and degrade performance t=23s Fast particle stabilised sawteeth destabilised with ICCD Large sawteeth created by ICRF accelerated fast particles Sawteeth destabilised subsequently, with the application of ICCD Magnetic shear Pulse No: 58934 Time (s) PRF (MW) Te0 (keV) r/a J. ONGENA (EX/P6-9) FRI am F. PORCELLI (EX/7-4RA) FRI am

Slide21: 

Energy & pitch angle of lost fast particles from scintillator probe Fast particle losses (p, T, D) during tornado phase different signature to those during sawtooth crash Sawteeth losses characteristic of ICRH-accelerated ions (p, D) Multichannel interferometer (and X-mode reflectometer) enable mode localisation Core interferometer channel shows tornado modes before sawtooth crash Modes not seen on edge channel, confirming core localisation Observation of fast particle losses from core MHD (sawteeth and tornado modes) Sawteeth & tornado modes appear with q0<1 Spectrograms showing tornado modes 67673 1.8MA/2.7T 225 230 235 240 245 220 230 235 240 245 Frequency (kHz) Interferometer (core channel) 16.8 17.0 17.2 17.4 Time (s) 225 220 Magnetics X-mode refl. During sawtooth crash Between sawteeth

Slide22: 

Merged JET-AUG database on density peaking in ITER Baseline ELMy H-modes Significant density peaking expected on ITER Multi-machine data confirm collisionality, eff, as most relevant parameter for density peaking Increasing peaking with decreasing eff Peaking requires anomalous particle pinch, in addition to neutral sources Scaling of density peaking to ITER with eff as regression variable  ne0/<ne> > 1.35 Could impact on impurity accumulation New ITER-like ICRH antenna on JET (installation April 2007) will allow database to be extended to higher power, neutral source free RF heated plasmas Favourable for fusion output, bootstrap current fraction, density limit eff n0/<n>vol H. WEISEN (EX/8-4) FRI pm

Slide23: 

Measured poloidal velocity in ITB much higher than neoclassical estimates Measured poloidal velocity in ITB layer (60km/s) highly anomalous, far higher than neoclassical (~5-10km/s) ITB layer with steep temperature gradient Ion temperature profiles during ITB formation Poloidal velocity from charge exchange, during ITB formation Er and ExB shear much larger with measured Vq Weiland model with measured Vq (rather than neoclassical) matches experiment better Rmid (m) Rmid (m) Ti (keV) V (km/s)

Slide24: 

New fast IR camera 1MJ  0.2MJm-2 on divertor  25000C Type I ELMs on ITER could expel transiently 3-8% of 350MJ stored energy  0.6-3.4MJm-2 Type I ELM energy deposition in the JET MarkII SRP gas box divertor ELM energy depositon on inner divertor ~ 2 x outer divertor Load between ELMs on outer divertor May relax outer divertor load on ITER ELMs can cause damage and must be controlled Filamentary power deposition Clear field aligned structures Type I ELMs on JET

Passive ELM control by plasma shaping, similar to ASDEX Upgrade with QDN: 

Blue: New #66476 Red:Previous experiment #62430 Passive ELM control by plasma shaping, similar to ASDEX Upgrade with QDN ELM behaviour constant over pulse Very fine scale activity - distinct ELMs almost indistinguishable Previous JET studies gave only transient Type II behaviour. Refined shape leads to stationary benign ELM regime with good confinement Magnetic configurations in new and previous JET studies Turbulent magnetic fluctuations coincide with Da bursts

Active ELM control at >30MW with an ITB and neon seeding: 

Active ELM control at >30MW with an ITB and neon seeding ELM control with Neon (4-8s) Prad~17MW dithering H-mode B~3.1T, I~1.9MA, q95~5 PNBI~19.5MW, PICRH~8MW, PLHCD~3.2MW Wdia~5.6MJ, bN~2 JET AT database quasi-stationary (/E>10) pulses at high N and high  Target for JET-EP2 AT regimes with 45MW planned power upgrades bN

Slide27: 

Basic Diagnostics : measurements of density and temperature Te, ne , Ti , ni by Thomson Scattering

Measurement by Thomson Scattering: 

Measurement by Thomson Scattering A laser beam is injected into the plasma The diffused light is collected at a fixed angle The spectral width of the scattered radiation is measured This width measures the electron temperature The intensity ( i.e. the number of photons) is proportional to the eletron density

LIDAR Thomson Scattering : 

LIDAR Thomson Scattering

Field created by moving charges (non relativistic,b=v/c<<1): 

Field created by moving charges (non relativistic,b=v/c<<1) Fraction of incident power scattered by electrons with density ne

Slide32: 

electron origin Ri r xi observation point s i=index running on electrons

Slide33: 

Calculation of the scattered electric field

Slide34: 

Coherent and incoherent scattering important parameter k lD =1/a lD = Debye length a<1 incoherent scattering a >1 coherent scattering qs

Slide35: 

Geometry of the scattering Ki Ks qs K B

Slide36: 

Scattered power incoherently scattered by a system of electrons with distribution function f(v)

Slide37: 

In principle Thomson Scattering measures the velocity ditribution function along the vector K=Ki-Ks The spectrum of the scattered light features the electron distribution function

Slide38: 

Collective Thomson Scattering for the measurements of fast ions ( tokamak TEXTOR ) a >1 Coherent scattering

conclusions: 

conclusions The link between the safety factor spatial profile and teh confinement propeties of the discharges is now the main field of study Important kinetic measurements are done by Thomson scattering