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Overview of tokamak activities and correlations withRFP physics M . Valisa Consorzio RFX RFX general meeting - Padova 22/01/2009. The Tokamak Physics Program of CONSORZIO RFX.

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Overview of tokamak activities and correlations withRFP physicsM . ValisaConsorzio RFX RFX general meeting - Padova 22/01/2009


The Tokamak Physics Program of CONSORZIO RFX

  • In the ITER era it is vital for the RFP to get a closer and stronger collaboration with the wider fusion community including Tokamaks Stellarators and other configurations
  • Such type of “contamination” :
  • Widens research horizon
  • - Stimulates creative thinking (new ideas)
  • Helps purposeful (re-)direction of research
  • Offers more opportunities for testing ideas and benchmarking models
  • Both the recent FESAC report and the EU Facility Review Panel acknowledged the potential role of RFP’s (based on results and appealing intrinsic characteristics)

Main tasks of The Tokamak Physics Program

  • emphasize the synergy between the RFP and the Tokamak
  • promote and coordinate research on Tokamaks in those areas in which a mutual interest exists ( also a good way to disseminate information on the potentiality of the RFX facilityand of the RFP configuration)
  • thus encourage the partecipation of the Tokamak community to RFP experiments
  • derive from the Tokamak experience inputs to the RFX programme


  • - The 2009 Tokamak Physics program :collaborations
  • More on areas of mutual interest between Tokamaks and RFP’s

RFX Tokamaks

Tokamaks RFX


FAST Tokamak

  • FAST is the project proposed by the Italian Association as an ITER European satellite device.
  • Key objectives of the FAST project are the study of the physics of fast ions in reactor relevant regimes , aws well of RF-plasma coupling and high power disposal issues.
  • Collaboration activity
  • Physics of the beam-plasma interaction (under evaluation
  • Prediction of beam generated fast ion population in the plasma (under evaluation).
  • RWM control in advanced scenarios (high Beta)
  • Diagnostics






  • An RFX physicist as the leader of the JET Task Force on Diagnostics.
  • Participation to the construction, installation and commissioning of the Enhanced Radial Field Amplifier, to improve plasma vertical stability and to allow larger ELMs amplitude.
  • Analysis of NTMs in high performance scenarios
  • Analysis of experiments on impurity transport already performed at JET
  • and possibly from a new session proposed for 2009.
  • Analysis of High Resolution Thomson Scattering data in discharges with ELM control by means of the Error Field Correction Coils.
  • - Disruption Prediction, (collaboration with the University of Cagliari).

DIII and JT60 SA


DIII-D is among the large Tokamaks the device best equipped for RWM studies and therefore the device where the expertise acquired on RFX-mod could be best enriched.

Collaboration on active stabilization of RWMs is thus foreseen.

Possible collaboration on DIII D experiment under evaluation


Collaboration on the evaluation of the RWM behaviour for the specification of the feedback control system, whose power supply is to be procured by Consorzio RFX via the participation to the Broader Approach programme.


ASDEX Upgrade

  • Edge physics, in collaboration with ÖAW and RISØ labs , using a probe with Multiple Langmuir probes and three-axial magnetic pick-up coils for electrostatic and magnetic fluctuation measurements.
  • Physics of momentum transport: the probe can investigate both poloidal and toroidal rotation, evaluate the Maxwell stress and its relation with electrostatic Reynolds stress.
  • Turbulent particle flux in L and H mode regimes.
  • Investigations of the magnetic structure of ELM, associated filaments, precursors and comparisons of triggered and natural ELMs.
  • Prediction of disruption in collaboration with the University of Cagliari.


Analysis of Cmod Gas Puffing Imaging Diagnostics: Characterisation of turbulence behaviour in L-H transition


Integrated Tokamak Model EFDA Task

Infrastructure Support Project .From RFX one of the project leaders.

Equilibrium and stability

Integration of the code FLOW within the ITM framework and development a free-boundary ITM integrated version of the code.

Nonlinear MHD

Contribution to the integration of the CarMa code within the ITM structure


Integration of impurity transport model in the plasma coupling core and edge. To be benchmarked against JET data.

ITER Scenario Modelling

- Resistive Wall Mode modelling.

In collaboration with CREATE, applications of the CarMa code

- Disruption modelling

collaboration with US groups (PPPL, Courant Institute NY) will continue through M3D MHD code towards high resolution numerical simulation of disruptions in their nonlinear phase


RWM physics

Interest from IPP Garching ,DIII and JT60 SA which adds

to the already estabilished collaboration with CREATE

Edge Physics: Interest from Castor and C-mod

Impurity studies – interest for W spectra in low/ medium temperature plasmas

Helical states – interest from the Stellarator community (Boozer this meeting)

Ion temperature dynamics – collaboration on the NPA with IPP Greiswald

Density control: -Collaboration with FTU on Lithization ( Mazzitelli this meeting)

Modelling. RFX has imported and adapted to RFX fluid and gyrokinetic models developed for Tokamkas ( TRB/Garbet and GS2/ Kotchenreuter . To study lelectrostatic (TEM /ITG).

Electron Bernstein Wave (EBW) current drive

O-X mode conversion scheme at the wave absorption layer, with a theoretically predicted efficiency of about 55%. in collaboration with IPP Garching and IFP Milano

(Volpe and Bilato this meeting)


Themes Summary

MHD PHYSICS (coordination of the EFDA topical MHD group (P.Martin))

( NTM’s / RWM study and control , RMP) experiments and modelling

( Bolzonella, Villone, Reimerdes, Okabayashi,Takechi, Igochine talks in this workshop)

Edge Physics: Turbulence/ momentum and particle transport / current filaments. ELM studies

The edge of Tokamaks and RFP’s display many similarities / Common physics facilitates use of experimental tools and models

(Agostini (turbulence), Martines (filaments) , this workshop

PWI physics /Lithization

Helical Equilibrium

Impurity Studies including Gyrokinetic simulation.

Impurity accumulation in Tokamaks and means to control it are under investigation

In RFX preliminary results suggest that Ni does not quite feel the QSH barrier– probably too collisional.


Other themes of common interest between RFP’s and Tokamaks for which we do not plan direct collaborative activities in 2009 (as yet)

Transport Barriers./ transport / neoclassical vs electrostatic

( see also Gobbin this workshop)

RFX shows, with QSH, electron transport barriers , which do not appear to be ion tranport barriers (MST similar barriers in PPCD See Chapman’s talk this wkshop). Is transport dominated by similar physics in RFP and Tokamaks (electrostatic turbulence) ?

Barriers and flow shear

In Tokamak toroidal and poloidal flow change across the barrier. In RFP’s?


Auxiliary systems for active control

In Tokamaks they play a fundamental role in the integrated feedback control of AT plasmas ( Control of NTM and tearing modes via heating or current injection in the island- beta value stable via feedback on heating – NBI and or ICRH.... density profile control and impurity pump out via central electron heating...)

Good example experiment at Textor

With DED and heating NTM tabilisation (with artificial excitation of NTM and subsequent control via EC Heating)

On MST development of LH current drive & Bernstein wave heating + power NBI in progress

AT RFX-mod RF heating /current drive proof of principle studies in progress

(see Veltri this workshop)

The TPE 1.5 MW NBI (30keV 50 A) is to be installed during 2009 (this will be mostly for fast ions studies)


Radiation shield

Invoked for ITER and other Tokamaks to protect PFC’s especially with W wall

Use of N2 and Ne / Ar on JET has led to good inter-ELM reduction of the power loading at the divertor albeit accompanied by confinement degradation (20% less)

i.e. The issue is to have good Prad maintaining a good H-mode pedestal.

This exercize , projected to ITER, requires an upgrade of Ip from 15 to 17 MA (J. Rapp)

JET attached plasma JETdetached plasma

40% radiative power fraction 90% radiative power fraction

type-I ELMs type-III ELMs

J Rapp et al


Radiation shield

On ASDEX (with full W coverage) N2 is injected to substitute the no longer existing C radiation: power loading decreases , ELM frequency unchanged (reduces instead with Ne /Ar producing accumulation) and confinement improves as a result of an improved pedestal energy content ( for the same density).

Possible explanation for the opposite results in JET and AUG is perhaps that on AUG f_Greenwald was only 65% against the 80-90% on JET.


Similar density shots

From A. Kallembach at al


Radiation shield

On RFX we showed that P_Ohm-P_rad decreases with P_rad only at high densities.

QSH prefers instead high Lundquist numbers (i.e. High Te and low ne)

Would QSH be compatible with cold edge?

In any case an experiment has been proposed to test, with the RFX-mod TS capability, the effect of edge localised Te perturbation on QSH “equilibrium”.

As we raise Ip we will raise the absolute density but we need a model to predict

the scaling of Pohm-Prad vs Ip

Neon in RFX RFX-mod high n @m=0 island

(toroidally symmetric but at locking) ) (toroidal localized structure)


Plasma flow / momentum

spontaneous rotation / Modes and flow coupling /stabilisation

Important for stabilization to the point that now schemes with ICRH ( MC) are used to drive momentum

Collisionality scalings of transport

In Tokamaks clear correlation

between collisionality and density peaking

Turbulence stabilization mechanisms

(magnetic shear stabilization, shear flow and q profile) .

Angioni Weisen et al PPCF 2007


Thermal ion dynamics /heating

In RFX strong el heating and ions mainly heated via equipartition with electrons and barriers seem mainly on electrons

In tokamaks Ti/Te nifluences ITG/TEM stability . In experiments High Ti/Te associated to better confinement

Can we think of a Ti/Te scan in a RFP?

RFX-mod Ti database from passive OVIII ( 607 nm) /validation in progress

by F Bonomo.


Fast particles .

In 2007 and 2008 collaborations with IPP Garching

Stability boundaries of energetic ion collective mode excitations nonlinear dynamics in the RFP equilibrium topology.

Nice experiments on MST have shown that in RFP’s fast particle ( 30 keV) have longer confinement time than thermal ions ( due to different resonances in phase space due to their drift)

Both MST and RFX have this topic in their programs

Reactor studies

Have alphas any role in a RFP reactor ? Fusion plasma power balance in a RFP? Would collective or direct losses lead to signicant wall loading and damage of plasma facing material?

See J. Sarff’s talk this meeting


Density limit

The interesting question (personal view) is not just why RFP’s and Tok share the limit ( which in Tok can be overcome, and we saw also in MST, transiently)

but rather why Stellarators have a much higher Limit ( Sudo Criterion)

as an edge density limit.

Would an m=0 controlled RFP plasma avoid the Grenwald density limit?

In Tokamaks and Stellarators average densities well above the “DL”

have been achieved.

Is the RFP intrinsically limited in density due to its topology and

the need of an internal dynamo?

IN RFX ULQ discharges Greenwald is well reached with stationary current

Can we conceive a high density RFP with peaked profiles and sufficiently

low edge density to overcome the greenwald limit/ would lithization + pellet help

avoiding hollow profiles at high density??



Integrated modelling

Tokamaks are addresing the issue of a “full fly simulator”, whose run will probably be a prerequisit for allowing an ITER discharge

but many codes are now available ( ASTRA , CRONOS , JETTO TRANSP)

RFP’s need similar tools



While looking around outside the RFP world ,

Stellarators coudl also be enlighting

We have seen helical equilibria and density limit

but may be also Mode Fluctuation studies and g modes

Secondary modes



m/n = 1/1

The amplitude of the mode in the periphery strongly

depends on the magnetic Reynolds number,

which is close to that of the growth rate and/or the radial

mode width of the resistive interchange instability.



Tokamaks now oriented on High priority ITER R&D issues

Integrated Scenarios, Baseline H-mode and Advanced Scenarios:

• Profile control methods: especially j(r) with LHCD and bootstrap


- Core transport regimes with equilibrated el.&ions/ dominant electron heating:

with and without momentum input

- Collisionality & density peaking & n/nG (covariance broken on Cmod)

Decoupling heating and fueling.

- Turbulence stabilization mechanisms

(magnetic shear stabilization, shear flow generation and q profile)

profile; compare these mechanisms to theory.

• Develop common integrated modelling

( including frameworks, interfaces, data structures)


Pedestal Physics

- L-H power threshold /effects of neutrals/opacity

- Role of rotation in the H-mode transition.

• mitigated or low ELM / quiescent H-mode regimes

• ELM control techniques: stochastic fields with external coils

Plasma Wall interaction

Fuel ( and T) retention/ T removal in High Z PFC

Post disruption cleaning


ICRH induced impurity generation

Power handling/impurity control / SOL transport/ Radiative /detached divertor



Disruption (energy loss, halo current) radiated power

Disruption mitigation / killer gas// LHCD fast electron control/suppression

NTM physics/ rotation/ LHCD stabilisation

Intermediate n Alfven Eigenmodes (AE’s); Damping and stability of AE’s:

Active MHD antennas

Fast particle redistribution from AE’s; ICRH ion tale and AE destabilisation;

RFP’s while pursuing their own roadmap can contribute to some ITER R&D issues. In the same time a great deal of the experience on Tokamak can be of help in RFP research.