Transcript Tokamaks: current trends

Overview of tokamak activities
and correlations withRFP physics
M . Valisa
Consorzio RFX
RFX general meeting - Padova 22/01/2009
RFX meeting Jan 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)
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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 facility and
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
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Outline
RFX Tokamaks
- The 2009 Tokamak Physics program :collaborations
Tokamaks RFX
- More on areas of mutual interest between Tokamaks and RFP’s
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The 2009 Tokamak Physics program
RFX
Tokamaks
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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
MW
MW
MW
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JET
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).
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DIII and JT60 SA
DIIID
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
JT60-SA
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.
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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.
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C-mod
Analysis of Cmod Gas Puffing Imaging Diagnostics: Characterisation of turbulence
behaviour in L-H transition
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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 freeboundary ITM integrated version of the code.
Nonlinear MHD
Contribution to the integration of the CarMa code within the ITM structure
Transport
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
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Tokamaks
RFX
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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)
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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.
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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?
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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)
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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
type-I ELMs
90% radiative power fraction
J Rapp et al
type-III ELMs
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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
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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)
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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
Angioni Weisen et al PPCF 2007
Collisionality scalings of transport
In Tokamaks clear correlation
between collisionality and density peaking
Turbulence stabilization mechanisms
(magnetic shear stabilization, shear flow and q profile) .
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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.
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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
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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??
MODEL REQUIRED
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RFX
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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
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Stellarators
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
LHD
Secondary modes RFX
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.
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Conclusion
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
Transport
- 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)
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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
Boronization
ICRH induced impurity generation
Power handling/impurity control / SOL transport/ Radiative /detached
divertor
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Macrostability
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.
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Thanks
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