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