RFX/RFP mode control issues

RFX/RFP mode control RFX/RFP mode control issuesissues

Piero Martin & Sergio OrtolaniPiero Martin & Sergio Ortolani

Consorzio RFX Consorzio RFX Associazione Euratom-ENEA sulla fusioneAssociazione Euratom-ENEA sulla fusione

Padova, ItalyPadova, Italy

Presented by P. MartinPresented by P. Martin at the 2003 workshop on “active control of MHD stability: at the 2003 workshop on “active control of MHD stability:

extension to the burning plasma regime”extension to the burning plasma regime”University of Texas-AustinUniversity of Texas-Austin

Nov. 3-5, 2003Nov. 3-5, 2003

CONTRIBUTORSCONTRIBUTORS

L. Marrelli, G. Spizzo, P. Franz, P. Piovesan, I. Predebon, T.Bolzonella, S. Cappello, A. Cravotta, D.F. Escande, L. Frassinetti, S. Martini, R. Paccagnella, D. Terranova and the RFX team

And fruitful collaborations with the

MST team: B.E. Chapman, D. Craig, S.C. Prager, J.S. Sarff

EXTRAP T2R team: P. Brunsell, J.-A. Malmberg, J. Drake

TPE-RX team: Y. Yagi, H. Koguchi, Y. Hirano

Hopefully this is the last workshop…Hopefully this is the last workshop…

……. . without RFX !without RFX !

……. RFX reconstruction is in the final phase . RFX reconstruction is in the final phase and first plasmas are expected in Sept. 2004and first plasmas are expected in Sept. 2004

The new RFX will be a “state of the art” The new RFX will be a “state of the art” MHD MHD MODE CONTROL FACILITY:MODE CONTROL FACILITY:

192 ACTIVE COILS, INDEPENDENTLY DRIVEN, 192 ACTIVE COILS, INDEPENDENTLY DRIVEN, COVERING THE WHOLE PLASMA SURFACECOVERING THE WHOLE PLASMA SURFACE

Outline of the talkOutline of the talk

1.1. Status of the RFX reconstructionStatus of the RFX reconstruction

2.2. RFP mode control issuesRFP mode control issues

a.a. Mode rotationMode rotation

b.b. The monochromatic dynamoThe monochromatic dynamo

c.c. Suppression of dynamo modesSuppression of dynamo modes

d.d. RWMsRWMs

3.3. RFX operational scenariosRFX operational scenarios


2. RFP mode control issues

a. Mode rotation

b. The monochromatic dynamo

c. Suppression of dynamo modes

d. RWMs

3. RFX operational scenarios

The new RFX deviceThe new RFX device

Main new components:Main new components:

1.1. 192 saddle coils, covering the whole plasma boundary, each 192 saddle coils, covering the whole plasma boundary, each independently powered and feedback controlledindependently powered and feedback controlled

2.2. a smoother and thinner shella smoother and thinner shell

3.3. the first wall with higher power handling capabilitiesthe first wall with higher power handling capabilities

4.4. an in-vessel system of magnetic and electrostatic probesan in-vessel system of magnetic and electrostatic probes

5.5. the toroidal field power supplythe toroidal field power supply

R R //aa = 2.0 / 0.46 (m) - = 2.0 / 0.46 (m) - II up to 2 MA up to 2 MA

Overview of the magnetic boundaryOverview of the magnetic boundary

- 4 coils in the poloidal direction: 90° spaced– 48 coils in the toroidal direction: 7.5° spaced

shellshellvessevessell

Active Active saddle saddle coilscoils

Saddle coil performanceSaddle coil performance

each independently powered24 kAt: 400 A x 60 turns

Wide spectrum of Fourier Wide spectrum of Fourier components can be components can be produced:produced:

•m=1,2•n ≤ 24•DC < f < 100 Hz

Significant amplitude available. For example: edge br for (1,8) mode:

• 20 mT@10 Hz• 1.3 mT @100 Hz

The new RFX shellThe new RFX shell

• 3 mm Cu layer3 mm Cu layer

• 50 ms time 50 ms time constant (450 ms constant (450 ms before)before)

• High reduction of High reduction of gap field errorgap field error

•1 overlapped poloidal gap

•1 toroidal gap on high field side.

Magnetic probeMagnetic probe

•97 Electrostatic (Langmuir) probes•139 Magnetic pick up probes •8 Calorimetric probes

Langmuir probeLangmuir probe

Integrated System of the Internal Sensors Integrated System of the Internal Sensors (ISIS)(ISIS)

Test of RFX mode control equipment in Test of RFX mode control equipment in T2RT2R

Some RFX digital controllers have been moved to Some RFX digital controllers have been moved to Stockholm to be tested in an “intelligent shell” Stockholm to be tested in an “intelligent shell” experiment, which will be done in the EXTRAP T2R device experiment, which will be done in the EXTRAP T2R device as a joint T2R-RFX collaboration.as a joint T2R-RFX collaboration.

Preliminary results with analog controllers developed by Preliminary results with analog controllers developed by KTH positive!KTH positive!

MORE IN JIM DRAKE’S TALK WEDNESDAY!MORE IN JIM DRAKE’S TALK WEDNESDAY!

16 coilsPartial

coverage




a. Mode rotation



d. RWMs


What shall we use the new RFX for ?What shall we use the new RFX for ?

To explore the RFP physics and to optimize the To explore the RFP physics and to optimize the RFP confinement performance in a steady fashion RFP confinement performance in a steady fashion in the MA current rangein the MA current range

To contribute to the worldwide program on MHD To contribute to the worldwide program on MHD modes control in fusion devicesmodes control in fusion devices

What do we use the new RFX for ?What do we use the new RFX for ?

To explore the RFP physics and to optimize the To explore the RFP physics and to optimize the RFP confinement performance in a steady fashion RFP confinement performance in a steady fashion in the MA current rangein the MA current range

Control of MHD modes:Control of MHD modes: m=1 “dynamo” modes (resonant inside the Bt reversal surface)m=1 “dynamo” modes (resonant inside the Bt reversal surface) m=0 non-linearly generated and/or linearly unstablem=0 non-linearly generated and/or linearly unstable

The standard RFP has many of these modes with 1% B amplitude simultaneously The standard RFP has many of these modes with 1% B amplitude simultaneously present, and they spoil confinement!present, and they spoil confinement!

RWM when the shell is resistive (reactor relevance)RWM when the shell is resistive (reactor relevance)

The modes we have to deal withThe modes we have to deal with

mm=0=0 various various nn: resonant at the B: resonant at the Btt

reversal surfacereversal surfacemm=1=1

|n| ≥ 2R/a|n| ≥ 2R/a,, resonant inside the B resonant inside the Btt reversal surface (resistive kink, reversal surface (resistive kink, “dynamo modes”)“dynamo modes”)

|n| ≤ 2R/a,|n| ≤ 2R/a, internally non internally non resonant from above (RWM, with resonant from above (RWM, with the same helicity as the the same helicity as the “dynamo” modes and the same “dynamo” modes and the same handedness as the core handedness as the core BB))

|n| ≤ R/a,|n| ≤ R/a, externally non externally non resonant (RWM, with opposite resonant (RWM, with opposite helicity)helicity)

1.0 TOKAMAK

RFP

m=1, n=1

m=1n=8

n=9n=10

0.1

q=rB

RB

a

The RFP dynamo issueThe RFP dynamo issue

The electrical currents flowing in a RFP can not be directly The electrical currents flowing in a RFP can not be directly driven by the inductive electric field driven by the inductive electric field EEoo

…….but RFP plasmas last for times much longer than the .but RFP plasmas last for times much longer than the resistive diffusion time ! (actually, as long as resistive diffusion time ! (actually, as long as EEo o is applied)is applied)

The RFP dynamo: E + vxB = The RFP dynamo: E + vxB = JJ

An additional electric field, besides that externally An additional electric field, besides that externally applied, is necessary applied, is necessary to sustain and amplify the to sustain and amplify the toroidal magnetic fluxtoroidal magnetic flux..

A Lorentz contribution vxB is necessary, which A Lorentz contribution vxB is necessary, which implies the existence of a implies the existence of a self-organized velocityself-organized velocity field in the plasma.field in the plasma.

The origin of this contribution is the The origin of this contribution is the classical RFP classical RFP dynamo problemdynamo problem

Turbulent dynamo: remarkable self-Turbulent dynamo: remarkable self-organizationorganization

-8

-6

-4

-2

1000 3000 5000 7000

log b2

1n

t/A

A wide experimental and numerical database supports the A wide experimental and numerical database supports the MHD turbulent dynamo theory:MHD turbulent dynamo theory:

the dynamo electric field is the dynamo electric field is produced by the coherent (and produced by the coherent (and non-linear) interaction of a large non-linear) interaction of a large number of MHD modes: number of MHD modes:

Multiple Helicity (MH) Multiple Helicity (MH) dynamodynamo

bvEd~~

The standard Multiple Helicity (MH) The standard Multiple Helicity (MH) RFPRFP

m=1 “dynamo” modes (resonant inside the Bt reversal surface)m=1 “dynamo” modes (resonant inside the Bt reversal surface) m=0 non-linearly generated and/or linearly unstablem=0 non-linearly generated and/or linearly unstable

Magnetic stochasticity Magnetic stochasticity allover the plasma !allover the plasma !

… … and severe plasma-wall and severe plasma-wall interaction if the modes interaction if the modes lock in phase and to the lock in phase and to the wall !wall !

The strategy towards dynamo modesThe strategy towards dynamo modes

Keep them rotating in the lab frameKeep them rotating in the lab frame Reduces amplitude bReduces amplitude brr

Optimizes the basic standard target plasmaOptimizes the basic standard target plasma

Make their amplitude lowerMake their amplitude lower ……but you must provide dynamo electric field from outsidebut you must provide dynamo electric field from outside Run the plasma in a regime where resort to dynamo is reducedRun the plasma in a regime where resort to dynamo is reduced

Work in a regime where their spatial spectrum is Work in a regime where their spatial spectrum is monochromatic, i.e. dynamo is driven only by ONE monochromatic, i.e. dynamo is driven only by ONE INDIVIDUAL SATURATED MODEINDIVIDUAL SATURATED MODE

ALL THESE TOPICS MIGHT BE ALL THESE TOPICS MIGHT BE INFLUENCED BY ACTIVE CONTROL !INFLUENCED BY ACTIVE CONTROL !


1. Status of the RFX reconstruction


a.a. Mode rotationMode rotation



d. RWMs


Mode dynamics in RFPsMode dynamics in RFPs

Previous experimental evidence in several Previous experimental evidence in several different devices shows that the evolution of MHD different devices shows that the evolution of MHD modes, including the dynamo modes, depends on modes, including the dynamo modes, depends on the magnetic boundarythe magnetic boundary, and in particular on the , and in particular on the shell:shell:

thicknessthickness proximity proximity geometrygeometry

ExperimentExperiment R/a (m)R/a (m) b/ab/a shellshellmms)s)

pulsepulse (ms) (ms) pulse/pulse/shelshel

RFX92RFX92 2/0.4572/0.457 1.241.24 450450 150150 1/31/3

RFX newRFX new 2/0.4592/0.459 1.111.11 5050 ~ 150~ 150 ≥ ≥ 33

MSTMST 1.5/0.511.5/0.51 1.071.07 400400 60-9060-90 ¼¼

TPE RXTPE RX 1.72/0.451.72/0.451.081.08

1.161.1610 10

3303306060

6 6

1/51/5

T2RT2R 1.24/0.1831.24/0.183 1.081.08 66 2020 >3>3

The RFP synopsisThe RFP synopsis

TPE-RX spontaneous mode rotationTPE-RX spontaneous mode rotation

b1/a = 1.08 thin shell, b2/a = 1.16 thick shell

tshell =10 ms tshell =330 ms

Spontaneous Rotation in EXTRAP T2RSpontaneous Rotation in EXTRAP T2R

RWM’s

RWM’s

•Tearing modes rotate

From Malmberg Brunsell PoP 2002

MST modes spontaneous rotationMST modes spontaneous rotation

…….listen Brett Chapman’s invited talk !.listen Brett Chapman’s invited talk !

Conclusions on mode rotationsConclusions on mode rotations

Mode rotation is beneficial and depends on magnetic Mode rotation is beneficial and depends on magnetic boundaryboundary

Modes were locked to the wall in the old RFX and this lead Modes were locked to the wall in the old RFX and this lead to a serious deterioration of performanceto a serious deterioration of performance

Slow rotation of modes was actively driven in RFX Slow rotation of modes was actively driven in RFX ( Bartiromo et al, PRL 99)( Bartiromo et al, PRL 99)

Dynamo modes are spontaneously rotating in RFP devices Dynamo modes are spontaneously rotating in RFP devices with boundary conditions similar to the new RFX.with boundary conditions similar to the new RFX.

There is a reasonable basis to hope for spontaneous mode There is a reasonable basis to hope for spontaneous mode rotation in the new RFX (even if a threshold in current rotation in the new RFX (even if a threshold in current might exist)might exist)




a. Mode rotation

b.b. The monochromatic dynamoThe monochromatic dynamo


d. RWMs


Magnetic chaos is not intrinsic to RFPMagnetic chaos is not intrinsic to RFP

-8

-6

-4

-2

1000 3000 5000 7000

log b2

1n

t/A

DYNAMO CAN BE PRODUCED BY DYNAMO CAN BE PRODUCED BY A SINGLE MHD MODEA SINGLE MHD MODE

bvEd~~

The Single Helicity (SH) dynamoThe Single Helicity (SH) dynamo

a theoretically predicted state with a unique a theoretically predicted state with a unique m m = 1 saturated resistive = 1 saturated resistive kink (kink (a pure helix wound on a torusa pure helix wound on a torus), ),

Stationary Stationary LAMINARLAMINAR dynamo mechanism with good helical flux surfaces dynamo mechanism with good helical flux surfaces

MAC-302MAC-302

Escande et al., PRL 85 (2000)Escande et al., PRL 85 (2000)

Magnetic order with SH dynamoMagnetic order with SH dynamoGood magnetic flux surfaces in SHGood magnetic flux surfaces in SH

SHSH Turbulent (MH)Turbulent (MH)

Overlapping of Overlapping of many modes !many modes !

Helical states in the experimentHelical states in the experiment

Quasi Single Helicity (QSH) spectra have been observed in Quasi Single Helicity (QSH) spectra have been observed in all RFP devices, under a variety of boundary conditions all RFP devices, under a variety of boundary conditions (Martin, NF 2003).(Martin, NF 2003).

The mode spectrum is dominated by one geometrical helicityThe mode spectrum is dominated by one geometrical helicity

The other modes have still non-zero amplitudeThe other modes have still non-zero amplitude

Stationary Quasi-Single HelicityStationary Quasi-Single Helicity Stationary QSH spectra have been observed in the Stationary QSH spectra have been observed in the

RFX deviceRFX device with a helical coherent structure emerging from magnetic with a helical coherent structure emerging from magnetic

chaos in the plasma core.chaos in the plasma core.

Toroidal mode number n spectrum vs. time

RFX pulse length

Flow velocities measurements in QSH Flow velocities measurements in QSH plasmasplasmas

Plasma flow velocity fluctuations measured in MST with Doppler spectroscopy (Den Hartog et al., Phys Plasmas 99)

In QSH not only the spectrum of In QSH not only the spectrum of magnetic fluctuation spectra become magnetic fluctuation spectra become narrower in comparison with MH, but narrower in comparison with MH, but also also that of flow velocity that of flow velocity fluctuationsfluctuations

bvEd~~

Remember:

Work due to D. Craig, L. Marrelli, P. Piovesan in MST

Magnetic and Flow velocity fluctuations toroidal Magnetic and Flow velocity fluctuations toroidal spectraspectra

b~

v~

Dynamo electric field in QSHDynamo electric field in QSH

Dynamo in QSH becomes more concentrated in Dynamo in QSH becomes more concentrated in one mode than in standard MHD plasmas!one mode than in standard MHD plasmas!

)~~( bv

MH vs. QSH vs. SHMH vs. QSH vs. SH

QSH and mode wall lockingQSH and mode wall locking

The access to QSH regime is beneficial for the The access to QSH regime is beneficial for the problem of modes wall locking.problem of modes wall locking.

The dominant (big) mode might be more prone to The dominant (big) mode might be more prone to lock to the wall (see Brett Chapman’s talk), but…lock to the wall (see Brett Chapman’s talk), but…

Non-linear interaction between modes Non-linear interaction between modes decreasesdecreases

The “strength” of mode locking decreasesThe “strength” of mode locking decreases Easier rotation for secondary modesEasier rotation for secondary modes

Spontaneous mode rotation in RFX during Spontaneous mode rotation in RFX during QSHQSH

Dominant and Dominant and RotatingRotatingMode amplitude Mode amplitude

Phase of Rotating ModePhase of Rotating Mode

From Bolzonella,Terranova, PPCF 2002

This is consistent with theoretical calculations (Guo-Chu, Fitzpartick,Chapman), which predict that modes rotate more easily if they

are smaller

PWI in QSH is milder anyway !PWI in QSH is milder anyway !

Vertical Vertical displacement displacement of the plasma of the plasma column in column in RFXRFX

Toroidal angle Toroidal angle

Edge Edge fluctuatinfluctuating g magnetic magnetic fieldfield

MH QSH

Favorable conditions for QSH active Favorable conditions for QSH active controlcontrol

1.1. There are already plasma regimes where There are already plasma regimes where monochromatic spectra are more easily obtained monochromatic spectra are more easily obtained spontaneously spontaneously

a.a. At higher plasma currentAt higher plasma current

b.b. With shallower reversalWith shallower reversal

2.2. We can also “select” the toroidal mode number We can also “select” the toroidal mode number nn we wish to be the dominant one.we wish to be the dominant one.

Mode selectionMode selection

Note that the pre-programming the magnetic Note that the pre-programming the magnetic equilibrium allows to select efficiently the mode that equilibrium allows to select efficiently the mode that will dominate the spectrum!will dominate the spectrum!

Shallow reversal, m=0 modes and QSHShallow reversal, m=0 modes and QSH

Shallow reversal brings outwards Shallow reversal brings outwards the reversal surface, where q=0.the reversal surface, where q=0.

Narrower stochastic region Narrower stochastic region produced by produced by m m =0 when the =0 when the reversal surface is closer to the reversal surface is closer to the plasma edge.plasma edge.

This provides a smoother plasma This provides a smoother plasma boundary, which helps the onset of boundary, which helps the onset of QSHQSH

In the new RFX m=0 modes are In the new RFX m=0 modes are not any more LINEARLY unstable, not any more LINEARLY unstable, as they were in the OLD device.as they were in the OLD device.

Positive feedback, since in QSH Positive feedback, since in QSH non-linear generation of m=0 non-linear generation of m=0 modes is strongly reduced.modes is strongly reduced.

Remember we can apply with the saddle coils up to ~20 mT

on a single m=1 mode

10-9

10-8

10-7

10-6

10-5

0.0001

0.001

0.5 1 1.5 2 2.5

eps42wf3_4/f5_10

Wr( 0, 1)Wr( 0, 2)Wr( 1, 1)Wr( 1, 2)Wr( 1, 3)Wr( 1, 4)Wr( 1, 5)Wr( 1, -1)Wr( 1, -2)Wr( 1, -3)Wr( 1, -4)Wr( 1, -5)Wr( 1, -6)Wr( 1, -7)Wr( 1, -8)Wr( 1, -9)Wr( 1,-10)Wr( 1,-11)Wr( 1,-12)Wr( 1,-13)

Time

Numerical studies on active control: successful drive and sustainment of m=1 n=7 SH state starting from MH

conditions

•Low dissipation Low dissipation conditionsconditions

•Thin shellThin shell

•Simoultaneous Simoultaneous active control of active control of RWMs !RWMs !

Paccagnella, MHD workshop 2002

Conclusions on Single HelicityConclusions on Single Helicity

There is enough theoretical understanding and There is enough theoretical understanding and experimental evidence which support the idea experimental evidence which support the idea that this regime might lead to significant that this regime might lead to significant improvement of RFP performanceimprovement of RFP performance

We know how to produce a target plasma, which We know how to produce a target plasma, which more easily could achieve a QSH spectrum.more easily could achieve a QSH spectrum.

From an active control point of view, QSH is a From an active control point of view, QSH is a robust state: robust state: One big mode, well identified, selectable in advanceOne big mode, well identified, selectable in advance

RFX has more than enough power to deal with RFX has more than enough power to deal with QSHQSH




a. Mode rotation


c.c. Suppression of dynamo modesSuppression of dynamo modes

d. RWMs


Dynamo modes active reductionDynamo modes active reduction

Pulsed Poloidal Current Pulsed Poloidal Current Drive (PPCD): Drive (PPCD):

the induction of a poloidal the induction of a poloidal current at the plasma current at the plasma edge causes a dramatic edge causes a dramatic reduction of the magnetic reduction of the magnetic turbulence (MST + RFX turbulence (MST + RFX PRLs) and STRONG PRLs) and STRONG PLASMA HEATINGPLASMA HEATING

ROBUST TECHNIQUE ROBUST TECHNIQUE (recently performed in T2R (recently performed in T2R at high aspect ratio-many at high aspect ratio-many modes to suppress!-modes to suppress!-Cecconello, PPCF 2003)Cecconello, PPCF 2003)

plasma

VJ

It is TRANSIENT, but in RFX a quasi-stationary version has been implementedIt is TRANSIENT, but in RFX a quasi-stationary version has been implemented

Oscillating Poloidal Current Drive Oscillating Poloidal Current Drive (OPCD)(OPCD)

Periodic (oscillating) applied inductive variations of the poloidal Periodic (oscillating) applied inductive variations of the poloidal electric field allows to extend the PPCD benefits in a stationary fashionelectric field allows to extend the PPCD benefits in a stationary fashion

0

20

40

60 W1,sec

(a.u.)

0

20

40

60

20 30 40 50 60 70 80

W1,7

(a.u.)

t (ms)

150

250

350

450T

e0 (eV)

stationary average improvement of confinement obtained with OPCD in RFX

(Bolzonella et al., PRL 2001)

PPCD action strongly affects MHD in PPCD action strongly affects MHD in the RFPthe RFP

Though transient (but quasi stationary version is feasible), Though transient (but quasi stationary version is feasible), PPCD is an efficient tool to interact actively with MHD PPCD is an efficient tool to interact actively with MHD modes in the RFP.modes in the RFP.

Why might be useful for future operation in the new Why might be useful for future operation in the new RFX ?RFX ?

1.1. ““per se”: the new RFX coils system allow optimized, high per se”: the new RFX coils system allow optimized, high power, quasi stationary PCD. This is a technique for improving power, quasi stationary PCD. This is a technique for improving confinement.confinement.

2.2. It can set-up an improved collisionless target plasma on which It can set-up an improved collisionless target plasma on which to work with feedbackto work with feedback Record reduction of magnetic stochasticityRecord reduction of magnetic stochasticity Change the properties of broadband magnetic turbulenceChange the properties of broadband magnetic turbulence

Active control issue: PPCD triggers QSH Active control issue: PPCD triggers QSH spectraspectra

Evolution of m=1 modes in MST following the Evolution of m=1 modes in MST following the application of PPCDapplication of PPCD

Heat pulse propagation observed Heat pulse propagation observed

Significant transport barrier present in the plasmaSignificant transport barrier present in the plasma

time (ms)

SX

R b

rightn

ess

(W

/m2)

Modes decreased to very low Modes decreased to very low amplitude!amplitude!

Beating in the SXR signalsBeating in the SXR signals of of the frequencies corresponding the frequencies corresponding to TWO helical structures: to TWO helical structures: the (1,6) and the (1,7) modethe (1,6) and the (1,7) mode

Beating recorded:Beating recorded:

at the dominant frequencyat the dominant frequency envelope @ envelope @ f ~ ff ~ f1,61,6-f-f1,71,7

and at the first harmonicand at the first harmonic envelope @2*envelope @2*ff

Two rotating islandsTwo rotating islands

Modes are so small that Modes are so small that magnetic chaos is strongly reducedmagnetic chaos is strongly reduced We observe individual TINY rotating magnetic islands We observe individual TINY rotating magnetic islands

associated with the (1,6) and (1,7) modes: a marker of associated with the (1,6) and (1,7) modes: a marker of stochasticity suppression.stochasticity suppression.

2 3 41

t1 t2 t3 t4

Franz, Marrelli et al, submitted to PRL

Numerical simulation confirmsNumerical simulation confirms

ORBIT used for Poincare’ ORBIT used for Poincare’ maps of the magnetic maps of the magnetic field lines (with field lines (with experimental mode experimental mode amplitudes as inputs) amplitudes as inputs) confirms the presence of confirms the presence of two islandstwo islands




a. Mode rotation



d.d. RWMsRWMs


RFP & RWMs (see J. Drake’s talk)RFP & RWMs (see J. Drake’s talk) EXTRAP T2R EXTRAP T2R

experience (thin experience (thin shell device) shell device) demonstrates that demonstrates that RFP discharges RFP discharges with duration ≥2 with duration ≥2 shell times can be shell times can be produced without produced without significant effects significant effects due to RWMsdue to RWMs

If EXTRAP T2R experience is confirmed in RFX, time scales of dynamo If EXTRAP T2R experience is confirmed in RFX, time scales of dynamo and RWMs are separated and we should have a reasonable amount of and RWMs are separated and we should have a reasonable amount of time (≤ 100 ms) to cope with dynamo modes before dealing with RWMs.time (≤ 100 ms) to cope with dynamo modes before dealing with RWMs.




a. Mode rotation



d. RWMs

3.3. RFX operational scenariosRFX operational scenarios

Control strategies and plans - 1Control strategies and plans - 1

i.i. Benchmark and improve old RFX Benchmark and improve old RFX performance (passive or m=0 performance (passive or m=0 perturbations)perturbations)

ii.ii. Explore new regimes with active actions Explore new regimes with active actions on the MHD through the coilson the MHD through the coils

RFX operational scenarios - 1RFX operational scenarios - 1

Benchmark and improve old RFX Benchmark and improve old RFX performanceperformance

Actions through an applied Actions through an applied mm=0 mode =0 mode (TF coils):(TF coils):

a.a. Synchronous driving torque for mode Synchronous driving torque for mode rotation also in closed loop mode rotation also in closed loop mode

b.b. PPCDPPCD

c.c. OPCDOPCD


Active actions through 192 saddle coilsActive actions through 192 saddle coils::

Apply Apply mm=1 magnetic perturbations=1 magnetic perturbations

Work on individual modes: one at the time or several Work on individual modes: one at the time or several simultaneouslysimultaneously

Realize an intelligent shellRealize an intelligent shell

Zeroing of radial field at the edge to maintain an Zeroing of radial field at the edge to maintain an effective close fitting shell.effective close fitting shell.

Might be interesting for QSH studies, since we have Might be interesting for QSH studies, since we have evidence that a smooth magnetic boundary facilitates evidence that a smooth magnetic boundary facilitates their onset.their onset.


Drive of mDrive of m=1 magnetic perturbations=1 magnetic perturbations

Apply a monochromatic perturbation to affect one individual Apply a monochromatic perturbation to affect one individual mode:mode:i.i. ““pumping” the mode to drive QSH states through helical fields pumping” the mode to drive QSH states through helical fields

at the plasma boundaryat the plasma boundary

ii.ii. Feedback stabilization of individual modesFeedback stabilization of individual modes

iii.iii. inducing rotation of a single modeinducing rotation of a single mode

Apply several simultaneous geometrical helicities (various Apply several simultaneous geometrical helicities (various nn’s):’s):a.a. damping of main “dynamo modes”damping of main “dynamo modes”

b.b. feedback stabilization of RWM feedback stabilization of RWM

c.c. breaking phase locking among “dynamo modes” with induction breaking phase locking among “dynamo modes” with induction of modes differential rotationsof modes differential rotations


Low current scenarioLow current scenario1.1. Theoretical work (Guo, Fitzpatrick et al) and experimental data (TPE-Theoretical work (Guo, Fitzpatrick et al) and experimental data (TPE-

RX, EXTRAP T2R, MST) suggest that low current operation could RX, EXTRAP T2R, MST) suggest that low current operation could allow for spontaneous dynamo mode rotation.allow for spontaneous dynamo mode rotation.

2.2. If dynamo modes rotate, this scenario is more suitable to If dynamo modes rotate, this scenario is more suitable to concentrate efforts on RWM controlconcentrate efforts on RWM control

High current scenario (> 1 MA)High current scenario (> 1 MA) Better for confinement improvement techniques Better for confinement improvement techniques

(OPCD) and for interaction with “dynamo” modes (but (OPCD) and for interaction with “dynamo” modes (but higher wall-locking probability).higher wall-locking probability).

Passive shell (and EXTRAP T2R experience) might Passive shell (and EXTRAP T2R experience) might postpone RWM issue up to ≈50-100 mspostpone RWM issue up to ≈50-100 ms

RFX IS THE ONLY EXPERIMENT DESIGNED TO EXPLORE RFX IS THE ONLY EXPERIMENT DESIGNED TO EXPLORE RFP PHYSICS IN THE MA REGIME !RFP PHYSICS IN THE MA REGIME !

Thanks to the flexibility of the coils system, different Thanks to the flexibility of the coils system, different actions can coexist in the same pulseactions can coexist in the same pulse

> 1 > 1 MAMA

QSH

Self-similar decay + QSH

PPCD

T

~50-70 ms

~50 ms

Active drive of (1,ndom)

Feedback on RWM

feedback on m=0

… … comments, and comments, and collaborations, welcome !collaborations, welcome !

Documents

RFX/RFP mode control issues