M.F.F. Nave 1 ITPA 22 March 2010 Intrinsic Rotation in JET M. F. F. Nave 22 nd March 2010.

M.F.F. Nave 1 ITPA 22 March 2010

Intrinsic Rotation in JET

M. F. F. Nave22nd March 2010


This talkDiagnostics toolsIntrinsic rotation measurements standard ripple:

Ohmic heating, ICRF heating, LHCD

Ripple effects on JET intrinsic rotation studied in Ohmic and ICRF

JET intrinsic rotation scaling (comparison with Rice’s scaling)

Observations’ conclusions

Modelling in progressThanks to

T. Johnson, A. Salmi, L. Eriksson, C. Giroud, K.-D. Zastrow, R. Sartori, P. de Vries, V. Parail, J. Mailloux and

TFH (M. Mayoral, J. Ongena) ,TF T(T. Tala)


What we mean by intrinsic rotation

Know sources of momentum input :NBI: this is the largest source of momentum input in present tokamaks

JET: NBI drives co-current rotation in the usual Ip and Bt configuration

ICRH: we can choose wave phasing to produce a small toroidal momentum in either co or counter-current direction.

These will not be discuss these.

Intrinsic rotation :Rotation measured in plasmas with no momentum input: such as in

Ohmic

ICRH: with dipole wave phasing/ minority heating

LHCD


Motivation to study intrinsic rotation

In ITER and in fusion reactors: momentum input is expected to be small even with NBIOther sources of rotation need to be found and understood.

Rice’s scaling (Rice NF 2007): inter-machine intrinsic rotation scaling predicts a significant rotation for ITER (~300km/s at edge).WE NEED TO VERIFY IF JET ALSO FOLLOWS RICE’ SCALING LAW

As an experimental tool: We need to understand how to control the direction of rotation

Rotation is a useful experimental tool as it plays many critical roles in plasma performance:

Turbulence suppression (ExB shear)Mode stabilisation (RWM, NTM, sawteeth etc.)Tolerance to magnetic field errorsOnset of H-mode and ITB

Co-rotation: (e.g. better ELMy H-modes)Counter-rotation (QH Modes, small sawteeth regimes, etc)


(i) Charge exchange (CX)Toroidal angular frequency profiles are obtained from charge exchange recombination spectroscopy of C+6 during NBI blips (PNBI~1MW). NBI provides a toroidal momentum source. In the normal JET configuration (BT//Ip) NBI plasmas are co-rotating. For diagnostic purposes only measurements taken within the first 30 ms can be used. From 2007:Improved measurements () NON- PERTURBATIVE METHODS: (ii) X-ray crystal spectrometry (XCS)The toroidal angular frequency in the plasma core is measured with a high resolution X-ray crystal spectrometer that observes the spectrum near the resonance line of the helium-like nickel (Ni+26) of the plasma. •Information on Ti, Te and direction and magnitude of rotation in the plasma core (T~3-8 Kev). From 2006: broken detector ()

(iii) MHD mode analysisThe observed frequency of MHD modes can provide information on plasma rotation at different radial positions.

Rotation measurement toolsIntrinsic rotation is quite difficult to measure


XCS del_omega

-15

-10

-5

0

5

10

40 45 50 55 60 65 70

time(s)

del_

omeg

a (k

rad/

s)

• Good agreement from different diagnostics.

• In this example with ICRF:XCS, CX and MHD data (sawtooth

pre-cursors) indicate co-rotation

Rotation measurement toolsGood agreement from different diagnostics.

RF

Ohmic

Krad/s


Rotation measurement tools (CX profiles at beginning of NBI blip are a good measurement of intrinsic

rotation)

Example: CX profile from Ohmic Plasma.

A- comparison between first CX time output and "linear fit + going back in time t=t0, show very small difference from t=t1(=10 ms)

B-Modelling with ASCOT (calculation of torque(t) from NBI PINI8/6) and JETTO (calculation of (t,r) using different models for momemtum transport) show10ms after onset of NBI is 10 x smaller than measured values

centre


• Observations with JET standard ripple (0.08%)


JET Intrinsic rotation: typical angular frequencies < 10 krad/s

Usual Bt and Ip configuration V< 30 km/s

One order of magnitude smaller than in NBI plasmas that have a large

momentum input

I

Ohmic

4 MW ICRH

12MW NBI


C

For the standard JET low ripple =0.08%:

Edge: co-rotating independent of scenario.

Core ICRF: either co- or counter-rotatingHigh Ip : peaked, co-rotatingLow Ip: sometimes hollow, counter-rotating Core Ohmic: hollow counter-rotating

Core LHCD: either co- or counter-rotating

JET database: mostly L-modes

L-mode ICRF: L-G Eriksson, T Hellsten, M F F Nave et al., Plasma Phys. Control. Fusion 51 No

4 (April 2009) 044008.

Typical observed intrinsic rotation- L-mode

(NB. In all three cases Te and Ti are peaked.)

PICRF=4MW


Typical observed intrinsic rotation – H-mode

Pulse from S1-2.4.6 NBI vs high ICRH fraction H-modes (SC R. Sartori) (PRF~10MW, Ip=2.5MA, BT=2.6T , ~1.3)

Ignore 1st blipToo close to NBI pre-heating

Blips 2 and 3 show very small rotation <2krad/s at core and

~ 2krad.s at edge

Very few measurements during H-modes are available

For N up to 1.3%, H-modes more co-rotating than L-modes, however range of

values similar to those observed in L-modes

doesn’t depend on PRF,Doesn’t depend on N

(Experiment T.3.1.14 to measure rotation with high

PRFand/or high N wasn’t done).


Typical observed intrinsic rotation – H-mode

Pulse from S1-2.4.6 NBI vs high ICRH fraction H-modes (SC R. Sartori) (PRF~10MW, Ip=2.5MA, BT=2.6T , ~1.3)

Ignore 1st blipToo close to NBI pre-heating

Blips 2 and 3 show very small rotation <2krad/s at core and

~ 2krad.s at edge

Very few measurements during H-modes are available

For N up to 1.3%, H-modes more co-rotating than L-modes, however range of

values similar to those observed in L-modes

doesn’t depend on PRF,Doesn’t depend on N

(Experiment T.3.1.14 to measure rotation with high

PRFand/or high N wasn’t done).


• Ripple Experiments


Effect of toroidal field ripple on intrinsic rotation

• Following B: |B|~B0[1+cos()+sin(N)] oscillate due to toroidicity and ripple.• The ripple is largest in the outboard of the plasma where the plasma is close to the toroidal

magnetic field coils. The ripple amplitude differs by several orders of magnitude between the plasma core and edge.

• the distance between TF coils is larger on the outboard, than the inboard side. The ripple max amplitude found at the separatrix near the outboard equatorial plane.

TF ripple can impart toroidal momentum by magnetic mirror forces

trapping in the mirror between field coils


Effect of TF ripple on intrinsic rotation• JET has 32 coils – very low levels of ripple (<0.08%).• JET can increase ripple by reducing current in every second TF coil

ripple was increased from 0.08% to 1.5%(ITER ripple values 0.5-1.2%)

AIMS of Intrinsic Rotation Experiments:• NBI experiments in previous JET ripple campaigns showed that ripple produced counter-rotation in plasmas with co-injected momentum. The object of the new experiment was to find out if ripple would also affect rotation. in plasmas with no momentum input and, in the case of Ohmic plasmas without fast ions.

•Separate ripple induced fast ion effects from thermal ion effectsRipple induced fast ion losses cannot totally explain edge counter-rotation

observed with NBI (P. de Vries 2007, A. Salmi 2007)

•Test existing theories on the role of ripple on plasma rotation

Experimental set up:Two plasma currents: 1.5 MA and 2.1MA (with BT-2.2T)

Ohmic and ICRF plasmas with PRF=1-4 MW, dipole Rotation Experiments with TF ripple – OHMIC ROTATION


OHMIC ROTATION with ripple

• Ohmic plasmas:Counter toroidal (and,

counter poloidal rotation) increases with ripple


OHMIC ROTATION with ripple

Ohmic Pulses with <BT>=2.1T, Ip=2.1MA

Counter rotation increases with rippleSimilar effect on edge and core


ICRF ROTATION with rippleRipple produces counter rotation. The effect is larger in the plasma core, indicating that fast ions as well as thermal ion effects may be involved.

L-mode/type III ELM phases more counter rotating than in type I ELM phases.

.

<BT>=2.1T, Ip=1.5MA, Picrf=3MW


ICRF Rotation with TF rippleFast ion losses

Core counter rotation increases before a monster sawtooth crash, when core-tae modes are present and fast-ion losses observed.

104

rad/s


ICRF Rotation with TF rippleICRF resonance position

Record counter rotation (~-20 krad/s) with ICRF on rhs.

Pulses with 1.5% ripple

ICRF off-axis

ICRF on-axis


• Extrapolation to ITER (Rice’ Scaling law)


Inter-machine Scaling (J. Rice et al, NF 2007)Predicted edge toroidal rotation for ITER: ~ 300 Km/s

Large intrinsic rotation predicted for ITER, now used as argument for not needing NBI system.

JET data (Mark 0 divertor, 1993) ICRF, r/a=0.3 (measured with crystal spectrometer) The high values of co-rotation ~20krads/s are no longer observed N.B. Mixes different heating schemes, ripple values, measurements at different raddii, different machine sizes.

W/Ip


Inter-machine Scaling (J.Rice et al, NF 2007) +new JET data

Type III Type I

JET ICRF H-mode data doesn’t follow Rice’s

scaling law.

For 0.08% ripple Mach-Alfven ~ 10 times

smaller for same N

For 0.5% ripple JET rotation ~ zero,

For 1-1.5% ripple JET is counter rotating


Toroidal intrinsic rotation has been measured in JET plasmasWithout Ripple:

Ohmic Plasmas: core counter rotating RF Plasmas: core either counter or co- rotating depending on Ip LHCD Plasmas: core either counter or co-rotating Edge co-rotating independent of regime

With RippleRipple has a significant effect on the rotation of both Ohmic and ICRH plasmasRipple drives counter rotationRipple effect seen both in the edge and core Ripple has to be taken into consideration when extrapolating to ITER

Rice’s Scaling and JET dataIntrinsic Rotation in JET has no clear dependency on N

JET ICRF rotation is very low, below Rice’ scaling law. For 0.5% ripple, JET plasmas are hardly rotating.For 1% ripple, JET ICRF plasmas are counter rotating

Summary- Observations


Modelling in Progress:Ripple effects

•Observation of increased counter-rotation in Ohmic plasmas indicates a strong torque due to non-ambipolar transport of thermal ions.

• In ICRH plasmas the rotation change in the plasma core is larger indicating that the torque source in this case would be less edge localised and that fast-ion as well as

thermal ion effects may be involved.

•To test these hypothesis numerical modeling is being performed with the Monte Carlo codes ASCOT (A. Salmi) and SELFO (T. Johnson).

Conclusion for Ohmic Plasmas: the toroidal torque driven by non-ambipolar transport of thermal ions is found to be significant (equivalent to torque from

PNBI=1.5 MW ). (A. Salmi)


Observation of increased counter-rotation in Ohmic plasmas indicates a strong torque due to non-ambipolar transport of thermal ions.

ASCOT calculation: the toroidal torque driven by non-ambipolar transport of thermal ions is found to be significant (equivalent to torque from PNBI=1.5 MW ). (A. Salmi)

Observed counter rotation freq. smaller than NC residual value

for~0.9 *NC

= 3.5/(ZieB)∂rTi ~ -4.7±2.7 krad/s.

Preliminary modelling results (Ohmic Plasmas)

*NC 1/ from K. Shaing, PoP 2003


Modelling in Progress

Role of Turbulence: Explore sources of momentum in a turbulent system, leading to an understanding of observations of intrinsic rotation in Ohmic Plasmas (no ripple). (collaboration with Oxford

Theoretical Physics: F. Parra, Alexander Schekochihin)

Modelling of LH plasmas – To be started (Y. Baranov)

How can to explain change of rotation direction in the middle of the plasma?


• EXTRA SLIDES


Ohmic Rotation with TF ripple

• Ohmic plasmas:Counter toroidal and,

counter poloidal rotation increases with ripple

Toroidal rotation

Poloidal rotation

3.8m

3.1m

3.2m

3.6m

5krad/s

3km/s


Ripple pulses with PRF~3MW, Ip=1.5MA,BT=2.1T

Blip1: Ohmic

Blip2:Type I~1.0

Blip3:Type III/Lmode

~0.5-0.7

H-modes observed with Ip=1.5 MA


Summary of previous results (no ripple)

L.-G. Erickson et al. to appear in PPCF 2009

Scaling

(L-mode data)

Core Ip

Edge Wdia/nel


ICRF Heating - L-mode study (no ripple)

Core Toroidal rotation is sensitive to the plasma currentHigh Ip: Peaked rotation profiles

Core Co-current rotation..

Low Ip: Hollow profiles.Core counter-rotation with angular frequencies < 10 krad/s (with or without sawtooth)

Core (R=3.1 m)


JETTO/ ASCOT modeling for Ohmic plasmas with Ripple

•Input for ASCOT calculation of toroidal torque driven by non-ambipolar transport of thermal ions:

•T and n profiles (don’t not change with ripple)•Erad calculated using JETTO/NCLASS

•CX toroidal velocity

Te (HRTS) and Ti (CX) for 3 ripple levels (0%-1%)

Te

Ti

2

1

keV


JETTO/ ASCOT modelling for Ohmic plasmas

0%

1.5%

Toroidal velocity CX data Poloidal velocity

NC

Core CX dataEdge >0.8 extrapolated1

0

-1

-2

104m/s

2

0

-2

-4

-6

103m/s


JETTO/ ASCOT modeling for Ohmic plasmas

Torque from thermal ions effects in Ohmic plasmas similar to torque from fast ion effects from 1-1.5 MW NBI


Observations with LHCD

(i) First measurements of rotation with LH (2 pulses) in 2007 were reported in the paper by

L-G Eriksson et al., Plasma Phys. Control. Fusion 51 No 4 (April 2009) 044008.

(ii) Further measurements of rotation with LH were done parasitically during the 2008-2009 HLC of the LH . However, these experiments were not optimized for LH power penetration.

While the 2008-2009 experiments showed counter-current rotation, the earlier L-G Eriksson's pulse showed co-current rotation.

Preliminary data analysis appears to indicate that core co-current rotation might only be observed in pulses with good core LH penetration (as it was the case in L-G Eriksson' pulse). Another unknown is the effect of magnetic shear (unlike the recent pulses, the L-G Eriksson's pulse was obtained with q(0)>1). However experiment T-3.1.15 to check the effect of LH wave penetration on rotation was never done.


New LHCD data: shows core counter-current rotationedge is always co-rotating

Core Toroidal Rotation with LH (n//=1/8) (CXRS at R=3.1m)

-8

-6

-4

-2

0

2

4

6

0 1 2 3 4

PLH (MW)

f (kr

ad/s

) LH (24/9/2008)

LH (L..Eriksson)

Ohmic

Co-current

Counter-current

NB. Larger counter-rotation for n//=2.3


Previous results with LHCD: Lars-Erikson’s experiment 2007

Indicating co-rotation when LH deposition is central (?)

L.-G. Ericksson et al. PPCF 2009

LH

LH+ICRF

Date post:	06-Jan-2018
Category:	Documents
Upload:	gladys-johnson
View:	223 times
Download:	6 times

M.F.F. Nave 1 ITPA 22 March 2010 Intrinsic Rotation in JET M. F. F. Nave 22 nd March 2010.

Documents