Introduction and motivations – I - IAEA NA · 2007. 6. 8. · 4th IAEA-TM on ECRH , Vienna 6-8...

4th IAEA-TM on ECRH , Vienna 6-8 June 2007, G.Ramponi et al. 1

Introduction and motivations – I

The ECH&CD system of ITER at f=170 GHz consists of up to 24 gyrotrons, for anominal injected power PEC of 20 MW directed to either the Equatorial Launcher (EL)or the Upper port (up to four ports) Launchers (UL), depending on the physicsapplication

The main functions of the whole system are: i) core heating, to access H mode and heat plasma to reach Q≥10 ii) on and off axis ECCD for q profile modifications and/or control iii) control of MHD modes, mainly NTMs & sawteeth

As originally defined, the UL should be dedicated only to NTM stabilization, while theEL should be used for all other physics applications imbalance between the two launchers!

The physics functionalities of the UL (based on 3 ports) and of the EL (present design)have limitations that can be resolved by introducing modifications


Introduction and motivations - II

Many of these modifications have been already incorporated in the UL design using 4ports (EPL), allowing to drive co-current up to q=1 location for ST control and asynergy with the EL.

Analysis shown here has been spurred by the ITER design review AIMS

to point out that further optimization could be obtained for the EPL by lowering theupper port location

to point out that the EL design should include cnt-ECCD as well as a tilt angle for

the top and low steering mirrors for central heating and applications as q profile control

to investigate the impact of reducing the magnetic field on the capabilities of the

system


Upgraded UL FS design, modified in order to access alarger region of the plasma ( 4 ports, 8 beams/port,2 SM per port)

Lower set of steering mirrors(LSM):16 beams (13.3 MW at plasma)dedicated to the outer region of theplasma

Upper set of steering mirrors(USM)16 beams (13.3 MW at plasma)dedicated to cover the radial range fromq=2 & q=3/2 of H-mode Scenarios 2,3and 5, up to the q=1 region(in the region where the two rows overlap20 MW are available)

Extended Physics Launcher (EPL) - I

Main applications :i) Stabilize 3/2 and 2/1 NTMii) Integrate the EL for sawtooth control


Extended Physics Launcher (EPL) - II

Figures of merit: - ηNTM = JEC/Jbs for NTM stabilization - ηS = IEC / wcd2 for sawtooth control

0

0.005

0.01

0.015

0.02

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

β=160

β=180

β=200

β=220

Jp/P

ECEOB2

q=3/2q=2

ρ_p

(MA/

MW/m

2 )

Both require high ICD& small wcd !

Optimization performed w.r.ttoroidal injection anglesand beam sizeG,Ramponi et al.,Proc. EC14,Santorini,2006)

0

0.005

0.01

0.015

0.02

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

C4_UC5_UC6_UC7_UC8_U

β=200

EOB2

ρ_p

(MA/

MW/m

2 )

q=3/2q=2However further optimization may obtained by

lowering the upper port location R.V.Harvey,F.V.Perkins, Nucl.Fus.41,1847,2001G.Ramponi et al.,2nd IAEA -TM, Kloster Seeon, 2003


EPL & DUL

EPL_LSM: (R,Z)=(6.90 m, 4.18 m)EPL_USM: (R,Z)=(6.85 m, 4.39 m)

DUL_LSM:(R,Z)=(7.70 m, 3.55 m)DUL_USM:(R,Z)=(7.56 m, 3.73 m)

ΔZ~ - 65 cm (1 blanket module)ΔR_USM= +71 cmΔR_LSM= +80 cm

Same beams, well focussed inside theplasma

To reachq=1high alphais required


EPL & DUL_Sc.2

LSM

0

0.01

0.02

0.03

0.5 0.6 0.7 0.8 0.9ρtor

J/P 0

(MA/M

W/m

2 )

q=3/2 q=2

DUL_LSMEPL_LSM

0

0.02

0.04

0.06

0.08

0 0.2 0.4 0.6 0.8 1

J/P 0

(M

A/M

W/m

2 )

ρtor

q=2q=3/2

DUL_USM EPL_USM

USM

0

20

40

60

0.5 0.6 0.7 0.8 0.9ρtor

α

q=3/2 q=2

DUL_LSMEPL_LSM

0

10

20

30

40

50

60

70

0 0.2 0.4 0.6 0.8 1

α

ρtor

q=2

q=3/2

DUL_USM EPL_USM

DUL versus EPL:(GRAY results)

•Higher Jcd, mainlydue to better relationbetween launcherlocation and geometryof flux surfaces(except at ρt >0.8, whereECCD by EPL occurs closerto the focus region)

•steering rangeshifted to lower α•better access to q=1region for DUL_USM


EPL & DUL performances for NTM stabilization

Analysis performed by for 3 H-mode Scenarios

PEC=13.3 MWfrom LSM

EPL_L DUL_L EPL_L DUL_L EPL_L DUL_LScenario qηNTM ηNTM wcd(cm) wcd(cm) ηNTM wcd ηNTM wcd

EOB2 2 2.8 3.4 2.4 2.3 6.7 7.83/2 1.8 3.4 3.8 2.5 6.8 8.5

EOB3 2 2.0 3.2 3.0 2.2 6.0 7.03/2 1.3 3.1 4.7 2.8 6.1 8.7

EOB5 2 1.7 1.5 2.0 2.7 3.4 4.03/2 1.4 2.0 2.8 2.8 3.9 5.6

•In both cases, all ηNTM>1.2

•DUL w.r.t. EPL:larger ηNTM and smaller wcd (except at q=2 of Scenario 5)increased values of ηNTM wcd (~25% on average)⇒ reduction of the power necessary to stabilize the modes

•Reduction of power would limit the deterioration of Q!!

O.Sauter et al.,21th IAEA Fusion Conf., Chengdu


Sawtooth control

• Control of ST period is important issue because long periods ST terminating by large crashes are believed to be one of the principal seedingmechanisms for NTM triggering in ITER.

• Control of ST period may be achieved by modifying the magnetic shear at q=1 with localized co/cnt-ECCD around q=1

• both EPL & DUL appear to be moreefficient ( PEC=13.3 MW) than EL (PEC=20 MW) to modify the local shearin the region: ρt >0.3 (EPL), ρt >0.2 (DUL)

• DUL has the largest efficiency, up to a factor ~6 at ρt ~0.3 w.r.t. EPL

0

100

200

300

400

500

0.1 0.2 0.3 0.4 0.5

I cd/Δρ_t2

(MA

)

13.3 MW

EOB2

ρ_tor

20 MWEL

DUL_USM

EPL_USM


Equatorial Launcher

α=0 α=±5Present design:- Only co-CD- No tilt angle

•More central capabilitiesadding a tilt angle forlow and top mirrors

•Cnt-ECCD would largely increasethe physics functionalities of the EL


EL - Physics analysis

AIM:• To provide potential range of theq profile control achievable by anoptimized EL.• Preliminary estimation of theECCD required for assisting hybridand advanced scenarios.

• 3 selected full-field H-modescenarios at EOB:

• Scen 2 (standard)• Scen 3 (hybrid)• Scen 4 (RS)

• Different q, T, n, BS profiles.


EL potentialities for Scenario 2

-4

-2

0

2

4

0 0.1 0.2 0.3 0.4 0.5ρ

t

Scen2|α|=5P=20 MW

|β|=20co-CDIcd = 0.45 MA

cnt-CD Icd = -0.47 MA

Jcd

(MA

/m2 )

GRAY code CHEASE code

CNT-ECCD

CO-ECCD

•flexibility in controlling q0 with full power co- or cnt-ECCD by improved EL•If heating with EC is needed, with present design:

limited to the blue region an unwanted peaking of current profile could be obtained


EL potentialities for Scenario 3

-3

-2

-1

0

1

2

3

0 0.1 0.2 0.3 0.4 0.5ρ

t

Scen3|α|=5P=20 MW


cnt-CD Icd = -0.54 MA

Jcd

(MA

/m2 )


1 row in CNT-ECCD(1/3 PEC)

---10, 20MW in CO-ECCD

•Even with 6.7MW of cnt-ECCD, q can be raised above 1 allowing possibility to avoid sawteeth•Co-ECCD could lead to appearance of q=1 surface


EL potential for advanced Scenario 4

-3

-2

-1

0

1

2

3

0 0.1 0.2 0.3 0.4 0.5

Jcd

(MA

/m2 )

ρt

Scen4|α|=5P=20 MW


cntr-CD Icd = -0.67 MA


3 MWin CNT-ECCD

---10, 20MW in CO-ECCD

•High flexibility to control central q with co- and cnt-ECCD in reverse shear Sc.4•If heating with EC is needed, with present design we are limited to the blue region profile range


Reduced B field analysisScaling of plasma parameters

B, Ip and kinetic profiles have been scaled by using thefollowing constrains :

BT scaling : BT → g BT where g


EPLMagnetic field reduction of 10%, 15%, 20%

4.25 T < B ≤ 5.3 T

−ΔB/B ≥ 10% ⇒Innermost surfaces notreachable(no sawtooth control)

-q=2 from LSM & USM ⇒ ok

-q=3/2 surface ΔB/B = 15% ⇒ marginal ΔB/B > 15% ⇒ no

ηNTM increasesas B decreases(if we assume JBS ∝ B)

0

0.01

0.02

0.03

0.5 0.6 0.7 0.8 0.9ρtor

J/P 0

(MA

/MW

/m2 )

O-modeEPL_LSM

B=5.30 TB=4.77 TB=4.55 TB=4.24 T

q=3/2 q=2

0

0.01

0.02

0.03

0.3 0.4 0.5 0.6 0.7 0.8

J/P 0

(M

A/M

W/m

2 )

ρtor

OM1EPL_USM

B=5.30 TB=4.77 TB=4.55 TB=4.24 T

q=2q=3/2


DULMagnetic field reduction of 10%, 15%, 20%

4.25 T < B ≤ 5.3 T

DUL vs EPL•better access to inner

surfaces

•q=3/2 still reachable forΔB/B = 15%

•wider B range of operation

0

0.01

0.02

0.03

0.5 0.6 0.7 0.8 0.9ρtor

J/P 0

(MA

/MW

/m2 )

O-mode

B=5.30 TB=4.77 TB=4.55 TB=4.24 T q=3/2 q=2

DUL_LSM

0

0.02

0.04

0.06

0.3 0.4 0.5 0.6 0.7 0.8

J/P 0

(M

A/M

W/m

2 )

ρtor

B=5.30 TB=4.77 TB=4.55 TB=4.24 T

q=2q=3/2DUL_USMO-mode


Equatorial Launcher Magnetic field reduction of 10%, 15%, 20%

4.25 T < B ≤ 5.3 T

When B decreases, the effectivebeta range decreases due toincomplete power absorption.

Co-current is driven in the range

0 < ρt< ρmax with 0.2 < ρmax < 0.45

(for 4.77 T !)

In addition to co-ECCD,a counter current may be drivendue to second harmonic interaction(dotted lines).

0

0.1

0.2

0.3

0.4

0.5

20 25 30 35 40 45

ρ tor

β

O-modeEL- Mid Row B=5.3 T

B=4.77 TB=4.5 TB=4.24 T

0

10

20

30

40

50

20 25 30 35 40 45

I cd/P

(kA

/MW

)

β

B=5.3 TB=4.77 TB=4.5 TB=4.24 T

O-modeEL- Mid Row


Summary

• Good performances for both NTM stabilization and sawthooth control maybe obtained with an improved FS design based on 4 ports UL (EPL)

• Comparison with a dropped upper launcher (DUL) showed that furtheroptimization of the ECCD profiles can be achieved, leading to increasedlocalization & Jcd ⇒ better performances for both NTM stabilization andsawthooth control ⇒ reduction of PEC ⇒ lower impact on Q

• With improved EL design a large range of variation of q0 can be obtained withaddition of co-/cnt -ECCD (in particular cnt) for all scenarios

• The EL can control very efficiently the q profiles within ρt =0.2-0.4 in hybridand advanced scenarios, in particular if there is also the option of cnt-ECCD

• 10% B reductionEPL : innermost surfaces not reachable ⇒ no sawtooth controlDUL vs EPL : better access to inner surfaces, wider B rangeEL : access only to the region ρt

Introduction and motivations – I - IAEA NA · 2007. 6. 8. · 4th IAEA-TM on ECRH , Vienna 6-8...

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Transcript of Introduction and motivations – I - IAEA NA · 2007. 6. 8. · 4th IAEA-TM on ECRH , Vienna 6-8...