Conceptual study on

K-DEMO current drive scenario

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J. S. Kang1†, K. Kim1, and Y. S. Hwang1

1FUSMA, Dept. of Nuclear Engineering, Seoul National University.

†jskangst@gmail.com

Outline

I. Introduction to K-DEMO study

II. Conceptual current drive scenario- Motivation- Calculation strategy & method

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- Calculation strategy & method- Calculation result

III. ConclusionsIV. Future work

I. IntroductionDesign Features of Korean Demonstration fusion reactor

Main Missionl Demonstrate net electricity generation and self-sustained tritium cyclel Play a role as a component test facility at the first phase, and

generate net electricity on the order of 500 MWe at the second phase

Design Philosophyl Similar major radius & aspect ratio to ITERl Extrapolation of ITER operation regime to High Magnetic Field operation

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Ø Size of K-DEMO is limited to that of ITER to minimize the construction cost and engineering risks.

Ø To incorporate the plasma physics accumulated from KSTAR and ITER operations, the aspect ratio of K-DEMO shall be in similar range of 3-3.5.

Ø Using high performance Nb3Sn-based superconducting strand currently available, high magnetic field at the plasma center of ~8 T (maximum field limit of 16T) is chosen.

Thermal Fusion power target 1st phase 1500MWth2nd phase 3000MWth (ITER : 3~500MW)

KDEMO-Ia - High confinement - Extrapolation ITER WS scenario [1] to high bN .- Large bootstrap fraction with high bN & BT.- Require improvement of confinement &

stability with high b N & low IP.

KDEMO-Ib

I. IntroductionDesign Features of Korean Demonstration fusion reactor

Phased approach suggestion

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KDEMO-Ib- Extrapolation ITER inductive scenario[2]

to the same IP & high bN.- Major fusion power increase by BTè not requiring confinement improvement

- Require high current drive power due to relatively low fBS è low Q.

KDEMO-II- Can be achieved only when both

improved performance of KDEMO-Iahigh current drive power of KDEMO-Ibimplemented together at the same machine.

[1] M. Murakami et al, Nucl. Fusion 51 (2011) 103006

[2] C. E. Kessel et al, Nucl. Fusion 49 (2009) 085034

II. Conceptual Current Drive Scenario- Motivation I : Uncertainty of zero dimensional CD analysis

Target fusion power seems to be achievable.

There’re Uncertainties of 0d analysis especially

on plasma current profile.

current drive location- radial current drive location is

the key factor to make an equilibrium current profile & advanced operation

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current profile & advanced operation

bootstrap current estimation- pressure gradient is the origin of bootstrap current

current drive efficiency- efficiency at the fixed temperature

of 20keV could make over- or under-estimation.

II. Conceptual Current Drive Scenario- Motivation II : Evaluation of Demo models from CD calculation

External heating power must satisfy power balance & current drive condition.

POPCON analysis of K-DEMO II

1

1.5 00 0

0

100200

200300

300

Greenwald limit

[102

0/m

3 ]

PF = 3000MW

Operation point satisfying fusion power & beta limit.

In this operation point.

If Pext > PCD

More room in CD scenario.

Change model parameter?

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5 10 15 20 25 300

0.5

0 0

100

100

200

200

300

Temperature [keV]

<ne>

[10

*L-H transitionβN = 4

Required heating power[MW]

Change model parameter?(ex. Ip ↑ & lower betaN ↓)

If Pext < PCD

More room in confinement.

Change model parameter?ex.) Ip ↓ & betaN ↑

II. Conceptual Current Drive Scenario- Calculation strategy & method : ASTRA coupled with TORAYOne dimensional equilibrium calculation and current drive simulation

with ASTRA coupled with TORAY

External driven current profile

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Cur

rent

den

sity

Bootstrap current profile

Total current density profile

Cur

rent

den

sity

Current drive calculation and bootstrap current calculation are aligned to total current profile to consider those uncertainties.

II. Conceptual Current Drive Scenario- Calculation strategy & method : INPUT & OUTPUT variables

Equilibrium calculation for total current density profile & bootstrap profile

Current drive calculation for driven current density profile

Inputdensity profile, temperature profilesafety factor profile

Outputtotal current density profile

Input Output

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Inputdensity profile, temperature profilesafety factor profileCurrent drive methodCD powerCD location(radial & vertical positions, angle)

OutputDriven current profileTotal amount of currentPower deposition

ü Density, temperature, total current density profiles are set to be constant during calculation.

II. Conceptual Current Drive Scenario- Calculation strategy & method : WS scenario benchmarking [1,2]

How to determine pressure & q profiles? – benchmarking ITER & EU-DEMOThose two scenarios show the possibility of weak shear steady state operation

in betaN 2.5~4 regime.

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[1] M. Murakami et al, Nucl. Fusion 51 (2011) 103006

ITER WS scenario temperature (a), density (b), and safety factor (c) profiles.

BS 5MA NB 2.3MA EC 0.8MA FW 0.7MA

External CD and bootstrap current clearly construct total current profile.

[2] J. Garcia et al, Nucl. Fusion 48 (2008) 075007

II. Conceptual Current Drive Scenario- Calculation strategy & method : Current drive method selection

Requirements guiding K-DEMO heating and current drive system

■ Fully non-inductive current drive~ 60% bootstrap current~ 40% external non-inductive current drive

central current drive method – NB? or EC? or FW?

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■ Stable, reliable technological level with the assumption of successful operation of ITER.

■ Appropriate method at high magnetic field operation(7.72T)

à (EC) Higher frequency gyrotron is required.

■ Steady-state operation with high efficiency

Type State of the art[1](Assume successful ITER)

WallplugEfficiency[2]

Source Launcher Additional Issues

NBI 16.5MW 40A, 1Mev beams

Pulse up to 3600s

~0.13 Ebeam (>1MeV) for high neNeutron shielding

Tritium Contamination

Difficulty in separation of

H&CD

FW 40~55MHz, 20MW steady-state source

~0.09 Multi-MW in 50~100MHz

Cooling Coupling

Peak central CD

HHFW

Not in ITEROff-axis CD & efficient

CD are expected[3]~0.15§

High power Klystron available

Cooling Less experience

II. Conceptual Current Drive Scenario- Calculation strategy & method : Current drive method selection

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CD are expected[3] available

EC 170GHz Gyrotrons1MW(~800s)

2MW(short pulse)

~0.08 frequency(>200GHz) ,high power, efficiency

transmission line and window technology

CD efficiencySteeringmirror

LH ~5GHz 20MW steady state source

~0.08 High frequency

(>5GHz) High power

Vacuum propagation from

launcher to plasma

Edge-localized

CD

[1] David Rasmussen, ‘Overview of ITER Heating and Current Drive Systems, APS-DPP USBPO ITER Town Meeting November 15, 2011[2] D. Stork, 3rd Karlsruhe Inttl School on Fusion Technology, Sep 2009[3] R. Koch et al, AIP Conf. Proc. 1406, 349(2011)

NB & EC is set to be the reference current drive methodfor its efficiency and local current drive capability.

l Neutral beam injector technology

- <1.5MeV Beam could be obtained with electrostatic accelerator.[1]- Merging beam system may provide a solution for neutron shielding.[1]- R&D for steady-state source is essential(ex. filamentless, Cs-free)- Advanced neutralizer should be developed to increase efficiency.

II. Conceptual Current Drive Scenario- Calculation strategy & method : Current drive method selection

NB & EC Technology seems to be promising!

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[1] T. Inoue, 1st Technical Workshop on Fusion Eng. and Tech. beyond ITER between KODA and JADA[2] S. Sakamoto, 1st Technical Workshop on Fusion Eng. and Tech. beyond ITER between KODA and JADA

l Electron cyclotron source technology- 170GHz for ITER under development : long pulse not yet- Over 170GHz Gyrotron (ex. 236GHz, 200GHz) may be developed with high

efficiency.- Frequency sweeping about 1GHz/1sec may be achievable [2]

à eliminate steering mirror?

ü Feasibility for Demo conditions such as high magnetic field and high heat/radiation load, but need further demonstration for long-pulse.

ASTRA calculation of KDEMO-II model

II. Conceptual Current Drive Scenario- Calculation Result : NB driven case

Cur

rent

Den

sity

[ M

A/m

2 ]

q

0.5

1

1.5

JTOTJBSJNB

2

4

6

8

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l Total 2 beam lines are used: 43MW(1.3MeV) 70MW(1MeV) l 1.3MeV beam can be realized with electrostatic accelerator.

l Bootstrap current has a peak value at pedestal region caused by high pressure gradient. l Neutral beam is launched mainly to near-axis region where less self-driven current exists. l Bootstrap and driven current profiles are aligned to an equilibrium total current profile.

l Safety factor has the lowest value near r=0.25 and slightly higher value on axis.

rho(a/R)

Cur

rent

Den

sity

[ M

A/m

rho(a/R)0 0.2 0.4 0.6 0.8 10 0 0.2 0.4 0.6 0.8 10

ASTRA calculation of KDEMO-II model

II. Conceptual Current Drive Scenario- Calculation Result : Central EC Off-axis NB case

Cur

rent

Den

sity

[ M

A/m

2 ]

q

0.5

1

1.5

JTOTJBSJNBJEC

2

4

6

8

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l 243GHz (central resonance) ECH (120MW) and 1MeV NB (90MW) are usedl Off-axis ECCD less efficient than on axis ECCD → Use off axis NBCD

l EC is launched to on-axis region where less self-driven current exists. l Bootstrap and external driven current profiles are aligned to an equilibrium total current profile.

l Show the possibility of EC central current drive, but still need better efficiency for less CD power.

rho(a/R)

Cur

rent

Den

sity

[ M

A/m

rho(a/R)0 0.2 0.4 0.6 0.8 10

0 0.2 0.4 0.6 0.8 10

2

Ia(NB) Ia(EC,NB) Ib(NB) Ib(EC,NB) II(NB) II(EC,NB)Bootstrap current (MA) 7.1 7.5 7 7 8.5 8.6NBI driven current (MA) 4 3 8 7 6.5 5.5NBI power (MW) 53 40 170 140 113 90NBI beam line number /power of each line (MeV)

21.3, 1

11

21.3, 1

11

21.3, 1

11

ECH driven current (MA) - 0.5 - 1 - 1ECH power (MW) - 55 - 136 - 120ECH frequency (GHz) - 243 - 243 - 243

II. Conceptual Current Drive Scenario- Calculation Result : Summary Table

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§ Overall efficiency Low Ip & high b N è High fbs & high Te è low PCD : Model-IaHigh Ip & low b N è Low fbs & low Te è high PCD : Model-IbModerate conditions : Model-II

§ High power & efficient NB&EC source development seems to be essentialsince total ITER power source is only 33(NB)~20(EC)MW.

§ 1.3 MeV beam is used to drive central current. -Electron density of each model is different, central current drive is possible by changing injection angle & position.§ HHFW may be considered to replace NB or EC as a backup current drive method.

If HHFW shows more experimental CD result, they can be strong methods with good efficiency.

ECH frequency (GHz) - 243 - 243 - 243

§ Relatively low current drive power→ Model Ia has a flexibility for current drive scenario.

Ia(NB) Ia(EC,NB) Ib(NB) Ib(EC,NB) II(NB) II(EC,NB)Plasma current (MA) 11 15 15Required heating power(MW) 85 76 107Total CD power(MW) 53 95 140 276 113 210Beta N 4 2.4 4H factor 2 1.1 1.5

II. Conceptual Current Drive Scenario- Calculation Result : Evaluation of each model

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Model Ia has a flexibility for current drive scenario.

NBCD is a strong candidate, but ECCD is possible with slight improvement of efficiency.Other less efficient methods may be used if they are developed earlier than DEMO period.

§ Confinement problemH factor 2 is a challenging task. Alternative approach

- CD power margin(PCD<Pext) → Larger Ip & low fbs → PCD ↑(PCD~Pext) - Large Ip → Good confinement(H factor ↓) & Less beta N requirement

§ Relatively high current drive power→ Model Ib has a problem for current drive power.

Ia(NB) Ia(EC,NB) Ib(NB) Ib(EC,NB) II(NB) II(EC,NB)Plasma current (MA) 11 15 15Required heating power(MW) 85 76 107Total CD power(MW) 53 95 140 276 113 210Beta N 4 2.4 4H factor 2 1.1 1.5

II. Conceptual Current Drive Scenario- Calculation Result : Evaluation of each model

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Model Ib has a problem for current drive power.

How to solve?

∙ Lowering plasma current since it has a realistic confinement time(H factor 1.1)Reverse approach of previous page could be possible.

∙ Advanced scenarioEven NB current drive power is too high.If bootstrap current fraction is increased to ~ 90%(ex. Strong shear scenario), the amount of external driven current can be significantly decreased. Consequently, lowe current drive power may be required.

§ Pext ~ PCD(NB case)→ Model II has a relatively reasonable current drive power for NB case.

Ia(NB) Ia(EC,NB) Ib(NB) Ib(EC,NB) II(NB) II(EC,NB)Plasma current (MA) 11 15 15Required heating power(MW) 85 76 107Total CD power(MW) 53 95 140 276 113 210Beta N 4 2.4 4H factor 2 1.1 1.5

II. Conceptual Current Drive Scenario- Calculation Result : Evaluation of each model

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Model II has a relatively reasonable current drive power for NB case.

Current drive method with NB level efficiency could be backup current drive method.EC current drive power is too high.

If HHFW is feasible, it can be used to enlarge current drive capability of model-II.

Advanced scenarioIf even NB technology is not available at demo period, advanced scenario should be developed to support such a high current since model II does not have plasma current margin(model Ia) or confinement margin(model Ib).

II. Conceptual Current Drive Scenario- Remark of approach path

Physics and technological advance is the key to determine the path for DEMO

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III. Conclusions

ü K-DEMO concept is suggested with recent progress of magnet technology which leads to the level of demonstration power at the ITER-size machine. Three models are strategically suggested and classified with fusion

power, plasma current, and plasma normalized beta.

ü Conceptual current drive study is conducted to evaluate K-DEMO approach.

ü Various types of current drive techniques are investigated to find reference current drive methods for K-DEMO by considering current drive location,

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current drive methods for K-DEMO by considering current drive location, efficiency, and technological readiness. NB and EC are selected as main candidates.

ü One dimensional current drive calculation is conducted with central NB or EC CD scenario and showed the possibility of steady-state operation.

ü Technically feasible CD methods with better CD efficiency of NBCD are required to realize KDEMO models satisfying power balance analysis.

IV. Future workü More research on various current drive method and advanced scenario

with high bootstrap fraction (~90 %) will be performed to extend K-DEMO operation capability.

ü Current drive scenario calculation will progress to the self-consistent operation scenario to consider alpha particle effect on power & current drive.

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Thank you for your attention!