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Burning Plasma Relevant Control Development: Advanced Magnetic Divertor Configurations, Divertor Detachment and Burn Control by E. Kolemen 1 with B.A. Grierson 2 , R. Nazikian 2 , W. Solomon 2 , S.L. Allen 3 , M.A. Makowski 3 , V.A.

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1

  • E. Kolemen /IAEA/ Oct 2014

by

  • E. Kolemen1

with B.A. Grierson2, R. Nazikian2, W. Solomon2, S.L. Allen3, M.A. Makowski3, V.A. Soukhanovskii3, B.D. Bray4, D. Eldon4, D.A. Humphreys4, A. Hyatt4, R. Johnson4, A.W. Leonard4, C. Liu4,

  • C. Paz-Soldan4, B.G. Penaflor4, T.W. Petrie4, A.G. McLean5, E.A.

Unterberg5, and S. Wolfe6

1Princeton University, NJ USA 2Princeton Plasma Physics Laboratory, Princeton, NJ, USA 3Lawrence Livermore National Laboratory, Livermore, CA, USA 4General Atomics, San Diego, CA, USA 5Oak Ridge National Laboratory, Oak Ridge, TN, USA 6MIT, Cambridge, MA, USA

Presented at the

25th IAEA Fusion Energy Conference Saint Petersburg, Russia October 13–18, 2014

Burning Plasma Relevant Control Development: Advanced Magnetic Divertor Configurations, Divertor Detachment and Burn Control

Detachment Control Snowflake Control Burn Control

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  • E. Kolemen /IAEA/ Oct 2014
  • There are technological limits on

heat flux removal, and the problem gets more challenging for future devices

  • High fidelity control gives
  • pportunity to solve some of

these challenges

Focus: How to Achieve Acceptable Heat Flux Exhaust Compatible with Attractive Core Plasma

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SLIDE 3

3

  • E. Kolemen /IAEA/ Oct 2014
  • There are technological limits on

heat flux removal, and the problem gets more challenging for future devices

  • High fidelity control gives
  • pportunity to solve some of

these challenges

  • 1. Snowflake Divertor:
  • Reduce peak heat flux
  • Possibly reactor

application

Focus: How to Achieve Acceptable Heat Flux Exhaust Compatible with Attractive Core Plasma

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4

  • E. Kolemen /IAEA/ Oct 2014
  • There are technological limits on

heat flux removal, and the problem gets more challenging for future devices

  • High fidelity control gives
  • pportunity to solve some of

these challenges

  • 1. Snowflake Divertor:
  • Reduce peak heat flux
  • Possibly reactor

application

  • 2. Partial detachment control
  • Reduce target plasma

temperature & erosion

  • ITER relevant

Focus: How to Achieve Acceptable Heat Flux Exhaust Compatible with Attractive Core Plasma

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SLIDE 5

5

  • E. Kolemen /IAEA/ Oct 2014
  • There are technological limits on

heat flux removal, and the problem gets more challenging for future devices

  • High fidelity control gives
  • pportunity to solve some of

these challenges

  • 1. Snowflake Divertor:
  • Reduce peak heat flux
  • Possibly reactor

application

  • 2. Partial detachment control
  • Reduce target plasma

temperature & erosion

  • ITER relevant

Focus: How to Achieve Acceptable Heat Flux Exhaust Compatible with Attractive Core Plasma

  • 3. Burn control
  • Regulate

heat source

  • ITER/Reacto

r relevant

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6

  • E. Kolemen /IAEA/ Oct 2014

Heat Flux Reduction via

  • 1. Snowflake Divertor Control
  • 2. Detachment Control
  • 3. Burn Control with 3D Coils
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  • E. Kolemen / St. Petersburg / Oct 2014

Snowflake Divertor (SFD) Has Advantages Compared to the Standard X-point Divertor

  • Snowflake divertor(SFD): second-order null (2 X-points)
  • Geometric changes compared to standard divertor can lead to:

– High poloidal flux expansion, large plasma-wetted area reduce peak qdiv – Four strike points  share Pdiv

  • –

–

  • 2nd X-Point in

SOL

  • –

–

  • –

–

  • 4-18
  • 21

2nd X-Point in Private Flux

  • –

–

  • 18

2 P

Exact Snowflake

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  • E. Kolemen / St. Petersburg / Oct 2014

Snowflake Control System

SFD (-) SFD (+) SFD locator Desired SFD SFD controller IPF

  • +

DIII-D

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  • E. Kolemen /IAEA/ Oct 2014

Br = -1 r

¶ Y

exp

¶dz = 0 = Bz = 1

r

¶ Y

exp

¶dx = 0

{drX1(cexp),dzX1(cexp),drX2(cexp),dzX2(cexp)}

Y exp = Y(cexp,dr,dz)

SFD locator Desired SFD SFD controller IPF

  • +

DIII-D

  • Locally expand the Grad-Shafranov

equation in toroidal coordinates:

  • Keep the 3rd order terms
  • Find coefficients, cexp, from sample

points

  • Find the null points (X-points) <250us
  • Snowflake Locator: Finding the Two X-points

 SFD (+)

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10

  • E. Kolemen /IAEA/ Oct 2014

SFD locator Desired SFD SFD controller IPF

  • +

DIII-D

  • Snowflake parameters:θ, ρ, rc, zc
  • Calculate A matrix which shows

how PF coils affect X-points (2 ms)

  • 3 closest PF coils are used for

controlling the formation

Snowflake Control: Controlling the PF Coil Currents

x x x Location of the X-points and Centroid F8B F4B F5B ρ θ

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  • E. Kolemen /IAEA/ Oct 2014

Snowflake Control: Obtaining Exact Snowflake (ρ Scan)

Simulation

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  • E. Kolemen /IAEA/ Oct 2014

Snowflake Control: Obtaining Exact Snowflake (ρ Scan)

Simulation

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  • E. Kolemen /IAEA/ Oct 2014
  • Obtained long stable S-F close to exact S-F

– No adverse confinement degradation – Pedestal profile for S-F has little change compared to regular divertor – Observed broadening of heat flux profiles with snowflake

Snowflake Control: Obtaining Snowflake (Exact, + and -)

Snowflake Control (Control Starts at 3 s) Near Exact Snowflake

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  • E. Kolemen /IAEA/ Oct 2014

Snowflake Control: Scanning the Angle

Simulation

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15

  • E. Kolemen /IAEA/ Oct 2014

Snowflake Control: Scanning the Angle

Simulation

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  • E. Kolemen /IAEA/ Oct 2014

Snowflake Control: Angle Control (+80° to -45°)

Angle requested Angle achieved

  • 45° x

x

Time [ms]

x 80° x

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  • E. Kolemen /IAEA/ Oct 2014

Snowflake with 2.5x Reduced Heat Flux Compatible with High Performance Plasmas

  • βN = 3.0 and H98(y,2) ≅

1.35 conditions preserved with SF with no adverse effects – Peak heat flux outer reduced by 2.5x for the SF AT – SF: qP

⊥,Iin > qP ⊥,out

  • standard

Snowflake q^ (MW/m2)

4

Z (m) R (m) Z (m) R (m)

  • 1.3 0 1.0 1.6 -1.3 0 1.0 1.6

IN OUT IN OUT

  • Z (m) R (m) Z (m) R (m)
  • 1.3 0 1.0 1.6 -1.3 0 1.0 1.6
  • .6-1.3 01.0

Z (m) RED – Before gas puffing BLUE – Radiating

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  • E. Kolemen /IAEA/ Oct 2014

Heat Flux Reduction via

  • 1. Snowflake Divertor Control
  • 2. Detachment Control
  • 3. Burn Control with 3D Coils
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  • E. Kolemen /IAEA/ Oct 2014
  • Not enough detachment  Te and heat flux too high  Erosion
  • Too much detachment  Instabilities (MARFE) and core degradation
  • MARFE Instability:

– Full detachment  large cold areas – Neutrals/Impurities influx  high radiation from the core – Thermal instability of the whole plasma

Partial Detachment Control Needed for ITER

www.efda.org efda.org

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  • E. Kolemen /IAEA/ Oct 2014

Effective Detachment Control at Constant Core Density Requires Two Feedback Channels

D2 Fueling: Core Density Control D2 Fueling: Detachment Control

RT-Divertor Thomson Interferometer Chord

Density Meas. (Interferometer) Core Density Request Density controller

  • +

Upper Gas Valve Detachment Meas. (rt-Divertor Thom.) Detachment Request Detachment controller

  • +

Lower Gas Valve

  • Goal: Keep the core density and

detachment level constant

  • Feedback Control Method:
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  • E. Kolemen / St. Petersburg / Oct 2014

Detachment Control in Action

Strike Point

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  • E. Kolemen /IAEA/ Oct 2014

Inner Wall

CIII Emission – Visible (465 nm)

Outer Strike Point X-Point

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  • E. Kolemen /IAEA/ Oct 2014

CIII Emission – Visible (465 nm)

Inner Wall Outer Strike Point X-Point

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  • E. Kolemen / St. Petersburg / Oct 2014

Partial Detachment Control: Forms a Cold Front in L-mode

No Control (#153814) Control (#153816) Te profile Cold front shown in blue

eV

  • Control achieves partial detachment
  • Keep the cold front midway between the X-point and strike point
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  • E. Kolemen / St. Petersburg / Oct 2014

1.5 2 2.5 3 3.5 4 2 4 6 x 10

19

Core Density [m−3] Time [s] 1.5 2 2.5 3 3.5 4 1 2 x 10

20

Time [s] Divertor Density [m−3] 1.5 2 2.5 3 3.5 4 10 20 Time [s] Divertor Temperature [eV]

Control Stabilized Divertor Temperature (Detachment) but Keeps Core Density Constant

Control (#153816) No Control (#153814)

  • Divertor Density Increases
  • But Core Density constant
  • Divertor Temperature

reduces to 1 eV

control start

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26

  • E. Kolemen / St. Petersburg / Oct 2014

1.5 2 2.5 3 3.5 4 2 4 6 x 10

19

Core Density [m−3] Time [s] 1.5 2 2.5 3 3.5 4 1 2 x 10

20

Time [s] Divertor Density [m−3] 1.5 2 2.5 3 3.5 4 10 20 Time [s] Divertor Temperature [eV]

Control (#153816) No Control (#153814) control start

Control Stabilized Divertor Temperature (Detachment) but Keeps Core Density Constant

  • Divertor Density Increases
  • But Core Density constant
  • Divertor Temperature

reduces to 1 eV

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  • E. Kolemen /IAEA/ Oct 2014

Heat Flux Regulation via

  • 1. Snowflake Divertor Control
  • 2. Detachment Control
  • 3. Burn Control with 3D Coils
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  • E. Kolemen /IAEA/ Oct 2014
  • Burn: D + T  He + n + 17.6 MeV
  • ITER concerned with power surges during burning phase and

burn entry/exit conditions

  • Normal methods (heating, density) are slow

– Auxiliary heating control: more heating power capability – cost – Density control is limited:

  • Upper density set by Greenwald limit
  • Lower density set by detached divertor

– Impurity injection: significant time delays for penetration?

Burn Control: We Need Methods for Faster Control of Fusion Burn Rate

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  • E. Kolemen /IAEA/ Oct 2014

DIII-D I coils C coils

  • 10% change in energy confinement near ignition

 factor of 2 reduction in fusion power

  • 3D magnetic field (n=3) reduces confinement in many plasma

conditions by increasing edge stochasticity 3D coils actuator to control confinement time & fusion power

Burn Control by Non-Axisymmetric (3D) Coils (Hawryluk, PPC/P2-33)

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  • E. Kolemen /IAEA/ Oct 2014
  • Simulate the surge with

Neutral Beams (NBI)

  • Add NBI steps (0.8 and 1.6

MW) to see the effect on control

  • Control keeps the Burn

(Stored Energy) constant: 1. Adjust 3D coil current 2. 3D coils in turn control the confinement time 3. This keeps fusion power constant

Non-Axisymmetric (3D) Coils Can Control Burn (Stored Energy) with Simulated Power Surge

τE (s) 3D Field (kA)

6

Stored Energy (MJ)

  • Preprog. Power Step

3D Field (kA)

0.1 0.2 2 6 10 0.4 1.0 0.6 0.8 4 2 2000 3000 4000 5000 Time (ms)

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  • E. Kolemen /IAEA/ Oct 2014

Non-Axisymmetric (3D) Coils Can Control Burn (Stored Energy) with Simulated Power Surge

τE (s) 3D Field (kA)

6

Stored Energy (MJ) Power Step 3D Field (kA)

0.1 0.2 2 6 10 0.4 1.0 0.6 0.8 4 2 2000 3000 4000 5000 Time (ms)

  • Simulate the surge with

Neutral Beams (NBI)

  • Add NBI steps (0.8 and 1.6

MW) to see the effect on control

  • Control keeps the Burn

(Stored Energy) constant: 1. Adjust 3D coil current 2. 3D coils in turn control the confinement time 3. This keeps fusion power constant

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SLIDE 32

32

  • E. Kolemen /IAEA/ Oct 2014

Non-Axisymmetric (3D) Coils Can Control Burn (Stored Energy) with Simulated Power Surge

τE (s) 3D Field (kA)

6

Stored Energy (MJ) Power Step 3D Field (kA)

0.1 0.2 2 6 10 0.4 1.0 0.6 0.8 4 2 2000 3000 4000 5000 Time (ms)

  • Simulate the surge with

Neutral Beams (NBI)

  • Add NBI steps (0.8 and 1.6

MW) to see the effect on control

  • Control keeps the Burn

(Stored Energy) constant: 1. Adjust 3D coil current 2. 3D coils in turn control the confinement time 3. This keeps fusion power constant

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SLIDE 33

33

  • E. Kolemen /IAEA/ Oct 2014

Non-Axisymmetric (3D) Coils Can Control Burn (Stored Energy) with Simulated Power Surge

τE (s) 3D Field (kA)

6

Stored Energy (MJ) Power Step 3D Field (kA)

0.1 0.2 2 6 10 0.4 1.0 0.6 0.8 4 2 2000 3000 4000 5000 Time (ms)

  • Simulate the surge with

Neutral Beams (NBI)

  • Add NBI steps (0.8 and 1.6

MW) to see the effect on control

  • Control keeps the Burn

(Stored Energy) constant: 1. Adjust 3D coil current 2. 3D coils in turn control the confinement time 3. This keeps fusion power constant

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SLIDE 34

34

  • E. Kolemen /IAEA/ Oct 2014

Non-Axisymmetric (3D) Coils Can Control Burn (Stored Energy) with Simulated Power Surge

τE (s) 3D Field (kA)

6

Stored Energy (MJ) Power Steps 3D Field (kA)

0.1 0.2 2 6 10 0.4 1.0 0.6 0.8 4 2 2000 3000 4000 5000 Time (ms)

  • Simulate the surge with

Neutral Beams (NBI)

  • Add NBI steps (0.8 and 1.6

MW) to see the effect on control

  • Control keeps the Burn

(Stored Energy) constant: 1. Adjust 3D coil current 2. 3D coils in turn control the confinement time 3. This keeps fusion power constant

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  • E. Kolemen /IAEA/ Oct 2014

Conclusion: New Control Solutions Enable Advances in Heat Flux Management

  • Advanced Magnetic Divertor Control reduces the peak heat

flux without affecting the core properties

  • Double feedback Partial Detachment Control keeps the

detachment front stable between the X-point and strike point, while keeping the core properties constant

  • Burn Control is feasible by using Non-Axisymmetric (3D) Coils
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  • E. Kolemen /IAEA/ Oct 2014

Extras

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  • E. Kolemen /IAEA/ Oct 2014

Snowflake Control: ρ Control

rho requested rho achieved

Distance Scan

  • Constantρof 3, 5, 7 cm
  • ρscan from 3 to 15 cm.

Distance Scans

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  • E. Kolemen /IAEA/ Oct 2014

Snowflake Control: Angle Control and Scans

Angle Control/Scans

  • Constant angle for -75, -45, +10, +50
  • Scan from -75 to +25.
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  • E. Kolemen /IAEA/ Oct 2014

Snowflake Control: Combined rho and Angle Manipulation

Snowflake (+) Snowflake (-)/exact

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  • E. Kolemen /IAEA/ Oct 2014

Divertor Peak Heat Flux Reduced by 2.5x in SF (-) Due To Changes in Divertor Geometry

Standard Divertor Snowflake

S.L. Alle

Snowflake (-)

Allen IAEA ‘12

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41

  • E. Kolemen /IAEA/ Oct 2014

AT DN radiating divertor similar reducing heat to SFD without radiating divertor

  • .3

Z (m) RED – Before gas puffing BLUE – Radiating

  • standard

Snowflake q^ (MW/m2)

4

Z (m) R (m) Z (m) R (m)

  • 1.3 0 1.0 1.6 -1.3 0 1.0 1.6

IN OUT IN OUT

  • 1.3 0

Z (m) RED – Before gas puffing BLUE – Radiating

  • .6-1.3 01.0

Z (m) RED – Before gas puffing BLUE – Radiating

  • Snowflake

standard

  • 1.3 0 1.0 1.6-1.3 01.0 1.6

4

q^ (MW/m2) IN OUT IN OUT RED – Before gas puffing BLUE – Radiating

  • rd

Snowflake ) Z (m) R (m)

1.6 -1.3 0 1.0 1.6

T IN OUT

  • Radiating divertor case:
  • A perturbing mix of

D2+neon had a greater effect on q⊥ in the outer divertor for the standard DN

  • SF heat flux similar to

radiating divertor RED – Before gas puffing BLUE – Radiating divertor

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  • E. Kolemen /IAEA/ Oct 2014

Snowflake with 2.5x Reduced Heat Flux Compatible with High Performance Plasmas

  • standard

Snowflake q^ (MW/m2)

4

Z (m) R (m) Z (m) R (m)

  • 1.3 0 1.0 1.6 -1.3 0 1.0 1.6

IN OUT IN OUT

  • 1.3 0 1

Z (m) RED – Before gas puffing BLUE – Radiating

  • .6-1.3 01.0

Z (m) RED – Before gas puffing BLUE – Radiating

  • standard

Snowflake q^ (MW/m2)

4

Z (m) R (m) Z (m) R (m)

  • 1.3 0 1.0 1.6 -1.3 0 1.0 1.6

IN OUT IN OUT

  • βN = 3.0 and H98(y,2) ≅

1.35 conditions preserved with SF with no adverse effects

  • Outer:

– SF bifurcating targets – Peak heat flux outer reduced by 2.5x for the SF AT

  • Inner:

– Similar heat flux profiles at the inner target – SF: qP

⊥,Iin > qP ⊥,out

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  • E. Kolemen /IAEA/ Oct 2014

Snowflake Control: rho scan in Snowflake (-) (-45 deg)

Angle Control/Scans

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  • E. Kolemen /IAEA/ Oct 2014

Snowflake Control: rho scan in Snowflake (+) (+55 deg)

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  • E. Kolemen /IAEA/ Oct 2014

Snowflake Control: Snowflake from t=2 sec

Time [ms] ρ [cm] θ [degrees] PF4B [Amp] PF5B[Amp] PF8B [Amp]