Capabilities of the ITER Electron Cyclotron Equatorial Launcher for Heating and Current Drive

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Capabilities of the ITER

Electron Cyclotron Equatorial Launcher

for Heating and Current Drive

Daniela Farina

L Figini, M Henderson, G. Ramponi, and G Saibene

Istituto di Fisica del Plasma, CNR, EURATOM-ENEA Association, Milano, Italy ITER Organization, Saint-Paul-lez-Durance France

Fusion for Energy, Barcelona, Spain

acknowledgments

A. Loarte, T. Casper, K. Kajiwara, K Takahashi

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Outline

•

 

ITER Equatorial Launcher (EL) goals

•

 

EC capabilities within present EL design

–

 

ECCD in scenarios at burn @ full field

–

 

ECCD in plasma current ramp-up phase @ full field

–

 

ECRH @ nominal and reduced B field

•

 

Proposal of a new EL design with poloidal

steering mirrors

work done under ITER Contracts see Farina et al NF 2012

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ITER EL design and physics goals

ITER Equatorial Launcher (EL)

170 GHz @ 20 MW

Present design

(still to be finalized)

•  3 sets of 8 beams, equatorial port

–  3 mirrors same R @ different z, TOP, MID, BOTTOM

•

 

Toroidal steering

Physics Objectives

•  Access in range of 0 ≤ ρ_T< 0.45)

•  Drive Current (co-ECCD)

•  Current Profile tailoring (co&cnt-ECCD)

•  Central Heating

•  Assist L-H transition

•  SS operation

•  Breakdown & Burnthrough

10.5.2012

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Beam tracing analysis

•  Beam tracing code GRAY (Farina, FS&T 2007)

:

–  astigmatic Gaussian beam propagation

–  relativistic power absorption (Farina, FS&T 2008)

–  ECCD moment conservation model (Maruschenko FS&T 2009)

•  J and p_d profile characterization

–  almost Gaussian profile:

•  ρtor , Δρtor: peak radius, profile width at 1/e

–  generic profiles:

•  <ρ>, σ_ρ=(<δρ2_>)1/2: “average” radius and width

•  Launching set up

–  3 mirror locations (beam / single ray analysis)

R=926.5 cm z=2, 62, 122 cm

–  poloidal

α

and toroidal

β

launching angles

tan

α

=N

z

/N

R

, sin

β

=

N

_φ ! <">=

#

"p(")dV p(")dV

#

= "dP

#

dP

#

! <"#2 >= (#$<#>) 2 p(#)dV

%

p(#)dV

%

0 0.01 0.02 0 0.1 0.2 0.3 0.4 0.5 dP/dV (MW/m 3 ) ! "! tor peak !_tor OM B 0=5.3T 0 0.001 0.002 0 0.2 0.4 0.6 0.8 1 dP/dV (MW/m 3 ) ! peak !_tor XM B 0=2.65T average <!>

20º

≤

|

β

|

≤

45º

α

=0º, ± 5º

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ITER Scenarios for ECRH&CD analysis

Two main ITER scenarios at full field

(ITER IDM):

a)  “15 MA Elmy H-mode Scenario”

Low Te & high ne ->low ECCD efficiency b)  “9 MA non inductive Scenario”

High Te & low ne -> high ECCD efficiency

10.5.2012 D Farina, EC-17 5 0 10 20 30 40 2 4 6 8 10 12 0 0.2 0.4 0.6 0.8 1 T e (keV) n e (10 19 m -3 ) ! 9 MA 15 MA n e n e T e T e β=20º, up to 60% 2nd _{harm. abs}.` β=20º, ~15% 2nd _{harm. abs}. R_axis shifted outward 1st _harm 2nd _harm 1st _harm 2nd _harm

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ECCD results at full field

SCEN 15 MA:

•  ~15% larger I_cd wrt old scen. 2

estimates

(momentum conservation model)

SCEN 9 MA:

•  quite large I_cd , up to 60 kA/MW

•  up to +50% more than for previous

scen. 4 (larger T_e)

dotted lines: non monotonic J profile (2nd _{harm contribution)}

Achievable radial range :

0 <

ρ

< 0.5

0 10 20 30 40 0 0.1 0.2 0.3 0.4 0.5 0.6 II cd I/P (kA/MW) TOP LOW MID ‹!› J (b) 15 MA 0 20 40 60 0 0.1 0.2 0.3 0.4 0.5 0.6 II cd

I/P (kA/MW) MID LOW TOP

‹!›

J

(b)

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ECCD profiles

The present EL design foresees co-injection from TOP and LOW rows and counter injection from MID row.

Various H&CD combinations are feasible delivering power either to a single row or to more than one row in different directions.

LIMITATION

upper radial limit around _ρ≈0.45

OPEN ISSUE

How to further optimize EC interaction region?

Current density profiles

10.5.2012 D Farina, EC-17 7                                                        

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EC potential at various time slices

4 time slices of a 15 MA Scenario

(courtesy T Casper, ITER):

a)  after diverting (L-mode)

b)  during current ramp-up (L-mode)

c)  at the end of current ramp-up (H-mode)

d)  at an early burn stage (H-mode)

case time slice I_pl (MA) n_e0

(1020 _m-3₎ T_e0 (keV) Fusion power (MW) (a) 11.7 s 3.7 0.075 4.6 0.002 (b) 58 s 11.5 0.30 8.0 1.6 (c) 80 s 15 0.40 14.4 4.4 (d) 130 s 15 0.85 29.0 471.7 -4 -2 0 2 4 4 5 6 7 8 z (m) R (m) -4 -2 0 2 4 4 5 6 7 8 z (m) R (m) -4 -2 0 2 4 4 5 6 7 8 z (m) R (m) t=11 s t=58 s t=80, 130 s                                        

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ECCD in the ramp-up phase

10.5.2012 D Farina, EC-17 9 0 50 100 150 200 0 0.1 0.2 0.3 0.4 0.5 0.6 II cd I/P (kA/MW) ‹‹›› J (a) TOP LOW MID XM 0 20 40 60 80 0 0.1 0.2 0.3 0.4 0.5 0.6 II cd I/P (kA/MW) ‹!› J 58 s 130 s 80 s 58 s MID ROW XM OM OM OM t=11 s t=130 s

•  wide radial deposition range •  lower ECCD efficiency due to 2nd

harm. parasitic absorption t=80 s

•  OM absorption, large ECCD efficiency

t=58 s

•  both XM & OM absorption but at

different location

•  higher I_cd for XM injection

t=11 s

•  XM absorption only, close to plasma

center

•  quite high I_cd because of low n_e

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XM absorption at low density

-4 -2 0 2 4 4 5 6 7 8 9 z (m) R (m) (a) -4 -2 0 2 4 4 5 6 7 8 9 z (m) R (m) (b) -4 -2 0 2 4 4 5 6 7 8 9 z (m) R (m) (c) -4 -2 0 2 4 4 5 6 7 8 9 z (m) R (m) (d)

XM1 interaction usually prevented in case of low field side injection due to presence of right cutoff

ωp2/ω2 = (1-N||2)(1- Ω/ω) (blue dotted line)

At low n_e and high T_e, XM absorption may occur along the trajectory far ahead of the EC cold resonance (red line) in the upshifted

resonance region at

Ω(x)/ω =[1-N||2(x)]1/2

(red dashed line)

Right cutoff shifts outwards for increasing n_e (a->d)

XM1 interaction cannot occur anymore after a given time depending on the injection angle.

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EC heating capabilities at B

≤

5.3 T

10.5.2012

D Farina, EC-17 11

radial power localization versus magnetic field

for 20º ≤ |_β| ≤ 42º and XM&OM injection, P_abs>95%

GOAL:

_{•  Central Heating:}

Power absorbed inside ρ ≤ 0.5 •  L to H-mode: Heat inside separatrix ρ ≤ 0.85 OM efficient •  at large T_e, n_e (t=80s, 130s) •  high B (OM1) XM efficient •  at low n_e (t≤58s) as XM1 •  at low B (XM2-3)

at B≈4 T: 1st _{harm. at hfs boundary & 2}nd _{harm. at lfs boundary}

                 _                    _                     _                     _   

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Heating potential at lower B

B 0 (T) P ins /P 0 (d) 0.5 0.85 2.5 3 3.5 4 4.5 5 0 0.2 0.4 0.6 0.8 1 l 0 0.2 0.4 0.6 0.8 1 P_ins(_ρ) =∫₀ρ p dV

High EC absorption in a quite wide B₀ range

ECRH efficient not only close to nominal and half values

5.3 T & 2.65 T

2 critical B₀ intervals:

•  3.6 T <B₀< 4 T : 1st and 2nd

harmonic are close to inner/outer plasma boundary

•  B₀<2.5 T : EC interaction occurs

at 2nd _{and 3}rd _{harmonic (less}

efficient, especially at low n_e & T_e).

maximum over OM&XM, and 20º ≤ |β|≤ 42º

Maximum EC power

deposited inside radius _ρ

B 0 (T) P ins /P 0 (b) 0.5 0.85 2.5 3 3.5 4 4.5 5 0 0.2 0.4 0.6 0.8 1 l 0 0.2 0.4 0.6 0.8 1 t=58 s t=130 s

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How to extend EC deposition region?

10.5.2012 D Farina, EC-17 13 9 MA – MID ROW 15 MA – MID ROW toroidal toroidal poloidal toroidal steering Driven EC current

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234 _{0.$,1&'2+-($1&-+0}

Which is the best path in

α

&

β

?

•  at present pure toroidal steering •  should we move to poloidal steering? •  or to a combination of the two?

•  PROS and CONS

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How to maximize ECCD?

15 D Farina, EC-17 10.5.2012 points: α=0 toroidal steer. points: α=0 toroidal steer. EL @ toroidal steering I_cd up to ρ≈0.45 UL @ poloidal steering I_cd at _ρ>0.5 0 10 20 30 40 0 0.2 0.4 0.6 0.8 1 Icd (kA/MW) ρ 0 10 20 30 40 50 60 0 0.2 0.4 0.6 0.8 1 Icd (kA/MW) ρ UL UL EL EL 18º≤β≤22º 45º≤α≤65º 18º≤β≤22º 45º≤α≤65º 20º≤β≤45º 20º≤β≤45º

EL poloidal steering allows to:

•  maximize I_cd at mid radius

•  drive current beyond mid

radius

Constraint on the choice of the toroidal angle:

•  β <~23º to allow for EC assisted

breakdown and startup from EL

CAVEAT

Present analysis based on 2 scenarios at burn, results sensitive to n&T values

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Toroidal versus poloidal steering

15 MA Scenario:

•  poloidal steering allows to

extend radial deposition region •  I_cd values almost the same as

for toroidal steering

15 MA

9 MA

TOP – MID - BOTTOM

β=20º solid lines

β=22º dotted lines

tor. steer. dots

β=20º solid lines

β=22º dotted lines

tor. steer. dots

0 10 20 30 40 0 0.2 0.4 0.6 0.8 1 Icd (kA/MW) ρ 0 10 20 30 40 50 60 0 0.2 0.4 0.6 0.8 1 Icd (kA/MW) 9 MA Scenario: •  much lower I_cd at 0.2<ρ<0.4

(2nd _{harm. absorption at low beta)}

•  much wider radial interaction

region in case of poloidal steering

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Conclusions

•

 

Two reference ITER scenarios investigated with new CD momentum

conservation model (+15% ECCD)

•

 

ECH&CD during plasma ramp-up conditions at nominal magnetic,

high to full absorption in spite of reduced n

_e

and T

_e

•

 

EC system applicable for central heating (inside mid radius) for the

majority of the toroidal magnetic field range from half to full field

•

 

Proposal for a poloidal steering EL setup to increase ECCD beyond

mid radius,

further investigation still required, final assessment in the near future

10.5.2012