7th ITPA IOS Meeting, Kyoto, 18-21 Oct. 2011

A.R. Polevoi

H, He and DD operational space and sensitivity studies
A.R. Polevoi1, R. Bilato2, T. Casper1, A. Ivanov3, A.S. Kukushkin1, A. Loarte1, T. Oikawa1, O. Sauter4, J. A. Snipes1,
D.J. Campbell1, V.A. Chuyanov1.
1

ITER Organization, Route de Vinon sur Verdon, 13115 St Paul Lez Durance, France, 2Max Planck IPP, Munchen, Germany,
3

Keldysh Institute of Appl. Math., Moscow, Russia, 4EPFL-CRPP, Lausanne, Switzerland

ABSTRACTThe results of assessment of stationary Type-I ELMy H-mode operation in
H, D and He plasmas studied by 1.5D modeling is presented. Sensitivity
studies are carried out. Possible extension of the operational space (OS) is
discussed. List of issues for further studies (by IOS TG?) is proposed.

OUTLINE● H-mode OS: benefits, issues, back-up solutions:-Hydrogen-Helium-Deuterium● Summary● Discussion

A. Polevoi

7th ITPA IOS Meeting, Kyoto, 18-21 Oct. 2011

2

Hydrogen plasma: Benefits
Independent core fuelling anddivertor control:
At high power, PSOL= 50-100 MW
predicted core fuelling from gas
puffing is small, Score< 10 Pa m3/s [2]Gas puffing is used to control thedivertor load, qpk<10 MW/m2 and to
avoid the plasma detachment, µ ≤ 1
Density control in the core can beprovided by High Field Side (HFS)
injection of hydrogen pellets

Type-III ELMy H-mode: PSOL> 2 PL-H,D
Full bore plasma[1]

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7th ITPA IOS Meeting, Kyoto, 18-21 Oct. 2011

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Hydrogen plasma: Issues
I. Power deficit for “good” H-mode:
High L-H threshold: PL-H,H= 2 PL-H,D
Reduced power: Paux< 20 + 33 MW (EC + NB) no ICRH for B = 2.65 T

II. High NBI shine-through density limit: PNB,load(nNB,min) = 4 MW/m2
nNB,min~4.5 1019m-3 (for Eb= 870keV in 100% hydrogen plasma)
nNB,min can be reduced by impurity seeding (at Zeff ~ 2)
nNB,min can be reducedby the NB energy reduction,
Eb= 870-740 keV, but with further reduction of power, Paux: PNB ~ EB2.5

III. More demanding fuelling requirements: τp ~ τE ~ 0.16 τE98,y2 ?
0.16 = 0.65 x 0.5 x 0.5 (Hydrogen x half current x L-mode)

Type-I ELMy H-mode looks unlikely.
Back-up solution: Operation in He

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7th ITPA IOS Meeting, Kyoto, 18-21 Oct. 2011

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Helium plasma: Benefits
I. Full installed power operation
Paux< 20 + 20 + 33 MW (IC + EC + NB)

II. Lower L-H threshold:
PLH,He= 1 - 1.4 PLH,D

III. Lower shine-through limit
nNB,min~2.9 1019m-3 for Eb= 870keV

IV. OS for Type-I ELMy H-mode:
PSOL > 1.4 PLH,He = 2 PLH,D:

Type-I ELMy H-mode: PSOL> 2 PL-H,D

nNB,min~ 2.9 - 5.3 1019m-3

Full bore plasma, 100% He[1]

7th ITPA IOS Meeting, Kyoto, 18-21 Oct. 2011

A. Polevoi

5Helium plasma: Issues
I. Low edge density:
ne,s~ 2 1019m-3 for fuelling by He only. (SOLPS [2])An anomalous pinch is required to provide n > nNB,min in 100% helium
or extra core fuelling by pellets (see next)

II. Capability of density control is limited.
Density increase for He puffing is limited by detachment, µ ≤ 1, andfor hydrogen pellets/puffing it is limited by He dilution. (no He pellets).

III. He dilution by hydrogen
increases shine-through and PL-H from the H0-NBI heating and in the cases
if pellet fuelling is required to provide acceptable shine through(small pinch), and for ELM pacing .

IV. Heating control
Could be complicated in case of possible synergy of H-NBI and ICH

Back-up solutions:-Plasma shaping (reduced PL-H ~ S by size reduction) [9]Transient H-mode [2]DD operation

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7th ITPA IOS Meeting, Kyoto, 18-21 Oct. 2011

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Type-I ELMy H-mode Operational Space: scan of shape and power

Fig. 1 Maximal possible reduction of power Fig. 2 Separatrix densities, ne,s, nHe,s nH,s, andthreshold by plasma shaping. Current is helium source in the core, GHe depend on
reduced from Ip= 7.5 MA to Ip= 6.5 MA to keep power, PSOL (SOLPS [2]).
q95 > 3 at B0 = 2.65 T.

7th ITPA IOS Meeting, Kyoto, 18-21 Oct. 2011

A. Polevoi

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Maximal OS for Type-I ELMy H-mode with He+H:
Minimal S (fig.1) + parameters from (fig.2). <ne,min,NBI> for 0.87 MeV H0-NBI.
a) scaling [8]PLH~ B0.8S0.94n0.7b) saturated PLH,min=PLH(n=3.5 1019m-3)

Fig. 3 PSOL> 1.4

PLH,He+H= (2 - 2.8) PLH,D = (100%He - 100%H)a):

PSOL,min~ 36 MW (100%He) - 55 MW (100%H)b):

PSOL,min~ 43 MW (100%He) - 62 MW (100%H)`

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7th ITPA IOS Meeting, Kyoto, 18-21 Oct. 20118

Type-I ELMy H-mode Operational Space for He dilution by hydrogen
ASDEX-U experiments (fig. 5):
F. Ryter, 2010

1.5

ASDEX Upgrade 2008 4He campaign

fH= nH/(nH + nHe) < 40%
fHe= nHe/(nH + nHe) > 60%
For dominant heating of electrons

Pthres/Pth-ITPA08

For moderate dilution by hydrogen,
1

0.5

ECRH
PLH dependence on dilution is week:
PLH(fHe=0.6) ~ 1.2 PLH,He(fHe=1)

0
0.2

H-NBI
ne 4 10 19m-3
ECRH
0.4

0.6
0.8
nHe/(nHe + nH)

1

Fig. 5 PL-H,He normalized to PL-H,D [8]In ASDEX-U experiments for conditions similar to ITER, dependence of the
L-H threshold on dilution is weak.
If auxiliary power is insufficient for Type- I ELMy H-mode in He + H:
Backup solutions: (1) Transient H-mode considered in [2],(2) DD operation [considered below]

A. Polevoi

7th ITPA IOS Meeting, Kyoto, 18-21 Oct. 20119DD plasma: Benefits
I. Full installed power operation
Paux< 20 + 20 + 33 MW (IC + EC + NB)

II. Lower L-H threshold:
PLH = PLH,D

III. Low shine-through for D0-NBI
nNB,min~3 1019m-3 for Eb = 1 MeV

IV. Independent core fuelling(by pellets) and divertor
control (by puffing)
V. Wide H-mode OS

H-mode OS: PSOL> PL-H,D
Full bore plasma[1]

Goal for pre-DT commissioning in D: Type-I ELMy H-mode withminimal neutron yield => short pulse, half-filed (minimal power)

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7th ITPA IOS Meeting, Kyoto, 18-21 Oct. 201110

Pre-DT commissioning in DD plasma: Issues
I. High neutron/tritium yield, St ≈ Sn in fusion reaction: Dbeam-Dthermal:> 10 times higher than in JET

Backup solution:> 3 times higher than w/o D-NBI

Replace D0-NBI by H0-NBI

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7th ITPA IOS Meeting, Kyoto, 18-21 Oct. 201111

Pre-DT commissioning in DD plasma: Issues
II. Low PSOL w/o NBI (PSOL< 0.9 Paux), high shine-through for H0-NBI

Low PSOL,RF < PEC+IC ≤ 40 MW
Backup:
H0-NBI is requiredHigh NBI shine-through for H0-NBI
Backup: Seeding by Be would help

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7th ITPA IOS Meeting, Kyoto, 18-21 Oct. 201112

DD plasma: Sensitivity studies - I
Heating mix, power, deposition and density scan: St ≈ Sn2.45~1-1.5 1017s-1

See more in the table below

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7th ITPA IOS Meeting, Kyoto, 18-21 Oct. 201113

DD plasma: Sensitivity studies – II
Comparison of neutron yield with reference case (=) in the range of uncertainty-3EC, MWn19,mn0,/np

4

1.25

0

=

=

=

NBI, MWχi/χ
χemode St,1016/s Sn,1016/s

H0

D0

40

0

0

2

H

7

7.3

15

25

=

=

=

=

6.4

6.7

=

15

25

=

=

1

=

7.9

8.3

=

1.8

=

=

=

=

=

=

9.8

10.4

=

=

=

23.5

=

16.5

=

=

23

27

4.2

=

=

23

16.5

=

=

=

8.3

8.8

4.2

=

15

8

16.5

=

=

=

7

7.4

=

=

=

4

=

=

=

L

0.58

0.58

=

=

=

=

=

=

=

OH

0.017

0.017

3

=

=

=

=

=

=

OH

0.031

0.031

on-ax. off-ax.

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7th ITPA IOS Meeting, Kyoto, 18-21 Oct. 201114

Summary - I (issues for R&D and simulations are highlighted)
Hydrogen-Commissioning of NBI at full power in hydrogen is possible if
fuelling can provide n > nNB,shine (~ 4.3 1019m-3 for 100% H)(high fuelling demanding?

-Type-III ELMy H-mode would be possible in half field case if
Sh-thr. density can be reduced to nNB,shine~3 1019m-3 by impurity seeding

A. Polevoi

7th ITPA IOS Meeting, Kyoto, 18-21 Oct. 201115

Summary - II (issues for R&D and simulations are highlighted)
Helium-Boundary density is governed by DIV control. W/o anomalous pinch
density by SOLPS is not sufficient to inject 16.5 MW NBI in 100% He.
In this case fuelling by hydrogen in He is required.

-

LFS ELM pacing by hydrogen pellets dilutes He by residual fuelling andrecycled hydrogen-

Type-I ELMy H-mode is more likely at half-field with reduced k and Ip
even in He + H if PNBI + PEC + PIC > 60 MW.
(PIC coupling?)-

Dilution by hydrogen increases NBI shine through loss and PL-H.
Dedicated experiments to define limitation are required.

-

Anomalous particle pinch (if any) increasing density increases power
required for Type-I ELMy H-mode-

Possible synergy of IC and H-NBI can affect control Purely IOS task!

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7th ITPA IOS Meeting, Kyoto, 18-21 Oct. 201116

Summary - III (issues for R&D and simulations are highlighted)
Deuterium-

DD operation in half-field will enable H-mode operation with smaller
neutron and tritium production, than for full field: St, Sn ~ 1017s-1-

Ohmic operation at maximal density minimise St, Sn at current ramp-up-

Commissioning in Type-I ELMy H-mode in short pulses in DD looks
possible for ne~4 1019m-3 provided PSOL>40 MW. Thus, NBI is required.

-

Neutron yield can be reduced by a factor of 3 using H0-NBI instead of
D0-NBI.

-

Usage of H0-NBI increases the NBI shine through, shrinking the OS.
Seeding by Be pellets (~ 5%) could help to recover the OS-

For short flat-top operation ∆t ~ 10 s ratio D/χχ becomes critical for
scenario feasibility (both minority(=>heating) and fuel (=>neutrons)).

-

Fraction of ion heating as a function of minority density for neutron
yield reduction-

Possible synergy of IC and H-NBI (neutron yield)

Purely IOS task?

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7th ITPA IOS Meeting, Kyoto, 18-21 Oct. 201117

DISCUSSION
Findings above should be taken into account in pre-DT scenario
development (simulations)?
Issues should be addressed in the analyses of experimental data(new experiments/simulation with validated codes?):(1) - Particle confinement: Ip scan, H, He, D plasmas, OH, L, H modes? All?
(2) - Particle transport: Dynamical experiments are required to assess
D/χχ for minority and fuel? Anomalous pinch (in He)? C-mod, …???
(3) - Residual fuelling from LFS pellets? DIIID, AUG, MAST, JET, …???
(4) - Dedicated experiments to define limit of He contamination by H for
H-L transition in ITER like conditions (e-heating, pellet fuelling) same?
(5) - PIC coupling for low densities in He (experiment? simulations?) ???
(6) - Optimization of PIC to minimize ion heating.

Goal opposite to DT!!

(7) - Development of DD scenarios with minimal neutron yield All?
(8) - Possible synergy between H-NBI & ICH PTRASP, TORIC, …?

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7th ITPA IOS Meeting, Kyoto, 18-21 Oct. 2011

BACKUP VIEWGRAPHS(density vs heat transport, transport model, He plasmas, references)18

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7th ITPA IOS Meeting, Kyoto, 18-21 Oct. 201119

Uncertainty of density transport:
Tritium puff experiments in JET (I. Voitsekhovitch, et al, PoP 12, 052508 s2005d,(see Fig.7):
Ratio (χχi + χe)/D strongly depends on density and varies by an order of magnitude.

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7th ITPA IOS Meeting, Kyoto, 18-21 Oct. 201120

Plasma Transport Model
Heat transport in the core
For core transport we use the scaling based model [4].
The heat diffusivities, χi= 2χ
χe, at the core are fitted to provide τE = 0.7ττ98y2,D,from the scaling prediction for deuterium τ98y2,D, which is valid both forhydrogen and He plasmas [7].

Heat transport in the pedestal
At the Edge Transport Barrier (ETB) the heat diffusivities, χi, χe are fitted toprovide the pedestal pressure according to [5]:Tpednped/Ip2 ~ βp,ped~ Ai0.48(PSOL/PLH,D)0.144nped-1/3, taking Ai = 1, as forhydrogen with the ETB width from [6], ∆ped = 0.076 βp,ped1/2.

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7th ITPA IOS Meeting, Kyoto, 18-21 Oct. 2011

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Particle transport coefficients
For all plasma species we assume the same diffusivities, D = 0.1 (χ
χi+χ
χe).
To assess the effect of density peaking, Fn = n(0)/nped = 1 - 1.5 we vary
particle pinch, V = 2 C D r/a2, C = 0 - 0.6.

Helium transport
Helium throughput, given by GHe= 0.027µ1.61PSOL1.69Sn– 0.2 GH [2], is fitted to
avoid plasma detachment: µ≤ 1, where µ is the normalized gas pressure in
the divertor. Operation with higher power enables higher edge densities,
nHe,s~ PSOL0.66. Maximal pumping speed, Sn = 1.27 (Seng= 75 m3/s [2]) close
to detachment, µ~ 1, reduces edge hydrogen density, nH,s~ (GH/Snµ)0.86,
reduces the hydrogen core source, GH,core~ GH/Snµ1.13 and increases the He
core source, GHe,core~ µ0.8. Thus, it is favorable for minimization ofundesirable helium dilution by hydrogen (fig.2).

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7th ITPA IOS Meeting, Kyoto, 18-21 Oct. 2011

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Hydrogen transport
Residual fuelling from the LFS hydrogen pellets for ELM pacing is
calculated [3]. For the pedestal parameters considered, the residual core
fuelling from pellets is negligible due to the outward drift. Thus, thesource of hydrogen is counted only in total throughput, GH.
The pellet frequency required to keep the ELM energy loss at theacceptable level, ∆WELM < ∆Wmax is determined from the scaling,
fpel= 0.2 PSOL/∆∆Wmax. We assume the conservative value, ∆Wmax= 0.6 MJ,
required for Ip = 15 MA.
Hydrogen throughput, GH = fpel Npel is calculated for the minimal foreseen
pellet size, Npel ~ 1.5 Pa m3.

Boundary conditions and particle sourcesin the core are taken from the parameterization of [2].

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7th ITPA IOS Meeting, Kyoto, 18-21 Oct. 201123

Type-I ELMy H-mode Operational SpaceThe OS is assessed for the maximal pumping speed, Seng= 75 m3/s at the
detachment limit, µ = 1 with the plasma model described above. This model
provides the boundary and pedestal parameters and core fuelling as functionsof PSOL. The plasma density is scanned by varying the pinch velocity and the
input power Paux. Control of density peaking by variation of the ECH location islimited. Thus, the operational point should be chosen to provide the Type-I
ELMy H-mode conditions, PSOL > αγkPLH,D~ B0.8S0.94n0.7 [8] for any density
peaking expected in ITER. In our analysis we assume α= 1.4, and γH= 2, γHe=1.4.
The OS is limited by n ≤ nmax,k~ (αγαγkPSOL/S)1.4 and the NBI shine through limit,n ≥ nmin,NBI (shown in fig. 3 for full bore plasma for pure hydrogen and pure
helium cases). As follows from the scaling [8], with assumed α and γ k, suchoperation will be possible even in pure hydrogen for PSOL> 55- 58 MW for Fn =1.

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7th ITPA IOS Meeting, Kyoto, 18-21 Oct. 201124

Type-I ELMy H-mode Operational Space: shrinking at low density
DIII-D, Gohil 2010

Dependence on density changes
Power threshold has a minimum
PL-H > PL-H,D (n~ 3.5 1019m-3)

ASDEX-U, Ryter 2009

JET, McDonald 2010

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7th ITPA IOS Meeting, Kyoto, 18-21 Oct. 201125

Type-I ELMy H-mode Operational Space for Full bore plasma.

abFig. 4 The same as fig. 3, but with full bore plasma.
With decrease of plasma size (fig. 1) boundaries of the operational domain with
PSOL/PLH,D > 2.8 spread (compare (figs. 4a, 4b): PSOL~65→60 MW, n(0)/nped~1.3→1.7

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7th ITPA IOS Meeting, Kyoto, 18-21 Oct. 2011

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Discussion
The OS where the stationary Type-I ELMy H-mode can be expected for any
contamination by hydrogen exists and corresponds to high power operation. It
is shown in orange in figures 3 and 4. This part of the OS in full bore plasma
exists for density peaking in the range Fn= 1 - 1.3.
The OS can be extended by reduction of plasma surface, S. In practice thepossibility of such reduction is limited (fig. 1) by variation of plasma
elongation. In the case of the reduced elongation, the part of the OS where thestationary Type-I ELMy H-mode is expected for arbitrary dilution extends from
PSOL~ 60 MW for the range of moderate peaking, Fn= 1 - 1.2 to PSOL~ 70 MW forthe range with high peaking Fn=1 - 1.7 (fig.4b).

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7th ITPA IOS Meeting, Kyoto, 18-21 Oct. 201127

It is worth noting that, for high power operation, the predicted separatrix
density is rather high [2], ne,s ~ 2.5 - 2.6 1019m-3. For D = 0.1 (χχI + χe), this ne,s issufficient to keep plasma density above the NBI shine-through limit, n ≥ nped:n ≥ nped~ 3 1019m-3> ne,min,NBI even without an anomalous pinch. This isimportant because for helium operation, the achievable density is limited by
the detachment condition, µ ≤ 1 for He puffing, and by the dilution forhydrogen pellet fuelling if the pinch is not sufficient.

The core plasma radiation, predicted for low B0, n and T, expected in He
plasmas without the impurity injection, is a factor of 10 smaller than predicted
for Q = 10 DT operation, Prad,He< 4 MW. In the high power case, Paux - Prad =PSOL> 60 MW our modeling predicts rather moderate fraction of hydrogen,nH/(nH + nHe) < 40 %, (nH/ne < 25%).

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7th ITPA IOS Meeting, Kyoto, 18-21 Oct. 201128

Conclusions
It is shown that for B0 = 2.65 T, Ip ≤ 7.5 MA the operational space for thestationary Type-I ELMy H-mode in Helium plasmas with substantial dilution byhydrogen can exist for a range of density peaking, Fn = 1 - 1.7, if the power
coupled to the plasma is sufficient to provide PSOL~ 60 - 70 MW.
Predicted stationary contamination by hydrogen remains moderate,nH/(nH+nHe)~ 38%, (nH/ne~ 24%). Thus, if the PLH dependence on the dilution is
weak (see ECRH in Fig. 5), the OS can spread on a wider range of n and Paux.

REFERENCES[1] A.R. Polevoi, et al., Proc. 22nd Fusion Energy Conference, Geneva, 2008, IT/P6-11[2] A.S. Kukushkin, et al., Proc. 23rd Fusion Energy Conference, Daejeon, 2010, ITR/P1-33[3] A.R. Polevoi and M. Shimada, Plasma Phys. Control. Fusion, 43 (2001) 1525
[4] A.R. Polevoi, et al, Nucl. Fusion 43 (2003) 1072
[5] M Sugihara, et al, Plasma Phys. Control. Fusion 45 (2003) L55[6] P.B. Snyder, et al, Nucl. Fusion 49 (2009) 085035[7] F. Ryter, et al, Nucl. Fusion 49 (2009) 062003[8] Y. Martin, et al, J. Phys., Conf. Ser. 123 (2008) 012033[9] A.R. Polevoi, et al, 38th EPS Plasma Physics Conf. (Strasbourg, France, 2011) P4.109