Analysis and Simulations of the ITER Hybrid Scenario

1
Analysis and Simulations of the ITER Hybrid
Scenario

• C. Kessel, R. Budny, K. Indireshkumar
• Princeton Plasma Physics Laboratory, USA
• ITPA Topical Group on Steady State Operation and
  Enhanced Performance
• Centro di Cultura Scientifica - A. Volta
• Societa del Casino, Como Italy, May 2005

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Contents

• Groundrules for Hybrid Scenario
• Goals
• Plasma parameters and operating modes
• Constraints
• 0D Systems analysis of Hybrid operating points
• Brief description
• Major parameters and effects of constraints
• Large scan and operating space
• 1.5 D simulations of the Hybrid Scenario with
  TSC-TRANSP
• Brief TSC-TRANSP description
• TSC simulation results with GLF23 energy
  transport, comments
• TRANSP source modeling
• Benchmarking of GLF23 energy transport DIII-D
  104276

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Hybrid Scenario in ITER

• Plasma parameter ranges
• ?E 1.0-1.5 ? ?E98(y,2)
• ?N lt ?Nno wall ( 3)
• fNI 50
• IP 12 MA
• n/nGr varied
• ?CD determined from TRANSP, or other analysis
• Impurities defined to provide acceptable divertor
  heat loading
• Operating Modes
• NNBI ICRF
• NNBI ICRF LH
• NNBI ICRF EC

• Prefer to avoid (or minimize) the sawtooth, q(0)
  1.0
• Maximize fNIoff-axis (IBS, ILH, IECCD)
• Maximize neutron fluence
• Nwall ? tflattop
• tflattop is minimum of tV-s or tnuc-heat
• Maximize fNI, Te(0) and avoid high Pfusion
• Remain within installed power limitations
• NNBI at 1.0 MeV, 33 MW
• ICRF at about 52 MHz, 20 MW
• EC at 170 GHz, 20 MW
• LH at 5 GHz, 30 MW (UPGRADE)

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Hybrid Scenario in ITER

• Constraints
• Fusion power vs pulse length 350 MW -- 3000s,
  500 MW -- 400 s, 700 MW -- 150s
• Installed auxiliary heating/CD power
• Divertor heat loads allowable of 20 MW/m2,
  leading to 10-12 MW/m2 conduction heat load to
  account for radiation and transients
• Divertor radiation?? 15 of power entering
  Scrape Off Layer is assumed radiated in divertor
  slots or about the X-point
• Core radiation requirement to meet divertor heat
  load 2 Be only (Zeff 1.3) unacceptable, 2 Be
  2 C 0.12 Ar (Zeff 2.2) is acceptable
• Within volt-second capability of OHPF maximum
  of 300 V-s, with 10 V-s in breakdown, and about
  15-20 V-s spare, based on reference H-mode
  scenario
• First wall surface heat flux?? 0.5 MW/m2, with
  peaking factor of 2.0, leading to 0.25 MW/m2
  average

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0D Operating Space Analysis
IP 12 MA BT 5.3 T R 6.2 m A 3.1 ?95
1.75 ?95 0.5 ?P/?E 5 ??total 300
V-s ??breakdown 10 V-s li 0.80 CE
0.45 ?NBCD 0.3 x 1020 A/W-m2 PCD 33 MW ?T
1.75, Ta/To 0.1 ?n 0.075, na/no 0.3 fBe
2.0 1.5 ?N 3.0 0.4 n/nGr 1.0 3.0 Q
12.0 0.0 fC 2.0 0.0 fAr 0.2
Energy balance Particle balance, ?P/?E and
quasi-neutrality Bosch-Hale fusion
reactivity Post-Jensen coronal
equilibrium Albajar cyclotron radiation
model Hirshman-Neilsen flux requirement (benchmar
ked with TSC) T(r) (To - Ta)1-(r/a)2?T
Ta Same for density profile Etc.
Input parameters
Scanned parameters
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ITER Hybrid Systems Analysis
Fusion power pulse length limitation
significantly reduces accessible fluence values,
and changes dependence on density
7
ITER Hybrid Systems Analysis
Operating space shows strong dependence on
allowable conducted peak heat flux on divertor,
which must be low enough to accommodate radiation
flux and transients
8
ITER Hybrid Systems Analysis
Increasing the power radiated in the divertor can
recover operating space at lower conducted peak
heat flux
9
ITER Hybrid Systems Analysis
Large Operating Space Scan 1.05 n(0)/?n?
1.25 1.5 T(0)/?T? 2.5 11.0 IP (MA)
13.0 1.5 ?N 3.0 0.4 n/nGr 1.0 3.0 Q
12.0 1 fBe 3 0 fC 2 0 fAr
0.2 Other input fixed at previous values
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ITER Hybrid Systems Analysis
BT 5.3 T, PCD 33 MW, Paux lt 39 MW, Pfusion
350 MW, Nw 0.49 MW/m2, tflattop 3000 s,
chosen to meet Nw x tflattop gt 1475 MW-s/m2
?n 0.05 --gt n(0)/ltngt 1.04, ?n 0.4 --gt
n(0)/ltngt 1.25 ?T 0.60 --gt T(0)/ltTgt 1.50, ?T
2.0 --gt T(0)ltTgt 2.50
?n ?n? ?T ?T? ?N q95 Ip HH fGr fBS fNI Zeff fBe fC fAr t/?J
0.40 0.57 1.3 12.8 1.8 4.38 12.0 1.27 0.65 0.26 0.50 1.82 1 0 .2 13.4
0.05 0.66 1.3 13.1 2.0 4.38 12.0 1.42 0.70 0.25 0.45 1.80 1 2 0 12.2
0.40 0.66 2.0 13.5 2.0 4.38 12.0 1.40 0.75 0.30 0.51 2.36 3 1 .2 13.5
0.05 0.69 2.0 11.2 2.0 4.79 11.0 1.40 0.80 0.27 0.48 1.93 2 0 .2 15.5
0.40 0.76 0.6 10.1 2.0 4.79 11.0 1.29 0.95 0.33 0.52 1.61 2 0 .1 16.8
0.40 0.76 1.3 10.4 2.0 4.79 11.0 1.29 0.95 0.33 0.52 1.73 3 1 0 16.8
0.05 0.86 1.3 10.6 2.3 4.79 11.0 1.46 1.00 0.30 0.47 2.03 3 2 0 15.3
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Results

• Fusion power pulse length limitation is most
  significant factor in determining Hybrid
  operating space
• Lowering density does not continuously lead to
  better operating points
• Higher H98(y,2) allows access to higher fluence
  and lower n/nGr
• High fusion power is not necessary or desirable
• Only low ?N 2 operating points are required
• Volt-seconds capability appears to be enough to
  offer few thousand second flattops
• Divertor heat load limits is next most
  significant factor for Hybrid operating space
• Combination of conducted power, power radiated in
  divertor, transient conducted power, and core
  radiated power
• First wall surface heat load limits do not appear
  to be limiting
• Available operating space shows that existing
  ITER design can provide reasonable fluence levels
  within a discharge, HOWEVER time between
  discharges is constrained
• Appears that cryoplant limitation sets
  tflat/(tflattdwell) 25

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Flow Diagram of TSC-TRANSP 1.5D Analysis
Combining Strengths of the Two Codes
Analysis with interfaces to TSC
Interpretive rerun of discharge simulation with
source models, fast ions, neutrals (TSC as expt.)
Discharge simulation with assumed source profiles
and evolving boundary
TSC
TRANSP
Plasma geometry T, n profiles q profile
Accurate source profiles fed back to TSC
Analysis with interfaces to TRANSP
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TSC and TRANSP, a Few Attributes

• TRANSP
• Interpretive
• Fixed boundary Eq. Solvers
• Monte Carlo NB and ? heating
• SPRUCE/TORIC/CURRAY for ICRF
• TORAY for EC
• LSC for LH
• Fluxes and transport from local conservation
  particles, energy, momentum
• Fast ions
• Neutrals

• TSC
• Predictive
• Free-boundary/structures/PF coils/feedback
  control systems
• T, n, j transport with model or data coefficients
  (?, ?, D, v)
• LSC for LH (benchmark with other LH codes)
• Assumed P and j deposition for NB, EC, and ICRF
  typically use off-line analysis to derive these

In addition, both codes have models for
bootstrap current, radiation, sawteeth, ripple
loss, pellet fueling, impurities, etc. TRANSP
has predictive capability
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TRANSP NBCD Results for Various Conditions in the
ITER Hybrid Simulations, t 500 s
IP 12 MA, PNB 33 MW, PICRF variable, 20 MW
Wth 300 MJ Wth 350 MJ
Wth 300 MJ
Wth 300 MJ
INB 2.4 MA INB 2.1 MA
INB 2.2 MA INB 2.1 MA
INB 2.1 MA INB 1.8 MA
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ICRF He3 Minority Heating Used as Heating Source
to Allow NINB to Drive Current
fICRF 52.5 MHz nHe3 2 nDT EHe3 up to 120 keV
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TSC Simulation Description

• Density evolution prescribed, magnitude and
  profile
• Impurity is 2 Be for reference, and 2 Be 2 C
  0.12 Ar for high Zeff cases
• GLF23 thermal diffusivities, no rotation
  stabilization, and with rotation stabilization
  (plasma rotation from TRANSP assuming ?momentum
  ?i)
• Prescribed pedestal amended to GLF23 thermal
  diffusivities
• Control plasma current, radial position, vertical
  position and shape
• Plasma grown from limited starting point on
  outboard limiter, early heating required to keep
  q(0) gt 1, keep Pheat lt 10 MW
• Control on plasma stored energy, PICRF in
  controller, PNB not in controller since it is
  supplying NICD

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TSC ITER Hybrid Scenario
IP 12 MA, BT 5.3 T, Vsurf 0.05V, q(0)
0.99, q95 3.95, li(1) 0.8,, ?t 2.2, n/nGr
0.79, Wth 300 MJ, n20(0) 0.77, n(0)/ltngt
1.05, ?N 2.0, H98(y,2) 1.33, Te,i(0) 22.5
keV, Te,i(0)/ltTgt 2.0, ? 1.83, ?
0.46, ??rampup 150 V-s, P? 65 MW, Paux 35
MW, PNINB 33 MW, Zeff 1.3, INI 5.3 MA, IBS
3 MA, ININB 2.2, Tped 7.5-8 keV
GLF23, no stab.
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TSC ITER Hybrid Scenario
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TSC ITER Hybrid Scenario
Shape control points
GLF23, no stabilization
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Variation of Tped With GLF23 no stabilization
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Variation of Tped with GLF23 with ExB shear
stabilization
TRANSP plasma rotation assuming ?mom ?i
Lost Wth control
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Benchmark of GLF23 Transport in DIII-D 104276
Hybrid Discharge
TSC free-boundary, discharge simulation DIII-D
104276 data PF coil currents Te,i(?), n(?),
v(?) NB data TRANSP Use n(?) directly TSC
derives ?e, ?I to reproduce Te and Ti Turn on
GLF23 in place of expt thermal diffusivities Test
GLF23 w/o ExB and w EXB shear stabilization
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TSC Simulation Benchmark of DIII-D 104276
Discharge
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GLF23 w/o EXB (or ?-stab) Shows Lower T(0) Values
Than Those in Expt
However, these do not agree with GLF23 analysis
presented by Kinsey at IAEA Cases with ExB shear
and ?-stabilization have not been completed
Profiles from TSC and TVTS and CER data at t 5 s
No ?-stabilization
GLF23 turned on
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Conclusions

• Based on GLF23 no stab. energy transport,
  pedestal temperatures appear high (gt6.5 keV) to
  obtain good performance
• Including EXB shear stabilization in GLF23, with
  velocity from TRANSP assuming ?mom ?I, does not
  improve the situation
• Higher density operating points can improve this
• Directly applying experimental Hybrid discharge
  characteristics to ITER may be optimistic
• Lower rotation in ITER by 10x
• Ti Te in ITER
• Density peaking in expts. from NB fueling and
  ExB shear or other particle transport effects,
  may not exist in ITER
• Application of GLF23 to full discharge
  simulations is continuing
• No stabilization application is robust in TSC
• With stabilization has start up difficulties, are
  being resolved
• Will apply to L-mode and H-mode phases
• Benchmark simulations with hybrid discharges is
  continuing

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(Possible) Future Work

• Determine engineering constraints for use in 0D
  systems analysis in greater detail
• Is the cryoplant limitation for real??
• Complete higher density and higher Zeff Hybrid
  1.5D scenarios
• Examine slight density peaking in 1.5D scenarios
• Turn off stored energy control, examine Q vs.
  Tped vs. vExB
• Examine higher velocities in ExB shear stabilized
  cases
• Examine strategies for coupled stored energy and
  NICD feedback control
• Use alternative energy transport models, less
  stiff models to see the dependence on required
  pedestal temperatures
• Expand benchmark simulations to other Hybrid
  discharges in DIII-D
• Further development of TSC-TRANSP modeling
• Etc.