Analysis and Simulations of the ITER Hybrid Scenario

C. Kessel, R. Budny, K. IndireshkumarPrinceton 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

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

Hybrid Scenario in ITER

• Plasma parameter ranges E ≈ 1.0-1.5 E

98(y,2)

N < 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 fNI

off-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)

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 OH+PF: 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

0D Operating Space Analysis

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(benchmarked with TSC)

T(r) = (To - Ta)[1-(r/a)2]T + Ta

Same for density profile

Etc.

IP = 12 MABT = 5.3 TR = 6.2 mA = 3.195 = 1.7595 = 0.5P*/E = 5∆total = 300 V-s∆breakdown = 10 V-sli = 0.80CE = 0.45NBCD = 0.3 x 1020 A/W-m2

PCD = 33 MWT = 1.75, Ta/To = 0.1n = 0.075, na/no = 0.3fBe = 2.0%

1.5 ≤ N ≤ 3.00.4 ≤ n/nGr ≤ 1.03.0 ≤ Q ≤ 12.00.0 ≤ fC ≤ 2.0%0.0 ≤ fAr ≤ 0.2%

Input parameters

Scanned parameters

ITER Hybrid Systems Analysis

Fusion power pulse length limitation significantly reduces accessible fluence values, and changes dependence on density

ITER Hybrid Systems AnalysisOperating space shows strong dependence on allowable conducted peak heat flux on divertor, which must be low enough to accommodate radiation flux and transients

ITER Hybrid Systems Analysis

Increasing the power radiated in the divertor can recover operating space at lower conducted peak heat flux

ITER Hybrid Systems Analysis

Large Operating Space Scan

1.05 ≤ n(0)/n ≤ 1.251.5 ≤ T(0)/T ≤ 2.511.0 ≤ IP (MA) ≤ 13.01.5 ≤ N ≤ 3.00.4 ≤ n/nGr ≤ 1.03.0 ≤ Q ≤ 12.01% ≤ fBe ≤ 3%0% ≤ fC ≤ 2%0% ≤ fAr ≤ 0.2%

Other input fixed at previous values

ITER Hybrid Systems Analysis

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

BT = 5.3 T, PCD = 33 MW, Paux < 39 MW, Pfusion = 350 MW, Nw = 0.49 MW/m2, tflattop = 3000 s, chosen to meet Nw x tflattop > 1475 MW-s/m2

n = 0.05 --> n(0)/<n> = 1.04, n = 0.4 --> n(0)/<n> = 1.25T = 0.60 --> T(0)/<T> = 1.50, T = 2.0 --> T(0)<T> = 2.50

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/(tflat+tdwell) ≈ 25%

TSC TRANSP

Discharge simulation with assumed source profiles and evolving boundary

Plasma geometryT, n profilesq profile

Interpretive rerun of discharge simulation with source models, fast ions, neutrals (TSC as expt.)

Accurate source profiles fed back to TSC Analysis with interfaces

to TRANSP

Analysis with interfaces to TSC

Flow Diagram of TSC-TRANSP 1.5D Analysis Combining Strengths of the Two

Codes

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

TRANSP NBCD Results for Various Conditions in the ITER Hybrid Simulations, t

= 500 sIP = 12 MA, PNB = 33 MW, PICRF = variable, ≤ 20 MW

Wth = 300 MJWth = 300 MJWth = 300 MJWth = 350 MJ

INB = 2.4 MAINB = 2.1 MA

INB = 2.2 MAINB = 2.1 MA

INB = 2.1 MAINB = 1.8 MA

ICRF He3 Minority Heating Used as Heating Source to Allow NINB to Drive Current

fICRF = 52.5 MHznHe3 = 2% nDT

EHe3 up to 120 keV

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) > 1, keep Pheat < 10 MW

• Control on plasma stored energy, PICRF in controller, PNB not in controller since it is supplying NICD

TSC ITER Hybrid ScenarioIP = 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)/<n> = 1.05,N = 2.0, H98(y,2) = 1.33, Te,i(0) = 22.5 keV, Te,i(0)/<T> = 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.

TSC ITER Hybrid Scenario

TSC ITER Hybrid Scenario

GLF23, no stabilizationShape control points

Variation of Tped With GLF23 no stabilization

Variation of Tped with GLF23 with ExB shear stabilization

TRANSP plasma rotation assuming mom = i

Lost Wth control

Benchmark of GLF23 Transport in DIII-D 104276 Hybrid DischargeTSC free-boundary, discharge simulation

DIII-D 104276 dataPF coil currentsTe,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

TSC Simulation Benchmark of DIII-D 104276 Discharge

No -stabilization

GLF23 turned on

Profiles from TSC and TVTS and CER data at t = 5 s

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 IAEACases with ExB shear and -stabilization have not been completed

Conclusions• Based on GLF23 no stab. energy transport, pedestal

temperatures appear high (>6.5 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

(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.