GA A22627 TRANSPORT MODEL TESTING AND COMPARISONS USING THE ITER AND DIII D PROFILE DATABASES

Transcription

1 GA A22627 TRANSPORT MODEL TESTING AND COMPARISONS USING THE ITER AND DIII D PROFILE DATABASES by J.E. KINSEY, R.E. WALTZ, and D.P. SCHISSEL JUNE 1997

2 DISCLAIMER Ths report was prepared as an account of work sponsored by an agency of the Unted States Government. Nether the Unted States Government nor any agency thereof, nor any of ther employees, makes any warranty, express or mpled, or assumes any legal lablty or responsblty for the accuracy, completeness, or usefulness of any nformaton, apparatus, produce, or process dsclosed, or represents that ts use would not nfrnge prvately owned rghts. Reference heren to any specfc commercal product, process, or servce by trade name, trademark, manufacturer, or otherwse, does not necessarly consttute or mply ts endorsement, recommendaton, or favorng by the Unted States Government or any agency thereof. The vews and opnons of authors expressed heren do not necessarly state or reflect those of the Unted States Government or any agency thereof.

3 GA A22627 TRANSPORT MODEL TESTING AND COMPARISONS USING THE ITER AND DIII D PROFILE DATABASES by J.E. KINSEY,* R.E. WALTZ, and D.P. SCHISSEL Ths s a preprnt of a paper to be presented at the Twenty- Fourth European Conference on Controlled Fuson and Plasma Physcs, June 9 14, 1997, Berchtesgaden, Germany, and to be publshed n the Proceedngs. *Oak Rdge Assocated Unverstes, Oak Rdge, Tennessee. Work supported by the U.S. Department of Energy under Grant No. DE-FG03-95ER54309 GA PROJECT 3726 JUNE 1997

4 TRANSPORT MODEL TESTING AND COMPARISONS J.E. Knsey, et al. TRANSPORT MODEL TESTING AND COMPARISONS * J.E. Knsey, R.E. Waltz, and D.P. Schssel General Atomcs, P.O. Box 85608, San Dego, Calforna USA A fast steady-state transport code s used to test and compare several theory-based transport models ncludng the IFS/PPPL, GLF23, Multmode, and Itoh-Itoh-Fukuyama (IIF) models. Statstcs for both local and global quanttes as a rato of model to experment are computed to assess the performance of each model aganst a profle database comprsed of more than 50 L and H mode dscharges. These dscharges, whch nclude parameter scans n gyroradus, collsonalty, beta, plasma current, densty, and power, have been obtaned from the DIII D and ITER profle databases. I. OBJECTIVE TESTING OF TRANSPORT MODELS In ths paper we assess the performance of several theory-based transport models by comparng the predctons for the temperature profles aganst expermental data from DIII D, TFTR, and JET usng the MLT transport code. We use an expermental database comprsed of nearly 50 L and H mode dscharges from the ITER and DIII D profle databases [1]. All the models are treated equally wthn a sngle transport code usng the same methodology and fgures of mert to quantfy the level of agreement wth both global and local quanttes. Usng the expermental densty profles and analyzed sources, the boundary condtons are set at ρ/a = 0.90 for all smulatons. Here, no consderaton s made to test the models aganst data from Ohmc dscharges or from plasmas n advanced operatng regmes (e.g. supershots, VH mode, reversed shear). Included n the study are the IFS/PPPL model [2] and the more comprehensve GLF23 model [3] whch are based upon gyroflud smulatons of the torodal on temperature gradent (ITG) mode n a three-dmensonal nonlnear balloonng mode representaton wth extrapolated trapped electron (TEM) physcs. The Multmode model [4] combnes the Weland twodmensonal ITG/TEM model wth contrbutons from drft-resstve and knetc balloonng modes. Whle ts physcs s not as rgorous as the gyrolandau flud models, t has been more extensvely tested n a full tme-dependent transport code to successfully predct the evoluton of densty and temperature profles from a wde range of dscharges. All three are crtcal gradent models and can be characterzed n terms of ther stffness whch determnes how much power flow s needed to move away from margnalty. In general, the gyroflud models tend to be very stff whle the Multmode model s moderately stff. The IIF model [5] dffers n that t s not a drft wave based transport model. It can be characterzed as a current-dffusve model based upon one flud electrostatc nertal" MHD equaton. Unlke the ITG based models, t has no threshold and, therefore, lttle stffness. Whle testng the IIF model we found that better agreement wth the database s found f the thermal dffusvtes were reduced by 50%. Ths s justfable snce the model was not orgnally calbrated aganst a large database. All results shown here are for the recalbrated verson. * Work supported by the U.S. Department of Energy under Grant No. DE-FG03-95ER Oak Rdge Assocated Unverstes, Oak Rdge, Tennessee. General Atomcs Report GA A

5 J.E. Knsey, et al. TRANSPORT MODEL TESTING AND COMPARISONS II. SIMULATION RESULTS AND RANKING OF MODELS To assess the performance of each transport model, quanttatve comparsons are made between the model predctons and the expermental data for both global and local quanttes. Fgure 1 shows that the Multmode model yelds the best overall agreement wth the database followed by the IFS/PPPL model (wthout E B shear), IIF, and GLF23 (wth E B shear) models, respectvely. 1 R W = 26.9% <R W > = 1.05 L-mode H-mode (21) (25) R W = 21.8% <R W > = GLF23.v4 w/ ExB Shear R W = 14.7% <R W > = 0.98 IFS/PPPL w/o ExB Shear R W = 24.1% <R W > = Mult-mode Recalbrated Itoh-Itoh-Fukuyama Fg. 1. Stored energy offset for the GLF23, IFS/PPPL, Multmode, and IIF models. Here, the stored energy offset f W, defned as W s /W x 1, s plotted versus dscharge for each of the four transport models. The L and H mode results are dvded left and rght by a thck black lne wth the dscharges also beng convenently grouped accordng to machne. Here, a postve (negatve) offset ndcates the model overpredcts (underpredcts) the stored energy. A hollow crcles shown when no numercal result was found for a partcular dscharge. In the upper left corner of each panel s the average and the root-mean-square error (rms) for the total stored energy. Furthermore, we fnd that the rankng of the models s ndependent of the fgure of mert chosen. Here, the global fgures of mert nclude the average R W and rms error RW for the total stored energy RW Ws Wx N RW = Ws Wx 1 2 N (1) where N s the total number of dscharges and W s,x refer to the smulaton and expermental stored energes, respectvely. The local fgures of mert nclude the offset f T and rms error σ T between the predcted and expermental temperature profles where = ( ) ( ) ( ) ( ) 2 ft = Ts Tx T2 x σ T = T s T x T2 x (2) Table 1 shows the average and rms error for the total stored energy along wth the rms error and average offset for the temperature profles. Notce that agreement wth the database gets worse when E B shear s ncluded n the IFS/PPPL model, but agreement mproves when 2 General Atomcs Report GA A22627

6 TRANSPORT MODEL TESTING AND COMPARISONS J.E. Knsey, et al. ncluded n the GLF23 model. Specfcally, the offset becomes closer to unty and the average error remans essentally unchanged for the GLF23 model whle the offset ncreases from 0.94 (too cold) to 1.20 (too hot) and the average error worsens from 22% to 37% for the IFS/PPPL model. Ths llustrates that the mplementaton of E B shear effects s crucal and can be as mportant as descrbng the physcs wthn the ITG model tself. In fact, t s a necessary ngredent n reproducng the expermental profles n reversed shear dscharges where models lackng E B shear sgnfcantly underpredct the observed temperature profles. Table I. Rank Accordng to Fgures of Mert R W R W σ Te σ T f Te f T Multmode IFS-PPPL (w/o E B) IIF (recalbrated) GLF23.v4 (w/ E B) GLF23.v4 (w/o E B) IFS-PPPL (w/ E B) III. SCANS IN MACHINES AND DIMENSIONLESS PARAMETERS To test the ntrnsc scalng propertes of the models we examned smulatons of DIII D parameter scans wthn the database ncludng H mode scans n plasma current, heatng power, and electron densty. Also studed were L and H mode dmensonless smlarty experments where the normalzed gyroradus, collsonalty, and beta were systematcally vared. Table II detals the predcted transport confnement scalngs for the DIII D H mode scans n plasma current (I p vared from 0.75 to 1.5~MA at fxed P b, n e ), neutral beam power (P b vared from 4.7 to 13.6~MW at fxed I p, n e ), and electron densty (power changed as densty vared from 2.9 to m 3 to keep temperature gradents fxed). All the models fal to reproduce the observed scalng n one or more of the scans. Table II. Scalng Exponents for DIII D Fxed Parameter Scans τ I 1 p, P a p, n N τ B B e β ν *, β τ 1 2 Scan I p P n e ρ * ρ * ν * ν * β β Type H H H Low-q H Hgh-q H L H L H Exponent I P N B B Multmode IFS-PPPL (w/o E B) GLF23 (w/ ExB) IIF Experment In H mode plasmas a substantal porton of the stored energy s n the pedestal regon. Therefore, t s of nterest to test the extent n whch the predcted scalngs from the models result from enforcng the boundary condtons at the top of the pedestal. We fnd that f the pedestal temperatures are held fxed gong from the low to hgh current dscharge that the General Atomcs Report GA A

7 J.E. Knsey, et al. TRANSPORT MODEL TESTING AND COMPARISONS observed lnear current dependence s not reproduced. Ths mples that most (>70%) of the H mode current scalng s an artfact of the changng temperatures at the top of the pedestal. In the experment, T e and T at ρ/a = 0.9 changed by factors of 3.5 and 1.8, respectvely. For the power scan, however, we fnd that the expermental power scalng s reproduced when holdng the boundary temperatures fxed gong from the low to hgh power dscharge suggestng that the power scalng s not determned by the pedestal boundary condtons. Table II also descrbes the results for the H mode ρ * and L and H mode ν * and β scans. Interestngly, t s found that all the models, whch are ntrnscally gyrobohm, follow the apparent change from gyrobohm confnement for low-q H mode dscharges to Goldston-lke confnement for hgh-q dscharges where the normalzed gyroradus was vared by a factor of 1.6 holdng all other dmensonless quanttes fxed. Wth the excepton of the L mode β-scan, all the models reproduced the observed weak dependence of B τ tr on collsonalty and thermal beta n the L and H mode where ν * was vared by a factor of eght n the ν * - scans and β th was vared by a factor of two n the β-scans. IV. ITER PROJECTIONS To test the ntrnsc scalng propertes of the models we examned smulatons of DIII D parameter scans wthn the database ncludng H mode scans n plasma current, heatng power, and electron densty. Also studed were L and H mode dmensonless smlarty experments where the normalzed gyroradus, collsonalty, and beta were systematcally vared. Table II detals the predcted transport confnement scalngs for the DIII D H mode scans n plasma current (I p vared from 0.75 to 1.5 MA at fxed P b, n e ), neutral beam power (P b vared from 4.7 to 13.6 MW at fxed I p, n e ), and electron densty (power changed as densty vared from 2.9 to m 3 to keep temperature gradents fxed). All the models fal to reproduce the observed scalng n one or more of the scans. A large uncertanty n projectng to ITER gnton s whether or not H mode pedestal temperatures can be sustaned. Ths s crucal because many transport models are relatvely senstve to the pedestal temperature. Comparng the predctons from the models, we see that they vary consderably from very optmstc (IIF actually exceeds β-lmt) to optmstc (Multmode) to pessmstc (IFS, GLF). Fgure 2 llustrates the senstvty of the model predcted fuson power gan (Q = Q IFS/PPPL (94') GLF23.v4 Multmode IIF (recal) T ped (kev) Fg. 2. Fuson energy gan versus pedestal temperature. 5/[P aux /P ]) to the pedestal temperature assumng a lne-averaged densty of m 3, τ He = 10 τ E, and P aux = 100 MW. Typcally, the Multmode model predcts gnton even for L mode edge temperatures. [1] J.W. Connor, et al., n Proc. of the 16th IAEA Fuson Energy Conf., Montreal, 1996 (Internatonal Atomc Energy Agency, Venna, n press), paper F1-CN-64/FP-21. [2] M. Kotschenreuther, W. Dorland, M. Beer, and G. Hammett, Phys. Plasmas 2, 2381 (1995). [3] R.E. Waltz, G.M. Staebler, G. Hammett, and J.P. Konngs, n Proc. of the 16th IAEA Fuson Energy Conf., Montreal, 1996 (Internatonal Atomc Energy Agency, Venna, n press), paper F1-CN-64/D1-6. [4] J.E. Knsey and G. Bateman, Phys. Plasmas 3, 3344 (1996). [5] S.I. Itoh, K. Itoh, A. Fukuyama, and M. Yag, Phys. Rev Lett. 72, 1200 (1994). 4 General Atomcs Report GA A22627