28pC06
ITERにおける電流分布計測の総合性能評価に関する研究
Comprehensive assessment of current profile measurement on ITER
今澤良太、河野康則、草間義紀
Ryota IMAZAWA, Yasunori KAWANO, Yoshinori KUSAMA
日本原子力研究開発機構
Japan Atomic Energy Agency
In ITER, the poloidal polarimeter and motional Starkeffect (MSE) diagnostic based on the heating neutralbeam (HNB) are classified as primary diagnostics forthe measurement of the current profile (safety factor, q,profile). The measurement requirements (MR) for q
have been defined in ITER Project Requirements [1];the required accuracy of q-value is 10 % and therequired radial position accuracy of q=1.5, 2.0 and
qmin is 50 mm. Previous studies [2,3] carried out
assessment of the current profile measurement byusing either the poloidal polarimeter or MSE at thestart-of-burn (SOB) phase. In this study, CUPID(Current Profile Identification) code [2] is applied toassess the accuracy of the current profile measurement
under the various conditions; q profile measurement
with/without error of auxiliary data, q profile
measurement utilizing both the poloidal polarimeterand MSE, q profile measurement utilizing the tiltedHNB, q profile measurement in the case of plasma
with current-hole configuration, and q profile
measurement during the start-up phase [4].
CUPID determines a current profile consistent withthe measurement data from the poloidal polarimeter,
MSE, the position and shape of LCFS (A), the total
plasma current (Ip) and the electron density (ne) andtemperature (Te) measured by Thomson scattering. We
added random errors to the input data, ran CUPID 100
times and evaluated the maximum error of q(assessment method discussed in [4]). In the case of A,Ip, ne and Te, random errors were added in compliancewith MR [1]. The measurement data of the poloidal
polarimeter are orientation, θ, and ellipticity angle, ε,of the polarization state of the probe laser beam. Thevalue of θ and ε mainly corresponds to the Faraday
and Cotton-Mouton effect, respectively. The
measurement data of MSE is pitch angle, γ. We
estimate the maximum error of q-identification withvarying standard deviation of θ, ε, and γ (σθ, σε, and σγ)
and with on/off-axis HNB. The value of σε waspegged at 6 times that of σθ in this study (for thereason discussed in [2]).
Fig. 1 is one example of our comprehensive
assessments and shows maximum errors of q-profile
measurements utilizing only poloidal polarimeter as afunction of σθ at the SOB of ITER S2 (inductive) andS4 (steady-state) operation scenarios. Open symbols
denote the reconstructions that only include error

related to PoPola data; filled symbols denote thereconstruction that also includes the auxiliary data (A,Ip, ne and Te). The errors for S4 are larger than for S2,so S4 establishes the more severe test of the system.
Nonetheless, as long as the measurement error of thePolarimeter is less than ~0.4° the polarimeter is able
to meet or exceed MR. Errors from the externallysupplied data contribute between 10% and 30% to theoverall error. This shrinks the allowable error budget
for the PoPola system to σθ < ~0.1°.
The results under the various conditions suggested
that at least one of σθ or σγ with 0.1° or less wasneeded to satisfy the required accuracy of q (10 %),and that the influence of the off-axis HNB for theq-profile measurement was small. The value of 0.1° isfeasible, based on the results of polarimeteries andMSEs in existing tokamaks.

FIGURE 1. Maximum errors of the q-profile
measurement utilizing only poloidal polarimeter as afunction of σθ at the SOB of ITER S2 and S4 scenarios.
(Δ: S2, ○: S4, Filled mark: All input data include
error, Open mark: Only PoPola data include error)[1] G. Vayakis, et al., Proceedings of the 24th IAEA
Fusion Energy Conference, ITR/P5-37.
[2] R. Imazawa et al., Nucl. Fusion 51, 113022 (2011).
[3] E. L. Foley et al., Rev. Sci. Instrum. 79, 10F521(2008).
[4] R. Imazawa, et al., Proceedings of the 24th IAEA
Fusion Energy Conference, ITR/P5-38.
----------------------------------------------------------------The views and opinions expressed herein do notnecessarily reflect those of the ITER Organization.