23P096-P
Observation of TAE Induced Convective/Diffusive Losses
and Comparison with Orbit Following Model in LHD
大型ヘリカル装置におけるトロイダルアルヴェン固有モードに起因する対流・拡散損失の観測と、粒子軌道シミュレーションとの比較
Kunihiro Ogawa2, Mitsutaka Isobe1, Kazuo Toi1, Donald A. Spong3, LHD Experiment Group1
小川国大2, 磯部光孝1,東井和夫1,Donald A. Spong3,LHD実験グループ1
2

Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292, Japan
3
Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6169, USA2
名古屋大学工学研究科, 〒 464-8603 名古屋市千種区不老町1
自然科学研究機構 核融合科学研究所, 〒509-5292 土岐市下石町322-6
3
オークリッジ国立研究所, 〒 37831-6169 アメリカ テネシー州オークリッジ
1Fast ions lost from the LHD plasma due to toroidal Alfvén eigenmode (TAE) together with the energy E
and the pitch angle χ of them is measured by the scintillator-based lost-fast ion probe (SLIP). The numberof lost fast ions detected by the SLIP grows with the increase of the magnetic fluctuation amplitude, andthe dependence becomes steeper as the increase of Shafranov shift. Fast ion loss due to TAE is simulatedwith orbit following models. The loss-flux dependence on magnetic fluctuation has the same tendency as
obtained in experiments.

1. Introduction
One of the critical issues in realizing
self-sustained DT burning plasma is that how
well fast ions such as alpha particles will beconfined. Better understanding on the loss
process of fast ions due to fast-ion-driven MHD
instabilities is required to find a scenario tocontrol and/or reduce fast-ion loss [1]. In thelarge helical device (LHD), the anomaloustransport or loss of co-going beam ions due totoroidal Alfven eigenmodes (TAEs) [2] have beenrecognized by an E//B neutral particle analyser
with a tangential line of sight [3] and ascintillator-based lost fast ion probe (SLIP) [4] inthe position of magnetic axis in vacuum Rax of 3.60
m with a large Shafranov shift plasma.
Understanding on the anomalous transport andthe consequent fast ion loss due to TAEs, amagnetic configuration effect on the fast ion loss
needs to be studied. At the same time, amodelling of the fast ion loss caused by TAEs isalso the task.
2. TAE induced loss measured on a plasma withsmall and large Shafranov shift
Experiments of TAE excitation were conductedin LHD. Strong TAE modes are excited using threeneutralbeam
injectors(NBIs);
its
acceleration-energy is up to 190 keV. The SLIP
gives the energy E and the pitch angle χ of the lost
fast ion simultaneously [5]. Mirnov coil array set on
the vacuum vessel measures the amplitude of thefluctuation of TAE modes bTAE and thetoroidal/poloidal mode number (m and n).
The study on TAE induced loss was conducted atrelatively-low-field experiments (Bt=0.60 T) on Raxof 3.60 m with a small Shafranov shift (Rmag of 3.75m) and a large shift (Rmag of 3.86 m). TAE having
m/n=1/1 induced loss is observed in the range ofE/χ ~50~190 keV/~40°. The normalized energetic
ion loss flux due to TAE ΔΓSLIP/PNBcoτse dependence
on bTAE/Bt is shown in Fig. 1. Here, the ΔΓSLIP isnormalized by the energetic ion content generated
by co-injected NBIs (PNBco τse). Loss flux
dependence on magnetic fluctuation amplitude
indicates convective type at the plasma with small
Shafranov shift and indicates diffusive type loss atthe plasma with large Shafranov shift, respectively[6]. The Shafranov shift can modify the safety
factor profile appreciably and also expand the loss
boundary because of large orbit deviation from themagnetic surfaces [7, 8]. TAE induce the resonant
drift near the loss boundary at small-shift case. On
the other hand, fast ions transported diffusively due
to the relatively large amplitude and wider TAE toloss domains on a large shift case.
3. TAE induced loss reaching the SLIP in thecalculation
Simulation of fast ion losses due to TAE isdemonstrated based on the orbit following modelwith a TAE fluctuation. Equilibrium isreconstructed using VME2000 [9] with using theelectron temperature Te and the electron density neFig.2. Fast ion loss flux dependence on fluctuation
amplitude at the TAE centre in calculation.
Fig.1. Fast ion loss flux dependence on fluctuation
amplitude of TAE measured with magnetic probe.

profile measured with the Thomson scattering
diagnostics [10]. A birth profile and the initial pitchangle of beam ions are given by HFREYA [11]using the profile of Te and ne and the position of ion
sources. Guiding-centre orbit of each beam ion inthe boozer coordinate is followed using DELTA5D[12] including the TAE fluctuations. Thefluctuation is assumed as b = ∇ × (α B ) : α = ∇ / /φ ,where b and φ indicate the magnetic fluctuation andthe eigenfunction of the mode, respectively [13]. φis obtained using AE3D [14] code by assuming thecharge neutrality ni = ne, and the pure hydrogenplasma (Zeff=1). An orbit from the last closed flux
surface to the SLIP is followed using the Larmor
orbit code with using the magnetic field in avacuum. We judged a fast ion reaches the SLIP if
distance between a guiding-centre orbit and a
Lorentz orbit is in the poloidal Larmor radii ±20 %,the difference of pitch angle is less than 5 degrees,
and the energy difference is less than 5 keV. In
these calculations, the TAE fluctuation is included
after a slowing down of the fast ions and sums all
the results to simulate the slowing-down profile offast ions. Frequency of the mode in the calculation
is down from 70 kHz to 50 kHz in 1 ms. An
increment of loss induced by TAE dependence on
fluctuation amplitude at the TAE peak b0 is shownin Fig. 2. The loss flux grows with the increase ofb0 and Shafranov shift. The loss flux dependence on
b0 becomes steeper as increase of Shafranov shift.
These tendencies agree with that of theexperiments.
4. Summary
Measurement of E and χ of lost fast ions
induced by m/n=1/1 TAE were carried out on Rax =3.60 m with a small and a large Shafranov shift.
The normalized loss flux grows with the increaseof the TAE amplitude measured with the Mirnov
coil set on vacuum vessel. TAE induced loss
becomes larger and the loss flux dependence onbTAE becomes steeper at large shift case than small
shift case. Wider eigenfunction of TAE and an
expansion of loss region are candidate to explain
the changing. TAE induced loss is simulated using
the orbit following model using DELTA5D andLorentz orbit code. The loss flux induced by TAE
grows with increasing of b0 and Rmag shift asobtained in the experiments.
Acknowledgments
This work was supported in part by theGrant-in-Aid for Scientific Research fromMEXT, No. 16082209 and from JSPS No.
21360457, No. 21340175, and No. 22-7912, andthe LHD project budget (NIFS10ULHH011).
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