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Beam-Tracing-Based Quantitative Reconstruction of Density Fluctuations in QUEST Using Doppler Backscattering
Authors:
T. Kinoshita,
T. Tokuzawa,
V. H. Hall-Chen,
Y. T. Tan,
T. Ido,
H. Idei,
R. Ikezoe,
K. Hanada,
M. Hasegawa,
T. Onchi,
Y. Peng
Abstract:
A three-channel X-/Ku-band Doppler backscattering (DBS) system has been developed and installed on QUEST for turbulence and electric-field measurements. In spherical tokamaks, the large magnetic-field pitch angle increases the geometric mismatch between the probing beam wave vector and the local magnetic-field vector, reducing the effective perpendicular projection and resulting in a systematic un…
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A three-channel X-/Ku-band Doppler backscattering (DBS) system has been developed and installed on QUEST for turbulence and electric-field measurements. In spherical tokamaks, the large magnetic-field pitch angle increases the geometric mismatch between the probing beam wave vector and the local magnetic-field vector, reducing the effective perpendicular projection and resulting in a systematic underestimation of the measured scattering intensity. In addition, in QUEST, where low plasma density requires a low-frequency probe beam, beam propagation effects become increasingly significant, further complicating the interpretation of the measured DBS power in terms of local density fluctuation amplitude. To address these issues, a quantitative correction methodology based on the synthetic DBS code SCOTTY was established. All relevant diagnostic response effects were evaluated using SCOTTY along ray trajectories, yielding a correction factor for reconstructing the local turbulence amplitude from the measured scattering signal. The correction factor exhibits strong spatial and frequency dependence, varying by up to an order of magnitude between the plasma core and edge regions, highlighting the necessity of frequency-dependent corrections. By applying the derived correction factor to experimental measurements, quantitative density fluctuation amplitudes were reconstructed from the detected scattering signals. Evaluation of the fluctuation amplitude indicates enhanced turbulence activity in the plasma edge region, where a finite negative radial electric field is inferred. This work demonstrates the first quantitative turbulence evaluation using low-frequency X-/Ku-band DBS measurements in QUEST and establishes a framework for quantitative DBS analysis in spherical tokamaks.
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Submitted 18 August, 2026;
originally announced August 2026.
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Scalable predictive processing framework for multitask caregiving robots
Authors:
Hayato Idei,
Tamon Miyake,
Tetsuya Ogata,
Yuichi Yamashita
Abstract:
The rapid aging of societies is intensifying demand for autonomous care robots; however, most existing systems are task-specific and rely on handcrafted preprocessing, limiting their ability to generalize across diverse scenarios. A prevailing theory in cognitive neuroscience proposes that the human brain operates through hierarchical predictive processing, which underlies flexible cognition and b…
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The rapid aging of societies is intensifying demand for autonomous care robots; however, most existing systems are task-specific and rely on handcrafted preprocessing, limiting their ability to generalize across diverse scenarios. A prevailing theory in cognitive neuroscience proposes that the human brain operates through hierarchical predictive processing, which underlies flexible cognition and behavior by integrating multimodal sensory signals. Inspired by this principle, we introduce a hierarchical multimodal recurrent neural network grounded in predictive processing under the free-energy principle, capable of directly integrating over 30,000-dimensional visuo-proprioceptive inputs without dimensionality reduction. The model was able to learn two representative caregiving tasks, rigid-body repositioning and flexible-towel wiping, without task-specific feature engineering. We demonstrate three key properties: (i) self-organization of hierarchical latent dynamics that regulate task transitions, capture variability in uncertainty, and infer occluded states; (ii) robustness to degraded vision through visuo-proprioceptive integration; and (iii) asymmetric interference in multitask learning, where the more variable wiping task had little influence on repositioning, whereas learning the repositioning task led to a modest reduction in wiping performance, while the model maintained overall robustness. Although the evaluation was limited to simulation, these results establish predictive processing as a universal and scalable computational principle, pointing toward robust, flexible, and autonomous caregiving robots while offering theoretical insight into the human brain's ability to achieve flexible adaptation in uncertain real-world environments.
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Submitted 28 October, 2025;
originally announced October 2025.
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Emergence of sensory attenuation based upon the free-energy principle
Authors:
Hayato Idei,
Wataru Ohata,
Yuichi Yamashita,
Tetsuya Ogata,
Jun Tani
Abstract:
The brain attenuates its responses to self-produced exteroceptions (e.g., we cannot tickle ourselves). Is this phenomenon, known as sensory attenuation, enabled innately, or acquired through learning? Here, our simulation study using a multimodal hierarchical recurrent neural network model, based on variational free-energy minimization, shows that a mechanism for sensory attenuation can develop th…
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The brain attenuates its responses to self-produced exteroceptions (e.g., we cannot tickle ourselves). Is this phenomenon, known as sensory attenuation, enabled innately, or acquired through learning? Here, our simulation study using a multimodal hierarchical recurrent neural network model, based on variational free-energy minimization, shows that a mechanism for sensory attenuation can develop through learning of two distinct types of sensorimotor experience, involving self-produced or externally produced exteroceptions. For each sensorimotor context, a particular free-energy state emerged through interaction between top-down prediction with precision and bottom-up sensory prediction error from each sensory area. The executive area in the network served as an information hub. Consequently, shifts between the two sensorimotor contexts triggered transitions from one free-energy state to another in the network via executive control, which caused shifts between attenuating and amplifying prediction-error-induced responses in the sensory areas. This study situates emergence of sensory attenuation (or self-other distinction) in development of distinct free-energy states in the dynamic hierarchical neural system.
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Submitted 12 August, 2022; v1 submitted 4 November, 2021;
originally announced November 2021.
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Temperature-dependent local structure of superconducting BaPd$_2$As$_2$ and SrPd$_2$As$_2$
Authors:
K. Terashima,
E. Paris,
L. Simonelli,
E. Salas-Colera,
A. Puri,
T. Wakita,
Y. Yamada,
S. Nakano,
H. Idei,
K. Kudo,
M. Nohara,
Y. Muraoka,
T. Mizokawa,
T. Yokoya,
N. L. Saini
Abstract:
The local structures of 122-type paradium arsenides, namely BaPd$_2$As$_2$ and SrPd$_2$As$_2$, are examined by As K-edge extended x-ray absorption fine structure measurements to find a possible correlation between the variation of their superconducting transition temperature and the local structure. The local atomic distances are found to be consistent with average distances measured by diffractio…
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The local structures of 122-type paradium arsenides, namely BaPd$_2$As$_2$ and SrPd$_2$As$_2$, are examined by As K-edge extended x-ray absorption fine structure measurements to find a possible correlation between the variation of their superconducting transition temperature and the local structure. The local atomic distances are found to be consistent with average distances measured by diffraction techniques. The temperature dependence of mean square relative displacements reveal that, while BaPd$_2$As$_2$ is characterized by a local As-Pd soft mode, albeit with larger atomic disorder, SrPd$_2$As$_2$ shows anomalous As-Pd correlations with a kink at $\sim$160 K due to hardening by raising temperature. We have discussed implications of these results and possible mechanism of differing superconducting transition temperature in relation with the structural instability.
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Submitted 1 October, 2018;
originally announced October 2018.
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Estimation of Power Balance in Steady State LHCD Discharges on TRIAM-1M
Authors:
Tomoya Sugata,
K. Hanada,
N. Imamura,
M. Sakamoto,
H. Zushi,
H. Idei,
A. Iyomasa,
S. Kawasaki,
K. Sato,
H. Nakashima,
K. Nakamura,
M. Hasegawa,
A. Higashijima
Abstract:
On TRIAM-1M, a long duration discharge for more than 5 h was achieved successfully by fully non-inductive lower hybrid current drive. Heat load distribution to the plasma facing components (PFCs) in the 5 h discharge was investigated by using calorimetric measurements. The injected RF power was coincident with the total amount of heat load to PFCs estimated by calorimetric measurement. The power…
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On TRIAM-1M, a long duration discharge for more than 5 h was achieved successfully by fully non-inductive lower hybrid current drive. Heat load distribution to the plasma facing components (PFCs) in the 5 h discharge was investigated by using calorimetric measurements. The injected RF power was coincident with the total amount of heat load to PFCs estimated by calorimetric measurement. The power balance including the portion of direct loss power of fast electron, heat flux due to the charge exchange process was able to be estimated in this long duration discharge.
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Submitted 23 October, 2004;
originally announced October 2004.
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Ion acceleration during internal magnetic reconnection events in TST-2
Authors:
Hiroyuki Hoshika,
H. Zushi,
M. Aramasu,
H. Idei,
A. Iyomasa,
A. Ejiri,
S. Ohara,
H. Kasahara,
Y. Kamada,
S. Kawasaki,
M. Sakamoto,
K. Sasaki,
K. Sato,
S. Shiraiwa,
Y. Takagi,
Y. Takase,
H. Nakashima,
K. Nakamura,
M. Hasegawa,
K. Hanada,
A. Higashijima,
T. Yamada
Abstract:
Characteristics of ion acceleration in the internal magnetic reconnection events (IRE) have been studied by means of a neutral particle energy analyzer (NPA) in Tokyo Spherical Tokamak (TST-2). The major and minor radii are 0.38 m and 0.25m, respectively. The magnetic field strength is 0.3T and the maximum plasma current is up to 140 kA. The electron and ion temperatures are 0.4-0.5 keV and 0.1…
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Characteristics of ion acceleration in the internal magnetic reconnection events (IRE) have been studied by means of a neutral particle energy analyzer (NPA) in Tokyo Spherical Tokamak (TST-2). The major and minor radii are 0.38 m and 0.25m, respectively. The magnetic field strength is 0.3T and the maximum plasma current is up to 140 kA. The electron and ion temperatures are 0.4-0.5 keV and 0.1 keV, respectively and the electron density is ~1x1019 m-3. The NPA can be scanned toroidally from q = 74° (cw) to q = 114° (ccw), where q = 90° corresponds to the perpendicular sightline. The direction of the plasma current is cw. The NPA signals are digitized at every 50 ms. The NPA is calibrated in the energy range of 0.1 keV < E < 8.4 keV. When the IRE occurs, it is observed that the plasma current increases by ~ 20% and the loop voltage drops from 0.6 V to-5 V for ~ 0.1 ms. The enhanced charge exchange flux is observed by more than one order of magnitude at ~ 1 keV for this reconnection phase. The ion temperature increases by 80 eV at IREs. The angle q dependence of increment of Ti shows that DTi (q = 74°) is higher than that for q = 114°. This observation suggests that an ion is accelerated initially in the direction of magnetic field lines. The time evolution of the ion distribution function is simulated with a Fokker-Planck code taking into account the electric field effects.
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Submitted 23 October, 2004;
originally announced October 2004.
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Transport barrier formation by LHCD on TRIAM-1M
Authors:
K. Hanada,
A. Iyomasa,
H. Zushi,
M. Hasegawa,
K. Sasaki,
H. Hoshika,
K. Nakamura,
M. Sakamoto,
K. N. Sato,
H. Idei,
S. Kawasaki,
H. Nakashima,
A. Higashijima
Abstract:
Internal transport barrier (ITB) has been obtained in full lower hybrid current driven (LHCD) plasmas on a superconducting tokamak, TRIMA-1M (R=0.84m, a x b=0.12mx0.18m, BT<8T). The formation of ITB depends on the current density profile, j(r), varied by the power deposition of the lower hybrid (LH). The plasma with ITB can be maintained by the LH power deposited around the foot point of ITB up…
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Internal transport barrier (ITB) has been obtained in full lower hybrid current driven (LHCD) plasmas on a superconducting tokamak, TRIMA-1M (R=0.84m, a x b=0.12mx0.18m, BT<8T). The formation of ITB depends on the current density profile, j(r), varied by the power deposition of the lower hybrid (LH). The plasma with ITB can be maintained by the LH power deposited around the foot point of ITB up to 25 sec, which corresponds to more than 100 times of current diffusion time, $τ$L/R. ITB is terminated by the reduction of current drive efficiency caused by metal impurities accumulation. In some condition, self-organized slow sawtooth oscillations (SSSO) of plasma current, density, temperature, and so on with the period comparable to the current diffusion time have been also observed during ITB discharge. The oscillation has the capability of particle exhaust, as the result, it may play an role in the avoidance of the impurity accumulation and the dilution in the future steady state fusion plasma with ITB, as the edge-localized mode in H-mode.
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Submitted 20 October, 2004;
originally announced October 2004.