arXiv subjects

Santanu Banerjee

Publications and source records attributed to Santanu Banerjee.

5 recordsLinked to original sources

arXiv2026

Impurity-driven turbulence opens a pathway to ELM-free operation and enhanced pedestal stability in tokamaks

Edge-localized modes (ELMs) impose severe transient heat, and particle loads on plasma-facing components, posing a critical challenge for steady-state operation of tokamak fusion reactors. Existing ELM control techniques either rely on externally applied perturbations or operate within narrow parameter windows, raising concerns for reactor scalability. Here we demonstrate that controlled injection of a low-Z impurity can fundamentally modify pedestal transport and stability, enabling access to long ELM-free periods through impurity-driven turbulence. Using boron (B) powder injection in the DIII-D tokamak, we observe a progressive reduction of ELM frequency, culminating in long ELM-free phases. Pedestal stability analysis reveals a pronounced decoupling of peeling and ballooning stability boundaries at moderate B injection levels, opening a stability channel toward super-high confinement operation. At higher injection rates, long (~300 ms) ELM-free periods are achieved. Fluctuation measurements show that B injection selectively enhances low-frequency pedestal turbulence, increasing inter-ELM particle transport and regulating pedestal gradients. The establishment of a feedback loop between turbulence, particle transport, and the resulting modification of pedestal conditions, indicated by the observed hysteresis loop in the evolution of density fluctuations in response to the B injection rate, is presented.

physics.plasm-ph↗

arXiv2025

$T_i/T_e$ Dependence of Core Turbulence and Transport in DIII-D QH-Mode Plasmas

This study investigates the effect of the ion-to-electron temperature ratio ($T_i/T_e$) on microturbulence driven transport in Quiescent H-mode (QH-mode) plasmas in the DIII-D tokamak. Utilizing the Gyrokinetic Toroidal Code (GTC) and the QH-mode equilibrium, we perform linear and nonlinear simulations to analyze transport properties and instability dynamics under variations of $T_i$ and $T_e$. Our results demonstrate that decreasing $T_i/T_e$ leads to a relative destabilization of trapped electron modes (TEM) over ion temperature gradient (ITG) modes, with the transition between these regimes dictated by $T_i/T_e$. When the electron temperature is increased at fixed ion temperature, we observe an increase in transport saturation levels. In contrast, decreasing the ion temperature at fixed electron temperature results in more modest transport enhancement. The radial correlation length, which characterizes eddy size, increases with rising $T_e$ and decreases with falling $T_i$, consistent with the observed trends in turbulent transport. Additionally, we examine the impact of impurity addition on turbulence and growth rates, finding that impurity presence does not significantly alter transport quantities compared to the impurity-free case. Finally, investigating helium as an alternative main ion species, we find that helium plasmas exhibit higher linear growth rates but result in lower transport saturation levels than deuterium plasmas, suggesting potential confinement benefits. These findings provide quantitative insights into the temperature ratio dependence in QH-mode plasmas and highlight the role of temperature profiles and zonal flows in influencing plasma confinement.

physics.plasm-ph↗

arXiv2025

Rich Vehicle Routing Problem in Disaster Management enabling Temporally-causal Transhipments across Multi-Modal Transportation Network

A rich vehicle routing problem is considered, allowing multiple trips of heterogeneous vehicles stationed at geographically distributed vehicle depots having access to different modes of transportation. The problem arises from the real-world requirement of optimizing the disaster response time by minimizing the makespan of vehicular routes. Multiple diversely-functional vertices are considered, including Transhipment Ports as inter-modal resource transfer stations. Both simultaneous and split pickup and delivery are considered, for multiple cargo types, along with Vehicle-Cargo and Transhipment Port-Cargo compatibilities. The superiority of the proposed cascaded minimization approach is demonstrated over the existing makespan minimization approaches through our developed Mixed-Integer Linear Programming formulation. To solve the problem quickly for practical implementation in a Disaster Management-specific Decision Support System, an extensive Heuristic Algorithm is devised which utilizes Decision Tree based structuring of possible routes; the Decision Tree approach helps to inherently capture the compatibility issues, while also explore the solution space through stochastic weights. Preferential generation of small route elements is performed, which are integrated into route clusters; we consider multiple different logical integration approaches, as well as shuffling the logics to simultaneously produce multiple independent solutions. Finally, perturbations of the different solutions are done to find better neighbouring solutions. The computational performance of the PSR-GIP Heuristic, on our created novel datasets, indicates that it is able to give good solutions swiftly for practical problems involving large integer instances that the MILP is unable to solve.

math.OC↗

arXiv2024

A novel internship program in HEP

The U.S. CMS collaboration has designed a novel internship program for undergraduates to enhance the participation of students from under-represented populations, including those at minority serving institutions, in High Energy Physics (HEP). These students traditionally face several barriers including lack of research infrastructure and opportunities, insufficient mentoring, lack of support networks, and financial hardship, among many others, resulting in a lack of participation in STEM fields. We had recently reported about a fully virtual 10-week internship pilot program called "U.S. CMS - PURSUE (Program for Undergraduate Research SUmmer Experience)" to address dismantling such barriers. The 2023 iteration of this program builds on it by imparting not only an in-person summer internship experience but extends it into the academic semester as well. Students are selected predominantly from Minority Serving Institutions with no research program in HEP and from under-represented groups. They experience a structured hands-on research experience with an initial two-week "bootcamp" on software training modules followed by an 8-week HEP project targeting physics analysis, software, computing or instrumentation work on the CMS Experiment. A subset of interns continue the experience into the academic semester, enabling a further in-depth knowledge of the field and a motivation to persist in STEM areas. In this paper, we describe our recent experience with this upgraded internship program. The paper is dedicated to the memory of Prof. Meenakshi Narain (Brown University) who was the driving force behind this internship program and U.S CMS diversity, equity and inclusion efforts.

physics.ed-ph↗

arXiv2017

Modeling of eddy current distribution in the SST-1 tokamak

The time varying currents in the Ohmic transformer in the SST-1 tokamak induce voltages that drive large eddy currents in the passive structures like the vacuum vessel and cryostat. Since the vacuum vessel and the cryostat are toroidally continuous without electrical breaks in SST- 1, this leads to a shielding effect on the flux penetrating the vacuum vessel. This reduces the magnitude of the loop voltage seen by the plasma as also delays its buildup. Also the induced currents alter the null location of magnetic field. This will have serious implications on the plasma breakdown and startup and corrective measures may be required in case of an insufficient loop voltage or an improper null. Further, the eddy currents distribution will be vital for the plasma equilibrium and need to be considered while reconstructing the equilibrium. Evolution of the toroidal eddy currents in SST-1 passive structures has been studied using a toroidal-filament model. The model calculations are compared with the measured signals in the magnetic diagnostics like the toroidal flux loops and magnetic pick-up coils installed on the SST-1.

physics.plasm-ph↗