Edge fluctuations in the ADITYA-U tokamak and their consequences by Harshita Raj

Edge fluctuations in the ADITYA-U tokamak and their consequences by Harshita Raj

by Harshita Raj · View the channel on PSI

Formal & Physical Sciences Physics PHFMaterialsPHFPPlasma physics
🎙 Harshita Raj 👥 74K 📅 September 30, 2026 ⏱ 57 min 👁 1 📄 original study 🧭 2026-09-30
Available in: English (current) Français

Keywords

ADITYA-Uedge turbulencesolide broadeninggas puffrunaway electrons

Summary

This scientific lecture, presented by experimental physicist Harshita Raj at the ICTS workshop on Plasma Turbulence, focuses on edge fluctuations in the ADITYA-U tokamak and their consequences. The talk begins with an introduction to edge fluctuations and their role in plasma-facing component heat loads. Raj describes the ADITYA-U tokamak (major radius 0.75 m, minor radius 0.25 m, typical parameters listed) and the use of gas puffs as actuators to perturb the edge. A wide array of Langmuir probes, including reciprocating and triple probes, provides detailed measurements of density, temperature, and floating potential. Key results show that gas puffs suppress broadband turbulence but unexpectedly lead to broadening of the scrape-off layer (SOL) width (λ_q up to 2× increase), attributed to enhanced intermittent cross-field transport (increased skewness and kurtosis). Simulations using UEDGE indicate a three-fold increase in effective cross-field diffusion after each puff. Pulse fueling maintains core confinement while reducing heat flux at the last closed flux surface by 30–60% compared to continuous fueling. The second part discusses runaway electrons: hard X-ray bursts correlate with gas puffs, indicating enhanced losses even in the absence of MHD modes, suggesting an electrostatic turbulence-driven transport channel. The talk underscores the complex interplay between edge turbulence, heat flux mitigation, and runaway electron dynamics.

207 words

Critical Evaluation

Value of the Information & Strength of the Argument

The talk’s value lies in presenting new experimental observations that challenge conventional assumptions: although edge turbulence is suppressed, the SOL broadening still occurs, indicating that intermittent transport dominates. The argumentation is solid, supported by multiple diagnostics and a clear cause-and-effect analysis. The presenter carefully rules out alternative explanations (e.g., changes in generation or population) for the runaway electron losses. The use of gas puffs as a controlled perturbation is a novel approach that allows systematic study of edge dynamics. The argument that pulse fueling can mitigate heat loads while maintaining core performance is practically significant. The reasoning is transparent, with limitations acknowledged (e.g., the need for broader radial scans to quantify E×B shear).

Scientific Rigor, Source Quality, Title Accuracy

The scientific rigor is high: the talk presents original experimental data, uses standard and custom diagnostics, and references prior work (e.g., studies on HL-2A and D3D showing turbulence effects on SOL width). The description includes links to relevant fusion programs (ITER, MAST-U, SPARC, etc.) which provide context for the importance of edge control in compact devices. The title is perfectly aligned with the content. No external references are explicitly cited in the transcript, but the talk appears consistent with published literature. The methodology (gas puff perturbation, Langmuir probe analysis) is well-established. The presenter does not overclaim and notes ongoing work (e.g., GPI imaging to directly observe blob dynamics).

236 words

Title / Content Match

The title accurately reflects the content, which indeed addresses edge fluctuations in ADITYA-U and their consequences.

Quality & Reliability

8/10

Presentation of detailed experimental results using multiple diagnostics (Langmuir probes, Mirnov coils, hard X-ray detector) with statistical analysis and comparison to simulations. Methods and limitations are clearly discussed.

Key Moments

Markers derived by PSI from the transcript: the creator did not define chapters.

Cited Sources

Contribution & Novelties

The talk contributes original experimental evidence that gas puff perturbation leads to SOL broadening despite suppression of broadband turbulence, driven by enhanced intermittent transport. It also shows a correlation between edge electrostatic turbulence and runaway electron losses, proposing a non-MHD mechanism. The pulse fueling advantage for heat flux mitigation is a practical insight. The use of multiple Langmuir probes and reciprocating drives is notable.

Pour aller plus loin :

  • Tokamak — Fundamental device concept.
  • Scrape-off layer — Region where edge fluctuations and heat flux broaden.
  • Runaway electron — Generation and loss mechanisms.
  • Plasma turbulence — Overview of turbulence in plasmas.

100 words

Radar Profile

The radar profile shows high scores across all dimensions, with notably high technical depth and information quantity. The quality and reliability are strong, reflecting the experimental rigor. The talk is highly specialized, resulting in a high technical level. Overall, it's a dense and authoritative presentation.

Reliability 8/10