{
  "abstract": "Isoflux control in spherical tokamaks requires coordinated plasma-current and boundary regulation under coil-voltage and computational constraints. This study develops observer-based constrained model predictive control (MPC) for EXL-50U. Vacuum-vessel spatial coarsening reduces a 538-state linearized model to 40 states while retaining control-relevant responses. A Kalman observer provides full-state estimates, and MPC jointly optimizes current and boundary-flux tracking with explicit voltage bounds. Matrix precomputation, specialized solver code generation, and structured linear-system solution reduce online computation. Nonlinear free-boundary Grad--Shafranov evolutive simulations evaluate nominal operation, measurement noise, configuration mismatch, a one-step delay, and combined noise and delay against proportional--integral--derivative (PID) control and a linear--quadratic regulator (LQR). Nominal MPC root-mean-square errors are 1.126 kA for plasma current, 0.0164 m for last-closed-flux-surface geometry, and 2.463 mWb for the worst flux channel, all below both baselines. With noise, the boundary error is 0.0199 m over the common evaluation window, and regulation is sustained throughout the test. MPC completes a limiter-to-divertor transition without relinearization or retuning and maintains regulation under delay and combined disturbances. Across all five cases, mean MPC computation times are 0.413--0.441 ms, with all 99th percentiles below 1 ms. These results support joint current and isoflux regulation and millisecond-scale computational feasibility, providing a basis for future EXL-50U experiments.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.34076",
  "author_total": 4,
  "authors": [
    {
      "name": "Chang Lu"
    },
    {
      "name": "Jiayi Zhi"
    },
    {
      "name": "Xian Guo"
    },
    {
      "name": "Tianyuan Liu"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/arb501ennnjpb.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.34076",
  "fulltext_url": null,
  "id": "arb501ennnjpb",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.34076",
  "language": null,
  "licence": "LicenseRef-arXiv-nonexclusive-1.0",
  "licence_label": "arXiv licence",
  "licence_source": "article",
  "licence_url": "http://arxiv.org/licenses/nonexclusive-distrib/1.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "physics.plasm-ph"
    ],
    [
      "openalex",
      "2207|Advanced Control Systems Optimization"
    ]
  ],
  "openalex": "W7214709891",
  "pdf_url": "https://arxiv.org/pdf/2609.34076",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-28",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/arb501ennnjpb.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:25:12Z",
      "native_id": "2609.34076",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.34076"
    }
  ],
  "subjects": [
    {
      "field": "physics",
      "origin": "arxiv:physics.plasm-ph",
      "subfield": "plasma"
    }
  ],
  "title": "Observer-Based Model Predictive Control for Isoflux Regulation in the EXL-50U Spherical Tokamak",
  "title_text": "Observer-Based Model Predictive Control for Isoflux Regulation in the EXL-50U Spherical Tokamak",
  "type": "preprint",
  "updated_at": "2026-10-30T12:25:12Z",
  "url": "https://research.draconitic.com/paper/arb501ennnjpb",
  "venue": "arXiv",
  "versions": []
}