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In the High-Beta Tokamak-Extended Pulse (HBT-EP) device, hard x-rays (HXRs) are produced through thick-target bremsstrahlung radiation when energetic electrons are deconfined and strike limiting surfaces. This paper describes a new HXR detector system composed of ten scintillator detectors and a visible-light fast camera, which is used to detect fast bursts of HXR emission that correlate with magnetohydrodynamic (MHD) perturbations. Hard x-rays cause spatially uncorrelated speckling on the fast camera, and the appearance of speckles is strongly correlated in time with x-ray bursts. We also observe a threshold below which an HXR signal is insufficient to produce a given speckle signal. Using these detectors, HBT-EP can measure the toroidal and temporal characteristics of HXRs, which are used to infer the characteristics of deconfined electrons. We report a strong correlation between the phase of a rotating n = 1 HXR source and an n = 1 MHD mode, suggesting that MHD activity directly enhances the radial transport of energetic electrons.<\/jats:p>","DOI":"10.1063\/5.0350773","type":"journal-article","created":{"date-parts":[[2026,10,13]],"date-time":"2026-10-13T12:59:56Z","timestamp":1791896396000},"update-policy":"https:\/\/doi.org\/10.1063\/aip-crossmark-policy-page","source":"Crossref","is-referenced-by-count":0,"title":["Fast-detection of hard x-ray emission and correlation with magnetohydrodynamic instabilities on the High-Beta Tokamak-Extended Pulse (HBT-EP)"],"prefix":"10.1063","volume":"97","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-6507-2924","authenticated-orcid":false,"given":"N. 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