{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,29]],"date-time":"2026-09-29T13:03:33Z","timestamp":1790687013332,"version":"4.1.0"},"reference-count":18,"publisher":"AIP Publishing","issue":"9","funder":[{"name":"US DOE","award":["DEAC0500OR22725"],"award-info":[{"award-number":["DEAC0500OR22725"]}]},{"name":"EPSRC","award":["EP\/W006839\/1"],"award-info":[{"award-number":["EP\/W006839\/1"]}],"id":[{"id":"https:\/\/ror.org\/0439y7842","id-type":"ROR","asserted-by":"crossref"}]}],"content-domain":{"domain":["pubs.aip.org"],"crossmark-restriction":true},"short-container-title":[],"published-print":{"date-parts":[[2026,9,1]]},"abstract":"<jats:p>The suite of spectrometers monitoring the lower divertor [Verhaegh et\u00a0al., Nucl. Fusion 63, 016014 (2022)] on the MAST Upgrade tokamak has been extended before the start of the MU04 campaign. A new fiber bundle with good transmission in the near-Ultraviolet was installed to increase the number of instruments viewing the same radial profile in the divertor to a maximum of 4. This was done to accommodate a dedicated instrument to measure the Balmer series-limit recombination continuum around 365\u00a0nm. The ratio of the continuum above and below the recombination \u201cedge,\u201d as well as the spectral shape of the free\u2013bound continuum, allows us to derive the electron temperature in recombining plasmas independently of the excitation pathways [Lomanowski et\u00a0al., Plasma Phys. Controlled Fusion 62, 065006 (2020)]. The electron temperature is key to understanding heat exhaust processes in the divertor, which is essential for future fusion power plant design. A good diagnosis has been achieved of deeply detached, electron impact recombining plasmas, confirming Te = 0.05\u20130.3\u00a0eV [Verhaegh et\u00a0al., Nucl. Fusion 63, 126023 (2023)]. The electron temperature derived from the wavelength dependence of the continuum below 365\u00a0nm is in good agreement with the electron temperature derived from the intensity ratios of the high-n Balmer lines for ne = 1018\u20131019\u00a0m\u22123. At higher divertor temperatures, molecular assisted recombination mechanisms dominate, and the emission of CD and C2 molecules dominates the spectra, making it difficult to extract the temperature from the continuum.<\/jats:p>","DOI":"10.1063\/5.0350239","type":"journal-article","created":{"date-parts":[[2026,9,29]],"date-time":"2026-09-29T12:37:49Z","timestamp":1790685469000},"update-policy":"https:\/\/doi.org\/10.1063\/aip-crossmark-policy-page","source":"Crossref","is-referenced-by-count":0,"title":["Interpretation of the Balmer series-limit recombination spectrum in the MAST-U divertor"],"prefix":"10.1063","volume":"97","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-9834-874X","authenticated-orcid":false,"given":"E.","family":"Delabie","sequence":"first","affiliation":[{"name":"Oak Ridge National Laboratory 1 , Oak Ridge, Tennessee 37831-6305,","place":["USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3250-0256","authenticated-orcid":false,"given":"S.","family":"Menmuir","sequence":"additional","affiliation":[{"name":"UKAEA, Culham Campus 2 , Abingdon,","place":["United Kingdom"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2226-2004","authenticated-orcid":false,"given":"B.","family":"Lomanowski","sequence":"additional","affiliation":[{"name":"Oak Ridge National Laboratory 1 , Oak Ridge, Tennessee 37831-6305,","place":["USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9192-465X","authenticated-orcid":false,"given":"J. D.","family":"Lore","sequence":"additional","affiliation":[{"name":"Oak Ridge National Laboratory 1 , Oak Ridge, Tennessee 37831-6305,","place":["USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2160-4546","authenticated-orcid":false,"given":"M. G.","family":"O\u2019Mullane","sequence":"additional","affiliation":[{"name":"UKAEA, Culham Campus 2 , Abingdon,","place":["United Kingdom"]},{"name":"Department of Physics, University of Strathclyde 3 , Glasgow G1 1XJ,","place":["United Kingdom"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1333-6331","authenticated-orcid":false,"given":"E.","family":"Pawelec","sequence":"additional","affiliation":[{"name":"Institute of Physics, University of Opole 4 , Opole,","place":["Poland"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"K.","family":"Verhaegh","sequence":"additional","affiliation":[{"name":"Eindhoven University of Technology 5 , Eindhoven,","place":["The Netherlands"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"name":"MAST Upgrade Team","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"317","published-online":{"date-parts":[[2026,9,29]]},"reference":[{"key":"2026092908374483400_c1","doi-asserted-by":"publisher","first-page":"016014","DOI":"10.1088\/1741-4326\/aca10a","article-title":"Spectroscopic investigations of detachment on the MAST upgrade super-X divertor","volume":"63","year":"2022","journal-title":"Nucl. Fusion"},{"key":"2026092908374483400_c2","doi-asserted-by":"publisher","first-page":"065006","DOI":"10.1088\/1361-6587\/ab7432","article-title":"Interpretation of Lyman opacity measurements in JET with the ITER-like wall using a particle balance approach","volume":"62","year":"2020","journal-title":"Plasma Phys. Controlled Fusion"},{"key":"2026092908374483400_c3","doi-asserted-by":"publisher","first-page":"126023","DOI":"10.1088\/1741-4326\/acf946","article-title":"The role of plasma\u2013atom and molecule interactions on power and particle balance during detachment on the MAST upgrade super-X divertor","volume":"63","year":"2023","journal-title":"Nucl. Fusion"},{"key":"2026092908374483400_c4","author":"National Academy of Engineering and National Academies of Sciences Engineering and Medicine","year":"2021"},{"key":"2026092908374483400_c5","doi-asserted-by":"publisher","first-page":"066030","DOI":"10.1088\/1741-4326\/ac5668","article-title":"Experimental study on the role of the target electron temperature as a key parameter linking recycling to plasma performance in JET-ILW","volume":"62","year":"2022","journal-title":"Nucl. Fusion"},{"key":"2026092908374483400_c6","doi-asserted-by":"publisher","first-page":"1217","DOI":"10.1109\/tps.2018.2815283","article-title":"MAST upgrade divertor facility: A test bed for novel divertor solutions","volume":"46","year":"2018","journal-title":"IEEE Trans. Plasma Sci."},{"key":"2026092908374483400_c7","doi-asserted-by":"publisher","first-page":"065019","DOI":"10.1088\/1361-6587\/ad4058","article-title":"Benefits of the super-X divertor configuration for scenario integration on MAST upgrade","volume":"66","year":"2024","journal-title":"Plasma Phys. Controlled Fusion"},{"key":"2026092908374483400_c8","doi-asserted-by":"publisher","first-page":"10E532","DOI":"10.1063\/1.3502322","article-title":"Enhancement of JET\u2019s mirror-link near-ultraviolet to near-infrared divertor spectroscopy system","volume":"81","year":"2010","journal-title":"Rev. Sci. Instrum."},{"key":"2026092908374483400_c9","unstructured":"H. P.\n            Summers\n          , The ADAS User Manual, version 2.6, http:\/\/www.adas.ac.uk, 2004."},{"key":"2026092908374483400_c10","doi-asserted-by":"publisher","first-page":"1163","DOI":"10.1088\/0741-3335\/49\/8\/005","article-title":"Experimental verification of complete LTE plasma formation in hydrogen pellet cloud","volume":"49","year":"2007","journal-title":"Plasma Phys. Controlled Fusion"},{"key":"2026092908374483400_c11","doi-asserted-by":"publisher","first-page":"3511","DOI":"10.1088\/0022-3700\/12\/21\/009","article-title":"The bound-free photodetachment cross section of H\u2212","volume":"12","year":"1979","journal-title":"J.\u00a0Phys. B: At. Mol. Phys."},{"key":"2026092908374483400_c12","doi-asserted-by":"publisher","first-page":"2555","DOI":"10.1063\/1.872234","article-title":"Radiative and three-body recombination in the Alcator C-Mod divertor","volume":"4","year":"1997","journal-title":"Phys. Plasmas"},{"key":"2026092908374483400_c13","doi-asserted-by":"publisher","first-page":"2055","DOI":"10.1088\/0741-3335\/40\/12\/006","article-title":"Study of the discrete-to-continuum transition in a Balmer spectrum from Alcator C-Mod divertor plasmas","volume":"40","year":"1998","journal-title":"Plasma Phys. Controlled Fusion"},{"key":"2026092908374483400_c14","year":"2007"},{"key":"2026092908374483400_c15","doi-asserted-by":"publisher","first-page":"083536","DOI":"10.1063\/5.0219427","article-title":"The CXSFIT spectral fitting code: Past, present and future","volume":"95","year":"2024","journal-title":"Rev. Sci. Instrum."},{"key":"2026092908374483400_c16","doi-asserted-by":"publisher","first-page":"1058","DOI":"10.1016\/j.jnucmat.2004.10.114","article-title":"Identification of molecular carbon sources in the JET divertor by means of emission spectroscopy","volume":"337\u2013339","year":"2005","journal-title":"J.\u00a0Nucl. Mater."},{"key":"2026092908374483400_c17","doi-asserted-by":"publisher","first-page":"624","DOI":"10.1016\/j.jnucmat.2010.12.097","article-title":"Impact of nitrogen seeding on carbon erosion in the JET divertor","volume":"417","year":"2011","journal-title":"J.\u00a0Nucl. Mater."},{"key":"2026092908374483400_c18","unstructured":"C. M. Western (2018). \u201cPGOPHER version 10.1,\u201d University of Bristol Research Data Repository. https:\/\/doi.org\/10.5523\/bris.3mqfb4glgkr8a2rev7f73t300c"}],"container-title":["Review of Scientific Instruments"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/pubs.aip.org\/aip\/rsi\/article-pdf\/doi\/10.1063\/5.0350239\/21154844\/093517_1_5.0350239.pdf","content-type":"application\/pdf","content-version":"vor","intended-application":"syndication"},{"URL":"https:\/\/pubs.aip.org\/aip\/rsi\/article-pdf\/doi\/10.1063\/5.0350239\/21154844\/093517_1_5.0350239.pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,9,29]],"date-time":"2026-09-29T12:37:52Z","timestamp":1790685472000},"score":1,"resource":{"primary":{"URL":"https:\/\/pubs.aip.org\/rsi\/article\/97\/9\/093517\/3405502\/Interpretation-of-the-Balmer-series-limit"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,9,1]]},"references-count":18,"journal-issue":{"issue":"9","published-print":{"date-parts":[[2026,9,1]]}},"URL":"https:\/\/doi.org\/10.1063\/5.0350239","relation":{},"ISSN":["0034-6748","1089-7623"],"issn-type":[{"value":"0034-6748","type":"print"},{"value":"1089-7623","type":"electronic"}],"subject":[],"published-other":{"date-parts":[[2026,9]]},"published":{"date-parts":[[2026,9,1]]},"article-number":"093517"}}