The effect of divertor closure on detachment onset in DIII-D
Experiments at DIII-D use different divertor geometries to measure the effect of divertor closure on detachment onset. We compare matched H-mode discharges in the closed (upper) divertor and the open (lower) divertor and use as a detachment onset metric the rollover in peak ion flux to the target, J...
| Main Authors: | , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Elsevier
2019-05-01
|
| Series: | Nuclear Materials and Energy |
| Online Access: | http://www.sciencedirect.com/science/article/pii/S2352179118302576 |
| _version_ | 1828864596303151104 |
|---|---|
| author | A.L. Moser A.W. Leonard A.G. McLean H.Q. Wang J.G. Watkins |
| author_facet | A.L. Moser A.W. Leonard A.G. McLean H.Q. Wang J.G. Watkins |
| author_sort | A.L. Moser |
| collection | DOAJ |
| description | Experiments at DIII-D use different divertor geometries to measure the effect of divertor closure on detachment onset. We compare matched H-mode discharges in the closed (upper) divertor and the open (lower) divertor and use as a detachment onset metric the rollover in peak ion flux to the target, Jsat, as a function of upstream pedestal top density, ne,ped. Measurements of electron temperature in the lower divertor confirm that this metric captures the transition from attached to detached divertor for this data set. Experiments at two different neutral beam injection powers demonstrate an ≈ 20–40% decrease in pedestal density at detachment onset in the closed case compared to the open. High-resolution edge density and temperature measurements and power balance analysis allow us to determine the difference in upstream separatrix density ne,sep at detachment onset, which we find to be ≈ 15–25% lower in the closed divertor case. The effect of closure on detachment seen in separatrix density is hence only about 60–75% the effect seen in pedestal density, with the remainder due to differences in ne,sep/ne,ped. Future devices are expected to have a scrape off layer that is opaque to neutrals, and hence will not have the same pedestal fueling to affect ne,sep/ne,ped; this suggests that the effect of closure on detachment onset seen in future devices will be less than that seen in current experiments, and closer to the magnitude of the effect we see here in the separatrix for a similar degree of divertor closure. Keywords: Tokamak, Divertor, Detachment, Fusion |
| first_indexed | 2024-12-13T04:10:51Z |
| format | Article |
| id | doaj.art-789d6e7107f14e35a2b25e0aef7e15d9 |
| institution | Directory Open Access Journal |
| issn | 2352-1791 |
| language | English |
| last_indexed | 2024-12-13T04:10:51Z |
| publishDate | 2019-05-01 |
| publisher | Elsevier |
| record_format | Article |
| series | Nuclear Materials and Energy |
| spelling | doaj.art-789d6e7107f14e35a2b25e0aef7e15d92022-12-22T00:00:05ZengElsevierNuclear Materials and Energy2352-17912019-05-01196771The effect of divertor closure on detachment onset in DIII-DA.L. Moser0A.W. Leonard1A.G. McLean2H.Q. Wang3J.G. Watkins4Corresponding author.; General Atomics, San Diego, CA 92186, USAGeneral Atomics, San Diego, CA 92186, USALawrence Livermore National Laboratory, Livermore, CA 94550, USAGeneral Atomics, San Diego, CA 92186, USASandia National Laboratory, Albuquerque, NM 87185, USAExperiments at DIII-D use different divertor geometries to measure the effect of divertor closure on detachment onset. We compare matched H-mode discharges in the closed (upper) divertor and the open (lower) divertor and use as a detachment onset metric the rollover in peak ion flux to the target, Jsat, as a function of upstream pedestal top density, ne,ped. Measurements of electron temperature in the lower divertor confirm that this metric captures the transition from attached to detached divertor for this data set. Experiments at two different neutral beam injection powers demonstrate an ≈ 20–40% decrease in pedestal density at detachment onset in the closed case compared to the open. High-resolution edge density and temperature measurements and power balance analysis allow us to determine the difference in upstream separatrix density ne,sep at detachment onset, which we find to be ≈ 15–25% lower in the closed divertor case. The effect of closure on detachment seen in separatrix density is hence only about 60–75% the effect seen in pedestal density, with the remainder due to differences in ne,sep/ne,ped. Future devices are expected to have a scrape off layer that is opaque to neutrals, and hence will not have the same pedestal fueling to affect ne,sep/ne,ped; this suggests that the effect of closure on detachment onset seen in future devices will be less than that seen in current experiments, and closer to the magnitude of the effect we see here in the separatrix for a similar degree of divertor closure. Keywords: Tokamak, Divertor, Detachment, Fusionhttp://www.sciencedirect.com/science/article/pii/S2352179118302576 |
| spellingShingle | A.L. Moser A.W. Leonard A.G. McLean H.Q. Wang J.G. Watkins The effect of divertor closure on detachment onset in DIII-D Nuclear Materials and Energy |
| title | The effect of divertor closure on detachment onset in DIII-D |
| title_full | The effect of divertor closure on detachment onset in DIII-D |
| title_fullStr | The effect of divertor closure on detachment onset in DIII-D |
| title_full_unstemmed | The effect of divertor closure on detachment onset in DIII-D |
| title_short | The effect of divertor closure on detachment onset in DIII-D |
| title_sort | effect of divertor closure on detachment onset in diii d |
| url | http://www.sciencedirect.com/science/article/pii/S2352179118302576 |
| work_keys_str_mv | AT almoser theeffectofdivertorclosureondetachmentonsetindiiid AT awleonard theeffectofdivertorclosureondetachmentonsetindiiid AT agmclean theeffectofdivertorclosureondetachmentonsetindiiid AT hqwang theeffectofdivertorclosureondetachmentonsetindiiid AT jgwatkins theeffectofdivertorclosureondetachmentonsetindiiid AT almoser effectofdivertorclosureondetachmentonsetindiiid AT awleonard effectofdivertorclosureondetachmentonsetindiiid AT agmclean effectofdivertorclosureondetachmentonsetindiiid AT hqwang effectofdivertorclosureondetachmentonsetindiiid AT jgwatkins effectofdivertorclosureondetachmentonsetindiiid |