Characterization of onset of parametric decay instability of lower hybrid waves
The goal of the lower hybrid current drive (LHCD) program on Alcator C-Mod is to develop and optimize ITER-relevant steady-state plasmas by controlling the current density profile. Using a 4×16 waveguide array, over 1 MW of LH power at 4.6 GHz has been successfully coupled to the plasmas. However, c...
| Main Authors: | , , , , , , , , , , , |
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| Format: | Article |
| Language: | en_US |
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American Institute of Physics (AIP)
2014
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| Online Access: | http://hdl.handle.net/1721.1/88533 https://orcid.org/0000-0002-9518-4097 https://orcid.org/0000-0003-4432-5504 https://orcid.org/0000-0002-8753-1124 https://orcid.org/0000-0001-8029-3525 https://orcid.org/0000-0002-7841-9261 https://orcid.org/0000-0002-1620-9680 https://orcid.org/0000-0001-5049-2769 |
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| author | Baek, Seung Gyou Bonoli, Paul T. Shiraiwa, Shunichi Wallace, Gregory Marriner Porkolab, Miklos Takase, Y. Brunner, Daniel Frederic Faust, Ian Charles Labombard, Brian Lau, C. Parker, R. Hubbard, Amanda E |
| author2 | Massachusetts Institute of Technology. Department of Electrical Engineering and Computer Science |
| author_facet | Massachusetts Institute of Technology. Department of Electrical Engineering and Computer Science Baek, Seung Gyou Bonoli, Paul T. Shiraiwa, Shunichi Wallace, Gregory Marriner Porkolab, Miklos Takase, Y. Brunner, Daniel Frederic Faust, Ian Charles Labombard, Brian Lau, C. Parker, R. Hubbard, Amanda E |
| author_sort | Baek, Seung Gyou |
| collection | MIT |
| description | The goal of the lower hybrid current drive (LHCD) program on Alcator C-Mod is to develop and optimize ITER-relevant steady-state plasmas by controlling the current density profile. Using a 4×16 waveguide array, over 1 MW of LH power at 4.6 GHz has been successfully coupled to the plasmas. However, current drive efficiency precipitously drops as the line averaged density (n̄ e ) increases above 10[superscript 20]m[superscript −3]. Previous numerical work shows that the observed loss of current drive efficiency in high density plasmas stems from the interactions of LH waves with edge/scrape-off layer (SOL) plasmas [Wallace et al., Physics of Plasmas 19, 062505 (2012)]. Recent observations of parametric decay instability (PDI) suggest that non-linear effects should be also taken into account to fully characterize the parasitic loss mechanisms [Baek et al., Plasma Phys. Control Fusion 55, 052001 (2013)]. In particular, magnetic configuration dependent ion cyclotron PDIs are observed using the probes near n̄[subscript e]≈1.2×10[superscript 20]m[superscript −3] . In upper single null plasmas, ion cyclotron PDI is excited near the low field side separatrix with no apparent indications of pump depletion. The observed ion cyclotron PDI becomes weaker in inner wall limited plasmas, which exhibit enhanced current drive effects. In lower single null plasmas, the dominant ion cyclotron PDI is excited near the high field side (HFS) separatrix. In this case, the onset of PDI is correlated with the decrease in pump power, indicating that pump wave power propagates to the HFS and is absorbed locally near the HFS separatrix. Comparing the observed spectra with the homogeneous growth rate calculation indicates that the observed ion cyclotron instability is excited near the plasma periphery. The incident pump power density is high enough to overcome the collisional homogeneous threshold. For C-Mod plasma parameters, the growth rate of ion sound quasi-modes is found to be typically smaller by an order of magnitude than that of ion cyclotron quasi-modes. When considering the convective threshold near the plasma edge, convective growth due to parallel coupling rather than perpendicular coupling is likely to be responsible for the observed strength of the sidebands. To demonstrate the improved LHCD efficiency in high density plasmas, an additional launcher has been designed. In conjunction with the existing launcher, this new launcher will allow access to an ITER-like high single pass absorption regime, replicating the JLH (r) expected in ITER. The predictions from the time domain discharge scenarios, in which the two launchers are used, will be also presented. |
| first_indexed | 2024-09-23T08:44:47Z |
| format | Article |
| id | mit-1721.1/88533 |
| institution | Massachusetts Institute of Technology |
| language | en_US |
| last_indexed | 2024-09-23T08:44:47Z |
| publishDate | 2014 |
| publisher | American Institute of Physics (AIP) |
| record_format | dspace |
| spelling | mit-1721.1/885332023-02-26T03:31:49Z Characterization of onset of parametric decay instability of lower hybrid waves Baek, Seung Gyou Bonoli, Paul T. Shiraiwa, Shunichi Wallace, Gregory Marriner Porkolab, Miklos Takase, Y. Brunner, Daniel Frederic Faust, Ian Charles Labombard, Brian Lau, C. Parker, R. Hubbard, Amanda E Massachusetts Institute of Technology. Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology. Department of Nuclear Science and Engineering Massachusetts Institute of Technology. Plasma Science and Fusion Center Baek, Seung Gyou Bonoli, Paul T. Parker, Ronald R. Shiraiwa, Shunichi Wallace, Gregory Marriner Porkolab, Miklos Brunner, Daniel Frederic Faust, Ian Charles Hubbard, Amanda E. Labombard, Brian Lau, C. The goal of the lower hybrid current drive (LHCD) program on Alcator C-Mod is to develop and optimize ITER-relevant steady-state plasmas by controlling the current density profile. Using a 4×16 waveguide array, over 1 MW of LH power at 4.6 GHz has been successfully coupled to the plasmas. However, current drive efficiency precipitously drops as the line averaged density (n̄ e ) increases above 10[superscript 20]m[superscript −3]. Previous numerical work shows that the observed loss of current drive efficiency in high density plasmas stems from the interactions of LH waves with edge/scrape-off layer (SOL) plasmas [Wallace et al., Physics of Plasmas 19, 062505 (2012)]. Recent observations of parametric decay instability (PDI) suggest that non-linear effects should be also taken into account to fully characterize the parasitic loss mechanisms [Baek et al., Plasma Phys. Control Fusion 55, 052001 (2013)]. In particular, magnetic configuration dependent ion cyclotron PDIs are observed using the probes near n̄[subscript e]≈1.2×10[superscript 20]m[superscript −3] . In upper single null plasmas, ion cyclotron PDI is excited near the low field side separatrix with no apparent indications of pump depletion. The observed ion cyclotron PDI becomes weaker in inner wall limited plasmas, which exhibit enhanced current drive effects. In lower single null plasmas, the dominant ion cyclotron PDI is excited near the high field side (HFS) separatrix. In this case, the onset of PDI is correlated with the decrease in pump power, indicating that pump wave power propagates to the HFS and is absorbed locally near the HFS separatrix. Comparing the observed spectra with the homogeneous growth rate calculation indicates that the observed ion cyclotron instability is excited near the plasma periphery. The incident pump power density is high enough to overcome the collisional homogeneous threshold. For C-Mod plasma parameters, the growth rate of ion sound quasi-modes is found to be typically smaller by an order of magnitude than that of ion cyclotron quasi-modes. When considering the convective threshold near the plasma edge, convective growth due to parallel coupling rather than perpendicular coupling is likely to be responsible for the observed strength of the sidebands. To demonstrate the improved LHCD efficiency in high density plasmas, an additional launcher has been designed. In conjunction with the existing launcher, this new launcher will allow access to an ITER-like high single pass absorption regime, replicating the JLH (r) expected in ITER. The predictions from the time domain discharge scenarios, in which the two launchers are used, will be also presented. United States. Dept. of Energy (Award No. DE-FC02-99ER54512) United States. Dept. of Energy (Award No. DE-AC02-76CH03073) 2014-08-05T13:58:17Z 2014-08-05T13:58:17Z 2014 Article http://purl.org/eprint/type/JournalArticle http://hdl.handle.net/1721.1/88533 Baek, S. G., P. T. Bonoli, R. R. Parker, S. Shiraiwa, G. M. Wallace, M. Porkolab, Y. Takase, et al. “Characterization of Onset of Parametric Decay Instability of Lower Hybrid Waves” (2014). https://orcid.org/0000-0002-9518-4097 https://orcid.org/0000-0003-4432-5504 https://orcid.org/0000-0002-8753-1124 https://orcid.org/0000-0001-8029-3525 https://orcid.org/0000-0002-7841-9261 https://orcid.org/0000-0002-1620-9680 https://orcid.org/0000-0001-5049-2769 en_US http://dx.doi.org/10.1063/1.4864510 AIP Conference Proceedings Creative Commons Attribution-Noncommercial-Share Alike http://creativecommons.org/licenses/by-nc-sa/4.0/ application/pdf American Institute of Physics (AIP) MIT web domain |
| spellingShingle | Baek, Seung Gyou Bonoli, Paul T. Shiraiwa, Shunichi Wallace, Gregory Marriner Porkolab, Miklos Takase, Y. Brunner, Daniel Frederic Faust, Ian Charles Labombard, Brian Lau, C. Parker, R. Hubbard, Amanda E Characterization of onset of parametric decay instability of lower hybrid waves |
| title | Characterization of onset of parametric decay instability of lower hybrid waves |
| title_full | Characterization of onset of parametric decay instability of lower hybrid waves |
| title_fullStr | Characterization of onset of parametric decay instability of lower hybrid waves |
| title_full_unstemmed | Characterization of onset of parametric decay instability of lower hybrid waves |
| title_short | Characterization of onset of parametric decay instability of lower hybrid waves |
| title_sort | characterization of onset of parametric decay instability of lower hybrid waves |
| url | http://hdl.handle.net/1721.1/88533 https://orcid.org/0000-0002-9518-4097 https://orcid.org/0000-0003-4432-5504 https://orcid.org/0000-0002-8753-1124 https://orcid.org/0000-0001-8029-3525 https://orcid.org/0000-0002-7841-9261 https://orcid.org/0000-0002-1620-9680 https://orcid.org/0000-0001-5049-2769 |
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