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Effect of Electrode Bias on Confinement and Stability in WHAM
Effect of Electrode Bias on Confinement and Stability in WHAM
상세정보
- 자료유형
- 학위논문 서양
- 최종처리일시
- 20260202105201
- ISBN
- 9798265451446
- DDC
- 530
- 저자명
- Qian, Tony.
- 서명/저자
- Effect of Electrode Bias on Confinement and Stability in WHAM
- 발행사항
- [Sl] : Princeton University, 2025
- 발행사항
- Ann Arbor : ProQuest Dissertations & Theses, 2025
- 형태사항
- 157 p
- 주기사항
- Source: Dissertations Abstracts International, Volume: 87-06, Section: B.
- 주기사항
- Advisor: Zarnstorff, Michael;Forest, Cary.
- 학위논문주기
- Thesis (Ph.D.)--Princeton University, 2025.
- 초록/해제
- 요약This is the first thesis to describe construction and physics results from WHAM, a 17 T axisymmetric mirror with a steady-state field produced by High Temperature Superconductor (HTS) coils and MW-class plasma heating systems. The high-field axisymmetric mirror is an attractive alternative to tokamaks and stellarators for magnetic confinement fusion because of its simple linear geometry, confinement of high-beta plasma with relatively small regions of high-field, and the potential to avoid plasma turbulence through large ion orbits and direct manipulation of radial electric fields through electrode bias along open field lines. This dissertation explores the use of electrode bias in the Wisconsin HTS Axisymmetric Mirror (WHAM).Electrode bias of ECH plasmas confirm the stabilization of density fluctuations and end cell particle flux, as seen in previous mirror experiments. New observations show that there exists a bias voltage threshold at which the stored energy doubles, and that the threshold exists for both positive and negative radial electric fields, depending on the electrode configuration. This suggests that it is the amplitude of bias current rather than the direction of rotation that enhances confinement. Impurity ion rotation is observed through optical emission spectroscopy. A two-fluid model is proposed, using gyroviscous-like forces, to explain the observed plasma impedance and rotation.In NBI experiments, bias is observed to be critical for sustaining any beam driven plasma. Analysis of soft x-ray photodiode and fast camera imaging indicate that the fluctuations in the plasma column centroid and radius are stabilized. We discover that a surprisingly sharp threshold in bias voltage separates successful NBI sustainment from a plasma that collapses without ECH. The bias threshold is observed to vary weakly with ECH power but strongly with target plasma density.Anisotropic MHD equilibria are reconstructed for fast electron and fast ion plasmas. We show that the measured axial pressure distribution p⊥(z) in fast-electron plasmas are consistent with that of a sloshing electron distribution injected at 15 degrees. We show, by using the axial pressure and radial density profiles, that the average ion energy in the highest temperature shots to date are bounded between 500 and 2,000 eV, depending on the radial peaking factor. For a separate shot, we show that the peak perpendicular pressure exceeds beta_perp 10%.Linear stability calculations are underway using the reconstructed equilibrium data in the FLORA framework.The overall conclusions of this thesis are: (i) electrode bias increases stored energy and electron density of a plasma with heating and fueling otherwise unchanged. (ii) the mechanism for confinement enhancement is plasma stability as measured by reduced fluctuation amplitude. (iii) while bias is observed to drive rotation, in the case of NBI heating, rotation alone is not sufficient to explain the threshold for increased plasma parameters. Instead, rotation is principally useful for stability of the bulk plasma and maintaining a minimum density that allows NBI absorption to be high enough for sustainment.
- 일반주제명
- Plasma physics
- 일반주제명
- Applied physics
- 일반주제명
- Astrophysics
- 키워드
- Electrode bias
- 키워드
- Magnetic mirror
- 기타저자
- Princeton University Astrophysical Sciences-Plasma Physics Program
- 기본자료저록
- Dissertations Abstracts International. 87-06B.
- 전자적 위치 및 접속
- 로그인 후 원문을 볼 수 있습니다.
MARC
008260126s2025 us c eng d■001000017359706
■00520260202105201
■006m o d
■007cr#unu||||||||
■020 ▼a9798265451446
■035 ▼a(MiAaPQ)AAI32244974
■040 ▼aMiAaPQ▼cMiAaPQ
■0820 ▼a530
■1001 ▼aQian, Tony.
■24510▼aEffect of Electrode Bias on Confinement and Stability in WHAM
■260 ▼a[Sl]▼bPrinceton University▼c2025
■260 1▼aAnn Arbor▼bProQuest Dissertations & Theses▼c2025
■300 ▼a157 p
■500 ▼aSource: Dissertations Abstracts International, Volume: 87-06, Section: B.
■500 ▼aAdvisor: Zarnstorff, Michael;Forest, Cary.
■5021 ▼aThesis (Ph.D.)--Princeton University, 2025.
■520 ▼aThis is the first thesis to describe construction and physics results from WHAM, a 17 T axisymmetric mirror with a steady-state field produced by High Temperature Superconductor (HTS) coils and MW-class plasma heating systems. The high-field axisymmetric mirror is an attractive alternative to tokamaks and stellarators for magnetic confinement fusion because of its simple linear geometry, confinement of high-beta plasma with relatively small regions of high-field, and the potential to avoid plasma turbulence through large ion orbits and direct manipulation of radial electric fields through electrode bias along open field lines. This dissertation explores the use of electrode bias in the Wisconsin HTS Axisymmetric Mirror (WHAM).Electrode bias of ECH plasmas confirm the stabilization of density fluctuations and end cell particle flux, as seen in previous mirror experiments. New observations show that there exists a bias voltage threshold at which the stored energy doubles, and that the threshold exists for both positive and negative radial electric fields, depending on the electrode configuration. This suggests that it is the amplitude of bias current rather than the direction of rotation that enhances confinement. Impurity ion rotation is observed through optical emission spectroscopy. A two-fluid model is proposed, using gyroviscous-like forces, to explain the observed plasma impedance and rotation.In NBI experiments, bias is observed to be critical for sustaining any beam driven plasma. Analysis of soft x-ray photodiode and fast camera imaging indicate that the fluctuations in the plasma column centroid and radius are stabilized. We discover that a surprisingly sharp threshold in bias voltage separates successful NBI sustainment from a plasma that collapses without ECH. The bias threshold is observed to vary weakly with ECH power but strongly with target plasma density.Anisotropic MHD equilibria are reconstructed for fast electron and fast ion plasmas. We show that the measured axial pressure distribution p⊥(z) in fast-electron plasmas are consistent with that of a sloshing electron distribution injected at 15 degrees. We show, by using the axial pressure and radial density profiles, that the average ion energy in the highest temperature shots to date are bounded between 500 and 2,000 eV, depending on the radial peaking factor. For a separate shot, we show that the peak perpendicular pressure exceeds beta_perp 10%.Linear stability calculations are underway using the reconstructed equilibrium data in the FLORA framework.The overall conclusions of this thesis are: (i) electrode bias increases stored energy and electron density of a plasma with heating and fueling otherwise unchanged. (ii) the mechanism for confinement enhancement is plasma stability as measured by reduced fluctuation amplitude. (iii) while bias is observed to drive rotation, in the case of NBI heating, rotation alone is not sufficient to explain the threshold for increased plasma parameters. Instead, rotation is principally useful for stability of the bulk plasma and maintaining a minimum density that allows NBI absorption to be high enough for sustainment.
■590 ▼aSchool code: 0181.
■650 4▼aPlasma physics
■650 4▼aApplied physics
■650 4▼aAstrophysics
■653 ▼aElectrode bias
■653 ▼aEquilibrium reconstruction
■653 ▼aMagnetic mirror
■653 ▼aHigh Temperature Superconductor
■690 ▼a0759
■690 ▼a0596
■690 ▼a0215
■71020▼aPrinceton University▼bAstrophysical Sciences-Plasma Physics Program.
■7730 ▼tDissertations Abstracts International▼g87-06B.
■790 ▼a0181
■791 ▼aPh.D.
■792 ▼a2025
■793 ▼aEnglish
■85640▼uhttp://www.riss.kr/pdu/ddodLink.do?id=T17359706▼nKERIS▼z이 자료의 원문은 한국교육학술정보원에서 제공합니다.
