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Characterizing Desorbed Surface Contaminants Leading to Plasma Formation in Power Feeds of Pulsed Power Accelerators
Characterizing Desorbed Surface Contaminants Leading to Plasma Formation in Power Feeds of Pulsed Power Accelerators
상세정보
- 자료유형
- 학위논문 서양
- 최종처리일시
- 20260202105235
- ISBN
- 9798291567784
- DDC
- 530
- 서명/저자
- Characterizing Desorbed Surface Contaminants Leading to Plasma Formation in Power Feeds of Pulsed Power Accelerators
- 발행사항
- [Sl] : University of Michigan, 2025
- 발행사항
- Ann Arbor : ProQuest Dissertations & Theses, 2025
- 형태사항
- 204 p
- 주기사항
- Source: Dissertations Abstracts International, Volume: 87-02, Section: B.
- 주기사항
- Advisor: McBride, Ryan David.
- 학위논문주기
- Thesis (Ph.D.)--University of Michigan, 2025.
- 초록/해제
- 요약The Z machine at Sandia National Laboratories delivers a 20-30 MA current pulse to various experimental load configurations in as little as 100 ns. The pulse is transported to the load via magnetically insulated transmission lines (MITLs), which are nominally vacuum filled. However, measurements show that plasma forms in the MITLs and that not all the current makes it to the load.It is suspected that under shot ready vacuum conditions ( 3x10−5 Torr), a few monolayers of contaminants, particularly water, are present on the surfaces of the MITL electrodes. This is supported by previous visible spectroscopy measurements in the post-hole convolute and inner MITL regions on Z. As the current pulse ohmically heats the electrode material, the neutral surface contaminants ionize and break down into a plasma that can conduct current across the anode-cathode gap, limiting the total current delivered to the load.The goal of this dissertation research was to develop new techniques to study and characterize low-density power feed plasmas relevant to the Z facility using smaller and more accessible pulsed power drivers, such as the 1-MA, 100-ns MAIZE facility at the University of Michigan and the 1-MA, 100-ns Mykonos facility at Sandia National Laboratories. The hope is that some of the techniques developed (e.g., VUV spectroscopy) can be transferred to the Z facility in the future. A significant challenge to this research, however, is that on 1-MA-scale facilities, the electrode heating rates are typically not sufficient for generating detectable levels of low-density power feed plasma. Thus, the first step in this dissertation research was to develop a new platform for 1-MA drivers that mimics the electrode plasma formation found on the much larger Z facility. The new platform developed consists of a stripline structure that uses thin-foil electrode surfaces (5-500 μm thick) to increase the current densities and local heating rates in 1-MA-scale experiments. The foils are backed by 3D printed dielectric structures to maintain electrode shape during the experiment. By varying the foil thickness, the current density and heating rates are controlled. Using this platform on MAIZE, high-speed imaging revealed gap-closure velocities of 1-10 cm/μs, which is comparable to the gap-closure velocities found on Z.With the platform developed, the aim of this research then shifted to identifying and quantifying the contaminant species that desorb off the thin-foil stripline surfaces during 1-MA discharges. With the ultimate goal being to understand how desorbed neutral contaminants affect the breakdown process, vacuum-ultraviolet (VUV) and visible-light spectroscopy were used to measure the neutral densities and temperatures of contaminant species within the stripline structure before, during, and after breakdown.For this dissertation, the neutral atomic hydrogen density with spatial resolution across the stripline anode-cathode gap was measured. This was done using a gated vacuum ultraviolet spectrometer to collect and analyze the absolute line intensity of the hydrogen Lyman-a transition. The VUV spectra collected prior to breakdown show a Lyman-a transition density of 109-1010 transitions/cm3, indicating an atomic hydrogen number density of 1012-1013 particles/cm3. After breakdown, a Lyman-a transition density of 1011-1012 transitions/cm3, was measured indicating that the neutral hydrogen number density had increased to 1013- 1014 particles/cm3. The ratios between molecular hydrogen bands indicates that the temperature is in the range of 5000-6000 K before breakdown and 5000-9000 K after breakdown.From the post-breakdown VUV measurements, there is a correlation between the decrease in transition densities of the lower order molecular hydrogen Lyman band, an increase in transition densities of the higher order molecular hydrogen Werner band, and an increase in the atomic hydrogen Lyman-α transition densities. This shows shows a distinct change in energetics of the neutrals present, as the pathways for molecular hydrogen dissociation into atomic hydrogen through collisions with electrons occur at higher temperatures. This change in energetics, leading to a change in molecular and atomic populations, can be seen in the population rate coefficients from collisional radiative modeling. Additionally, after breakdown, the VUV data show that atomic and molecular hydrogen is still present in the anode-cathode gap, indicating that not all of the contaminant particles are ionized after breakdown, as previously thought.Streaked visible spectroscopy (SVS) was used to collect graybody spectra from the stripline's cathode surface. This was done by focusing the SVS collection optics onto the cathode surface and using a line of sight with at least a small component normal to the cathode surface. From the graybody data collected after breakdown (i.e., after plasma formation), plasma temperatures in the range of 1-2 eV were inferred.The SVS system was also fielded with a side-on view of the stripline's anode-cathode gap (i.e., with a line of sight that is orthogonal to the plane set by the stripline's gap). This was done to collect line-emission spectra from the plasma that filled the space between the stripline's anode and cathode. The line-emission spectra was used to identify the various species present. For example, early in time, oxygen was found to be present. The oxygen's presence then persisted into late times, when iron became detectable, indicating that the stripline's foil surface had melted, and when gaseous and ionized elements of the foil material had begun to cross the anode-cathode gap.The experimental data presented in this dissertation will be helpful to researchers who are presently developing models of contaminant plasma formation in high-power MITLs.
- 일반주제명
- Physics
- 일반주제명
- Electromagnetics
- 일반주제명
- Plasma physics
- 일반주제명
- Optics
- 키워드
- Plasma formation
- 키워드
- Spectroscopy
- 기타저자
- University of Michigan Nuclear Engineering & Radiological Sciences
- 기본자료저록
- Dissertations Abstracts International. 87-02B.
- 전자적 위치 및 접속
- 로그인 후 원문을 볼 수 있습니다.
MARC
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■020 ▼a9798291567784
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■035 ▼a(MiAaPQ)umichrackham006477
■040 ▼aMiAaPQ▼cMiAaPQ
■0820 ▼a530
■1001 ▼aSmith, Trevor Johannes.
■24510▼aCharacterizing Desorbed Surface Contaminants Leading to Plasma Formation in Power Feeds of Pulsed Power Accelerators
■260 ▼a[Sl]▼bUniversity of Michigan▼c2025
■260 1▼aAnn Arbor▼bProQuest Dissertations & Theses▼c2025
■300 ▼a204 p
■500 ▼aSource: Dissertations Abstracts International, Volume: 87-02, Section: B.
■500 ▼aAdvisor: McBride, Ryan David.
■5021 ▼aThesis (Ph.D.)--University of Michigan, 2025.
■520 ▼aThe Z machine at Sandia National Laboratories delivers a 20-30 MA current pulse to various experimental load configurations in as little as 100 ns. The pulse is transported to the load via magnetically insulated transmission lines (MITLs), which are nominally vacuum filled. However, measurements show that plasma forms in the MITLs and that not all the current makes it to the load.It is suspected that under shot ready vacuum conditions ( 3x10−5 Torr), a few monolayers of contaminants, particularly water, are present on the surfaces of the MITL electrodes. This is supported by previous visible spectroscopy measurements in the post-hole convolute and inner MITL regions on Z. As the current pulse ohmically heats the electrode material, the neutral surface contaminants ionize and break down into a plasma that can conduct current across the anode-cathode gap, limiting the total current delivered to the load.The goal of this dissertation research was to develop new techniques to study and characterize low-density power feed plasmas relevant to the Z facility using smaller and more accessible pulsed power drivers, such as the 1-MA, 100-ns MAIZE facility at the University of Michigan and the 1-MA, 100-ns Mykonos facility at Sandia National Laboratories. The hope is that some of the techniques developed (e.g., VUV spectroscopy) can be transferred to the Z facility in the future. A significant challenge to this research, however, is that on 1-MA-scale facilities, the electrode heating rates are typically not sufficient for generating detectable levels of low-density power feed plasma. Thus, the first step in this dissertation research was to develop a new platform for 1-MA drivers that mimics the electrode plasma formation found on the much larger Z facility. The new platform developed consists of a stripline structure that uses thin-foil electrode surfaces (5-500 μm thick) to increase the current densities and local heating rates in 1-MA-scale experiments. The foils are backed by 3D printed dielectric structures to maintain electrode shape during the experiment. By varying the foil thickness, the current density and heating rates are controlled. Using this platform on MAIZE, high-speed imaging revealed gap-closure velocities of 1-10 cm/μs, which is comparable to the gap-closure velocities found on Z.With the platform developed, the aim of this research then shifted to identifying and quantifying the contaminant species that desorb off the thin-foil stripline surfaces during 1-MA discharges. With the ultimate goal being to understand how desorbed neutral contaminants affect the breakdown process, vacuum-ultraviolet (VUV) and visible-light spectroscopy were used to measure the neutral densities and temperatures of contaminant species within the stripline structure before, during, and after breakdown.For this dissertation, the neutral atomic hydrogen density with spatial resolution across the stripline anode-cathode gap was measured. This was done using a gated vacuum ultraviolet spectrometer to collect and analyze the absolute line intensity of the hydrogen Lyman-a transition. The VUV spectra collected prior to breakdown show a Lyman-a transition density of 109-1010 transitions/cm3, indicating an atomic hydrogen number density of 1012-1013 particles/cm3. After breakdown, a Lyman-a transition density of 1011-1012 transitions/cm3, was measured indicating that the neutral hydrogen number density had increased to 1013- 1014 particles/cm3. The ratios between molecular hydrogen bands indicates that the temperature is in the range of 5000-6000 K before breakdown and 5000-9000 K after breakdown.From the post-breakdown VUV measurements, there is a correlation between the decrease in transition densities of the lower order molecular hydrogen Lyman band, an increase in transition densities of the higher order molecular hydrogen Werner band, and an increase in the atomic hydrogen Lyman-α transition densities. This shows shows a distinct change in energetics of the neutrals present, as the pathways for molecular hydrogen dissociation into atomic hydrogen through collisions with electrons occur at higher temperatures. This change in energetics, leading to a change in molecular and atomic populations, can be seen in the population rate coefficients from collisional radiative modeling. Additionally, after breakdown, the VUV data show that atomic and molecular hydrogen is still present in the anode-cathode gap, indicating that not all of the contaminant particles are ionized after breakdown, as previously thought.Streaked visible spectroscopy (SVS) was used to collect graybody spectra from the stripline's cathode surface. This was done by focusing the SVS collection optics onto the cathode surface and using a line of sight with at least a small component normal to the cathode surface. From the graybody data collected after breakdown (i.e., after plasma formation), plasma temperatures in the range of 1-2 eV were inferred.The SVS system was also fielded with a side-on view of the stripline's anode-cathode gap (i.e., with a line of sight that is orthogonal to the plane set by the stripline's gap). This was done to collect line-emission spectra from the plasma that filled the space between the stripline's anode and cathode. The line-emission spectra was used to identify the various species present. For example, early in time, oxygen was found to be present. The oxygen's presence then persisted into late times, when iron became detectable, indicating that the stripline's foil surface had melted, and when gaseous and ionized elements of the foil material had begun to cross the anode-cathode gap.The experimental data presented in this dissertation will be helpful to researchers who are presently developing models of contaminant plasma formation in high-power MITLs.
■590 ▼aSchool code: 0127.
■650 4▼aPhysics
■650 4▼aElectromagnetics
■650 4▼aPlasma physics
■650 4▼aOptics
■653 ▼aSurface contaminants
■653 ▼aPlasma formation
■653 ▼aPulsed power accelerators
■653 ▼aMagnetically insulated transmission lines
■653 ▼aSpectroscopy
■690 ▼a0605
■690 ▼a0752
■690 ▼a0607
■690 ▼a0759
■71020▼aUniversity of Michigan▼bNuclear Engineering & Radiological Sciences.
■7730 ▼tDissertations Abstracts International▼g87-02B.
■790 ▼a0127
■791 ▼aPh.D.
■792 ▼a2025
■793 ▼aEnglish
■85640▼uhttp://www.riss.kr/pdu/ddodLink.do?id=T17359916▼nKERIS▼z이 자료의 원문은 한국교육학술정보원에서 제공합니다.
