Modeling magnetically insulated devices using flow impedance

Mendel, C. W.; Rosenthal, S.E.

doi:10.1063/1.871345

Cited by 101 publications

(46 citation statements)

References 14 publications

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“…8 and its separation from the anode is associated with the flow impedance of the MITL [21]. For strongly insulated systems, this value is close to the vacuum impedance of the line, resulting from an electron sheath close to the cathode surface.…”

Section: Particle-in-cell Simulationsmentioning

confidence: 92%

“…where Z f , the flow impedance [21], is the effective wave impedance associated with the distance between the anode and the location of the electron sheath (or the centroid of the sheath if the sheath has non-negligible thickness). If the electron sheath is close to the cathode, the flow impedance approaches the vacuum impedance.…”

Section: -4mentioning

confidence: 99%

“…z for a coaxial line), and the inductance per unit length is equal to the wave impedance, Z v , divided by the wave propagation velocity in vacuum, c. The spatial distribution of the MITL's anode potential is directly related to this inductance profile. We assume that at each position, the anode and cathode currents can be expressed in terms of the line voltage, V a , through local electromagnetic pressure-balance considerations [15,21],…”

Section: A Impedance Profilesmentioning

confidence: 99%

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Tailoring of electron flow current in magnetically insulated transmission lines

Martin

Savage

Pointon

et al. 2009

Phys. Rev. ST Accel. Beams

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It is desirable to optimize (minimizing both the inductance and electron flow) the magnetically insulated vacuum sections of low impedance pulsed-power drivers. The goal of low inductance is understandable from basic efficiency arguments. The goal of low electron flow results from two observations: (1) flowing electrons generally do not deliver energy to (or even reach) most loads, and thus constitute a loss mechanism; (2) energetic electrons deposited in a small area can cause anode damage and anode plasma formation. Low inductance and low electron flow are competing goals; an optimized system requires a balance of the two. While magnetically insulated systems are generally forgiving, there are times when optimization is crucial. For example, in large pulsed-power drivers used to energize high energy density physics loads, the electron flow as a fraction of total current is small, but that flow often reaches the anode in relatively small regions. If the anode temperature becomes high enough to desorb gas, the resulting plasma initiates a gap closure process that can impact system performance. Magnetic-pressure driven (z pinches and material equation of state) loads behave like a fixed inductor for much of the drive pulse. It is clear that neither fixed gap nor constant-impedance transmission lines are optimal for driving inductive loads. This work shows a technique for developing the optimal impedance profile for the magnetically insulated section of a high-current driver. Particle-in-cell calculations are used to validate the impedance profiles developed in a radial disk magnetically insulated transmission line geometry. The input parameters are the spacing and location of the minimum gap, the effective load inductance, and the desired electron flow profile. The radial electron flow profiles from these simulations are in good agreement with theoretical predictions when driven at relatively high voltage (i.e., V ! 2 MV).

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Section: Particle-in-cell Simulationsmentioning

confidence: 92%

Section: -4mentioning

confidence: 99%

Section: A Impedance Profilesmentioning

confidence: 99%

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Tailoring of electron flow current in magnetically insulated transmission lines

Martin

Savage

Pointon

et al. 2009

Phys. Rev. ST Accel. Beams

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“…The magnetic drive pressure for 60MA through a 0.254 cm radius capsule after converging a factor of 12 is 8x10 14 Pa--which is equivalent to an ablation pressure of 868 eV.…”

Section: Qsdd2-quasi Spherical Direct Drive Single Shell Capsulesmentioning

confidence: 99%

Quasi-spherical direct drive fusion.

VanDevender¹,

Abbott²,

Langston³

et al. 2007

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We present designs of quasi-spherical direct drive z-pinch loads for machines such as ZR at 28 MA load current with a 150 ns implosion time (QSDD1). A double shell system for ZR has produced a 2D simulated yield of 12 MJ, but the drive for this system on ZR has essentially no margin. A double shell system for a 56 MA driver at 150 ns implosion has produced a simulated yield of 130 MJ with considerable margin in attaining the necessary temperature and density-radius product for ignition. We also present designs for a magnetically insulated current amplifier, (MICA), that modify the attainable ZR load current to 36 MA with a 28 ns rise time. The faster pulse provided by a MICA makes it possible to drive quasispherical single shell implosions (QSDD2). We will present results from 1D LASNEX and 2D MACH2 simulations of promising low-adiabat cryogenic QSDD2 capsules and 1D LASNEX results of high-adiabat cryogenic QSDD2 capsules. 4 5

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“…A low MITL impedance is advantageous for a z-pinch IFE system as it minimizes the inductance between the driver and the load; thus, the voltage generated by dI/dt (required to drive the z-pinch) is minimized [15]. The effective impedance of the MITL is described best by the flow impedance Z f , which is a function of both the geometry and the voltage [16][17][18][19][20][21][22][23][24] and is less than the vacuum impedance of the line Z 0 because of the distributed electron current. Additionally, high current resistively heats the electrode surfaces; when the anode surface is heated above T = 400° C [25][26][27][28][29][30], ions are emitted.…”

Section: Recyclable Transmission Line (Rtl) (C L Olson Snl)mentioning

confidence: 99%

Recyclable transmission line (RTL) and linear transformer driver (LTD) development for Z-pinch inertial fusion energy (Z-IFE) and high yield.

Sharpe¹,

Kingsep

Smith³

et al. 2007

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Z-Pinch Inertial Fusion Energy (Z-IFE) complements and extends the single-shot zpinch fusion program on Z to a repetitive, high-yield, power plant scenario that can be used for the production of electricity, transmutation of nuclear waste, and hydrogen production, all with no CO 2 production and no long-lived radioactive nuclear waste. The Z-IFE concept uses a Linear Transformer Driver (LTD) accelerator, and a Recyclable Transmission Line (RTL) to connect the LTD driver to a high-yield fusion target inside a thick-liquid-wall power plant chamber.Results of RTL and LTD research are reported here, that include: (1) The key physics issues for RTLs involve the power flow at the high linear current densities that occur near the target (up to 5 MA/cm). These issues include surface heating, melting, ablation, plasma formation, electron flow, magnetic insulation, conductivity changes, magnetic field diffusion changes, possible ion flow, and RTL mass motion. These issues are studied theoretically, computationally (with the ALEGRA and LSP codes), and 4 will work at 5 MA/cm or higher, with anode-cathode gaps as small as 2 mm. (2) An RTL misalignment sensitivity study has been performed using a 3D circuit model. Results show very small load current variations for significant RTL misalignments. (3) The key structural issues for RTLs involve optimizing the RTL strength (varying shape, ribs, etc.) while minimizing the RTL mass. Optimization studies show RTL mass reductions by factors of three or more. (4) Fabrication and pressure testing of Z-PoP (Proof-ofPrinciple) size RTLs are successfully reported here. (5) Modeling of the effect of initial RTL imperfections on the buckling pressure has been performed. Results show that the curved RTL offers a much greater buckling pressure as well as less sensitivity to imperfections than three other RTL designs. (6) Repetitive operation of a 0.5 MA, 100 kV, 100 ns, LTD cavity with gas purging between shots and automated operation is demonstrated at the SNL Z-IFE LTD laboratory with rep-rates up to 10.3 seconds between shots (this is essentially at the goal of 10 seconds for Z-IFE). (7) A single LTD switch at Tomsk was fired repetitively every 12 seconds for 36,000 shots with no failures. Present results from all of these power flow studies validate the whole LTD/RTL concept for single-shot ICF high yield, and for repetitive-shot IFE.

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Modeling magnetically insulated devices using flow impedance

Cited by 101 publications

References 14 publications

Tailoring of electron flow current in magnetically insulated transmission lines

Tailoring of electron flow current in magnetically insulated transmission lines

Quasi-spherical direct drive fusion.

Recyclable transmission line (RTL) and linear transformer driver (LTD) development for Z-pinch inertial fusion energy (Z-IFE) and high yield.

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