PBFA-Z vacuum section design using TLCODE simulations

Corcoran, P.; Douglas, J.; Smith, I.; Spence, P.; Stygar, W. A.; Struve, K. W.; Martin, T. H.; Spielman, R. B.; Ives, H.C.

doi:10.1109/ppc.1997.679375

Cited by 19 publications

(16 citation statements)

References 4 publications

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“…[15], where the vacuum impedance is varying slowly with radius. Furthermore, these PIC simulations show that the electron flow current near the load is considerably less than what was originally predicted from circuit model calculations [37]. It is hypothesized in Ref.…”

Section: Introductionmentioning

confidence: 59%

“…Choosing an appropriate vacuum impedance profile (i.e., the spacing of the A-K gap as it varies as a function of distance from the load) consistent with the current and local voltage allows for the MITL's self-inductance to be optimized as the total current in flowing electrons is reduced. One such optimization was done for the Z pulser at Sandia National Laboratories [35][36][37][38]. In the design of the conical MITLs for that system, Stygar et al [36] demonstrated a procedure for developing radial impedance profiles which were designed to minimize the vacuum inductance of the system while limiting the electron flow current entering the load.…”

Section: Introductionmentioning

confidence: 99%

“…The design was implemented using localized pressure-balance calculations, which permitted the magnitude of the electron flow current to be expressed in terms of the local voltage and total current [12], with the additional restriction that electron flow current could never decrease in the direction of power flow. The geometry of the vacuum section was optimized through iterative computer modeling in order to produce the desired electrical performance at the load [37]. Clearly, when vacuum-flowing electrons are sufficiently insulated from reaching the anode and cannot return to the cathode, the least inductive A-K gap profile for this geometry results from a radially invariant electron flow distribution.…”

Section: Introductionmentioning

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: Introductionmentioning

confidence: 59%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

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 experiments presented in this paper were performed with the Z accelerator before its refurbishment, [6][7][8][9][10][11][12][13][14] which could drive up to 20 MA current within $100 ns through a wire array load. The Z pulsed power design is based on the conventional Sandia pulsed power technology of Marx generators, water-pulse-forming and transmission lines, vacuum MITLs, and post-hole convolutes.…”

Section: Experimental Arrangementmentioning

confidence: 99%

Wire number dependence of the implosion dynamics, stagnation, and radiation output of tungsten wire arrays at Z driver

et al. 2011

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We report results of the experimental campaign, which studied the initiation, implosion dynamics, and radiation yield of tungsten wire arrays as a function of the wire number. The wire array dimensions and mass were those of interest for the Z-pinch driven Inertial Confinement Fusion (ICF) program. An optimization study of the x-ray emitted peak power, rise time, and full width at half maximum was effectuated by varying the wire number while keeping the total array mass constant and equal to $5.8 mg. The driver utilized was the $20-MA Z accelerator before refurbishment in its usual short pulse mode of 100 ns. We studied single arrays of 20-mm diameter and 1-cm height. The smaller wire number studied was 30 and the largest 600. It appears that 600 is the highest achievable wire number with present day's technology. Radial and axial diagnostics were utilized including crystal monochromatic x-ray backlighter. An optimum wire number of $375 was observed which was very close to the routinely utilized 300 for the ICF program in Sandia.

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“…Large-area water-insulated electrical components are often incorporated in the designs of multiterawatt pulsedpower accelerators, such as the Z [1][2][3][4][5][6][7][8][9][10] and ZR [11] machines. Water-insulated components are also proposed for use in future accelerators [12][13][14][15][16][17][18][19].…”

mentioning

confidence: 99%

Dielectric-breakdown tests of water at 6 MV

Stygar

Savage

Wagoner

et al. 2009

Phys. Rev. ST Accel. Beams

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We have conducted dielectric-breakdown tests on water subject to a single unipolar pulse. The peak voltages used for the tests range from 5.8 to 6.8 MV; the effective pulse widths range from 0.60 to 1:1 s; and the effective areas tested range from 1:8 Â 10 5 to 3:6 Â 10 6 cm 2 . The tests were conducted on waterinsulated coaxial capacitors. Large-area water-insulated electrical components are often incorporated in the designs of multiterawatt pulsedpower accelerators, such as the Z [1-10] and ZR [11] machines. Water-insulated components are also proposed for use in future accelerators [12][13][14][15][16][17][18][19]. Optimizing the design of such an accelerator requires a knowledge of the conditions under which its water-insulated components can be operated reliably.Reference [20] proposes that the characteristic time delay delay between the application of a voltage to a water-insulated anode-cathode gap, and the completion of dielectric failure of that gap, can be approximated as follows:In this expression stat is the statistical component of the delay time; i.e., the characteristic time between the application of the voltage and the appearance of free electrons and ions that initiate the formation of streamers in the water. We define form to be the formative component: the time required for the streamers to propagate across the gap and evolve sufficiently to produce complete dielectric failure.To inhibit electrical breakdown, water-insulated components are usually designed to produce a nominally uniform electric field over most of the component's area. We assume that, when the area of a water-insulated system with a uniform field is sufficiently large, the appearance of free electrons and ions necessary to initiate a breakdown occurs somewhere in the system very early in the voltage pulse [20]. Under this condition the statistical time delay stat can be neglected, and the breakdown delay is dominated by its formative component:In principle, dielectric breakdown dominated by the formative component can be studied with an electrode geometry that consists of a point anode and a planar cathode [20][21][22]. Although measurements with an infinitely field-enhanced anode point and an infinitely extended flat cathode are not possible, a number of dielectric-breakdown measurements between a significantly field-enhanced anode electrode and a less-enhanced cathode have been described in the literature.Using these measurements, Ref.[20] finds that complete dielectric failure is likely to occur in water between a fieldenhanced anode and a less-enhanced cathode when In this expression E p V p =d is the peak value in time of the spatially averaged electric field between the anode and cathode (in MV=cm, where V p is the peak voltage difference and d is the minimum distance between the electrodes), and eff is the temporal width (in s) of the voltage pulse at 63% of peak. This relation is based on 25 measurements for which 1 V p 4:10 MV, 1:25 d 22 cm, and 0:011 eff 0:6 s.To develop a tentative design criterion for a large-area...

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PBFA-Z vacuum section design using TLCODE simulations

Cited by 19 publications

References 4 publications

Tailoring of electron flow current in magnetically insulated transmission lines

Tailoring of electron flow current in magnetically insulated transmission lines

Wire number dependence of the implosion dynamics, stagnation, and radiation output of tungsten wire arrays at Z driver

Dielectric-breakdown tests of water at 6 MV

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