Abstract
Presented are voltage measurements taken near the load region on the $Z$ pulsed-power accelerator using an inductive voltage monitor (IVM). Specifically, the IVM was connected to, and thus monitored the voltage at, the bottom level of the accelerator's vacuum double post-hole convolute. Additional voltage and current measurements were taken at the accelerator's vacuum-insulator stack (at a radius of 1.6 m) by using standard $D$-dot and $B$-dot probes, respectively. During postprocessing, the measurements taken at the stack were translated to the location of the IVM measurements by using a lossless propagation model of the $Z$ accelerator's magnetically insulated transmission lines (MITLs) and a lumped inductor model of the vacuum post-hole convolute. Across a wide variety of experiments conducted on the $Z$ accelerator, the voltage histories obtained from the IVM and the lossless propagation technique agree well in overall shape and magnitude. However, large-amplitude, high-frequency oscillations are more pronounced in the IVM records. It is unclear whether these larger oscillations represent true voltage oscillations at the convolute or if they are due to noise pickup and/or transit-time effects and other resonant modes in the IVM. Results using a transit-time-correction technique and Fourier analysis support the latter. Regardless of which interpretation is correct, both true voltage oscillations and the excitement of resonant modes could be the result of transient electrical breakdowns in the post-hole convolute, though more information is required to determine definitively if such breakdowns occurred. Despite the larger oscillations in the IVM records, the general agreement found between the lossless propagation results and the results of the IVM shows that large voltages are transmitted efficiently through the MITLs on $Z$. These results are complementary to previous studies [R. D. McBride et al., Phys. Rev. ST Accel. Beams 13, 120401 (2010)] that showed efficient transmission of large currents through the MITLs on $Z$. Taken together, the two studies demonstrate the overall efficient delivery of very large electrical powers through the MITLs on $Z$.
Highlights
The architecture of the refurbished Z accelerator is discussed in detail in Refs. [3,4]
At the vacuum-insulator stack, which is at a radial position of about 1.6 m from the Z axis of symmetry, voltage (D_ ) and current (B_ ) measurements are made on all four levels and at multiple azimuthal locations (Fig. 2) [26,27]
We have developed an inductive voltage monitor (IVM) for Z
Summary
The refurbished Z pulsed-power accelerator [1,2,3,4] delivers approximately 3-MV, 25-MA, 100–600-ns electrical pulses to various loads for research efforts in inertial confinement fusion (ICF) [5,6,7,8], pulsed-power physics [9,10,11,12], z-pinch physics [13,14], K-shell x-ray sources [15], radiation physics [16,17], fundamental science and laboratory astrophysics [18,19], dynamic material properties [20,21,22,23], and other high-energy-density physics applications [24]. Each ring connects to one of four electrically parallel vacuum magnetically insulated transmission lines (MITLs) [10]. At the vacuum-insulator stack, which is at a radial position of about 1.6 m from the Z axis of symmetry, voltage (D_ ) and current (B_ ) measurements are made on all four levels and at multiple azimuthal locations (Fig. 2) [26,27]. The voltages and currents measured at each of the vacuum-insulator stack’s four levels can be translated to the post-hole convolute location by using a lossless transmission-line-equivalent (TLE) model of the four-level MITL system [10,12,29,30,31,32].
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