Zebra

The Zebra 2 TW pulsed power generator has three stages of power amplification. The Marx bank consists of 32 1.3 μF capacitors charged in parallel up to 100 kV and discharged in series, which can store a total energy of up to 200 kJ. The bank is discharged in a second stage of power amplification with a coaxial capacitor (28 nF, 3.5 MV) using water as dielectric, and an SF6-insulated Rimfire switch. When this intermediate storage capacitor is about 80% charged, the switch is electrically triggered or self-breaks and connects to a third stage of pulse compression. It consists of a 50 ns, 1.9 Ω coaxial vertical transmission line and an eight channel self-breaking water switch. Once this switch is closed, a voltage pulse with amplitude of about 2 MV is applied on the final feed to the load, located in a vacuum chamber on top of the last, vertical, transmission line. Finally, a current pulse with maximum intensity of up to 1.2 MA and 90 ns rise time is delivered to the load.

Current and voltage measurements are taken in all sections of Zebra, in the Marx section, close to the load region and at the insulator stack. The voltage is measured with V-dot (capacitive divider) and resistive dividers. The current measurement is taken by B-dot monitors (pick-up coil) or CVR's. Current through the load is measured with three differential B-dot monitors located about 15 cm from the chamber axis at three different azimuthal locations.

Typically, the Zebra Marx bank charging voltage is 85 kV and the energy stored is 150 kJ.

Two load current pulse regimes are currently available:

In the short pulse regime, the current has a pedestal that increases approximately linearly for about 100 ns to about 5% of the maximum current intensity. The long pulse regime is obtained by forgoing the last stage of power amplification (water gap switches are closed), thereby, eliminating the >300g acceleration of the load region components associated with the water gaps firing.

The Zebra experiment chamber has 16 diagnostics ports, equally spaced at 22.5 degrees, with alternating diameters of 7.6 cm and 4.4 cm. In the current configuration, the chamber wall plays the role of current return conductor, so all diagnostics have to be installed outside the wall, at a minimum distance of 30 cm from the chamber axis.

Trigger pulses with jitter lower than 5 ns rms with respect to the maximum load current intensity are available for diagnostics that require delay times shorter than 350 ns. If the delay required is longer, the trigger pulses available have jitter around 15 ns rms.

Being a high impedance generator (1.9 Ω), Zebra can accommodate a variety of loads without a significant effect on the load current pulse characteristics. Examples of Zebra experiments and loads frequently used include:

Short pulse high intensity laser pulses (from the 50 TW Leopard laser) are commonly transported to the Zebra vacuum chamber through an evacuated beam line. Currently, the laser beam can be focused with refractive optics in a region of about 5 cm diameter around the center of the Zebra experiment chamber.