PUFFIN is designed to deliver an intense pulse of electrical current over long timescales. In this context, intense means around one million Amperes (compare that to a standard 15 amp socket at home!) and long means around one millionth of a second, or a microsecond, which is plenty long enough to produce and sustain interesting plasmas.
The microsecond-length current pulses on PUFFIN are in contrast to fast rise-time pulsers such as MAIZE and HADES, which drive rapid implosions to reach extreme conditions. Instead, the long timescales on PUFFIN allow us to sustain plasmas in a quasi-steady-state, which is ideal for studying fundamental plasma processes.
PUFFIN is built around the LTD5 modules developed at CEA Gramat. LTDs are Linear Transformer Drivers, a relatively new pulsed-power technology which encloses the capacitive energy store and switch in a single conducting cavity. This reduces the inductance of the system and provides shielding from electromagnetic pulses.
PUFFIN is currently in the design phase. We have secured a supplier for these LTD5 modules and we expect the first components to arrive in early 2022. The conceptual design above uses eight LTD5 modules (or stages) arranged in four lines of two modules each. The modules stacked in series increase the overall voltage of the pulse, and the modules stacked in parallel increase the total current. The capacitors (shown in brown) will be charged to around 70 kV, and then discharged through triggered multi-channel, low inductance switches into a vacuum coaxial transmission line.
The four transmission lines converge inside a vacuum chamber (shown in a cutaway view above) and the transmission line tapers vertically to present a coaxial transmission line at the base of the large cylindrical vacuum chamber. The tall windows will provide excellent diagnostic access for laser based diagnostics such as interferometry, Thomson scattering and Faraday rotation imaging.
The initial version of PUFFIN will use two LTD5 modules, arranged into two lines of one module each. We will use the results from this initial version of PUFFIN to secure funding for the upgraded version shown above.
- “A primer on pulsed power and linear transformer drivers for high energy density physics applications” by McBride et al. A very thorough review of LTDs and pulsed-power in general.
- “Status on the SPHINX machine based on the 1 microsecond LTD technology” by Lassalle et al. An overview of the LTD5 stages to be used on PUFFIN.