Not quite--a conventional thermonuclear weapon uses a "tamper" surrounding the secondary, essentially a cylinder of uranium that's designed to eat the spike of

Not quite--a conventional thermonuclear weapon uses a "tamper" surrounding the secondary, essentially a cylinder of uranium that's designed to eat the spike of x-rays coming off the primary and convert it into a compressive force by ablating away on the exterior. This compressive force generates the pressures necessary to drive the fusion reaction (and is potentially fissile itself, if you use enriched material). It's physically heavy, and bringing that mass to speed requires a pretty powerful primary relative to the overall yield. It seems that the conjectured Ripple design uses some sort of wave-shaping barrier between the primary and secondary to convert the single massive spike of x-rays into a series of pressure waves that, via constructive interference, are able to compress the secondary directly without the need for the intervening tamper. Being able to do direct compression this way means you can do away with the weight of the tamper, and since you're applying the force directly you can get away with a much smaller primary (e.g. a 15MT device with a 15kT primary gives you a 99.99% "clean" design). Still requires the primary though.