This used beryllium oxide to convert the X-rays released by a small bomb into longer wavelength radiation, which explosively vaporized a tamper material, normally tungsten, causing it to carry away much of the bomb's energy as kinetic energy in the form of tungsten plasma.
These weapons would have yields of a few kilotons, could convert about 50% of that energy into a plasma jet with a velocity of 280 kilometers per second, and could theoretically get beam angles as low as 0.1 radians (5.73 degrees), quite wide but considerably narrower than the propulsion unit.
[2] The nuclear shaped charge concept was also studied extensively in the 1980s as part of Project Prometheus, along with bomb-pumped lasers.
During the test, codenamed 'Chamita', the intent was to use a nuclear detonation to accelerate a one kilogram mass of tungsten at one hundred kilometers per second, in the form of small particles focused in a cone-shaped beam.
Princeton nuclear physicist Dan L. Fenstermacher stated that there is a fundamental problem associated with the Casaba Howitzer concept that becomes dire at higher yields: a good portion of the bomb's energy inevitably becomes black-body radiation, which would quickly overtake the propelled mass.