Current multiplier for better generator-to-load coupling in direct-drive PRS experiments

Recent experiments show potential for driving long-implosion-time plasma radiation source (PRS) loads directly coupled to a capacitor bank. The LC generator inductance, L ₀, is typically several times greater than that of the load, L _d limiting the energy efficiency in those direct drive systems. We suggest a simple modification to improve the generator-to-load coupling, increasing the load current in the case of interest, where L ₀ ≫ L _d. An intermediate current multiplier circuit element, representing an N:1 transformer, is considered for N = 2. It consists of an additional large vacuum volume having inductance L and is connected through a single convolute to both generator and load. Analysis of the modified electrical circuit with constant load inductance demonstrates the benefits of the proposed hardware: having possibly one additional unknown, the convolute, the load current could be multiplied by the factor of I _d/I ₀ = 2L/(L + L _d), where L can be easily made much greater than L _d. The value of inductance added to the generator inductance is 4LL _d/(L + L _d) and can be much smaller than the original generator inductance, L ₀. Therefore, the load current could be increased without increasing the current rise-time very much. For existing multi-MA LC generators, circuit simulations coupled to the OD/MQK PRS model show potential for substantial K-shell yield increase. The PRS load height necessary for a given radiated energy could be decreased, facilitating further potential applications. The absence of plasma armatures in the scheme allowed preliminary experimental tests with decreased size hardware, scaled 1:4 with respect to the full scale design for the ECF2 generator. The tests are performed in two regimes, where the current multiplier volume electrodes are solid or transparent to the magnetic field, and they provide information of geometry optimization at low power.