Advances in microwave sources with high peak and average power depend on continued development of reliable modulators capable of testing high-voltage HPM sources at rep-rates up to 100 Hz. In light of budget limitations, new pulser development must be accomplished cost-effectively. This proposal is for a design study of a new 100Hz modulator which provides 600 kV, l (magnetic moment)s pulsewidth to discretely variable loads of 10 to 50 (omega particle). We propose to conduct the following tasks: (1) Design the optimum modulator meeting the specifications without regard to cost. In this task, the study will include the use of technology promising the highest performance and reliability. (2) Design the modulator meeting the above requirements with deference to budget limitations. Thus, for example, switches (as in the primary circuit of the pulse transformer) may be gas-blown spark-gaps as opposed to more costly high-voltage thyratrons. (3) List and establish availability of existing equipment and determine if a system can be assembled to the new specifications cost-effectively. In this case, performance requirements such as reduced pulse fall time and enhanced fault mode protection would be emphasized in anticipation of increased resources to address advanced development in specific areas