High power microwave generation at high repetition rates
Generation of microwaves at high power has progressed largely with single shot devices. Yet applications require repetitive operation at substantial repetition rates, implying high average power. This requires operation in a new domain for microwave devices. The technical challenge is to achieve very high electric fields in the source on a repetitive basis. We describe experiments on CLIA, a Compact Linear Induction Accelerator, generating 750 kV, 10 kA using magnetic switching to produce 60 ns pulses. We describe experiments with relativistic magnetrons and klystrons in the 1 GW, 100 Hz domain. As a first application we used CLIA to drive a water-cooled L-band magnetron at repetition rates as high as 250 Hz with no breakdown or pulse shortening. This gave 6.3 kW average power. A short burst at 1 kHz operated at ≈25 kW. In this regime operation is not limited by gas build-up, electrode erosion or microwhisker depletion. We are now operating on CLIA with relativistic klystrons of both the high current and low current varieties. Beams with modulated current powers of ≈ 1 GW have been generated at 200 Hz for bursts as long as 1000 pulses.
Repetitively pulsed electron beam diode lifetime and stability
Repetitively pulsed vacuum beam diodes will be required for most projected inertially confined fusion systems. Yet data on the operation of diodes under repetitive pulsing is sparse. This paper discusses the operation of a 250 kV, 1.5 kA/cm/sup 2/ diode at repetition rates to 30 Hz for sustained runs. Short term stability is typically 3 percent (standard deviation). Longer term there is a drift toward higher impedance at the start of the pulse. Details on this drift and a comparison of this process for a rather blunt versus a sharp edged cathode are presented.
Shape and surface texture of molten droplets deposited on cold surfaces
When a molten droplet impacts on a cold surface, the interaction between solidification and fluid dynamics can lead to different shapes and surface textures of deposited droplets. This article presents an experimental study on deposition of small droplets (39 μm diameter) of molten wax ink on solid surfaces. Our results show that both the final shape and the surface texture of deposited droplets are extremely sensitive to deposition conditions, which include initial temperature of droplets, type of substrate surface and distance between substrate and printhead. Different surface textures are observed and shown to depend on the thermal and flow histories of ink droplets during the process of impact. A test using crystalline wax reveals crystallization as one of the major factors in determining the final texture.