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.
Coronoid reconstruction using osteochondral grafts: a biomechanical study.
HYPOTHESIS
The purposes of this study were to test the hypothesis that coronoid deficiency in the setting of posteromedial rotatory instability (PMRI) must be reconstructed to restore articular contact pressures to normal and to compare 3 different osteochondral grafts for this purpose.


METHODS
After creation of a anteromedial fracture, six cadaveric elbows were tested under gravity varus stress using a custom-made machine designed to simulate muscle loads and to passively flex the elbow. Mean articular surface contact pressure data were collected and processed using TekScan sensors and software. After testing of the intact specimen (intact condition), a PMRI injury was created (PMRI condition). Testing was repeated after reconstruction of the lateral collateral ligament (LCL) (LCL-only condition), followed by reconstruction of the coronoid with 3 different osteochondral graft techniques (reconstructed conditions).


RESULTS
Contact pressure was consistently significantly higher in the PMRI elbow compared with the intact, LCL-only, and reconstructed conditions (P < .006). The LCL-only elbow contact pressure was significantly higher than that of the intact and reconstructed conditions from 5° to 55° of flexion (P = .018). The contact pressure of the intact elbow was never significantly different from that of the reconstructed elbow, except at 5° of flexion (P ≤ .008). No significant difference was detected between each of the reconstructed techniques (P ≥ .15). However, the annular surface of the radial head was the only graft that yielded contact pressures not significantly different from normal at any flexion angle.


CONCLUSION
Isolated reconstruction of the LCL did not restore native articular surface contact pressure, and reconstruction of the coronoid using osteochondral graft was necessary. There was no difference in contact pressures among the 3 coronoid reconstruction techniques.