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Haimson, J.

Paper Title Page
WEPMS084 A Solid State Driven, Parasitic Oscillation Suppressed, 17 GHz High Gain TW Klystron for Stable Operation with High Gradient Linac Structures 2529
  • J. Haimson, B. A. Ishii, B. L. Mecklenburg, G. A. Stowell
    HRC, Santa Clara, California
  Funding: Work performed under the auspices of the U. S. Department of Energy SBIR Grant No. DE-FG02-04ER83973.

The gain of a high power TW relativistic klystron can be increased substantially with the use of a varying phase velocity, large beam aperture, lengthened output structure, designed for asynchronous interaction to control space charge fields and provide near-adiabatic bunch compression during the power extraction process. While this technique enables the replacement of a pulsed vacuum tube driver system with a small, inexpensive solid state RF source, lengthening the output circuit increases the number (and reduces the separation) of the longitudinal mode resonances in the TM01 operating band. Thus, the probability of exciting parasitic oscillations is increased, especially when the klystron is operated into a mismatched load or a high Q structure. The prevention of such oscillations, even when in close proximity to the operating frequency, using a technique that is unaffected by the phase or amplitude of reflected signals is described; and test results are presented of a solid state driven, 76dB gain 17GHz TW relativistic klystron, recently installed in the linac test facility at the MIT Plasma Science and Fusion Center.

WEPMS085 A 17 GHz High Gradient Linac having Stainless Steel Surfaces in the High Intensity Magnetic and Electric Field Regions of the Structure 2532
  • J. Haimson, B. L. Mecklenburg
    HRC, Santa Clara, California
  Funding: Work performed under the auspices of the U. S. Department of Energy SBIR Grant No. DE-FG02-05ER84362.

To avoid surface erosion damage and to assist in understanding RF breakdown limitations imposed on high gradient linac operation, a gradient hardened structure is being fabricated having high temperature brazed and machined stainless steel surfaces located in the high E-field region of the beam apertures and in the high H-field regions of the racetrack shaped coupling cavities. The microwave design parameters and physical dimensions of this 17GHz, 2pi/3 mode, 22-cavity structure were established specifically to allow comparison of its high gradient performance to that of a similar all-copper structure tested under identical conditions, using an existing 4X power amplifying, RF recirculating dual ring system. Use of the 6X thicker skin depth material, the resulting de-Q-ing effects and the minimal reduction of beam energy (2%) associated with the strategically located lossy surfaces are discussed; fabrication techniques are described; and design parameters of the gradient hardened linac and the 17GHz power amplifying system are presented.