R. S. Callin

Breakdown phenomena in high-power klystrons

In the course of developing new high-peak-power klystrons, high electric fields in several regions of these devices have become an important source of vacuum breakdown. In addition, a renewed interest in breakdown phenomena for nanosecond-pulse, megavolt-per-centimeter fields has been sparked by recent work in the area of gigawatt RF sources. The most important regions of electrical breakdown are in the output cavity gap area, the RF ceramic windows, and the gun ceramic insulator. The experiments and results on the breakdown in these regions are discussed, as well as the solutions to alleviate this breakdown problem. >

High-power vacuum window in WR10

Results are presented in this paper for fabrication and test of a WR10 waveguide window for use in ultrahigh vacuum at 91.4 GHz. Low-power bench measurements are compared with analytic and simulation results. Operation at /spl ap/4-kW peak power, duty factor 10/sup -6/, and 10/sup -9/-scale vacuum is noted.

100 MW klystron development at SLAC

A klystron designed to operate at 11.4 GHz and 440 kV is presently Stanford Linear Accelerator Centers (SLACs) strongest RF power source candidate for the Next Linear Collider. It is expected to provide 100 MW of RF power with a pulse width of 1 mu s. The authors describe progress in the development of this device including results from single- and double-gap output cavities and various styles of RF output windows. The design parameters for this klystron are shown. Three X-band klystrons have been designed to test various alternatives to RF windows, output cavities, and beam optics. At this time 72-MW RF power has been generated with a pulse width of 100 ns and 35 MW has been generated at 800 ns.<<ETX>>

Recent advances in high power rf windows at X-band

The peak rf power levels produced by advanced high frequency power sources is beyond the level that can safely be transmitted through a single rf window of conventional design. New approaches are required to keep the rf electric fields at a managable level in the vicinity of the rf window. This paper describes some of the recent rf window design considerations and test results. Included are rf windows using one or more of the following features: over-moded dimensions, multiple modes, rf corona shields, and forced electric field reduction.

Design of a 50 MW klystron at X-band

This paper describes the design and performance of the XL-1 klystron; a 50 MW klystron operating at a frequency of 11.424 GHz for use on the SLAC Next Linear Collider Test Accelerator (NLCTA). Problems associated with the development of high-power rf sources for NLC, and the solutions implemented on XL-1 are discussed.

RF breakdown studies in X-band klystron cavities

RF breakdown studies are presently being carried out at SLAC with klystron cavities in a traveling wave resonator (TWR). Different kinds of fabrication methods and several kinds of semiconducting and insulating coatings have been applied to X-Band TM/sub 010/ cavities. RF breakdown thresholds up to 250 MV/m have been obtained. Dark current levels were found to be depressed in TiN-coated and single-point diamond turned cavities. A new TM/sub 020/ cavity with demountable electrodes has been designed and will be used to test a variety of materials, coatings, and processes. Recent tests of klystron output windows at 119 MW are also presented in this paper.

Accelerator and RF system development for NLC

An experimental station for an X-band Next Linear Collider has been constructed at SLAC. This station consists of a klystron and modulator, a low-loss waveguide system for RF power distribution, a SLED II pulse-compression and peak-power multiplication system, acceleration sections and beam-line components (gun, pre-buncher, pre-accelerator, focussing elements and spectrometer). An extensive program of experiments to evaluate the performance of all components is underway. The station is described in detail in this paper, and results to date are presented.<<ETX>>

Development of multimegawatt klystrons for linear colliders

A number of experimental klystrons have been constructed and evaluated at SLAC, KEK and INP, aiming toward output power objectives of 100 and 120 MW at 11.4 GHz (SLAC and KEK respectively) or 150 MW at 14 GHz (INP), with pulse lengths of the order of 1 /spl mu/s. Since RF breakdown is considered to be the principal mechanism limiting power for such tubes, most of the effort has been concentrated on the design of output circuits that reduce RF gradients by distributing fields over a longer region of interaction. Another klystron component receiving emphasis has been the output window, where the approach for future tubes may be to use a circular TEO1-mode, half-wave window. Best results to date in this continuing international effort are: 50 MW with 1 /spl mu/s pulses, using a traveling-wave output circuit (SLAC and INP), and 85 MW with 200 ns. Pulses (SLAC), using two conventional reentrant, but uncoupled, output cavities. At KEK a klystron with a single, but not reentrant, cavity has produced 80 MW in 50 ns pulses. Finally, Haimson has demonstrated 100 MW at 50 ns with a traveling-wave output. This paper addresses primarily the work performed at SLAC during the last two years.<<ETX>>

Large diameter reduced field TE01 traveling wave window for X-band

A single overmoded sized window is being considered for use on the SLAC 75 MW X-band klystron. The 65 mm diameter window operates in the circular TE01 mode in the reduced field, traveling wave configuration. Double step transitions were designed using a MLEGO mode matching program to suppress conversion to TE02. This compact design has a maximum peak RF electric field of 3.4 MV/meter at 75 MW. Design details and high power test results are reported.

Reduced field TE/sub 01/ X-Band travelling wave window

The RF electric field is reduced by more than a factor of two using a pair of symmetrically located irises in a new type of klystron window operating in the TE/sub 01/ mode at X-Band. The advantages of this window over the usual TE/sub 01/ half-wave resonant window are discussed as well as theory and operating results. Ultra high purity alumina formed by the HIP process is used. This window has been successfully tested at 100 MW with a 1.5 microsecond RF pulse width and is being used on the XL series klystrons.