H.W. Matthews

Experimental studies of stability and amplification in a two-cavity second harmonic gyroklystron

We report the operating characteristics of a sequence of two-cavity second harmonic gyroklystrons which are derived in part from a previous fundamental tube and utilize output cavities which resonate at twice the drive frequency. We present results from the design simulations as well as details of the stable range of operating parameters. While the harmonic tube is somewhat more susceptible to spurious oscillations and more sensitive to parameter variations than the fundamental device, there is still considerable parameter space available for amplifier operation. Peak powers above 30 MW are obtained with efficiencies greater than 28% and large signal gains of 27 dB. These results depend critically on the magnetic field profile which has a slight up-taper at the optimum operating point. The nominal beam parameters include a pulse length of 1 /spl mu/s, a voltage near 450 kV, a current in the range 235-245 A, and a perpendicular to parallel velocity ratio (/spl alpha/=v/sub /spl perp///v/sub z/) near one. >

Amplification studies of a two‐cavity second harmonic gyroklystron with a mixed‐mode output cavity

The performance of a two‐cavity second harmonic gyroklystron employing a short, mixed‐mode output cavity with stepped radial transitions is described. The short cavity was employed to prevent low frequency spurious oscillations that can compete with the harmonic signal. The radial rf field profile in the cavity and the output radiation consisted of both the TE01 and TE02 circular waveguide modes. This device produced a peak output power of 20 MW at 19.782 GHz, with an efficiency of 23% and a gain of 26 dB. The nominal mode mixture of the radiated power during optimal operation was found to be about 60% TE02 and 40% TE01. Variations from this ratio are observed at lower powers and are attributed to shifts in the cavity rf field profiles. Systematic studies of amplifier performance as a function of beam parameters and magnetic field profile are described. The sensitivities of output power production to changes in operating parameters are compared to results from earlier harmonic and fundamental gyroklystron...

Experimental gyroklystron research at the University of Maryland for application to TeV linear colliders

X‐Band and K‐Band gyroklystrons are being evaluated for possible application to future linear colliders. So far we have examined then different two‐ and three‐cavity configurations. We have achieved a maximum peak power of 27 MW in ∼1 μs pulses at a gain of 36 dB and an efficiency exceeding 32%. The nominal parameters include a 430 kV, 150–200 A beam with an average perpendicular to parallel velocity ratio near one. In this paper, we detail our progress to data and describe our plans for future experiments that should culminate in amplifier outputs in excess of 100 MW in 1 μs pulses.

Operation of a K‐band second harmonic coaxial gyroklystron

Amplification studies of a two‐cavity second harmonic gyroklystron with a coaxial input cavity and drift tube are reported. The inner conductor is supported by tungsten pins which intercept the beam, and it utilizes lossy dielectric rings to enhance mode suppression. A double‐anode magnetron injection gun produces a 440 kV, 200–268 A, 1 μs beam with an average perpendicular‐to‐parallel velocity ratio near one. The TE011 input cavity is driven near 9.886 GHz and the TE021 output cavity resonates near 19.772 GHz. Peak powers near 30 MW have been achieved, although more easily reproducible peak powers hover closer to 20 MW. While stability is improved over previous devices, beam interception reduces the accessible range in parameter space and thus degrades amplifier performance. Pin erosion is also evident and qualitatively agrees well with theoretical predictions.

Initial operation of a high power, K-band, harmonic gyroklystron for accelerator applications

Experimental studies of amplification and stability in a series of multi-megawatt, 19.7 GHz, second harmonic gyroklystron amplifier tubes suitable for driving future linear supercolliders are reported. Four different two-cavity gyroklystron tubes have been constructed and tested, and each one has exhibited higher power, larger efficiency, and improved stability compared to its predecessor. The latest results include the production of peak output powers in excess of 29 MW, at an efficiency of 27% and a gain of 25 dB.<<ETX>>

Experimental studies of a 30 MW two-cavity second harmonic gyroklystron

We report the operating characteristics of a sequence of two-cavity second harmonic K-band gyroklystrons. The TE/sub 011/ input cavity is driven near 9.88 GHz. The first four tubes utilized smooth transition output cavities which resonate at twice the drive frequency in the TE/sub 021/ mode. Peak powers in excess of 30 MW were achieved with efficiencies greater than 28% and large signal gains of 27 dB. The results of an abrupt transition complex TE/sub 01/, TE/sub 02/ mixed mode output cavity are also discussed, as well as the prospect of placing a coaxial insert into the highest power tube.<<ETX>>

Experimental studies of a multi-megawatt, 19.7 GHz harmonic gyroklystron

Summary form only given. Experimental progress in the development of a two-cavity gyroklystron employing a 19.7-GHz, TE/sub 021/ second-harmonic output cavity and a 9.85-GHz, TE/sub 011/ fundamental input cavity is discussed. Output powers in excess of 7.5 MW for 0.5 /spl mu/s, at 11% efficiency and 20 dB gain, have been achieved with a 410 kV, 162 A, /spl alpha/ /spl ap/ 0.9 electron beam. Optimum performance required a magnetic field profile with an 8% up-taper between the input and output cavities. Studies of frequency response, output power vs. input power, and radiation power patterns at this and other operating points have been performed. Performance-limiting 6-8 GHz whole tube instabilities have been characterized, and improved suppression methods have been examined.

Studies of an X-band three-cavity gyroklystron with penultimate cavity tuning

The authors present experimental results of a 10 GHz TE/sub 01/ mode three-cavity gyroklystron. The beam is produced by a pulse line modulator and magnetron injection gun, which can operate to 433 kV and 225 A with 1 mu s flat-top and at a repetition rate of 3 Hz. Microwave power was measured by a mode-selective directional coupler and a flowing methanol calorimeter. Mode purity was determined by a large anechoic chamber. Initial testing of the first three-cavity circuit has produced a peak power of 23 MW with an efficiency of 27% and pulse energy of 36 J. A maximum gain of 39 dB at a peak power of 21 MW was obtained.<<ETX>>