Latest Results in SLAC 75 MW PPM Klystrons

Abstract

75 MW X-band klystrons utilizing Periodic Permanent Magnet (PPM) focusing have been undergoing design, fabrication and testing at the Stanford Linear Accelerator Center (SLAC) for almost nine years. The klystron development has been geared toward realizing the necessary components for the construction of the Next Linear Collider (NLC). The PPM devices built to date which fit this class of operation consist of a variety of 50 MW and 75 MW devices constructed by SLAC, KEK (Tsukuba, Japan ) and industry. All these tubes follow from the successful SLAC design of a 50 MW PPM klystron in 1996. In 2004 the latest two klystrons were constructed and tested with preliminary results reported at EPAC2004. The first of these two devices was tested to the full NLC specifications of 75 MW, 1.6 microseconds pulse length, and 120 Hz. This 14.4 kW average power operation came with a tube efficiency >50%. The most recent testing of these last two devices will be presented here. Design and manufacturing issues of the latest klystron, due to be tested by the Fall of 2005, are also discussed.

Design and Operation of a 2.7 MW Periodic Permanent Magnet Focused X-band Klystron

“…The difference can be attributed to the difference between the simulated and measured magnetic field, the somewhat sensitive nature of the weakly confined flow optics to variations, and the fact that all electron beams have a varying radial current-density distribution and halo electrons which are not readily known or modeled by the simulation codes. For comparison, the various SLAC PPMfocused klystrons that were made had reported beam-current transmissions ranging from 93% to 98.7% at saturated output [12], [13]. The small increase in transmission at 9320 MHz in the figure appears to be due to overall slightly faster moving electrons at that frequency.…”

The Development of the Electrically Controlled High Power RF Switch and Its Application to Active RF Pulse Compression Systems

“…Neither it is economical to build and operate a high power RF source such as a klystron with the output pulse width reduced to sub-microsecond level. When a certain klystron is being operated at such a short pulse width, the peak output does not increase significantly as the pulse width shrinks, and the RF power in one pulse is much lower compared to a longer pulse of several microseconds [5]. The efficiency of such a system will also be very low, since the switching time of the modulator is at the level of several hundred nanoseconds and the loss during the switching is huge.…”

Design of a 48 GHz Gyroklystron Amplifier

“…Although many promising results are summarized in [4] and [5], this line of study did not lead to the use of gyroklystrons as drivers for accelerating cavities and klystrons are still the industry standard. Commercially available klystrons can comfortably deliver the required power at the C-band and X-band drive frequencies which are currently favored in accelerator design [6].…”