G. Caryotakis

The klystron: A microwave source of surprising range and endurance

This year marks the 60th anniversary of the birth of the klystron at Stanford University. The tube was the first practical source of microwaves and its invention initiated a search for increasingly more powerful sources, which continues to this day. This paper reviews the scientific uses of the klystron and outlines its operating principles. The history of the device is traced from its scientific beginnings to its role in WWII and the Cold War, its subsequent decline in use for military systems, and to its current resurgence as the key component in a major accelerator project. Finally, the paper describes the development of a modular klystron, which may someday power future accelerators at millimeter wavelengths.

Design of a 11.4 GHz, 150‐MW, Sheet Beam, PPM‐Focused Klystron

The current baseline design for the 500‐GeV SLAC/KEK future collider requires approximately 5000 75‐MW, 1.6 μs, PPM pencil‐beam klystrons. A prototype is currently on test. Although the estimated cost of the klystrons is a small part of the total collider cost, this number of klystrons is at least an order of magnitude higher than the klystron population in any scientific or military system ever fielded. A back‐up sheet‐beam klystron design has been under study at SLAC for the last six years. It offers several advantages: If two sheet beams were employed in parallel, the current density at the two cathodes would be low, and the power density at the output cavity a fraction of that in the pencil‐beam klystron. Furthermore, because of significantly fewer vacuum parts, the 150‐MW SBK should have a substantially lower cost than the baseline 75‐MW pencil‐beam klystron. Finally, it is considered that because of the lower power density, a longer rf pulse (3.2 μs) could be employed. All this means is that, with m...

Development of X-band klystron technology at SLAC

The SLAC design for a 1-TeV collider (NLC) requires klystrons with a performance which is well beyond the state-of-the-art for microwave tubes in the United States or abroad. The electrical specifications for klystrons are not fully established, but approximately as follows: Frequency: 11.4 GHz Peak Power: 75 MW Pulse Length: 1.5 /spl mu/s Repetition Rate: 180 Hz Gain: 50 dB Efficiency: (including beam focusing) 50% SLAC is in the seventh year of a program to develop these klystrons. The choice of X-band as the operating frequency, along with the sheer size of the NLC, have resulted in some new, most demanding standards for the klystrons which may power this future machine. These are related to the overall efficiency required, to the high RF gradients that must be supported at the output circuit without vacuum breakdown, and to the manufacturing cost of the 5,000-10,000 klystrons needed for the collider.

X-band klystron development at the Stanford Linear Accelerator Center

X-band klystrons capable of 75 MW and utilizing either solenoidal or Periodic Permanent Magnet (PPM) focusing are undergoing design, fabrication and testing at the Stanford Linear Accelerator Center (SLAC). The klystron development is part of an effort to realize components necessary for the construction of the Next Linear Collider (NLC). SLAC has completed a solenoidal-focused X-band klystron development effort to study the design and operation of tubes with beam microperveances of 1.2. As of early 2000, nine 1.2 (mu) K klystrons have been tested to 50 MW at 1.5 microsecond(s) . The first 50 MW PPM klystron, constructed in 1996, was designed with a 0.6 (mu) K beam at 465 kV and uses a 5-cell traveling-wave output structure. Recent testing of this tube at wider pulsewidths has reached 50 MW at 55% efficiency, 2.4 microsecond(s) and 60 Hz. A 75 MW PPM klystron prototype was constructed in 1998 and has reached the NLC design target of 75 MW at 1.5 microsecond(s) . A new 75 MW PPM klystron design, which is aimed at reducing the cost and increasing the reliability of multi- megawatt PPM klystrons, is under investigation. The tube is scheduled for testing during early 2001.

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>>

Periodic permanent magnet development for linear collider X-band klystrons

The Stanford Linear Accelerator Center (SLAC) klystron group is currently designing, fabricating and testing 11.424 GHz klystrons with peak output powers from 50 to 75 MW at 1 to 2 μs rf pulsewidths as part of an effort to realize components necessary for the construction of the Next Linear Collider (NLC). In order to eliminate the projected operational-year energy bill for klystron solenoids, Periodic Permanent Magnet (PPM) focusing has been employed on our latest X-band klystron designs. A PPM beam tester has operated at the same repetition rate, voltage and average beam power required for a 75-MW NLC klystron. Prototype 50 and 75-MW PPM klystrons were built and tested during 1996 and 1997 which operate from 50 to 70 MW at efficiencies greater than 55%. Construction and testing of 75-MW research klystrons will continue while the design and reliability is perfected. This paper will discuss the design of these PPM klystrons and the results of testing to date along with future plans for the development of ...

1.2 MW KLYSTRON FOR ASYMMETRIC STORAGE RING B FACTORY

A cw klystron operating at 476 MHz has been developed jointly by SLAC and Varian Associates. The unique set of characteristics of this tube were strongly guided by requirements of the fast feedback necessary to prevent oscillations of the storage ring beams caused by the detuned accelerating cavity. This requires a combination of bandwidth and short group delay within the klystron. The RF feedback stabilization scheme also requires amplitude modulation making it necessary to operate the klystron about 10% below saturation. Performance specifications and initial operating results are presented.

Design, fabrication and test of the klystrino

Summary form only given. The klystrino program was initiated to develop a high power RF source at W-band for tabletop accelerator, radar and communications applications. The goal of the program was to produce a 95 GHz, PPM focused, 100 kW peak power, 1% duty klystron. At W-band, both the small cavity dimensions and the required surface finish present fabrication challenges. In order to overcome these difficulties, the RF circuit for the klystrino is fabricated using an X-ray lithographic process called LIGA. The LIGA process can produce deep features (/spl les/ 3 mm) with submicron accuracy and excellent surface finish(< 50 nm). The RF design of the klystrino is straightforward with five regular cavities plus a five-gap extended interaction output cavity. The planar cross-section of the LIGA fabricated cavities requires 3-D simulation codes to model the non-axisymmetric fields. The rectangular magnets and butterfly-shaped polepieces also require a 3-D magnetostatic code to model the magnetic fields. Development of accurate 3-D simulations has been an ongoing issue in the klystrino program. The 110 kV beam voltage was chosen to make PPM focusing easier by reducing the plasma frequency. The length of the output cavity is proportional to beam velocity, so the high voltage also results in additional surface area to dissipate heat. Post-LIGA machining operations have presented the most difficult challenges to the klystrino development. Normal machining processes are pushed to the limit to achieve the one to two micron tolerances required for alignment and machining of the beam tunnel and coupling irises. Initial klystrino testing will start in February and RF performance data will be presented.

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.

The design and performance of 150-MW S-band klystrons

As part of an international collaboration, the Stanford Linear Accelerator Center (SLAC) klystron group has designed, fabricated and tested a 60 Hz, 3 /spl mu/s, 150 MW klystron built for Deutsches Elektronen Synchrotron (DESY). A test diode with a 535 kV, 700 A electron beam was constructed to verify the gun operation. The first klystron was built and successfully met design specifications. This paper discusses design issues and experimental results of the diode and klystron including the suppression of gun oscillations.<<ETX>>