Search

In order to make millimeter-wave sources practical, improved fabrication methods are required. The use of Lithographie, Galvanoformung, Abformung; German acronym (LIGA) to fabricate a coupled-cavity traveling-wave tube (TWT) is presented. The proposed circuit design will focus on two-step LIGA fabrication and dual in-line ladder structure with a rectangular beam tunnel. The fabrication sequence of two-step LIGA is illustrated and the advantages and tradeoff of this approach are described. Three electromagnetic codes-HFSS, GdfidL, and MAGIC3D-are employed to analyze the circuit characteristics in cold and hot test simulations. Finally, the results from small and large signal analyses are presented to verify the validity of the circuit design.

The design and test results of a 35 GHz gyrotron oscillator, operating in the TE/sub041/ mode, will be presented. Output powers of 300 kW have been achieved. These results will be compared to computer simulation predictions.

Summary form only given, as follows. The main research goal focuses on design of an EIK (Extended Interaction Klystron) circuit capable of producing an improved performance in Ka-band with circuit efficiency larger than 14% and the gain over 40dB.

Summary form only given, as follows. The main focus in this paper is a hot test simulation using 3-dimensional PIC (particle-in-cell) code, MAGIC3D, to analyze a W-band coupled-cavity TWT circuit based on two-step LIGA fabrication.

Presents the design of a W-band LiGA (a German acronym for lithographe, galvanoformung, und abformung) fabricated three-dimensional five-gap coupled cavity. This paper focuses on analyzing the coupling slot effects on such a periodic structure's dispersion characteristics using the three-dimensional code MAFIA (Maxwell equation using finite integration algorithm). The different coupling slot sizes corresponding to LiGA fabrication and EDM (electric discharge machining) fabrication constraints have been modeled and discussed in detail. The equivalent circuit model of such a coupling slot in two-dimensional MAGIC code also has been studied.

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.

High average power millimeter wave sources are being developed in a collaboration between SLAC and CPI. CPI has developed a number of high-power, broadband, millimeter-wave, CCTWT amplifiers. The coupled cavity technology is now approaching the limits for generating power at millimeter wave frequencies. To generate significant increases in power, other technologies need to be considered. At SLAC, compact, lightweight, PPM-focused, klystrons, nicknamed 'klystrinos' are being developed, using lithographic fabrication methods (LIGA). These devices will operate at 100 kW peak power and 1 kW average power at 95 GHz. Two design areas are critical to the success of the klystrino. First is the electron beam optics and beam focusing. A beam tester is being built to evaluate the electron gun and the PPM focusing system. Results of the beam tests are presented. CPI has analyzed the electron gun and is investigating the addition of a control electrode for improved modulator efficiency. The second significant design area is the modeling of the klystrino. The combination of the rectangular LIGA structure and the multiple gap output section make modeling the klystrino difficult. MAFIA and MAGIC have been used to develop an equivalent 2D model of the 3D LIGA circuit. Thermal capacity of the circuit is also investigated at CPI using the ANSYS 3D FEA code. The analysis included both the expected RF losses and beam interception. The calculations include both transient response and steady state. The thermal analysis is used to predict the maximum allowable beam interception and duty cycle that the circuit can withstand without major problems.

In an effort to reach the gigawatt power level in the microsecond pulse length regime Los Alamos, in collaboration with SLAC, is developing an annular beam klystron (ABK) with a thermionic electron gun. We hope to address the causes of pulse shortening in very high peak power tubes by building a “hard‐vacuum” tube in the 10−10 Torr range with a thermionic electron gun producing a constant impedance electron‐beam. The ABK has been designed to operate at 5 Hz pulse repetition frequency to allow for RF conditioning. The electron gun has a magnetron injection gun configuration and uses a dispenser cathode running at 1100 °C to produce a 4 kA electron beam at 800 kV. The cathode is designed to run in the temperature‐limited mode to help maintain beam stability in the gun. The beam‐stick consisting of the electron gun, an input cavity, an idler cavity, and drift tube, and the collector has been designed collaboratively, fabricated at SLAC, then shipped to Los Alamos for testing. On the test stand at Los Alamos a low voltage emission test was performed, but unfortunately as we prepared for high voltage testing a problem with the cathode heater was encountered that prevented the cathode from reaching a high enough temperature for electron emission. A post‐mortem examination will be done shortly to determine the exact cause of the heater failure. The RF design has been proceeding and is almost complete. The output cavity presents a challenging design problem in trying to efficiently extract energy from the low impedance beam while maintaining a gap voltage low enough to avoid breakdown and a Q high enough to maintain mode purity. In the next iteration, the ABK will have a new cathode assembly installed along with the remainder of the RF circuit. This paper will discuss the electron gun and the design of the RF circuit along with a report on the status of the work.

A one-gigawatt, annular beam klystron (ABK) is being developed by Los Alamos National Laboratory in collaboration with the Stanford Linear Accelerator Center (SLAC). The pulse length is 1 µs, the pulse repetition frequency is 5 Hz, and the operating frequency is 1.3 GHz. The beam voltage and current are 800 kV and 4 kA. Since the electron beam parameters are considerably beyond the state-of the-art, an aggressive cathode and electron gun design is required. The magnetron injection gun (MIG) configuration was chosen over the standard Pierce geometry that is typically used in klystrons. The tube design, design issues, and status are presented. 1 BACKGROUND For many decades accelerators and radar systems have used high power klystrons to provide the RF energy for their operation. The klystrons for these applications use electron beams with a solid cross-section. The beams are typically produced by thermionic electron guns using a Pierce geometry. As the need increases for higher peak power, the voltage and current of the beam must increase. Since raising the beam voltage above 800 kV is expensive and impractical, one must instead raise the beam current. For a klystron with 1 GW output and a nominal efficiency of about 30%, the required beam current is 4 kA. Not only is this beam current well beyond what has been previously used in klystrons, but beam potential energy considerations dictate that an annular beam, rather than a solid beam must be used. The beam injection energy is partitioned into two parts: the kinetic energy and the potential energy due to the space charge fields. In a conventional klystron the current is low enough that the beam potential energy can be ignored. However, in an intense beam klystron the beam

The design and fabrication issues arising from the development of a 94 GHz, 100 kW klystron are discussed. The klystron beam is focused using periodic permanent magnets that are mounted in the vacuum envelope. Several circuit fabrication processes were considered before the “LIGA” lithographic process was chosen. LIGA has the dimensional tolerances and surface finish required for klystron operation at 94 GHz.

The klystrino developed at Stanford Linear Accelerator Center (SLAC) is a micro-fabricated klystron being the high-power source of microwaves [1]. The ultra-deep (UD) LIGA process is adopted to fabricate the millimeter cavities of this reported W-band (94 GHz) klystrino. The design addresses multiple applications in accelerators, radars, and communications. The goal of the program is to produce a 100KW peak, 1 KW average power modular klystrino in a small package. Figure 1 shows an example of four klystrino module that should produce 400KW peak power and 4 KW average power in a 4″ × 4″ × l4″ package with a weight of 2.41bs.

A proposed tunable three-cavity gyroklystron is described. Calculations with a particle simulation code for a two cavity gyroklystron predict efficiencies greater than 40%. Gains greater than 40 dB are extrapolatod from these calculations. Output powers greater than 100 kW should be obtained. The experiment will be performed at C band due to the availability of a magnetron injection gun suitable for this Frequency-range.

A 35-GHz gyrotron operating in the TE 041 mode has been built and tested. Output powers of 320 kW at 40-percent efficiency have been obtained. These test results agree closely with theoretically predicted results. Regions of stable operation in the TE 041 mode were also determined experimentally. These regions could be predicted by a small signal analysis of threshold currents.

A review of the recent research at the Naval Research Laboratory into gyrotron and ubitron amplifiers is given. In particular, we discuss applications to gyro-klystrons, tapered gyrotrons and gyro-harmonitrons. Ubitron work is devoted to the collective regime of operation and the effects of an axial guide field on the interaction.

A new invention — the thermal barrier — promises to improve the tandem mirror fusion reactor. The thermal barrier consists of a region of reduced magnetic field strength, plasma density, and plasma potential between each end plug and the central cell of a tandem mirror. The depressed plasma potential serves to thermally insulate the plug electrons from the central cell electrons. With barriers and auxiliary electron heating in the plugs, the central cell confining potential can be generated with a lower plug plasma density, magnetic field strength, and beam injection energy than for the case without barriers. This paper summarizes the status of the rapidly evolving physics knowledge concerning tandem mirrors with thermal barriers, describes end plug components typical for tandem mirror reactors — yin-yang magnets, neutral beams, and ECRH heating systems, and discusses central cell design.

This paper will describe the design of a 35 GHz gyrotron oscillator having objectives of 350-500 kW output power with an efficiency of approximately 50%. Test results will also be presented.

A proof-of-principle experimental device of a gyrotron backward-wave amplifier has been designed and is being fabricated. The TE 10 -mode device is electronically tunable over 18 to 26 GHz with an instantaneous bandwidth 1 to 3%. The possibility of enhanced bandwidth will be investigated by using a tapered waveguide in a tapered magnetic field.

The Naval Research Laboratory (NRL) is investigating the gyroklystron amplifier (GKA) concept. The purpose of this program is to assess GKA characteristics in order to determine if a microwave tube is capable of achieving the high efficiency, gain, and output power predicted by numerous theories. The first in a series of tubes to examine GKA behavior has been fabricated and is currently under test. This tube, GKLY-101, utilizes three rectangular cavities operating in the TE 101 mode. Design specifications include 100 kW output power, 30% efficiency, 40 dB gain, and 4.5 GHz operation (1). Preliminary test results have shown reasonable agreement with theoretical predictions. In particular, perpendicular efficiencies as high as 60% have been observed. The largest output power, to date, has been 51 kW. These results suggest that the desirable characteristics which have been predicted for the GKA can be realized with a microwave tube.

Research on the use of gyrotrons for electron cyclotron heating and preionization in Tokamaks is described. The program consists of research and development on gyrotrons, and their use in ECH experiments. Recently, experiments using an 100 kW, 20 ms, TE01 gyroton were completed on the ISX-B Tokamak at ORNL. We summarize the results of these, in which 60% absorption, resulting in a 50% rise in the electron temperature, was achieved. Currently, ECH experiments on the Versator-II Tokamak at MIT are being performed. These experiments are aimed toward a detailed examination of the physics of ECH, including the effects of polarization and injection angle. Plans for and results from this effort, as well as those for a highly efficient, 35 GHz, 300 kW gyrotron to be used in these experiments will be presented.

The theory of the Clustered-CavityTMKlystron (CCK) is discussed. Experimental results for two iterations of an experimental 13-cavity megawatt CCK are presented. Record bandwidth for a klystron of this power and length has been achieved.

This paper will be concerned with a method of designing magnetron injection guns which are capable of launching, high-perveance hollow.beams. Test results obtained from such guns together with several applications of these guns will also be discussed.

With the advent of sophisticated pulse compression radars, the phase linearity of the various components has become of utmost importance. A phase measurement program was initiated to determine the phase linearity of broad band high power microwave tube. Swept frequency phase measurements were made on three types of pulsed C-band tubes. These tube types are: (1) 5-kw helix TWT; (2) 3-megawatt cloverleaf TWT; and (3) 3-megawatt cloverleaf Twystron® (klystron input section, cloverleaf output section). The 5-kw tube is used as a driver tube for the megawatt tubes. The deviation from linearity and the output power was measured for several beam voltages and rf drive powers for each of these tube types. Swept frequency measurements were made over a frequency range of 5.4 to 5.9 kmc. In addition, measurements were also made to determine the phase shift as a function of drive power at individual frequencies.

With the advent of sophisticated pulse compression radars, the phase linearity of the various components has become of utmost importance. A phase measurement program was initiated to determine the phase linearity of broad band high power microwave tube. Swept frequency phase measurements were made on three types of pulsed C-band tubes. These tube types are: (1) 5-kw helix TWT; (2) 3-megawatt cloverleaf TWT; and (3) 3-megawatt cloverleaf Twystron® (klystron input section, cloverleaf output section). The 5-kw tube is used as a driver tube for the megawatt tubes. The deviation from linearity and the output power was measured for several beam voltages and rf drive powers for each of these tube types. Swept frequency measurements were made over a frequency range of 5.4 to 5.9 kmc. In addition, measurements were also made to determine the phase shift as a function of drive power at individual frequencies.