摘要:

Oversized, in particular, quasi‐optical components are natural to reduce Ohmic loss and to avoid RF breakdown and fatigue in high power RF generation, transmission and control systems. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1635126

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

High‐power applications of rf often require the use of overmoded waveguide to reduce the probability of rf breakdown by lowering surface fields, as well as to reduce the attenuation due to ohmic losses in transporting the power from the point of generation to the point of use. This is particularly true in the development of warm linear collider designs, such as NLC, JLC, and CLIC, especially the former two which involve extensive rf pulse compression / power distribution systems. Transitioning to and from overmoded waveguide and manipulating rf in such systems requires specialized components in whose design care must be taken to avoid parasitic mode loss and excessive field enhancement. Although fixed frequency operation means modest bandwidth requirements, power levels up to several hundred megawatts must be accommodated, and efficiency is important. Consequently, physicists working at laboratories engaged in the above efforts have produced a number of novel waveguide components in the past several years. These include tapers, mode converters, bends, directional couplers, power splitter/combiners, switches, phase shifters, etc. Often the circular TE01mode is used for its lack of surface electric field and low attenuation. A class of components using planar geometries for over‐height rectangular waveguide has been developed at the Stanford Linear Accelerator Center. The current paper describes a few additional passive high‐power components that have not been presented elsewhere — a height taper, a compact mode converter, a four‐way power splitter, fractional directional couplers and tap‐offs. These were designed at X‐band as part of the NLC R&D, but may find wider application. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1635127

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

A method to improve the selective properties of a waveguide resonator with Bragg reflectors on its ends is investigated. It is shown that additional mode conversions lead to a significantly rarefied spectrum of eigenoscillations. This can be achieved by using doubly periodic Bragg reflectors with different azimuthal symmetries forming four wave resonant field structures. The analysis of the dispersion properties is presented and is applicable for resonators of arbitrary relation of lengths of the reflectors and waveguide. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1635128

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Dielectric‐loaded accelerating structures offer the potential of a simple, inexpensive alternative to copper disk‐loaded structures for use in high‐gradient rf linear accelerators. However, a variety of potential problems must be studied in order to demonstrate this potential, including rf breakdown, joule heating, and gas desorption. A joint Argonne National Laboratory — Naval Research Laboratory program is under way to investigate these issues, using high‐power 11.424‐GHz radiation from the NRL Magnicon Facility. Recent tests using a copper accelerating tube with an alumina liner have shown no evidence of rf breakdown at up to 5 MW drive power (equivalent to 8 MV/m accelerating gradient). However, substantial absorption of the incident microwave radiation was observed, accompanied by visible light emission from the dielectric surface, indicating the presence of electron multipactor in the tube. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1635129

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Selection of spatial harmonics in pseudoperiodic waveguides depending on frequency is studied. The selection method is based on coordinated variation of the step and phase distribution of elements along the waveguide, which provides constant phase velocity of one spatial harmonic and destroys other spatial harmonics. Moreover, such nonuniform waveguide system represents a microwave filter whose frequency characteristic is also determined by the choice of elements and the steps of their location. A combined application of the conditions of selecting the spatial harmonics and choosing the necessary filter characteristics enables to create new types of broadband one‐wave slow‐wave systems. For example, the possibility of application of pseudoperiodic folded waveguide for creation of powerful broadband travelling‐wave tubes is shown. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1635130

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Conventional microwave sources utilize strong axial magnetic field to guide an electron beam through an interaction region. A plasma‐assisted slow‐wave microwave oscillator (Pasotron) can operate without external magnetic field because the presence of ions neutralizes the beam space charge and allows for radial motion of electrons under the action of transverse fields of the wave. The inherent efficiency of conventional microwave sources based on interaction of the backward wave with a 1‐D electron flow is typically limited to 15–20&percent;. By taking advantage of the 2‐D electron motion in the pasotron, a 50&percent; conversion efficiency of beam to microwave energy was demonstrated experimentally in a megawatt class device operating at a beam voltage of 40kV. Furthermore, theoretical studies indicated that an efficiency of 60–70&percent; might be possible. A research effort is now under way with the goal of extending this remarkable performance to even higher power and energy levels. The challenges associated with efficient, higher voltage/current operation of the pasotron are: beam dynamics and stability; spectral purity and mode competition; limiting currents. Most recent activities will be reviewed, with an emphasis on stationary and transient beam dynamics and scaling laws for high power pasotrons. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1635131

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Both relativistic and nonrelativistic magnetrons are under experimental and theoretical investigation at U of M. Relativistic (Titan‐6‐vane) magnetron experiments (300–400 kV, 1–10 kA, 0.5 microsecond) investigate mode control with various output coupling geometries. Mode competition between the pi mode and the 2/3 pi mode has been characterized for two‐versus‐three output extractors for comparison with particle in cell simulations. Phase measurements and time‐frequency‐analysis are performed for mode identification. Peak microwave output power on the order 0.5 GW has been measured, assuming equal output from 3 waveguides. Nonrelativistic (4 kV, <1A, kW microwave power) magnetron experiments are performed on commercial oven magnetrons for an in‐depth investigation of crossed‐field injection‐locking and noise. Injection‐locking is demonstrated by utilizing an oven magnetron as a reflection amplifier. Noise generation is explored as a function of injected signal and cathode conditions. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1635132

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Summary of the background presentation and synopsis of the subsequent discussion on microfabrication and THz sources. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1635133

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The Spallation Neutron Source (SNS) is an accelerator‐based neutron source being built in Oak Ridge, Tennessee, by the U.S. Department of Energy. The SNS will provide the most intense pulsed neutron beams in the world for scientific research and industrial development. CPI is supporting the effort by providing 550 kW pulsed klystrons for the superconducting portion of the accelerator. A total of 73 units are on order. The primary output power requirements are 550 kW peak, 49.5 kW average at 805 MHz, with an electron beam‐to‐rf conversion efficiency of 65&percent; and an rf gain of 50 dB. To date, 25 units have been factory tested. Performance specifications, computer‐model predictions, and operating results are presented. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1635134

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The MURI Innovative Vacuum Electronics Program is administered by Dr. Robert Barker of the Air Force Office of Scientific Research and consists of a collaboration between six premier universities actively engaged in all aspects of multidisciplinary basic research and graduate instruction in innovative microwave vacuum electronics (MIT, Stanford, University of California, Davis, University of Maryland — College Park, University of Michigan, and University of Wisconsin). The dual goals are to address basic research issues of critical importance to the DoD as well as to train the next generation. A wide range of fast wave amplifier concepts is under investigation at frequencies ranging from 15 GHz to 1 THz. Two representative examples are a TE01100 kW W‐Band gyro‐TWT under investigation at UC Davis and a 140 GHz confocal waveguide based gyro‐TWT concept developed at MIT. Novel, lightweight 100 kW, W‐Band klystrinos suitable for configuration in arrays are under investigation at Stanford using advanced microfabrication techniques. Extensive analytic and numerical analyses are underway at Wisconsin augmented by experimental measurements using a custom‐modified well diagnosed test TWT are aimed at an understanding of the complicated physics of multi‐toned ultra‐wideband traveling wave tubes including details of the beam‐wave interaction and the nonlinear time and space evolution of the carrier(s) and inter‐modulation products. A significant emphasis of the Maryland activity is on theoretical and experimental studies of various frequency‐multiplying gyroamplifier concepts which are both of fundamental interest as well as practical importance because of the relaxation on driver requirements. Finally, the Michigan team is devoting much of its attention to fundamental theoretical and experimental issues associated with crossed‐field devices. The latest results from these as well as other activities will be presented. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1635135

出版商:AIP    

年代:1903

数据来源: AIP