Efficient operation of a high-power X-band gyroklystron

Experimental studies of amplification in a two-cavity X-band gyroklystron are reported. The system utilizes a thermionic magnetron injection gun at voltages up to 440 kV and currents up to 190 A in 1-μs pulses. Optimum performance is achieved by tapering the magnetic-field profile. Peak powers of 20 MW in the TE01 mode at 9.87 GHz are measured with calibrated crystals and with methanol calorimetry. Resultant efficiencies are in excess of 31% and large-signal gains surpass 26 dB. The experimental results are in good agreement with simulated results from a partially self-consistent, nonlinear, steady-state code

High-power operation of a K-band second harmonic gyroklystron

Amplification studies of a two-cavity second-harmonic gyroklystron are reported. A magnetron injection gun produces a 440 kV, 200–245 A, 1 μs beam with an average perpendicular-to-parallel velocity ratio slightly less than 1. The TE011 input cavity is driven near 9.88 GHz and the TE021 output cavity resonates near 19.76 GHz. Peak powers exceeding 21 MW are achieved with an efficiency near 21% and a large signal gain above 25 dB. This performance represents the current state of the art for gyroklystrons in terms of the peak power normalized to the output wavelength squared

Chaotic synchronization of coupled electron-wave systems with backward waves

The chaotic synchronization of two electron-wave media with interacting backward waves and cubic phase nonlinearity is investigated in the paper. To detect the chaotic synchronization regime we use a new approach, the so-called time scale synchronization [Chaos, 14 (3) 603-610 (2004)]. This approach is based on the consideration of the infinite set of chaotic signals' phases introduced by means of continuous wavelet transform. The complex space-time dynamics of the active media and mechanisms of the time scale synchronization appearance are considered.Comment: 11 pages, 7 figures, published in CHAOS, 15 (2005) 01370

Propagation of gamma rays and production of free electrons in air

A new concept of remote detection of concealed radioactive materials has been recently proposed \cite{Gr.Nusin.2010}-\cite{NusinSprangle}. It is based on the breakdown in air at the focal point of a high-power beam of electromagnetic waves produced by a THz gyrotron. To initiate the avalanche breakdown, seed free electrons should be present in this focal region during the electromagnetic pulse. This paper is devoted to the analysis of production of free electrons by gamma rays leaking from radioactive materials. Within a hundred meters from the radiation source, the fluctuating free electrons appear with the rate that may exceed significantly the natural background ionization rate. During the gyrotron pulse of about 10 microsecond length, such electrons may seed the electric breakdown and create sufficiently dense plasma at the focal region to be detected as an unambiguous effect of the concealed radioactive material.Comment: 27 pages, 10 figure

Microwave generation for magnetic fusion energy applications. Progress report, July 15, 1992--July 14, 1993

This work strives to develop high average power FELs at voltages below I MV allowing for smaller and less costly power supplies. To achieve operation of an FEL with 100 GHZ {approx_lt} f {approx_lt} 150 GHz and with relatively modest voltage, we have been investigating the use of small period ({lambda}{sub {omega}} {approximately} 1 cm) planar wiggler magnets together with sheet electron beams. The sheet beam geometry allows for an FEL interaction region in the form of a narrow slit with high wiggler field at the center plane where the electrons are concentrated. The total current and power may then be increased without making current density excessive by increasing the wide dimension of the sheet beam. Sheet beam FEL design parameters for both a Proof-of-Principle (PoP) FEL experiment, which is current in progress, and an ITER relevant FEL design are shown. A central issue in the sheet beam FEL concept is propagation of the beam through the interaction region without excessive interception by the walls. In section 2 below we describe a successful experimental demonstration of sheet beam propagation through a 56 period uniform wiggler. Cold testing and initial hot test operation of the (PoP) FEL amplifier are also described. Finally, we present a theoretical investigation of the bandwidth of an FEL amplifier with a tapered wiggler operating in saturation is described

A depressed collector system for a quasi-optical gyrotron with precisely controlled magnetic flux lines

Design of a depressed collector system for a quasi-optical gyrotron, which had a severe constraint on the maximum allowable radius of the collector region is outlined. The needs for unwinding of spent beam and for energy sorting could be accommodated by precise control of the magnetic field profile, especially in the collector region. Techniques used for defining and obtaining such profiles; and for dovetailing the profile with the collector geometry are discussed. Results on profiles and electron trajectories are presented, which demonstrate the feasibility of the design. From primary electron trajectories a collector efficiency of up to 68% has been calculated for a three collector design.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44546/1/10762_2005_Article_BF01009406.pd

Cold War : a Transnational Approach to a Global Heritage

Although within living memory, many countries now consider their surviving Cold War architecture as part of their heritage. It can even be a priority for heritage managers given that significant buildings are often suitable for reuse while extensive ‘brownfield’ sites such as airfields can be used for large-scale redevelopment. In a number of countries whose work we refer to here (notably the United Kingdom and elsewhere in Europe), agencies responsible for managing their country’s heritage have approached this priority by creating national inventories of sites and buildings with a view to taking informed decisions on their future. This paper presents the argument that the wider international context of the Cold War provides a more appropriate (or additional, higher-level) framework for such decision making. Such a ‘transnational’ approach would allow the comparison of similar (e.g. European) sites not merely within national borders but across the full extent of their western NATO1 deployment in Europe and North America. Taking this approach would also allow comparison with related sites in countries that formed part of the eastern-bloc Warsaw Pact.2 After outlining some examples of how national agencies have approached their Cold War heritage, this paper presents the four stages of this transnational approach making provision for an improved understanding and management of Cold War heritage sites wherever they occur. With a specific focus on the direct comparison between England and Russia, and also referring to sites surviving elsewhere within the former NATO and Warsaw Pact regions, as well as the United States, we argue that this four-stage approach: provides new understandings of a complex archaeological and architectural record; gives fresh perspectives on significance; and (importantly in a time of geopolitical instability) does so in a spirit of cooperation and friendship