Nikolai Yu. Peskov

Experimental and theoretical study of 2D Bragg structures for a coaxial free electron maser

Abstract Experimental results are presented of the first observation of two-dimensional distributed feedback in a coaxial 2D-Bragg structure. The use of two-dimensional distributed feedback has been proposed as a method of producing spatially coherent radiation from extremely powerful large sized relativistic electron beams. To obtain coherent high-power (GW) microwave and millimetre wave radiation, 2D Bragg resonators are needed to overcome the problems of mode selection and synchronisation of radiation from different parts of an oversized beam. The design and cold microwave measurements of a 2D Bragg coaxial structure for use in a Free Electron Maser (FEM) driven by an annular electron beam of circumference 25 times larger than the radiation wavelength is presented. The cavity for the 2D Bragg FEM consists of two 2D Bragg coaxial reflectors separated by a regular coaxial waveguide. The formation of pure two-dimensional distributed feedback without a mixture of one-dimensional parasitic feedback was demonstrated for the first time in this series of experiments. The first experimental comparison of 2D and 1D Bragg structures was also conducted and good agreement between experimental results and theoretical predictions was observed. The eigenmodes of the two-mirror cavity were calculated and it was shown that a single-mode steady-state operation regime could be obtained in a FEM based on such a novel cavity.

Powerful short wavelength fems operated at harmonics of bounce frequency: Recent results and prospects

Summary form only given. High-efficiency narrow-band 30-GHz Bragg FEM-oscillator was elaborated during the last few years in JINR-IAP collaboration based on 0.8 MeV / 200 A / 250 ns LINAC LIU-3000 (JINR). An attractive solution to prospect FEM into short wave-lengths keeping beam energy and geometry of electron-optical system is operation at harmonics of bounce-frequency. Two FEM schemes exploiting this idea are under development at LIU-3000.

Cherenkov oscillators with two-dimensional distributed feedback

Possibility to use a 2D distributed feedback for generation of spatially coherent radiation by a rectilinear electron beams in Cherenkov type devises is discussed. Theoretical and experimental studies of a Ka-band coaxial BWO with external 2D Bragg structure which operates as a synchronizer are presented.

FEM with high-selective Bragg resonator based on coupling of propagating and cutoff waves

Bragg FEM with a two-mirror resonator including advanced Bragg structure based on coupling of propagating and quasi-cutoff waves was studied. Implication of the cutoff wave into the feedback loop improves selectivity of the Bragg resonators over transverse coordinates and allows advance of FEM into short wavelengths up to THz-band. Operability of Bragg resonator of a novel type has been demonstrated in Ka-band JINR-IAP FEM.

Co-axial Ka-band free electron maser using two-dimensional feedback

The first successful experimental studies of microwave radiation from a co‐axial Free‐Electron Maser (FEM) based on two‐dimensional (2D) distributed feedback have been recently conducted. This paper contains a description of the experimental set‐up and the results obtained. The high‐power pulsed power supply and high‐current accelerator (HCA) developed and used to drive the FEM are discussed. The results of the experimental study of the FEM operating in the Ka frequency band are presented and compared with theoretical predictions.

High power free electron maser based on a two-dimensional Bragg cavity

Summary form only given. The use of two-dimensional (2D) Bragg structures has been suggested for application in microwave electronics and integrated optics to synchronise radiation from different parts of an oversized active medium and to improve mode selection inside the interaction space. Computational modelling and experimental measurements of the field evolution inside co-axial 2D Bragg structures as well as recent progress in the use of these structures to define the cavity of a high power Free Electron Maser (FEM) will be presented. The 2D Bragg cavity has been designed and constructed. Microwave measurements have been performed using a Vector Network Analyser. Good agreement between the measured transmission properties of the 2D Bragg structures and PIC code (MAGIC) simulations was obtained. The high current accelerator to drive the FEM consists of a Marx bank power supply which resonantly charges a transmission line which subsequently discharges through a high pressure (16 Bar) nitrogen-filled spark gap providing a 200 ns duration flat-top high voltage pulse to an explosive emission electron (EEE) gun diode immersed in a 0.6 T guide field provided by a 30 cm diameter 2.25 m long solenoid. The guide magnetic field insulates and confines an annular relativistic electron beam of energy 500 keV. The oversized (7 cm diameter) annular electron beam was passed through an azimuthally symmetric wiggler with the interaction space defined by two-dimensional (2D) Bragg structures. The maximum possible beam current transportable through the diode region and interaction space was calculated using the 2.5 D PIC code KARAT. An electron beam of power 750 MW has been measured in the experiment. An FEM output efficiency of up to 15% has been predicted by the calculations. This paper will present the progress made towards the generation of /spl sim/100 MW of power from the co-axial 2D Bragg FEM operating at a frequency of 37.5 GHz.

Project of powerful 4-beam planar FEM with distributed feedback for 75 GHz band

Theoretical and numerical considerations have shown that a planar FEM with 2-D distributed feedback is suitable to be used as a module for constructing multichannel devices to produce microwave radiation of GW level. Computer simulations for operation of 4-modules FEM-generator have demonstrated a perfect synchronization of all modules even at a little bit different energies of the electron beams. The project of 4-channel FEM-generator is designed on the base of the “ELMF”-device.

Recent results in generation of powerful pulses of 75GHz radiation at ELMI-device

The novel scheme of separation of the mm-wave radiation from the intense electron beam using planar Bragg wave transformer, is suggested and realized. In the experiments at the planar FEM with the new scheme of separation, the generation of powerful 4-mm radiation pulses was observed. The duration of these pulses is increased in two times in comparison with the old scheme of the beam dump and has reached 300ns. By means of the panel with neon lamps the angular distribution of the generated radiation at the exit of the maser is registered. The distribution of the luminescence intensity qualitatively agrees with the results of “cold” measurements and computer simulations.

Multichannel planar FEM as a base for archiving large energy content in pulses of coherent mm-radiation

Novel approach to generate GW power microwave radiation on the basis of multichannel planar FEM-generator is investigated both theoretically and numerically. The problem of cophase operation of many generation channels is solved. The project of 4 channel FEM-generator is considered.