Therapeutic hyperthermia (including RF hyperthermia) in combination with radiotherapy (called thermoradiotherapy) is one of widely used contemporary cancer treatment methods. The independent electron linac and RF system or their combinations are necessary for effective therapy. Whole-body hyperthermia is used for treatment of metastatic cancer that was spread throughout the body, regional one is used for treatment of part of the body (for instance leg or abdominal cavity). Local hyperthermia with characteristic size of heating volume of 20-100 mm permits to heat tumour without overheating of healthy tissues. The thermometry of deep suited tissues during the hyperthermia process is an important and complex task. Invasive methods as thermistors, optical sensors or thermo-couples can not be widely used because all of them are able to transport tumor cells to the healthy region of the patient body. Distant methods of the temperature measurement such, as radiothermometry and acoustic thermometry can not be used for tissues seated deeper than 5-7 cm. One of possible ways to solve the problem of temperature measurement of the deep suited tissues is discussed in this article: it was proposed to use the same electrodes for RF hyperthermia and thermometry. As known electrodynamics characteristics of tissues are sufficiently depends on temperature. It was proposed to use this effect for active radiothermometry in local hyperthermia. Two opposite RF dipoles can be used as generator and receiver of pick-up signal.

A high-power broadband free electron maser (FEM) amplifier has been realized in collaboration between JINR (Dubna) and IAP RAS (Nizhny Novgorod) based on the linac LIU-3000 (0.8 MeV/200 A/250 ns). To achieve a wide frequency amplification band, the regime characterized by grazing of the dispersion curves of the beam electrons to the operating wave (the so-called grazing regime) was studied in the FEM. According to the simulations, such an operating regime allows an instant amplification band of up to 5%–7% with output power at the level ∼20 MW and a gain of about 30–35 dB to be obtained in the Ka band. The proof-of-principle experiments examined this scheme in the 30-GHz frequency range and confirmed the simulations. As a result, the predicted power level with design parameters has been achieved, and fast frequency tuning within the feeding magnetron band ±0.5 GHz has been demonstrated.

Splitting of the fundamental mode in an oversized Bragg resonator with a step of the corrugation phase, which operates over the feedback loop involving the waveguide waves of different transverse structures, was found to be the result of mutual influence of the neighboring zones of the Bragg scattering. Theoretical description of this effect was developed within the framework of the advanced (four-wave) coupled-wave approach. It is shown that mode splitting reduces the selective properties, restricts the output power, and decreases the stability of the narrow-band operating regime in the free-electron maser (FEM) oscillators based on such resonators. The results of the theoretical analysis were confirmed by 3D simulations and “cold” microwave tests. Experimental data on Bragg resonators with different parameters in a 30-GHz FEM are presented. The possibility of reducing the mode splitting by profiling the corrugation parameters is shown. The use of the mode splitting effect for the output power enhancement by passive compression of the double-frequency pulse generated in the FEM with such a resonator is discussed.

Powerful high-efficiency FEM-amplifier operating over Ka frequency range and aimed on accelerating applications is developed in collaboration between IAP RAS and JINR. To achieve a broad amplification band in a regular wiggler, we utilized the so-called grazing regime, in which about of 20 MW of output power was simulated in the frequency range of 30 ± 3 GHz. In the first stage of experiments, the designed power level and the instantaneous band of about 1 GHz (restricted by the tuning band of the driving magnetron) have been demonstrated. According to the simulations, the use of the regime of non-resonant trapping in tapered wiggler allows enhance in the output power up to 35-40 MW with simultaneous widening of the amplification band. Experimental realization of this novel FEM-amplifier scheme is currently in progress.

Therapeutic hyperthermia in combination with radiotherapy which is realized by means of modern linear electron accelerators (called thermoradiotherapy) is one of widely used contemporary cancer treatment methods. Hyperthermia provides increasing of the tumors sensibility to radiation. Thus the radiation dose could be decreased. The experience achieved at N.N. Blokhin Russian Cancer Research Center during 40 years shows that 5-year survival rate increases (15-40%) for a number of cancer types and localization. High dose can be easily delivered to the deep seated tumors but local heating is a big problem so far. One possible way to solve the problem of deep tissues local heating is discussed in this article, the brief review of previous simulations and latest results for experimental prototype setup are presented.

The frequency multiplication effects in high-power free-electron masers (FEM) with Bragg cavities were studied to provide the advance of the oscillators into short-wavelength bands. Theoretical analysis of frequency-multiplying FEMs was carried out within the framework of the averaged coupled-wave approach. Proof-of-principle experiments were performed based on a moderately relativistic induction linac LIU-3000 (JINR). As a result, an FEM multiplier operated with a megawatt power level in the 6-mm and 4-mm wavelength bands at the second and third harmonics, respectively, was realized. The possibility of using two-mode bichromatic FEMs for powering a double-frequency accelerating structure was discussed.

Hyperthermia is a promising approach to improve of the chemo- and the radiotherapy efficiency by means of increasing tumor's temperature. Hyperthermia is an additional method to conventional treatments of oncological disease wherein tumor temperature is increased up to 40...43 degrees C. The phased array of applicators for electromagnetic hyperthermia was suggested earlier. The heating is provided by absorption of electromagnetic energy focused in tumor by varying phases and amplitudes of each of dipoles. Operating frequency plays the significant role in specific absorption rate (SAR) distribution forming. The phased array antenna is under consideration. Principles of choosing of operating frequency are discussed. Numerical estimates of heat localization depending on the radiation area are presented. Also simulation results with voxel model are considered.

The possibility of using frequency multiplication in order to obtain high-power short-wavelength radiation from a free-electron maser (FEM) with a Bragg resonator has been studied. Preliminary experiments with an LIU-3000 (JINR) linear induction accelerator demonstrate the operation of a frequency-multiplying FEM at megawatt power in the 6- and 4-mm wave bands on the second and third harmonic, respectively.

The system for local hyperthermia of cancers was simulated. This system is based on independently phased dipoles with frequency 150 MHz. The electromagnetic field distributions are calculated in cut of tissue-equivalent phantom. It was shown that the electromagnetic field can be focused in,desirable volume by means of independent vary of amplitude and phase of each dipole. The advantages of combined therapy are discussed for common using of hyperthermia with chemotherapy, radiation therapy or surgery.

Experiments to investigate copper surface fatigue caused by pulsed rf radiation were carried out using the 30 GHz free electron maser. The copper surface of a special test cavity was exposed to 15-20 MW/150-200 ns rf pulses with a repetition rate of 1 Hz, providing a temperature rise of up to 250 degrees C in each pulse. An electron microscope was used to study the copper surface both before and after exposure to 10(4)-10(5) rf pulses. An examination of the copper microstructure and cracks which developed during the experiment was made. Dramatic degradation of the copper surface and causes of very frequent breakdown were observed when the total number of rf pulses reaches 6 x 10(4).

Thermal fatigue of the surface of copper subjected to multiply repeated pulsed microwave heating has been studied in order to estimate the maximum permissible acceleration rate for the CLIC collider at CERN. For this purpose, the damage of copper rings in a test cavity of the JINR-IAP facility was traced under the action of 104–105 microwave pulses at a temperature rise up to 190–250 K in every pulse. The test cavity was loaded by pulses of a high-power 30-GHz free-electron maser. Data on the dynamics of damage developed on the copper surface under the action of a strong electromagnetic field in the cavity are presented.

The facility for joint experiments of JINR-IAP RAS has been commissioned to investigate the lifetime dependence of the CLIC high-gradient accelerating structure on the surface damage by repetitive high-power RF pulses. The facility is based on the 30 GHz JINR free-electron maser, which uses an electron beam of the induction linear accelerator LIU-3000. Intermediate optical observations of the central ring allowed us to control the process of the damage evolution. The first damage of the copper surface have been observed after 1.6*10 pulses with the pulse heating of 250oK. After 6*10 pulses the damage of the surface of the oxygen-free copper cavity became strong enough to cause regular breakdowns inside the test cavity.

The possibility of using picosecond high-current relativistic electron beams for the formation of tubular rotating relativistic electron rings is investigated. Longitudinal compression of a tubular beam in a cusp is simulated numerically disregarding the space charge effects. The behavior of the characteristics of a compressed beam, which determines the tolerances in the initial parameters and magnetic system parameters, is investigated.

A model of the unstable stage of a spark discharge in vacuum is proposed, which describes all typical manifestations of this stage, including current spikes in the diode, an increase in the potential at the cathode flame front, collective acceleration of ions in vacuum and plasma diodes, change in the cathode erosion mechanism, and the emergence of electron microbeams with a high current density at the anode. It is shown that these processes are associated with the formation of a charged electron layer of a spatially inhomogeneous plasma at the cathode flame boundary at the unstable stage of the spark discharge in vacuum. The emergence of this layer is associated with a limited emissive ability of the plasma at the cathode flame front during its expansion in vacuum. This leads to disruption of the plasma (field-induced emission of electron from the boundary region of the flame) and the formation of a short-lived charged plasma, viz., high-density ion cluster at the cathode flame boundary. The estimates obtained using this model are in good agreement with the experimental data on physical processes at the unstable stage of a vacuum spark discharge.

The problem of non-linear beam dynamics simulations based on the moment method is discussed. A new simulation method allows the study of non-linear effects, such as increasing emittance, a varying density profile and asymptotic behavior of the beam.

The effect of random phase perturbations on the particle dynamics that arise when the microwave power is extracted from the two-beam accelerator driver with an accompanying wave is considered. The beam dynamics in the driver is simulated as a function of the phase perturbation. Tolerances of the wave amplitude and phase in the sections where the power is extracted from the driver are determined.

A project to generate powerful sub-mm pulses in JINR-IAP FEM-oscillator driven by 0.8 MeV / 200 A linac is in progress. Present paper describes recent design and key elements of the oscillator.

Beam-wave dynamics in two-beam accelerator driver with accompanying wave is studied with numerical simulations. Special attention is paid to the problems of phase stability and tolerances for microwave extraction facilities.