Theory of a frequency-step-tunable gyrotron for optimum plasma ECRH

A theory is presented which describes the dependence of the multimode operation of a gyrotron on the modulation and beam voltages. Nonlinear nonstationary processes are considered. An approximate start-up scenario of a gyrotron is determined which makes it possible to achieve single-mode excitation and high-efficiency operation in a desired mode, as well as to switch the tube to a similar operation in other modes     

On the π3He3He coupling

A critical discussion of different methods of estimation of the coupling constant f_π³He³He² is given. It is claimed that at present the best way of obtaining information on this coupling constant is to extrapolate certain differential cross sections, in particular, of the elastic ³He³H scattering, to the pion pole. The resulting value f_π³He³He² = 0.055 ± 0.020 is smaller than the corresponding pion-nucleon value. It supports the expected shadowing effects inside the nucleus but disagrees with other more model-dependent estimations.     

Extraction of nuclear coupling constants from data on nuclear charge form factors

A possibility of extracting nuclear coupling constants from data on nuclear charge form factors is discussed. The method exploits analytic properties of form factors in the momentum transfer plane. As an illustration the form factor of⁴He is considered in detail. In this case the value \(g_{4_{He^3 He(^3 H)} }^2 /4\pi = 16 \pm 1\) has been obtained in excellent agreement with earlier determinations by means of other methods. Similar analysis of the¹⁶O form factor yields the first estimate of the oxygen-nucleon coupling∶ \(g_{16_{O^{15} O(^{15} N)N} }^2 /4\pi = 64\) .     

A cavity with reduced mode conversion for gyrotrons

Mode conversion at discontinuities of an ordinary gyrotron cavity is examined. It is shown how the production of unwanted spurious modes can be reduced substantially by introducing smooth transition regions between the individual parts of the cavity. The cavity of the 140 GHz KfK gyrotron operating in the TE_10,4 mode is used as an example. Cavity and adjacent tapered output waveguide are optimized as a single unit.     

INFLUENCE OF MAGNETIC FIELD INHOMOGENEITY ON OPERATION OF THE THz GYROTRON WITH A PULSE MAGNET

Influence of magnetic field tapering on operation of a gyrotron working in the TE _4,12 mode at the second harmonic frequency 1013.67 GHz is investigated. It is found that the existing inhomogeneity of the magnetic field of the order of 0.25%–0.50% in the cavity allows one to achieve higher efficiencies. It improves also mode competition scenario by suppressing oscillations of the two parasitic TE _3,6⁺ and TE _5,5⁻ modes at the fundamental frequencies 513.35 GHz and 503.64 GHz, respectively.     

Design of Cavities for a Short Pulse Powerful Large Orbit Gyrotron

Designs of cavities for fundamental and high harmonic operation in Large Orbit Gyrotron (LOG) are discussed. The fundamental operation allows one to use beam currents in the range from 200 A to 300 A achieve output power of the order of 9–10 MW at frequency 143.6 GHz. Mode competition calculations show that stable oscillations in the TE^1,4 mode using high beam currents are possible even with the pitch factor 1.3 which is significantly lower than the design value 1.55. For the second harmonic operation, the maximum current used for excitation of the TE^2,4 mode is 60 A and the optimum magnetic field is 7.6 T. A cavity design for fourth harmonic operation using the TE^4,4 mode is also presented.     

Traces of Stochasticity in Electron Trajectories in Gyrotron Resonators

The Hamiltonian approach is used to analyze the equation describing the electron interaction in gyrotron resonators with realistic RF field profiles. A detailed numerical study of the behavior of electron trajectories for some specific values of parameters controlling the interaction is performed. It is found that in some cases chaos-like motions of electrons are possible.     

Magnetic field tapering in the KfK coaxial gyrotron

Equations describing the magnetic field tapering in a gyrotron cavity with allowance for the dependence of the radius of the electron guiding centers on the longitudinal coordinate are derived. Influence of the shift of the magnet of the KfK coaxial gyrotron along the gyrotron axis onefficiency is studied. It is found that for the operating voltage 90kV the optimal alignment is such that the maximum of the magnetic field is placed in the middle of the straight section of the cavity. For 80kV the absolute values of the field must be reduced by factor 1.017, or the maximum of the field must be placed in the output taper of the cavity.     

Theory of gyro-backward wave oscillators with tapered magneticfield and waveguide cross section

A theory is developed which describes gyro-backward wave oscillators (gyro-BWO's) with arbitrarily relativistic electron beams and tapered external magnetic field and waveguide wall radius. For the case of linear tapering the optimal parameters are found that correspond to highly efficient operation. The frequency tunability as the function of magnetic field and voltage deviations has been analyzed. It is shown how to use the results given in terms of normalized parameters for designing concrete gyro-BWO's. For one concrete design the effect of electron velocity spread on the efficiency has been studied     

Antiprotonic helium and lithium with one or two electrons

High rotational states of¯p He and¯pLi atoms with one or two electrons are calculated in the Born-Oppenheimer approximation, with a precision which allows a systematic study of diabatic effects. The lifetimes of the relevant¯peα and¯pee Li states are in the μs range.