• A. Opanasenko, V.V. Mytrochenko, S.A. Perezhogin
  NSC/KIPT, Kharkov

The electron injector for a storage ring is one of numerous applications of the rf linacs of intensive short-pulsed beams with duration about 100 ns, current about 1 A and energy of particles in a few ten MeB. Since acceleration of intensive short-pulsed beams takes place in transient mode, then the energy spread is determined by both intro- and multi- bunch spread. Getting the energy spread less than 1% is the actual problem. In this work we simulate numerically unsteady self-consistent dynamics of charged particles in an rf linac that consist of a low-voltage (25 keV) thermionic gun, a compact evanescent wave buncher, a traveling wave accelerating structure. For transient beam loading compensation a method of delay of a beam relatively rf pulse are applied. The simulation takes into account influence on the beam dynamic of such factors as: initial energy and phase spread; sliding of particles in relation to a wave in the initial part of accelerating section; temporal dependence of phase and energy of bunches at the enter of section; space charge field.

• A. Opanasenko
  NSC/KIPT, Kharkov

Acceleration of intensive electron beams in transient mode with energy spread less than 1% is the actual problem for rf linacs. The transient beam loading phenomenon, consisting in coherent radiation of sequence of charged bunches, results in time dependence of electron energy loss within a beam pulse. In this work a method of delay of a beam relatively rf pulse for energy compensation at accelerating intense short-pulsed electron beams is discussed. An efficiency of the given method in depending on dispersion of group speed, phase advance per cell of an rf structure, an envelope profile of pulses both current and input rf field is studied. Contribution of non-resonant counter waves in the beam energy spread is estimated.

• A. Opanasenko, V.S. Kovalenko, K. Kramarenko, V.A. Kushnir, V.V. Mytrochenko, Z.V. Zhiglo, A. I. Zykov
  NSC/KIPT, Kharkov

At present work the results of numeral simulation of electron dynamics in an unhomogeneous disk-loaded waveguide which is used in the S-band linac are presented. Two approaches taking into account the self-fields of beam radiation are considered: the first method estimative based on the power diffusion equation; the second one based on of self-consistent equations of field excitation and particles motion. The self-consistent approach showed the presence of substantial phase slipping of particles in the homogeneous part of the rf structure, conditioned by the reactive beam loading.

• V.V. Mytrochenko, M.I. Ayzatskiy, V.A. Kushnir, A. Opanasenko, S.A. Perezhogin, Z.V. Zhiglo
  NSC/KIPT, Kharkov

Simulation results of subpicosecond bunch formation due to phase motion of electrons in traveling wave are presented. It has been shown that at satisfying phase conditions of electron injection that are necessary for velocity bunching, relative phase velocity of the total wave excited both by RF generator and particles becomes different from unit increasing bunch compression. Simulation of transportation of obtained 8.5 MeV bunches through undulator with a period of 90.6 mm and estimation of bunch form-factor at 446 harmonic of bunch repetition rate of 2797.15 MHz also was carried out. The data obtained allow to expect coherent radiation from undulator at wave-length of 240 um.

• A. Opanasenko
  NSC/KIPT, Kharkov

In a 1956 article* Panofsky and Wenzel derived the relation for the net transverse kick experienced by a fast charge particle crossing a closed cavity excited in a single rf mode. Later on this relation, usually referred to the Panofsky-Wenzel theorem, was generalized for cavity containing wake field induced by a driving charge. This theorem has played very important role in the accelerator physics. One well-known conclusion of this paper was that in a TE mode the deflecting impulse of the electric field always cancels the impulse of the magnetic fields. In our presentation we more exactly rederive Panofsky and Wenzel's result and obtain correction terms to the transverse kick. We show that in a TE mode the net transverse kick does not zero but is determined by a ponderomotive force. Using the given approach we find correction terms to wake potentials which are inversely proportional to the relativistic factor. Practical implications of our results are discussed.

* W.K.H. Panofsky and W.A. Wenzel, Rev. Sci. Instrum. 27, 967 (1956).