Christos Kapetanakos - Academia.edu (original) (raw)
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Papers by Christos Kapetanakos
A detailed numerical and analytical study of the beam dynamics in a rebatron accelerator has show... more A detailed numerical and analytical study of the beam dynamics in a rebatron accelerator has shown that energies approaching 1 GeV can be achieved within 5-10 IlS. Since the acceleration in the rebatron occurs within a short time, the device may not be sensitive to the various instabilities, and the loss to synchrotron radiation should be small. The rapid acceleration is produced by convoluted parallel transmission lines, which provide a high-gradient electric field. At the initial stage of the acceleration, the beam is confined inside the torus by a strong focusing torsatron magnetic field, which makes the beam insensitive to the energy mismatch and to the external field index of a vertical magnetic field. This local field is generated by two coaxial cylindrical plates, located symmetrically around the major axis of the torus and carrying currents in opposite directions. The energy of the beam increases in synchronism with the vertical magnetic field so that the beam remains matched (i.e., the beam radius remains constant) during the entire acceleration. It was found that, as a result of the periodic nature of the acceleration, resonances can be excited, which cause the orbits to expand. The only disruptive resonance occurs at 'Y == 1830, i.e., when the vertical magnetic field reaches twice the value of the toroidal magnetic field.
Public reponang biuden for fte colecton of infoantilon is exbrnsted to average I h • w Per,eepone... more Public reponang biuden for fte colecton of infoantilon is exbrnsted to average I h • w Per,eepone. including the time for revewng istruetions. esercing exmiting dats sourcee, getheldo iand miairgining dh data needed. and comnplting end reviewing the collection of informetion. Send coments regarding the buden eetimete or any other aspect of thie
: Analytical and computer simulation results are reported on the effect of the external field ind... more : Analytical and computer simulation results are reported on the effect of the external field index fluctuations on the dynamics of a high current electron ring in a modified betatron. These non-linear studies clearly demonstrate that the external field index fluctuations are, in general, harmless to the high current ring. In addition, it was found that a small (1%) temperature spread parallel to the direction of propagation excites oscillations in the rms emittance, but the amplitude of these oscillations is substantially lower than in a conventional betatron. (Author)
The present invention is directed toward a modified betatron design. Betatron accelerators genera... more The present invention is directed toward a modified betatron design. Betatron accelerators generally comprise an annular or toroidal vacuum chamber with a time-varying magnetic field, referred to as the betatron field, disposed relative to the toroidal chamber for the purpose of accelerating charged particles injected in the chamber. Typically, the strength of this betatron field is designed to be maximal along the major axis of the toroid and is designed to decrease with radial distance. Accordingly, electrons injected tangentially are accelerated at a constant radius by this betatron field into a privileged orbit known as the betatron orbit.
Physical Review Letters, 1978
October, 1977, edited by R. M. DeV~ies (Univ. of Rochester, to be published).
Physics of Fluids B: Plasma Physics, 1991
This paper briefly surveys the three compact, high-current accelerators that are presently under ... more This paper briefly surveys the three compact, high-current accelerators that are presently under development in the United States in support of a national program. In addition, it reports recent experimental results from the Naval Research Laboratory (NRL) modified betatron [Phys. Rev. Lett. 64, 2374 (1990)] with emphasis on the electron-cyclotron resonance that presently limits the energy of the beam to approximately 18 MeV. Finally, it briefly addresses selective existing and prospective applications of accelerators.
IEEE Journal of Quantum Electronics, 2001
This paper describes numerical and analytical studies on the optimization of the ultra-broadband ... more This paper describes numerical and analytical studies on the optimization of the ultra-broadband infrared (IR) source, a novel high average-power device [1]. The main objective of current studies was the reduction of weight, size, and cost of the system by devising a scheme to generate the two closely spaced radiation lines with a single laser driver instead of the two CO 2 transversely excited atmospheric pressure (TEA) lasers envisioned in the initial work. By inducing the modulation instability in nonlinear media, we have obtained as good or better results as in our previous studies but with one of the TEA lasers replaced by a very low-power driver that provides the seed radiation for the excitation of the instability. Even more importantly, we have demonstrated that the second high peak-power TEA laser can be replaced by a compact, light weight, low peak-power driver by focusing the radiation to a tighter spot. The average power of the source is maintained at the previous level by operating at higher duty factor. In the new low-peak-power operating regime, the output spectrum is very similar to that of the high-power regime, provided that the ratio of the peak power to the nonlinear length that scales proportionally to the area of the laser spot remains fixed.
American Scientist, 1981
Page 1. Jeffry Golden Christos A. Kapetanakos John A. Pasour Redge A. Mahaffey The Generation and... more Page 1. Jeffry Golden Christos A. Kapetanakos John A. Pasour Redge A. Mahaffey The Generation and Application of ... He is currently a section head in the Beam Dynamics Program at NRL. Christos A. Kapetanakos holds a Ph.D. from the University of Maryland. ...
Analytical and computer simulation results are reported on the effect of spatial fluctuations of ... more Analytical and computer simulation results are reported on the effect of spatial fluctuations of the externalfield index on the dynamics of a high-current electron ring in a modified betatron. These nonlinear studies clearly demonstrate that the external field-index fluctuations are, in general, harmless to the high-current ring. In addition, it was found that a small (I"J 1%) temperature spread parallel to the direction of propagation excites oscillations in the rms emittance, but the amplitude of these oscillations is substantially lower than in a conventional betatron.
The dynamics of an intense electron ring confined in a modified betatron magnetic field is consid... more The dynamics of an intense electron ring confined in a modified betatron magnetic field is considered. The analysis assumes that the electron ring is located near the center of a conducting torus and includes self fields, induced fields from the walls surrounding the ring and toroidal effects. It has been found that the geometric center of the ring can perform circular motion around the minor axis of the torus. Based on this analysis, a scheme is proposed for the injection of an intense electron beam into a modified betatron accelerator.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1985
Abstract A two-stage FEL oscillator is proposed as a high-power source of infrared radiation. Suc... more Abstract A two-stage FEL oscillator is proposed as a high-power source of infrared radiation. Such a device is attractive because it employs a relatively low-energy electron beam, which can significantly reduce the size and cost of the system. The steady-state parameters for a 10-μm, 750-MW FEL are presented, and the start-up, resonator configuration and electron beam requirements are discussed. Although there are several significant technical issues and further analysis is required, it appears as if the approach is feasible.
Physical Review Letters, 1977
Results are reported from a numerical-simulation study on the propagation of a rotating proton pu... more Results are reported from a numerical-simulation study on the propagation of a rotating proton pulse and the formation and trapping of the resulting strong proton ring. It is observed that the self-magnetic field has a very pronounced effect on the dynamics of such systems, and is responsible for a somersaulting and energy spread of the beam.
Plasma Physics, 1973
The conclusions of Shen and Hsuan (see abstr. A44173 of 1971) are reexamined. It is shown here th... more The conclusions of Shen and Hsuan (see abstr. A44173 of 1971) are reexamined. It is shown here that in the case of linearly varying field the alleged 'anomalous drift' is the expected E*B/B2 drift of the guiding center of the gyrating particle, where E is the induced electric field computed in the position of the guiding center. In the case of sinusoidally varying field the 'anomalous drift' is probably due to a computational error. The case of each field is separately discussed.
A detailed numerical and analytical study of the beam dynamics in a rebatron accelerator has show... more A detailed numerical and analytical study of the beam dynamics in a rebatron accelerator has shown that energies approaching 1 GeV can be achieved within 5-10 IlS. Since the acceleration in the rebatron occurs within a short time, the device may not be sensitive to the various instabilities, and the loss to synchrotron radiation should be small. The rapid acceleration is produced by convoluted parallel transmission lines, which provide a high-gradient electric field. At the initial stage of the acceleration, the beam is confined inside the torus by a strong focusing torsatron magnetic field, which makes the beam insensitive to the energy mismatch and to the external field index of a vertical magnetic field. This local field is generated by two coaxial cylindrical plates, located symmetrically around the major axis of the torus and carrying currents in opposite directions. The energy of the beam increases in synchronism with the vertical magnetic field so that the beam remains matched (i.e., the beam radius remains constant) during the entire acceleration. It was found that, as a result of the periodic nature of the acceleration, resonances can be excited, which cause the orbits to expand. The only disruptive resonance occurs at 'Y == 1830, i.e., when the vertical magnetic field reaches twice the value of the toroidal magnetic field.
Public reponang biuden for fte colecton of infoantilon is exbrnsted to average I h • w Per,eepone... more Public reponang biuden for fte colecton of infoantilon is exbrnsted to average I h • w Per,eepone. including the time for revewng istruetions. esercing exmiting dats sourcee, getheldo iand miairgining dh data needed. and comnplting end reviewing the collection of informetion. Send coments regarding the buden eetimete or any other aspect of thie
: Analytical and computer simulation results are reported on the effect of the external field ind... more : Analytical and computer simulation results are reported on the effect of the external field index fluctuations on the dynamics of a high current electron ring in a modified betatron. These non-linear studies clearly demonstrate that the external field index fluctuations are, in general, harmless to the high current ring. In addition, it was found that a small (1%) temperature spread parallel to the direction of propagation excites oscillations in the rms emittance, but the amplitude of these oscillations is substantially lower than in a conventional betatron. (Author)
The present invention is directed toward a modified betatron design. Betatron accelerators genera... more The present invention is directed toward a modified betatron design. Betatron accelerators generally comprise an annular or toroidal vacuum chamber with a time-varying magnetic field, referred to as the betatron field, disposed relative to the toroidal chamber for the purpose of accelerating charged particles injected in the chamber. Typically, the strength of this betatron field is designed to be maximal along the major axis of the toroid and is designed to decrease with radial distance. Accordingly, electrons injected tangentially are accelerated at a constant radius by this betatron field into a privileged orbit known as the betatron orbit.
Physical Review Letters, 1978
October, 1977, edited by R. M. DeV~ies (Univ. of Rochester, to be published).
Physics of Fluids B: Plasma Physics, 1991
This paper briefly surveys the three compact, high-current accelerators that are presently under ... more This paper briefly surveys the three compact, high-current accelerators that are presently under development in the United States in support of a national program. In addition, it reports recent experimental results from the Naval Research Laboratory (NRL) modified betatron [Phys. Rev. Lett. 64, 2374 (1990)] with emphasis on the electron-cyclotron resonance that presently limits the energy of the beam to approximately 18 MeV. Finally, it briefly addresses selective existing and prospective applications of accelerators.
IEEE Journal of Quantum Electronics, 2001
This paper describes numerical and analytical studies on the optimization of the ultra-broadband ... more This paper describes numerical and analytical studies on the optimization of the ultra-broadband infrared (IR) source, a novel high average-power device [1]. The main objective of current studies was the reduction of weight, size, and cost of the system by devising a scheme to generate the two closely spaced radiation lines with a single laser driver instead of the two CO 2 transversely excited atmospheric pressure (TEA) lasers envisioned in the initial work. By inducing the modulation instability in nonlinear media, we have obtained as good or better results as in our previous studies but with one of the TEA lasers replaced by a very low-power driver that provides the seed radiation for the excitation of the instability. Even more importantly, we have demonstrated that the second high peak-power TEA laser can be replaced by a compact, light weight, low peak-power driver by focusing the radiation to a tighter spot. The average power of the source is maintained at the previous level by operating at higher duty factor. In the new low-peak-power operating regime, the output spectrum is very similar to that of the high-power regime, provided that the ratio of the peak power to the nonlinear length that scales proportionally to the area of the laser spot remains fixed.
American Scientist, 1981
Page 1. Jeffry Golden Christos A. Kapetanakos John A. Pasour Redge A. Mahaffey The Generation and... more Page 1. Jeffry Golden Christos A. Kapetanakos John A. Pasour Redge A. Mahaffey The Generation and Application of ... He is currently a section head in the Beam Dynamics Program at NRL. Christos A. Kapetanakos holds a Ph.D. from the University of Maryland. ...
Analytical and computer simulation results are reported on the effect of spatial fluctuations of ... more Analytical and computer simulation results are reported on the effect of spatial fluctuations of the externalfield index on the dynamics of a high-current electron ring in a modified betatron. These nonlinear studies clearly demonstrate that the external field-index fluctuations are, in general, harmless to the high-current ring. In addition, it was found that a small (I"J 1%) temperature spread parallel to the direction of propagation excites oscillations in the rms emittance, but the amplitude of these oscillations is substantially lower than in a conventional betatron.
The dynamics of an intense electron ring confined in a modified betatron magnetic field is consid... more The dynamics of an intense electron ring confined in a modified betatron magnetic field is considered. The analysis assumes that the electron ring is located near the center of a conducting torus and includes self fields, induced fields from the walls surrounding the ring and toroidal effects. It has been found that the geometric center of the ring can perform circular motion around the minor axis of the torus. Based on this analysis, a scheme is proposed for the injection of an intense electron beam into a modified betatron accelerator.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1985
Abstract A two-stage FEL oscillator is proposed as a high-power source of infrared radiation. Suc... more Abstract A two-stage FEL oscillator is proposed as a high-power source of infrared radiation. Such a device is attractive because it employs a relatively low-energy electron beam, which can significantly reduce the size and cost of the system. The steady-state parameters for a 10-μm, 750-MW FEL are presented, and the start-up, resonator configuration and electron beam requirements are discussed. Although there are several significant technical issues and further analysis is required, it appears as if the approach is feasible.
Physical Review Letters, 1977
Results are reported from a numerical-simulation study on the propagation of a rotating proton pu... more Results are reported from a numerical-simulation study on the propagation of a rotating proton pulse and the formation and trapping of the resulting strong proton ring. It is observed that the self-magnetic field has a very pronounced effect on the dynamics of such systems, and is responsible for a somersaulting and energy spread of the beam.
Plasma Physics, 1973
The conclusions of Shen and Hsuan (see abstr. A44173 of 1971) are reexamined. It is shown here th... more The conclusions of Shen and Hsuan (see abstr. A44173 of 1971) are reexamined. It is shown here that in the case of linearly varying field the alleged 'anomalous drift' is the expected E*B/B2 drift of the guiding center of the gyrating particle, where E is the induced electric field computed in the position of the guiding center. In the case of sinusoidally varying field the 'anomalous drift' is probably due to a computational error. The case of each field is separately discussed.