Stable Beam Transport Research Articles

Three Dimensional Alternating-Phase Focusing for Dielectric-Laser Electron Accelerators.

The concept of dielectric-laser acceleration (DLA) provides the highest gradients among breakdown-limited (nonplasma) particle accelerators and thus the potential of miniaturization. The implementation of a fully scalable electron accelerator on a microchip by two-dimensional alternating phase focusing (APF), which relies on homogeneous laser fields and external magnetic focusing in the third direction, was recently proposed. In this Letter, we generalize the APF for DLA scheme to 3D, such that stable beam transport and acceleration is attained without any external equipment, while the structures can still be fabricated by entirely two-dimensional lithographic techniques. In the new scheme, we obtain significantly higher accelerating gradients at given incident laser field by additionally exploiting the new horizontal edge. This enables ultralow injection energies of about 2.5keV (β=0.1) and bulky high voltage equipment as used in previous DLA experiments can be omitted. DLAs have applications in ultrafast time-resolved electron microscopy and diffraction. Our findings are crucial for the miniaturization of the entire setup and pave the way towards integration of DLAs in optical fiber driven endoscopes, e.g., for medical purposes.

Alternating-Phase Focusing for Dielectric-Laser Acceleration.

The concept of dielectric-laser acceleration provides the highest gradients among breakdown-limited (nonplasma) particle accelerators. However, stable beam transport and staging have not been shown experimentally yet. We present a scheme that confines the beam longitudinally and in one transverse direction. Confinement in the other direction is obtained by a single conventional quadrupole magnet. Within the small aperture of 420nm we find the matched distributions, which allow an optimized injection into pure transport, bunching, and accelerating structures. The combination of these resembles the photonics analogue of the radio frequency quadrupole, but since our setup is entirely two dimensional, it can be manufactured on a microchip by lithographic techniques. This is a crucial step towards relativistic electrons in the MeV range from low-cost, handheld devices and connects the two fields of attosecond physics and accelerator physics.

Heavy ion beam final transport through an insulator guide in heavy ion fusion

Key issues of heavy ion beam (HIB) inertial confinement fusion (ICF) include an efficient stable beam transport, beam focusing, uniform fuel pellet implosion, and so on. To realize a HIB fine focus on a fuel pellet, space-charge neutralization of incident focusing HIB is required at the HIB final transport just after a final focusing element in an HIB accelerator. In this article, an insulator annular tube guide is proposed at the final transport part, through which a HIB is transported. The physical mechanism of HIB charge neutralization based on an insulator annular guide is as follows: A local electric field created by HIB induces local discharges, and plasma is produced on the insulator inner surface. Then electrons are extracted from the plasma by the HIB net space charge. The electrons emitted neutralize the HIB space charge well.

Multimirror open Trap Gol-3: Recent Results

Review of the experimental results for the last two years on study of dense plasma heating and confinement in a long multimirror trap GOL-3 is presented. This facility is an open trap for confinement of hot (0.1-1 keV) dense (1015-1016 cm−3) plasma. The plasma heating is provided by a high-power electron beam (1 MeV, 30 kA, 8 μs) with energy content of up to 200 kJ. The upgrade to full-scale corrugation of a magnetic field was completed at the facility during last two years. In the 12-meter solenoid the multimirror sections of 4-m-length were made at the both ends of the solenoid (Bmax/Bmin = 5,2 / 3,2 T, cell length is 22 cm). The modified source of preliminary plasma was put in operation for improvement of macroscopically stable beam transport through the plasma column. New diagnostics were developed for the experiments. Search of optimal conditions for confinement of plasma with ~1015 cm−3 density and high ion temperature, and also for macroscopically stable system “electron beam - plasma” was carried out in the new configuration of facility. As a result of the experiments the plasma with density of (1-2)·1015 cm−3, neTe+niTi =(0.5-2)·1015 keV/cm3 and confinement time of 100-200 microseconds in a multimirror trap is obtained. The observations of high ion temperature and mechanism of ion heating is discussed in the paper.

Beam Transport Issues in High Current Linear Accelerators

Stable beam transport may be the limiting factor in the development of a new generation of high current linear induction accelerators. In this paper we analyze several important beam stability topics, including radial oscillations induced by an accelerating gap, the diocotron, resistive wall, and cyclotron maser instabilities, and the transverse beam breakup and image displacement instabilities. At present image displacement appears to represent the most serious limitation to high current beam transport in linear accelerator structures.