High-current e-Beam Formation
Formation of High Current Relativistic Electron Beam with Subnanosecond Front Duration by Means of a Shock Electromagnetic Wave.
Tech Area / Field
- PHY-PFA/Particles, Fields and Accelerator Physics/Physics
3 Approved without Funding
MRTI (Radio Techniques), Russia, Moscow
- VNIIEF, Russia, N. Novgorod reg., Sarov
- Los-Alamos National Laboratory, USA, NM, Los-Alamos\nImperial College of Science, Technology and Medicine / Blackett Laboratory, UK, London\nTexas Technical University / Pulsed Power Laboratory, USA, TX, Lubbock\nUniversity of California / Department of Physics, USA, CA, Irvine
Project summaryAt the present time there is a strong trend towards using high-power accelerator facility for technology applications. Great interest has been demonstrated by participants of the last international conferences (BEAMS'94, Pulse Power95) in this problem.
By now the technology of high-power high-current relativistic electron beams with submicrosecond duration has been developed. The same technology is used in high-power electric pulse generation. However also the high-power beams of subnanosecond front/pulse duration are necessary for some investigations and applications. The maximum power parameter achieved by means of the usual technology in this area is limited by a value in the range of 100 -300 MW (See diagram on the next page). For this reason a search for new ways to generate high-power REB (relativistic electron beams) of this kind is a topical problem. It is obvious that this problem may be reduced to the generation of pulses with a subnanosecond front duration. There are many methods to shorten a pulse duration to its front duration, for instance, by using parts of short-circuited transmission lines.
In view of the fact that the vacuum insulator of a diode of a high-power accelerator is the element with the minimum electric strength and the minimum transmitted flow of electromagnetic energy, final front shortening has to take place in the vacuum part of the high-voltage diode. In our opinion, a magnetically insulated transmission line (MITL) is the best place to sharpen the high-voltage pulse, because of its capacity to transmit a considerable flow of the electromagnetic energy.
The phenomenon of the front sharpening can take place in a MITL, because the velocity of the electron flow in a MITL depends on the voltage. However the finite time of electron emission and a weak nonliniarity lead to the limitations of this process. The best front duration achieved in a MITL is ~4 ns. The strong nonlinear element is effective at increasing the shock electromagnetic wave generation efficiency. A dielectric rod inserted in the inner electrode of the MITL may be considered as an element of this sort. The velocity of the electromagnetic wave and consequently the electron flow is determined by the speed of the flashover front along the dielectric surface. The flashover front converts the dielectric surface to the conducting state and allows the electromagnetic wave to propagate. It should be noted that the speed of the flashover front may be sufficiently high due to high value of the electric field in the front region, but this speed can not be a relativistic one because of the influence of the ions. In our opinion the region of the MITL with the inner dielectric insert is close to ideal for electromagnetic shock wave generation because of the very steep flashover characteristics.
Correlation between Peak Power and Pulses Rise Time
of High Power Generators and High Current Particle
A.High Power High-Current Particle Beam Accelerators (PBFA-II, Hermes-III, Aurora). 1 - Typical Accelerators.
2 - Special compact short pulse Accelerators.
B. High Power Electric Pulse and EMP Generators.
3 - Super Power EMP Generators.
4 - Typical EMP Generators.
5 - Semiconductor Generators.
C. Preliminary experiments in MRTI.
D. Our Hypothesis (the MITL with dielectric insert)
The MRTI Research Group in collaboration with the ARRIEP Research Group proposed to make investigation of a shock electromagnetic wave in a quite short modified magnetically insulated transmission line connected with a diode of a high-power electron accelerator. The line modification resides in an inner coaxial dielectric insert. High-current relativistic electron beam (20 - 30 kA, 2.5 - 3.0 MeV) with sub-nanosecond front duration is generated in this structure as a result of a shock electromagnetic wave excitation. Both experimental and theoretical studies of an influence of an insert material, a structure geometry and an external pulse magnetic field are suggested. Ones the experiments have been provided in the single mode regime, they are repeated in the repetitive mode with a repetitive rate 10-50 Hz.
To do this experimental work would require a pick up and monitoring system for signals in the range of picoseconds. The proposed project contains new solutions and designs in the aria of basic research of high-power relativistic electron beams. The investigations are unique in very high values of electron beam current and its energy. This work will provide an opportunity for the designers of accelerators for weapons applications to utilize their experience and talents for peaceful purposes and to use the generated electron beams in the field of industry (materials processing, the surface modification, pulse x-ray non-destructive testing, x-ray lithography), medicine and biology (as a source of bright x-ray pulses) and energy production (x-ray photography of control nuclear fusion and nuclear reactors).
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