The transport of a relativistic electron beam was studied experimentally and numerically in a magnetic field configuration which consists of a focusing wiggler as well as an additional axial guide field. A new beam divergence was found for the lower side of the magnetoresonance. It was identified as due to the effect of the second harmonic mode of the cyclotron frequency in the resonance, determined by /jft i i -A^rn for n =2. The harmonic resonance was detected for the planar wiggler first, and it could appear also for the helical one. PACS numbers: 41.75.Ht, 41.85.Ja, 52.75.MsSuccessful operation of a Raman free electron laser (FEL) using a relativistic electron beam (REB) has been reported for both planar and helical wiggler configurations [1][2][3][4]. To obtain a high-power performance of the FEL, a stable transport of the beam in the wiggler is one of the key issues. The introduction of an axial uniform guide field superimposed on the wiggler is usually required to keep the orbital stability in the transport, while it will involve some other complex features like the magnetoresonance between the cyclotron motions and the wiggling of the electrons [5]. It is well recognized that the beam diverges and spills out when the electron cyclotron frequency flu in the guide field B g approaches the wiggling frequency K w v\\, where k w is a wiggler wave number, Clw^eBg/yorrie, yo = {l "~ (v 2 /c 2 )} _1 *, v and c are electron and light speed, respectively, and the suffix II indicates axial components [6].In this Letter we describe an experimental and numerical study on the transport of a REB (£6~~0.8 MeV and /6~300 A) through a combination of a focusing type planar wiggler [7] and an axial field: We retain a relatively low additional B g to control the beam dynamics at the entrance of the wiggler and the FEL performance. We found a new type of beam loss at an axial field far lower than the value of B g corresponding to the fundamental magnetoresonance flii^&wm; e.g., the loss is in the parameter region of the so-called group I. Therefore it clearly differs from the "harmonic" gyroresonance which was predicted to occur in group II at flu ^nk w v\\ (n an integer) by Chu and Lin [8], where ft H is a timeaveraged cyclotron frequency in B\\. We need another explanation for the new resonance. We made an analytical study and a numerical simulation on the resonance and its effect on the beam transport through the wiggler. We carried out a similar numerical study for the case of a helical wiggler and the result suggests we will also have the same kind of resonance and beam degradation. The magnetic field in a planar focusing wiggler with a uniform field B g G z is given by B(r) = s

The principle of Project MACETIE and the preliminary experiment are described. The basis of our plan is the thought that the goal of controlled thermonuclear fusion may be accessible by the multistage alternating processes of adiabatic compression and irreversible expansion of plasma. In the latter process, the plasma compressed by a strong magnetic field is expanded into a region of weaker magnetic field. A static consideration of this expansion suggests that plasma temperature will not change appreciably in this process, and a second adiabatic compression of plasma in the weak field may further increase its temperature. Preliminary experiments are being carried out to examine the foregoing principle of irreversible expansion.

Under nonadiabatic conditions, rf plugging is accompanied by effective ion heating, which in turn causes increased particle losses from a cusp configuration. An empirical scaling relation for rf plugging of line cusp loss is obtained among the required rf electric field, the static magnetic field, and the plasma density, and is compared with the relation obtained by a linear theory.

The expansion process of a collision-dominated theta-pinch plasma in a homogeneous magnetic channel and the thermalization process of the kinetic energy of this plasma flow by a magnetic mirror field are studied on the BSG-II device. Previously it was reported that shock phenomena due to a mirror field were observed by several methods of measurement. In this paper four experimental results are presented: (1) the expansion of plasma along the homogeneous magnetic channel is adiabatic; it is well described by a model for one-dimensional isentropic flow of collision-dominated plasma; (2) the flow is supersonic and the occurrence of a shock in front of the mirror field is in accordance with a criterion concerning the supersonic-sonic transition of plasma flow; (3) the rate of plasma loss through the mirror field is reduced by the occurrence of the shock; (4) the values of the plasma parameters measured before and behind the shock front satisfy the Rankine-Hugoniot relations, though plasma pressure, flow velocity and Mach number are time-dependent.

Broadband microwave radiation in the X and KA bands was observed from a non-neutral electron layer prepared by passing a 2.5-MeV straight hollow electron beam through a narrow magnetic cusp. The mean beam radius shrank from 6 to 4.5 cm and the beam radial width increased from less than 1 to 2.7 cm in the postcusp e-layer drift region. When the beam was passed through a thin scattering foil prior to cusp transmission, the observed radiation decreased by two orders of magnitude and the beam width and radius remained at values consistent with single-particle calculations. Results are discussed in terms of the negative-mass instability.