W.B. Herrmannsfeldt

Ion sources and injectors for HIF induction linacs

Ion source and injector development is one of the major parts of the HIF program in the USA. Our challenge is to design a cost effective driver-scale injector and to build a multiple beam module within the next couple of years. In this paper, several current-voltage scaling laws are summarized for guiding the injector design. Following the traditional way of building injectors for HIF induction linac, we have produced a preliminary design for a multiple beam driver-scale injector. We also developed an alternate option for a high current density injector that is much smaller in size. One of the changes following this new option is the possibility of using other kinds of ion sources than the surface ionization sources. So far, we are still looking for an ideal ion source candidate that can readily meet all the essential requirements.

Fusion policy advisory committee: final report

Presentation des grandes orientations de la politique americaine de recherche et developpement en matiere de fusion nucleaire controlee

Design of a Magnetron Injection Gun for a 670-GHz 300-kW Gyrotron

A 300-kW 670-GHz gyrotron, operating with a pulsed coil at the fundamental cyclotron harmonic, is designed at the University of Maryland for an application of detecting concealed radioactive materials. The design of a low-spread diode-type magnetron injection gun for this gyrotron is presented. Constraints due to the pulsed coil design and the limitation of maximum electric field at the cathode result in a steep tilting angle of the cathode surface, 74°, along with a Pierce-type focusing section and a high magnetic compression ratio larger than 170. A pitch ratio of 1.34 and a low pitch ratio spread of 2.5% for a cold beam and 9.2% due to emitter surface temperature of 0.1 eV and 1-μm roughness were obtained. The results were benchmarked with three simulation codes: EGUN, TRAK, and MICHELLE. Numerical results were calculated for beam currents up to 19 A, accelerating voltage of 50-90 kV, and magnetic field of 25-30 T. A sensitivity analysis with respect to critical parameters such as the depth of the focusing section and the internal simulation parameters is provided.

Status of the BNL‐MIT‐SLAC cluster klystron project

A general description is given of the status of the cluster klystron project. This paper is chiefly concerned with the mechanical design, magnetic field, plasma wavelength analyses, and beam dynamics. Finally, an idea for a new type of output window is presented.

The Cluster klystron demonstration experiment

Abstract The cluster klystron is a new concept for providing a power source for future linear colliders. This type of klystron uses many parallel beams from magnetron injection gun sources inside a common solenoidal magnetic field. Since each individual beam has a low current, it should be possible to obtain high efficiency and after recombination of the beams, high output power. This paper describes the concept and preparations for a proof of principle experiment now underway at Brookhaven National Laboratory (BNL).

Fusion Energy Advisory Committee (FEAC): Panel 7 report on Inertial Fusion Energy

The charge to FEAC Panel 7 on inertial fusion energy (IFE) is encompassed in the four articles of correspondence. To briefly summarize, the scope of the panel`s review and analysis adhered to the following guidelines. (1) Consistent with previous recommendations by the Fusion Policy Advisory Committee (FPAC) and the National Academy of Science (NAS) panel on inertial fusion, the principal focus of FEAC Panel 7`s review and planning activities for next-generation experimental facilities in IFE was limited to heavy ions. (2) The panel considered the three budget cases:

Design of a LaB6 gun using EGN2 and INTMAG

5M,

Minimization of effects of backscattered electrons in gyrotrons with depressed collectors

10M, and

Influence of trapped backscattered electrons on parasitic oscillations in gyrotrons

15M annual funding at constant level-of-effort (FY92 dollars), with a time horizon of about five years. (3) While limiting the analysis of next-generation experimental facilities to heavy ions, the panel assessed both the induction and rf linac approaches, and factored European plans into its considerations as well. (4) Finally, the panel identified high-priority areas in system studies and supporting IFE technologies, taking into account how IFE can benefit from related activities funded by the Office of Fusion Energy and by Defense Programs. This report presents the technical assessment, findings, and recommendations on inertial fusion energy prepared by FEAC Panel 7.

Control of the profile of heat dissipation density in a high-power gyrotron

Abstract In order to launch a high-density electron beam to be focused in the 5 T superconducting solenoid of the Frankfurt EBIS [R. Becker et al., Nucl. Instr. and Meth. B24 (1987) 838], an electron gun has been designed, with a 0.5 mm diameter LaB 6 cathode (FEI Comp., Beaverton, USA) in a 70 mm diameter electrode geometry. The emitting surface is placed in the axial fringing field of the solenoid, modified by an axial shielding disk and a bucking coil, to provide either immersed flow or Brillouin flow conditions for the focused beam. Since the cathode diameter is small as compared to the electrodes, a new feature of EGN2 [W.B. Herrmannsfeldt, SLAC-331 (1988)] had to be used in order to have a sufficient number of meshes along the emitting surface. By starting a field line in the large geometry, a curved Neumann boundary is found for a subdivided part of the gun, which represents the influence of the larger part. EGN2 writes the coordinates of this field line on a file, which can be used by POLYGON [R. Becker, Nucl. Instr. and Meth. B42 (1989) 162] (a boundary setup program for EGN2) to define a curved Neumann boundary. By this procedure, it becomes possible to get a reliable simulation of the emission properties of a small cathode in large gun electrodes. The magnetostatic field calculations have been performed with INTMAG [R. Becker, Nucl. Instr. and Meth. B42 (1989) 303], which is a new program of the boundary element method type. Due to the integration calculus, the results do not need smoothing or “Maxwellisation” for the use in EGN2, where the off-axis fields are evaluated by radial expansion. INTMAG provides an output file, which is suitably formatted to be read in by EGN2. The gun design is based on space-charge-limited emission, but no Pierce-type electrode has been provided in the vicinity of the cathode; instead a Wehnelt electrode on negative bias with respect to the cathode is used to create the correct Pierce-type equipotential in free space, ending on the cathode edge with the correct angle. This gives an additional adjustment tool, if the axial position of the gun is not perfect and it relaxes the radial tolerance requirements considerably.