F.J. Deadrick

Progress toward a prototype recirculating induction accelerator for heavy-ion fusion

The US Inertial Fusion Energy (IFE) Program is developing induction accelerator technology toward the goal of electric power production using heavy-ion beam-driven inertial fusion (HIF). The recirculating induction accelerator promises driver cost reduction by repeatedly passing the beam through the same set of accelerating and focusing elements. We present plans for and progress toward a small (4.5-m diameter) prototype recirculator, which will accelerate K/sup +/ ions through 15 laps, from 80 to 320 keV and from 2 to 8 mA. Beam confinement is effected via permanent-magnet quadrupoles; bending is via electric dipoles. Scaling laws, and extensive particle and fluid simulations of the space-charge dominated beam behavior, have been used to arrive at the design. An injector and matching section are operational. Initial experiments are investigating intense-beam transport in a linear magnetic channel; near-term plans include studies of transport around a bend. Later experiments will study insertion/extraction and acceleration with centroid control.

Measurements of reduced corkscrew motion on the ETA-II linear induction accelerator

The ETA-II linear induction accelerator is used to drive a microwave free-electron laser (FEL). Corkscrew motion, which previously limited performance, has been reduced by: (1) an improved pulse distribution system which reduces energy sweep, (2) improved magnetic alignment achieved with a stretched wire alignment technique (SWAT), and (3) a unique magnetic tuning algorithm. Experiments have been carried out on a 20-cell version of ETA-II operating at 1500 A and 2.7 MeV. The measured transverse beam motion is less than 0.5 mm for 40 ns of the pulse, an improvement of a factor of 2 to 3 over previous results. Details of the computerized tuning procedure, estimates of the corkscrew phase, and relevance of these results to future FEL experiments are presented.<<ETX>>

2 MV injector as the Elise front-end and as an experimental facility

Abstract We report on progress in the preparation of the 2 MV injector at LBNL as the front end of Elise and as a multipurpose experimental facility for heavy ion fusion beam dynamics studies. Recent advances in the performance and understanding of the injector are described, and some of the ongoing experimental activities are summarized.

Recirculating induction accelerators for inertial fusion: Prospects and status

The US is developing the physics and technology of induction accelerators for heavy-ion beam-driven inertial fusion. The recirculating induction accelerator repeatedly passes beams through the same set of accelerating and focusing elements, thereby reducing both the length and gradient of the accelerator structure. This promises an attractive driver cost, if the technical challenges associated with recirculation can be met. Point designs for recirculator drivers were developed in a multi-year study by LLNL, LBNL, and FM Technologies, and that work is briefly reviewed here. To validate major elements of the recirculator concept, we are developing a small (4-5-m diameter) prototype recirculator which will accelerate a space-charge-dominated beam of K{sup +} ions through 15 laps, from 80 to 320 keV and from 2 to 8 mA. Transverse beam confinement is effected via permanent-magnet quadrupoles; bending is via electric dipoles. This ``Small Recirculator`` is being developed in a build-and-test sequence of experiments. An injector, matching section, and linear magnetic channel using seven half-lattice periods of permanent-magnet quadrupole lenses are operational. A prototype recirculator half-lattice period is being fabricated. This paper outlines the research program, and presents initial experimental results.

Development of beam position monitors for heavy ion recirculators

Work is underway at the Lawrence Livermore National Laboratory to design and build a small-scale, heavy ion recirculating induction accelerator. An essential part of this design work is the development of small non-intercepting diagnostics to measure beam current and position. This paper describes some of this work, with particular emphasis on the development of a small capacitive probe beam position monitor to resolve beam position to the 100 /spl mu/m level in a 6 cm diameter beam pipe. Initial measured results with an 80 keV potassium ion beam are presented.

Engineering conceptual design of the relativistic klystron two-beam accelerator based power source for 1 TeV Next Linear Collider

Ultra-high gradient radio frequency linacs require network current. Efficient and reliable power sources. The induction linac has proven to be a reliable source of low energy, high current and high brightness electron beams. The low energy beam is bunched, transported through resonant transfer cavities in which it radiates microwave energy that is coupled to an adjacent high energy accelerator. The low energy beam is maintained at a constant energy by periodic induction accelerator cells. This paper describes the engineering aspects of the induction accelerator based relativistic klystron. The physics issues are covered in another paper at this conference.

Heavy ion fusion 2 MV injector

A heavy-ion-fusion driver-scale injector has been constructed and operated at Lawrence Berkeley Laboratory. The injector has produced 2.3 MV and 950 mA of K/sup +/, 15% above original design goals in energy and current. Normalized edge emittance of less than 1 /spl pi/ mm-mr was measured over a broad range of parameters. The head-to-tail energy flatness is less than /spl plusmn/0.2% over the 1 /spl mu/s pulse.

Performance characteristics of an induction linac magnetic pulse compression modulator at multi-kilohertz pulse repetition frequencies

The ETA-II linear induction accelerator utilizes four pulse power conditioning chains. Magnetic pulse compression modulators (MAG1-Ds) form the last state of each chain. The upgrading and characterizing of the power conditioning chain on a high-average-power test stand (HAPTS) is reported. On the HAPTS, the pulse-to-pulse amplitude stability has been improved to less than 0.7% (one sigma) and the random jitter to 3-5 about a systematic timing variation. A description is presented of the work to achieve the desired performance level of the MAG1-D to allow high average power operation of ETA-II.<<ETX>>

Engineering development for a small-scale recirculator experiment

Lawrence Livermore National Laboratory (LLNL) is evaluating the physics and technology of recirculating induction accelerators for heavy-ion inertial-fusion drivers. As part of this evaluation, the authors are building a small-scale recirculator to demonstrate the concept and to use as a test bed for the development of recirculator technologies. System designs have been completed and components are presently being designed and developed for the small-scale recirculator. This paper discusses results of the design and development activities that are presently being conducted to implement the small-scale recirculator experiments. An, overview of the system design is presented along with a discussion of the implications of this design on the mechanical and electrical hardware. The paper focuses primarily on discussions of the development and design of the half-lattice period hardware and the advanced solid-state modulator.

ETA-II beam brightness measurement

ETA-II resumed operation in the Fall of 1990 with the injector and first two ten-cell accelerating blocks and nominal electron beam parameters of 1500 A, 2.5 MeV, and 70-ns pulse width at 1 Hz PRF. The beam brightness diagnostics consisted of a Cerenkov foil view port and a pepper-pot emittance diagnostic. The Cerenkov foil experiment was used to determine the beam energy at the accelerator exit. The pepper-pot emittance diagnostic was used to determine the whole beam brightness. The brightness as a function of beam radius and time within the beam pulse was also measured. The brightness is defined as the ratio of the beam current within a given radius to the normalized four-dimensional volume occupied by particles within that radius.<<ETX>>