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The use of ion sources in induction linacs for heavy ion fusion is fundamentally different from their use in the rf linac‐storage rings approach. Induction linacs require very high current, short pulse extraction usually with large apertures which are dictated by the injector design. One is faced with the problem of extracting beams in a pulsed fashion while maintaining high beam quality during the pulse (low emittance). Four types of sources have been studied for this application. The vacuum arc and the rf cusp field source are the plasma‐types and the porous plug and hot alumino–silicate surface source are the thermal types. The hot alumino–silicate potassium source has proved to be the best candidate for the next generation of scaled experiments. The porous plug for potassium is somewhat more difficult to use. The vacuum arc suffers from noise and lifetime problems and the rf cusp field source is difficult to use with very short pulses. Operational experience with all of these types of sources is prese...

A 2 MV, 800 mA, K+ injector for heavy-ion fusion studies is under construction. This new injector is a one-beam version of the proposed 4-beam ILSE injector. A new 36-module MARX is being built to achieve a 5 μs flat top. The high-voltage generator is stiff (

The Dual-Axis Radiographic Hydrodynamics Test (DARHT) facility will employ two perpendicular electron linear induction accelerators to produce intense, bremsstrahlung X-ray pulses for flash radiography. We intend to produce measurements containing three-dimensional information with sub-millimeter spatial resolution of the interior features of very dense, explosively driven objects. The facility will be completed in two phases with the first phase having become operational in July 1999 utilizing a single-pulse, 20 MeV, 2 kA, 60 ns accelerator, a high-resolution electrooptical X-ray imaging system, and other hydrodynamics testing systems. We describe this machine and discuss its current operating status. The first electron beams will be generated in the second phase of DARHT this year. The second DARHT accelerator consists of a 18.4 MeV, 2 kA, 2-microsecond pulse-width accelerator. Four short electron micropulses of variable pulse-width and spacing will be chopped out of the original, long accelerator pulse for producing time-resolved X-ray images. The second phase also features an extended, high-resolution electro-optical X-ray system with a framing speed of about 2 MHz. We discuss this accelerator by summarizing the overall design of the long-pulse injector and accelerator as well as some component test results. We also discuss the fast kicker used to separate the long-pulse beam into short bursts suitable for radiography.

The Dual-Axis Radiographic Hydrodynamics Test (DARHT) facility will employ two perpendicular electron linear induction accelerators to produce intense, bremsstrahlung X-ray pulses for flash radiography. The first DARHT accelerator became operational in July 1999 producing a single electron beam pulse at 20 MeV, 2 kA, and 60 ns pulse. The second DARHT accelerator consists of a 18.4 MeV, 2 kA, 2 microsecond pulse-width accelerator. Four short electron micropulses of variable pulse-width and spacing will be chopped out of the original, long accelerator pulse for producing time-resolved X-ray images. The first electron beam in this machine will be produced this year. We discuss the pulsed power systems associated with this machine. These include an injector driven by a Marx consisting of 88 type-E PFN stages driving a matched load at 3.2 MV with a 500 ns risetime, 2 microsecond e-beam pulse. The Metglas-filled induction cells making up the accelerator are described. Each induction cell is driven by a cell-driver that contains 4, 7-section E-network PFNs in a Marx configuration with a 20 /spl Omega/ impedance that delivers flattop of greater than 2 microseconds into a resistive load of 5 /spl Omega/ for a total drive current of 10 kA at 200 kV. The principal element of the electron beam transport system is the fast deflector, or kicker, used to generate four micropulses from the primary beam. The kicker modulator generates bi-polar 18 kV pulses of arbitrary pulse width and spacing using solid-state circuitry that is described. Component test data from the injector, accelerator, and kicker system is discussed.

We present the design for an induction linac that is fed by a long pulse injector that will generate a 20 MeV, 2 kA, 2 /spl mu/s electron beam pulse for the DARHT second axis at Los Alamos National Laboratory. The accelerator cells are shielded gap cavities with Mycalex insulators and Metglas cores. A large bore (14'') block of eight cells follow the injector while the remaining 80 cells have a 10'' bore. Blocks of eight cells are interspersed with intercells that provide pumping, diagnostics and space for cell removal. RF properties of the cells have been calculated and measured. Response to BBU modes and corkscrew have been calculated. Design details of the cells, solenoids, corrector coils, intercells and pulsers will be presented along with prototype data.

An update on the development of the 500-mA/beam sixteen-beam injector being built at Lawrence Berkeley Laboratory is presented. An inductively graded Marx bank provides the acceleration potential on the electrostatic column. A carbon arc source provides the pulsed current for the injector. Recent results on extracted beam parameters, column performance, generator performance and system design changes are reported. The carbon ion beam is diagnosed with Faraday cups and with a double-slit emittance measurement system. Controls for the final machine are also discussed. >

A program is underway to construct a 2 MV, 800 mA, K/sup +/ injector for heavy ion fusion. The electrostatic quadrupole injector configuration consists of a zeolite source, a diode of up to 1 MV, together with several electrostatic quadrupole units to simultaneously focus and accelerate the beam to 2 MV. The key issues of source technology, high voltage breakdown, beam aberrations, and transient effects are discussed. Results from ongoing experiments and simulations are presented. >

Heavy ion fusion experiments require very high current beams with excellent beam quality during a short pulse. Scaled experiments planned at LBL require very short pulses (/spl mu/sec) compared to what one expects in an HIF driver (20-30 /spl mu/s). A 1 MV acceleration column composed of aperture lenses has been constructed at LBL in order to study the propagation effects on such ion pulses. The column is initially empty of space charge but with the full acceleration potential applied. A short current pulse is then injected into the column with a planar diode "current valve". Effects on the pulse propagation due to rise time, pulse duration, and beam size have been studied. Experiments on transported beam current and emittance have been conducted using a carbon arc plasma source (2" and 5" diameter) and a 1" diameter potassium alumino-silicate ion source. Computer simulations using a 2.5D time dependent code are compared with the experimental data. >

An injector is being developed at LBL (Lawrence Berkeley Laboratory) that would serve as the front end of a scaled induction linac accelerator technology experiment in heavy ion fusion. The ion mass being used is in the range 10-18. It is a multi-beam device intended to accelerate up to 2 MeV with 500 mA in each beam. The first half of the accelerating column has been built and experiments with one carbon beam are underway at the 1 MeV level. >

An injector for the second axis of the Dual-Axis Radiographic Hydrotest Facility (DARHT) is been built at LBNL. The proposed injector consists of a single gap diode extracting 4 kAmps, 3 MV electrons from a thermionic dispenser cathode and powered through a high voltage ceramic insulator column by a Marx generator. The key issues in the design are the control of beam quality to meet the DARHT 2nd axis final focus requirements and to minimize high-voltage breakdown risks. We present the conceptual design of the injector as well as preliminary results on a scaled experiment and breakdown tests in vacuum using the Berkeley RTA facility.

Heavy ion fusion requires high current density, low‐emittance ion sources that are reliable and long lived. We report experimental and simulation results on the performance of carbon arc ion sources intended for use in a scaled induction linac experiment. These sources use a planar electrostatic plasma switch to prevent plasma from entering the extraction gap before the extraction voltage pulse is applied. This provides good beam optics for short pulse extraction. Measurements of current density and emittance are presented. Both double‐slit and channel plate‐pepper pot techniques are used for emittance measurement. Data presented are from a compact three‐arc source with plasma coupling of the cathodes. Data on lifetime and multiple arc triggering are also presented. The plasma switch performance has been modeled with a 2D explicit electrostatic particle‐in‐cell code. Results showing plasma shutoff phenomena and behavior during extraction are presented. A 2D steady‐state ion flow model is also used to pred...

We report on three experiments performed in connection with the 2MV electrostatic quadrupole (ESQ) injector under construction at Lawrence Berkeley Laboratory. Scaled experiments have been conducted to study possible beam emittance growth due to beam aberrations in an ESQ injector. The experiment uses the SBTE (Single Beam Transport Experiment) accelerator system, quarter-scale ESQ set-up and a potassium ion diode source. Measured emittance growth changes significantly with variations in current and diode energy, in good agreement with theoretical predictions. In addition, beam transport experiments were performed in a 1MV axisymmetric electrostatic aperture column using a zeolite 1″ diameter potassium ion source. Experimental measurements in good agreement with 2-1/2D simulations showed that low-emittance beams can be produced in axisymmetric structures. Finally, ESQ breakdown voltage tests without beam were performed at up to two times the quadrupole working voltage.

Summary form only given. The requirements of HIF place severe restrictions on the operating parameters of the ion source. In addition to the usual requirements of high brightness, constant current, and constant energy/nucleon, it is necessary to switch the ion flow on abruptly with enough ion flux so that the full HIF pulse current requirement can be met without the flow becoming source limited. A technique that shows promise is a combination of an arc source with control grids. The grids are biased with a potential to confine electrons and thus switch off any ion flow until the grid voltage is overpowered by the abrupt application of the extraction voltage. The plasma feed from the arc sources must satisfy various criteria so that the plasma electrons neutralize the flow up to this switch grid, but no further, so that space charge limited flow can be maintained between the switch and extraction grid. The plasma-grid interaction has been modeled with the particle-in-cell code GYMNOS in the relevant parameter regime to verify the understanding of the switch-off requirements followed by the switch-on stage. It was found that the arc source must provide plasma with density and flow rates within a small range of parameters; otherwise, the grid cannot properly confine electrons-the essential elements for constant current during the pulse

The use of ion sources in induction linacs for heavy ion fusion is fundamentally different from their use in the rf linac‐storage rings approach. Induction linacs require very high current, short pulse extraction usually with large apertures which are dictated by the injector design. One is faced with the problem of extracting beams in a pulsed fashion while maintaining high beam quality during the pulse (low emittance). Four types of sources have been studied for this application. The vacuum arc and the rf cusp field source are the plasma‐types and the porous plug and hot alumino–silicate surface source are the thermal types. The hot alumino–silicate potassium source has proved to be the best candidate for the next generation of scaled experiments. The porous plug for potassium is somewhat more difficult to use. The vacuum arc suffers from noise and lifetime problems and the rf cusp field source is difficult to use with very short pulses. Operational experience with all of these types of sources is prese...

A sixteen beam injector to supply 500mA per beam of C/sup +/ ions, which was initially designed and partially constructed at Los Alamos National Laboratory, is under further development at LBL. We report on development work involving single and multiple carbon arc sources. These sources are useful because they can easily supply the 25 mA/cm/sup 2/ needed for the device. They are pulsed sources which do not cause unacceptable background gas loads in the column. We present emittance and reproducibility data. Acceleration is by a high gradient column using a succession of aperture lenses to focus the beam. The electrodes are arranged with holes for parallel beams inside 28 inch alumina insulators. Data on beam propagation and electron trapping in the column is presented. The acceleration potential is provided by a Marx bank with inductive grading along the structure. The resulting 34 ..mu..sec rise time pulse allows the accelerating potential to equilibrate along the column before the current is injected. Acceleration occurs during a 1 ..mu..sec window at the peak of the pulse, kn which the voltage is flat within 0.1%. 8 refs., 7 figs.