H.L. Rutkowski

Sources of multiply charged ions for heavy-ion fusion

We report experiments on methods to raise the proportion of multiply charged ions for high‐flux‐ion extraction from vacuum‐arc plasma sources. Beams of doubly and triply charged ions have application to induction linacs for heavy‐ion fusion. We confirmed that the arc cathode material strongly influenced the ion‐charge‐state proportions. We believe the electrostatic potential of the plasma streaming from the arc played a major role in the transport of multiply charged ions. Reduction of electron losses from the plasma increased the observed fluxes of doubly charged ions. We inhibited electron loss and enhanced the flux of multiply charge ions by applying a bias voltage to the plasma source and by adding an axial magnetic field. We also investigated a method to increase the proportion of multiply charged ions by time‐of‐flight separation following rapid switching of the expanding plasma. We developed a new arc‐source geometry for the experiments. The source had a hollow anode and an axial magnetic field to ...

Status of the dual axis radiographic hydrodynamics test (DARHT) facility

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 electro-optical x-ray imaging system, and other hydrodynamics testing systems. We will briefly describe this machine. 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 will discuss this accelerator by summarizing the overall design of the long-pulse injector and accelerator. We will also discuss the fast kicker used to separate the long-pulse beam into short bursts suitable for radiography.

Development of arc ion sources for heavy ion fusion

An overview of the development of arc ion sources for heavy ion fusion is presented. Two approaches to heavy ion fusion (HIF)-the RF linac-storage ring approach and the induction linac approach-are described. RF linac schemes require low emittance and moderate current levels, because the beam is accumulated in storage rings before being focused on target. The induction linac approach requires low emittance and high current, because this is a single-pass approach to HIF and one wishes to limit the number of beams in the machine. The RF scheme generally uses long pulse sources together with a buncher of RFQ. The induction linac approach requires sources in the microsecond pulse length range, with good optics being maintained during the pulse. Emphasis is on the induction linac approach pursued at the Lawrence Berkeley Laboratory. >

Heavy Ion Fusion Injector Experiments

SummaryWe 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.

Pulsed-power systems for the Dual-Axis Radiographic Hydrodynamics Test (DARHT) facility

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.

Overview and status of the Dual-Axis Radiographic Hydrodynamics Test (DARHT) facility

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. 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 electro-optical x-ray imaging system, and other hydrodynamics testing systems. We will briefly describe this machine. 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 will discuss this accelerator by summarizing the overall design of the long-pulse injector and accelerator. We will also discuss the fast kicker used to separate the long-pulse beam into short bursts suitable for radiography.

High brightness electron beam injector for the DARHT facility

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.

An induction linac injector for scaled experiments

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.<<ETX>>