[en] The ILC positron system uses novel helical undulators to create a powerful photon beam from the main electron beam. This beam is passed through a titanium target to convert it into electron-positron pairs. The target is constructed as a 1 m diameter wheel spinning at 2000 RPM to smear the 1 ms ILC pulse train over 10 cm. A pulsed flux concentrating magnet is used to increase the positron capture efficiency. It is cooled to liquid nitrogen temperatures to maximize the flatness of the magnetic field over the 1 ms ILC pulse train. We report on prototyping effort on this system.

[en] The Positron Source for the International Linear Collider requires an optical matching device after the target to increase the capture efficiency for positrons. Pulsed flux concentrators have been used by previous machines to improve the capture efficiency but the ILC has a 1 ms long pulse train which is too long for a standard flux concentrator. A pulsed flux concentrator with a 40 ms flat top was created for a hyperon experiment in 1965 which used liquid nitrogen cooling to reduce the resistance of the concentrating plates and extend the lifetime of the pulse. We report on a design for a 1 ms device based on this concept.

[en] We are studying the flashover of vacuum insulators for applications where high voltage conditioning of the insulator and electrodes is not practical and for pulse lengths on the order of several microseconds. The study is centered about experiments performed with a 100-kV, 10-ms pulsed power system and supported by a combination of theoretical and computational modeling. The base line geometry is a cylindrically symmetric, +45^o insulator between flat electrodes. In the experiments, flashovers or breakdowns are localized by operating at field stresses slightly below the level needed for explosive emissions with the base line geometry. The electrodes and/or insulator are then seeded with an emission source, e.g. a tuft of velvet, or a known mechanical defect. Various standard techniques are employed to suppress cathode-originating flashovers/breakdowns. We present the results of our experiments and discuss the capabilities of modeling insulator flashover

[en] The design of an inexpensive, small, high bandwidth diagnostic for the study of vacuum insulator flashover is described. The diagnostic is based on the principle of capacitive coupling and is commonly referred to as a D-dot probe due to its sensitivity to the changing of the electric displacement field. The principle challenge for the design proved to be meeting the required mechanical size for the application rather than bandwidth. An array of these probes was fabricated and used in an insulator test stand. Data from the test stand with detailed analysis is presented. A highlight of the application of the probes to the test stand was the ability to detect the charging of the insulator surface by UV illumination as a prelude to the insulator flashover. The abrupt change in the insulator's surface charge during the flashover was also detected

[en] The injector of the Flash X-Ray (FXR) accelerator has a significantly larger than expected beam emittance. A computer modeling effort involving three different injector design codes was undertaken to characterize the FXR injector and determine the cause of the large emittance. There were some variations between the codes, but in general the simulations were consistent and pointed towards a much smaller normalized, rms emittance (36 cm-mr) than what was measured (193 cm-mr) at the exit of the injector using a pepperpot technique. The simulations also indicated that the present diode design was robust with respect to perturbations to the nominal design. Easily detected mechanical alignment/position errors and magnet errors did not lead to appreciable increase in the simulated emittance. The physics of electron emission was not modeled by any of the codes and could be the source of increased emittance. The nominal simulation assumed uniform Child-Langmuir Law emission from the velvet cathode and no shroud emission. Simulations that looked at extreme non-uniform cathode and shroud emission scenarios resulted in doubling of the emittance. An alternative approach was to question the pepperpot measurement. Simulations of the measurement showed that the pepperpot aperture foil could double the emittance with respect to the non-disturbed beam. This leads to a diplomatic explanation of the discrepancy between predicted and measured emittance where the fault is shared. The measured value is too high due to the effect of the diagnostic on the beam and the simulations are too low because of unaccounted cathode and/or shroud emission physics. Fortunately there is a relatively simple experiment that can resolve the emittance discrepancy. If the large measured emittance value is correct, the beam envelope is emittance dominated at modest values of focusing field and beam radius. Measurements of the beam envelope on an imaging foil at the exit of the injector would lead to an accurate value of the emittance. If the emittance was approximately half of the measured value, the beam envelope is slightly space charge dominated, but envelope measurements would set reasonable bounds on the emittance value. For an emittance much less than 100 cm-mr, the envelope measurements would be insensitive to emittance. The outcome of this envelope experiment determines if a redesigned diode is needed or if more sophisticated emittance measurements should be pursued

[en] Inertial Electrostatic Confinement (IEC) fusion was recently described by an Electric Power Research Institute (EPRI) review panel as potentially leading to a most attractive fusion reactor from a utility point of view, if the physics issues can be resolved. Consequently, a design for a small 25-MW electric D-³He fueled power plant has been explored. Key power plant components consist of the IEC, direct energy conversion and a step-down converter for electrical power transmission. (author)

[en] Light measurements of the balmer β-line of a deuterium plasma on an IEC (Inertial Electrostatic Confinement) device are used to investigate the ICC (Inertial Collisional Compression) theory proposed by Bussard. These measurements also serve as an important benchmark for the computer simulation code PDS-1 (Plasma Device Spherical 1-dimensional). The IEC consists of two electrodes: a negatively biased inner grid (cathode) and a grounded chamber wall (anode). Ionization of low pressure gas (mTorr) is done by applying a DC field (10's of kV) across the two electrodes. The ions created in the outer grid region accelerated through the transparent grid toward the center of the device. The bunching of ions and electrons in the form of concentric shells forms regions of virtual cathodes and anodes within the grid. This leads to the formation of a potential well structure with unique particle-trapping capabilities. Light emitted from the plasma is measured using a long, thin collimator (L/D:96/1) and detector system. Appropriate filters are used to select specific excitation emission lines. In a deuterium plasma, the authors have measured the balmer β-line emission resulting from H⁺ + H₂ collisions over a wide range of discharge conditions. The discharge voltage is varied from 10 to 80 kV while the cathode current is limited to 20 mA. The variation of the light intensity vs. ion current (5--20 mA) is compared to D-D fusion rates measured by neutron emission

[en] A variety of potential applications exist for a portable neutron generator with an output of MeV neutrons at a rate of 10⁶--10⁸ per second that can be switched on and off, can emit approximately monoenergetic fusion neutrons, and can be self-calibrating,. The development of an Inertial Electrostatic Confinement (IEC) fusion-based neutron generator has been proposed to meet these needs. The IEC device consists of a spherical stainless steel vacuum chamber (∼ 30 cm in diameter) with a concentric highly transparent spherical conducting grid suspended inside. The inner grid is biased negative (cathode) and the chamber wall is grounded. To operate, the cathode is brought to a high DC voltage (10s of kV), where the ionization of the background D₂ gas between electrodes sustains a steady-state discharge current (10s of mA). The neutrons are produced from beam-background and beam-beam fusion reactions. The isotropic, approximately monoenergetic, neutron output of the IEC is one of its primary advantages. The fusion core approximates a point source and the random angular distribution of interacting ions in it gives good isotropy. Engineering aspects, such as high voltage feedthroughs, however, may subtract slightly from the isotropy. These effects are device specific, but are easily quantified by measuring the thermalized neutron output as a function of detector position. At high input power (> 1 kW) the stainless steel grids of the IEC have a limited lifetime, due to the high operating temperatures and sputtering. However, tests conducted on grids of materials with different melting points, such as molybdenum and tungsten, show improved lifetimes. Grid design can also affect its lifetime. Tests of the lifetime of several different grid designs and materials are being conducted and the results will be reported. Present levels of operation of IEC devices have produced a record output of 3.5 x 10⁶ neutrons/s steady state

[en] A MJ-Class Dense Plasma Focus (DPF) facility, is being designed to develop the technology needed for plasma focus-type magnetoplasmadynamic (MPD) thrusters. The facility will be capable of studying various commercial applications of the plasma focus also, such as soft x-ray lithography. The facility will be located at the University of Illinois, Champaign/Urbana campus. The ultimate objective is to demonstrate the feasibility and attractiveness of the plasma focus MPD concept for very high specific-impulse space propulsion. Studies include scaling experiments up to and including the 1-MJ level and experiments using a gas-injected plasma focus, such as required in the hard vacuum environment of space. The plasma focus thruster differs from the conventional MPD in that it is capable of generating additional thrust from fusion energy released during the pinch phase of the arc run-down. The proposed 1-MJ facility would enable studies of these concepts at a meaningful energy level. If the results are encouraging, as expected, a next step would be to construct a prototype thruster for further studies, including space qualifications. In addition to thruster studies, the MJ-class facility offers considerable flexibility for the study of a variety of scientific applications requiring an intense, pulsed, radiation source. Examples of such uses range from studies of radiation hardening of electronics to transmutation of radioactive wastes. Consequently, upon completion, it is planned to invite outside users to access the MJ-facility in the time that remains after mainline research. A key objective is to establish the DPF facility as a National User's Facility. To accomplish this, it is planned to establish an advisory committee for use of the facility next year and host a workshop for potential users

[en] The application of the 'swimming electron layer' theory to the design of multilayer electrodes is discussed. A key advantage of this approach is that the enhanced reaction rate at interfaces between select metals results in a high power density throughout the volume of the electrode. Design criteria and fabrication techniques devised for the multilayer thin films are discussed. Initial experiments using a dense plasma focus (DPF) for loading these targets are described along with the design of an electrolytic cell intended to test scaling to high powers. (author)