[en] Fueling of plasma physics experiments by the injection of frozen hydrogenic pellets has been accomplished on many devices, including the Tokamak Fusion Test Reactor (TFTR), the Joint European Torus (JET), Tore Supra, and the Advance Toroidal Facility (ATF). Injection of pellets lead to density increases in the plasma with efficiencies varying from 50% to near 100%. Determination of the fueling efficiency requires knowledge of both the plasma density and the pellet mass. The pellet mass can be determined as the pellet passes through a microwave cavity by the change in power transmitted though the cavity. A one-to-one correspondence between the transmitted power and the pellet mass has been demonstrated, but this system must be calibrated by other techniques. The technique described here is measuring the pellet mass directly by measuring the pressure increase in a vacuum chamber into which the pellet is injected. A high-sensitivity capacitance manometer is used to absolutely measure the pressure profile pulse during pellet injection. Since these fuel pellets are hydrogenic, absorption of hydrogen onto the chamber wall must be accounted for in the calibration procedure. A fast (1 ms response time) pressure manometer allows measurement of the pressure pulse profile from which the absorption can be estimated, thereby allowing a determination of the pellet mass and a calibration of the microwave cavity technique. Results are presented and compared with other pellet size diagnostics

[en] The importance of radiation transport in inertial confinement fusion (ICF) target design is discussed. It is shown that a self similar solution of non-linear heat conduction can be used to estimate the penetration depth of radiation thermal waves (Marshak Waves) in ion-beam ICF pellets. An improved numerical treatment of non-linear heat conduction has been incorporated into the hydrodynamic code MEDUSA-KA to simulate radiation transport in ICF target design studies. The numerical results have been checked against self-similar solutions and a comparison between the two is presented and good agreement is found. The necessity of using a high-z radiation shield to protect the fuel from radiative preheat is also discussed. (author)

No abstract available

[en] 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 predict the optimum plasma switch geometry for producing minimum emittance generation at the switch surface

[en] A two module electron beam source operating over a wide range of output parameters has been designed and fabricated to be used in conjunction with a pair of electron beam sustained CO₂ lasers. Each module comprised a grid-controlled thermionic electron beam gun including a compact grid pulser for control of the electron beam, a 250 kV thyratron switched modulator for acceleration of the electron beam, a 1 kHz filament heater and a complex computerized control system. The system was designed to reliably produce 45 μs wide electron pulses of 150-200 keV energy, operate at repetition rates of 1-10 pps and current densities of 5-20 mA/cm². Additional parameters are listed. The high voltage cathode assembly employs 132 thoriated tungsten filaments distributed over the area of the 250 cm x 10 cm output window. The cathode assembly including the control grids is supported by two high voltage ceramic bushings in a stainless steel vacuum chamber. For acceleration of the electron beam, a pulsed 150-250 kV voltage is applied by a thyratron switched modulator, between the cathode and anode window. The fiber optically controlled grid pulser located in the modulator tank is floated at the applied cathode potential

[en] The field-reversed configuration (FRC) is a possible direction for future fusion experiments and reactor development. Its potential for either D-T or D-³He operation and the implication of the fuel choice on necessary reactor parameters (size, field, reversal factor,...) are the objective of the study reported in this paper. The high left-angle β right-angle and the divertor action of the open field lines are especially attractive for high power density operation and for direct energy conversion. The compact design, the cylindrical geometry, and the possibility of a translating the plassmoid from the formation chamber to the burn chamber are added positive features. Also theoretical studies indicates that charged fusion products can generate significant plasma current due to preferential loss directions. This, together with pellet injection may maintain sufficient current to sustain steady-state. Due to the early stage of development and the low effort compared to mainline devices, many problems are unsolved. A key one is particle and energy transport, unsolved. A key one is particle and energy transport, where several models offer different scaling laws. They range from the upper limit given by the loss sphere scattering model to more pessimistic laws based on anomalous lower hybrid transport. In the present study the authors use the loss sphere model by fitting it to the limited data base available and compare the results with other scaling laws. The emphasis here is the energetic and nuclear performance of both D-T and a D-³He fueled plasmas in such a device. A profile averaged O-D plasma model is used which includes all relevant physical processes

[en] Neutron spectrum measurement based on the foil activation technique was carried out as a part of the JAERI/USDOE collaborative program on fusion blanket neutronics. The adequacy of the foil activation technique and the current dosimetry nuclear data for the D-T fusion neutron field were examined through the analysis of the spectrum in a Li/sub 2/O blanket system enclosed with the Li/sub 2/CO/sub 3/. A method using a pair of activation indices (MPI) is newly proposed to evaluate the neutron flux around the MeV region of interest in a qualitative way. The multi-foil activation technique (MFA) with proper detector cross section data are promising to determine neutron spectra over a wide energy range

[en] The design of future Engineering Test Reactor (ETR) to demonstrate ignition is complicated by the uncertainties in the projected database for ignited plasmas. Application of uncertainty analysis to ETR design utilizing a figure-of-merit defined as the probability of ignition is presented. Performance evaluation from the uncertainty analysis in density-temperature space can locate an optimum operating window for ignition

[en] A heating scheme using radio-frequency (rf) power to heat a compact toroidal plasma to kilovolt temperatures using lower hybrid heating is proposed. The scheme requires the use of high-power pulsed klystrons. The experimental design is shown with the details of the rf power system and of the coupling antenna array. The so-called radiation barrier formed by the presence of oxygen and carbon impurities may be crossed by this type of pulsed heating source. The general atomic physics of this heating phase is described, with particular emphasis on the non-local thermodynamic equilibrium effects involved in the line and recombination impurity radiation. A survey of nonlinear parametric coupling effects is also given

[en] The development of a two-stage light gas gun to accelerate hydrogen isotope pellets to high speeds is under way at Oak Ridge National Laboratory. High velocities (>2 km/s) are desirable for plasma fueling applications, since the faster pellets can penetrate more deeply into large, hot plasmas and deposit atoms of fuel directly in a larger fraction of the plasma volume. In the initial configuration of the two-stage device, a 2.2-1 volume (≤55 bar) provides the gas to accelerate a 25.4-mm-diam piston in a 1-m-long pump tube; a burst disk or a fast valve initiates the acceleration process in the first stage. As the piston travels the length of the pump tube, the downstream gas (initially at <1 bar) is compressed (to pressures up to 2600 bar) and thus is driven to high temperature (≅5000 K). This provides the driving force for acceleration of a 4-mm pellet in a 1-m-long gun barrel. In preliminary tests using helium as the driver in both stages, 35-mg plastic pellets have been accelerated to speeds as high as 4.0 km/s. Projectiles composed of hydrogen ice will have a mass in the range from 5 to 20 mg ( rho≅0.087, 0.20, and 0.32 g/cm³ for frozen hydrogen isotopes). However, the use of sabots to encase and protect the cryogenic pellets from the high peak pressures will probably be required to realize speeds of ≅3 km/s or greater. The experimental plan includes acceleration of hydrogen isotopes as soon as the gun geometry and operating parameters are optimized; theoretical models are being used to aid in this process. The hardware is being designed to accommodate repetitive operation, which is the objective of this research and is required for future applications