Terry Kammash

Gasdynamic fusion propulsion system for space exploration

An open-ended fusion system in which a high-density plasma is confined and heated to thermonuclear temperatures is examined as a potential high specific power propulsion device that can be used for space exploration. With a collision mean free path much smaller than a characteristic dimension of the system, the plasma behaves much like a continuous medium (fluid) for which the confinement time is drastically different from that which characterizes a typical fusion power reactor. Noting that fact and using an appropriate set of balance equations we derive an expression for the length of the rocket in terms of the plasma parameters required for certain propulsive capabilities. We find that a moderately sized system can produce large values of specific impulse and thrust that would allow a massive rocket to make a round-trip to Mars in months instead of years. By carrying out a preliminary engineering design we also identify those technological areas that must be developed before such a system can become practical. Many of these technologies are surprisingly not out of reach today.

System analysis of the ion-ring-compressor approach to fusion

An overall systems analysis of a fusion reactor scheme based on strong rings of high-energy ions generate d by adiabatic compression of low-energy rings is presented. Consideration of the reactor aspects of such a system reveals the potential for a number of technologically and economically interesting features; in particular, those associated with the expected high-? confinement characteristics of such minimum-B configurations. Although insufficient knowledge on some of the related physics questions exists, no insurmountable problems regarding th e feasibility of such a scheme can be discerned at this point. A preliminary design study for a N ? 300-MW reactor (N being the number of simultaneously employed rings) is presented.

The theory and simulation of relativistic electron beam transport in the ion-focused regime.

Several recent experiments involving relativistic electron beam (REB) transport in plasma channels show two density regimes for efficient transport; a low‐density regime known as the ion‐focused regime (IFR) and a high‐pressure regime. The results obtained in this paper use three separate models to explain the dependency of REB transport efficiency on the plasma density in the IFR. Conditions for efficient beam transport are determined by examining equilibrium solutions of the Vlasov–Maxwell equations under conditions relevant to IFR transport. The dynamic force balance required for efficient IFR transport is studied using the particle‐in‐cell (PIC) method. These simulations provide new insight into the transient beam front physics as well as the dynamic approach to IFR equilibrium. Nonlinear solutions to the beam envelope are constructed to explain oscillations in the beam envelope observed in the PIC simulations but not contained in the Vlasov equilibrium analysis. A test particle analysis is also devel...

Microwave start-up of tokamak plasmas near electron cyclotron and upper hybrid resonances

The scenario of toroidal plasma start-up with microwave initiation and heating near the electron cyclotron frequency is suggested and examined in this paper. Microwave irradiation from the high-field side and an anomalously large absorption of the extraordinary waves near the upper hybrid resonance are assumed. The dominant electron energy losses are assumed to be due to magnetic-field curvature and parallel drifts, ionization of neutrals, cooling by ions, and radiation by low-Z impurities. It is shown by particle and energy balance considerations that electron temperatures around 250 eV and densities of 1012-1013 cm−3 can be maintained, at least in a narrow region near the upper hybrid resonance, with modest microwave powers in the Impurity Study Experiment (ISX) (120 kW at 28 GHz) and The Next Step (TNS) (0.57 MW at 120 GHz). The loop voltages required for start-up from these initial plasmas are also estimated. It is shown that the loop voltage can be reduced by a factor of five to ten from that for unassisted start-up without an increase in the resistive loss in volt-seconds. If this reduction in loop voltage is verified in the ISX experiments, substantial savings in the cost of power supplies for the Ohmic heating (OH) and equilibrium field (EF) coils can be realized in future large tokamaks.

The elastic-plastic cylinder subjected to radially distributed heat source, lateral pressure and axial force with application to nuclear reactor fuel elements

The elastic-plastic deformation of a solid cylinder in the presence of a distributed heat source and subjected to a lateral pressure p and an axial force F is considered. The general results are applied to the cylindrical nuclear reactor fuel element in the state of strain with a radially distributed Gaussian heat source, acting in its fissionable interior. The solution is expressed in closed form in terms of the exponential integral and the incomplete gamma function and is found to exhibit three stages of plastic deformation. Throughout the deformation the states of stress are found to exhibit regular progression. (auth)

Beam-induced tensor pressure tokamak equilibria

D-shaped tensor pressure tokamak equilibria induced by neutral-beam injection are computed. The beam pressure components are evaluated from the moments of a distribution function that is a solution of the Fokker-Planck equation in which the pitch-angle scattering operator is ignored. The level-p⊥ contours undergo a significant shift away from the outer edge of the device with respect to the flux surfaces for perpendicular beam injection into broad-pressure-profile equilibria. The p∥ contours undergo a somewhat smaller inward shift with respect to the flux surfaces for both parallel and perpendicular injection into broad-pressure-profile equilibria. For peaked-pressure-profile equilibria, the level pressure contours nearly co-incide with the flux surfaces.

Antiproton Catalyzed Fusion Propulsion for Interplanetary Missions

Interplanetary trips using chemical propellants require years to complete. A recently completed study on an antiproton catalyzed fusion reaction propulsion system has shown that the specie c impulses that can be obtained are between 1500 s for a contained system to over 100,000 s for a system that directly uses the fusion reaction products. Thrust-to-weight ratios exceeding 1 can be sustained. This allows considerably shorter solar system travel times than conventional chemical propellants. Missions considered range from inner to outer solar system distances. A tradeoff can be made between reducing travel time and reducing initial mass in low Earth orbit. Missions to the inner planets can be shortened considerably for a given mass ratio, whereas missions to the outermost planets will be several weeks in duration.

Improved Physics Model for the Gasdynamic Mirror Fusion Propulsion System

The propulsion capability of the gasdynamic mirror (GDM) fusion propulsion device was examined in several previous publications without taking into account the electrostatic potential inherent to plasma cone nement in this system. This potential arises as a result of the initial rapid escape of the electrons through the mirrors because of the smallness of their mass. The remaining excess positive charge gives rise to a positive electric potential that slows down the electrons while speeding up the ions until equalization in their axial diffusion is achieved. In a thruster, the energy of the ions emerging from the magnetic nozzle will therefore be enhanced relative to their energy as they leave the mirror by an amount equal to that of the potential. In typical GDM parameters, this effect can translate into signie cant increases in the specie c impulse and thrust produced by the system. Nomenclature Ac = area of plasma core A0 = mirror area D = axial diffusion coefe cient E = electric e eld Ee = electron energy EL = escape energy e = electron charge erf = error function k = gradient scale length L = length of plasma <n l = coulomb logarithm m = particle mass N = particle density n = monoenergetic particle density R = plasma mirror ratio T = temperature V = plasma volume v = monoenergetic particle velocity vth = thermal velocity x = parameter, Eq. (26) z = charge number G = velocity-averaged particle e ux g = monenergetic e ux d = parameter, Eq. (25) m = mobility t = cone nement time y = collision frequency f = electrostatic potential

High-Thrust-High-Specific Impulse Gasdynamic Fusion Propulsion System

The gasdynamic fusion propulsion system utilizes a simple mirror magnetic geometry in which a highdensity plasma is cone ned long enough to generate fusion energy while ejecting charged particles through one end to generate thrust. At high densities the collision mean free path becomes much shorter than the length, making the plasma behave much like a continuous medium, a e uid. Under these conditions the escape of the plasma is analogous to the e ow of a gas into a vacuum from a vessel with a hole. With the mirror serving as a magnetic nozzle the plasma-charged particles are ejected at very high energies, giving rise to specie c impulses of well over 200,000 s, but at modest thrusts because of the smallness of their mass. We examine methods by which the thrust of this engine can be enhanced. On the one hand we explore the use of a hydrogen propellant that is heated by the radiation emanating from the plasma, which, upon exhausting through a nozzle, generates the additional thrust. On the other hand we focus purely on changing the properties of the injected plasma to achieve the same objectives. We e nd in the case of a deuterium‐ tritium plasma that the use of hydrogen results in a degradation of the propulsive capability of the system, but we e nd it quite suitable for an engine that burns a mixture of deuterium and helium 3. The same results can be achieved by simply increasing the density of the injected plasma without encountering major adverse consequences. Because of engineering considerations, however, the use of a hydrogen propellant may prove to be inevitable if no other means are found to protect the walls of the reactor chamber against large heat loads.

Multigroup calculations of low-energy neutral transport in tokamak plasmas

Multigroup discrete ordinates methods avoid many of the approximations that have been used in previous neutral transport analyses. Of particular interest are the neutral profiles generatedas an integral part of larger plasma system simulation codes. To determine the appropriateness of utilizing a particular multigroup code, ANISN, for this purpose, results are compared with the neutral transport module of the Duchs code. For a typical TFTR plasma, predicted neutral densities differ by a maximum factor of three on axis and outfluxes at the plasma boundary by ~ 40%. This is found to be significant for a neutral transport module. Possible sources of the observed discrepancies are indicated from an analysis of the approximations used in the Duchs model. Recommendations are made concerning the future application of the multigroup method.