Magnetic electrostatic plasma confinement Abstract: Electrostatic plasma confinement and magnetic electrostatic
plasma confinement (MEPC) have been studied for four decades. The multiple
potential well hypothesis, postulated to explain high neutron yields from
Hirsch's colliding beam experiment, has been supported by several pieces of
evidence, but results were inconclusive. Magnetic shielding of the grid was
developed to reduce the required beam current and to prevent grid overheating.
Electrostatic plugging of magnetic cusps evolved to a similar configuration.
Due to low budgets, early MEPC experiments used spindle cusps, which are poor
for plasma confinement. Later experiments used multipole cusps or a linear set
of ring cusps, which have larger volumes of field-free plasma. Besides
producing electricity and synthetic fuels, MEPC reactors could be used for
heavy ion beams sources and neutron generators. The main issues of concern for
MEPC reactor development are electron transport, plasma purity and electrode
alignment and voltage holding.
CORRELATION BETWEEN POTENTIAL WELL STRUCTURE AND NEUTRON PRODUCTION IN
INERTIAL ELECTROSTATIC CONFINEMENT FUSION Abstract: The electrostatic potential well in inertial electrostatic
confinement (IEC) is studied using two approaches. First, the equilibrium
potential profile is obtained by solving the charge neutrality condition, i.e.
ni = ne, assuming the appropriate distribution functions
for the ions and the electrons. The formation of a double well structure is
demonstrated, with a depth depending upon the ratio between the focus radii of
the electrons and the ions. The correlations between the well depth and the
volume integrated neutron production due to deuterium-deuterium (DD) reactions
are obtained. Second, in order to study the stability of the well, the dynamic
behaviors of the potential well are calculated by performing time advancing
numerical simulations on the basis of the particle in cell method. Single,
double and triple wells, depending on the amount of injected ion current, are
observed to be formed for ions with a monoenergetic distribution. The well in
the centre of the multiwell structure is unstable and oscillates with a period
much longer than the inverse ion plasma frequency. A double well structure can
be formed even for ions with a spread out energy distribution when the ion
current is larger than the threshold value. The time averaged neutron
production by DD fusion events is proportional to a power of the ion current
involved in forming the double well structure. The results strongly suggest
that the high neutron production rate should be attributed to not only the
well depth but also the unstable behavior of the potential, i.e. the
intermittent peaking of the density in the centre region. A numerical
simulation reveals that IEC possesses a favorable dependence of fusion
reactions on the injected ion current for the application to a neutron source
or a fusion reactor.
Ion distribution function and radial profile of neutron production rate in
spherical inertial electrostatic containment plasmas Abstract: The radial profile of the neutron production rate in
spherical inertial electrostatic containment plasmas is investigated. The
electrostatic potential is obtained by solving the Poisson equation, and by
using the potential; the fuel ion velocity distribution function is determined
at each radial point. From the velocity distribution function, the neutron
production rate is accurately evaluated. Numerical results show that if it is
assumed that fuel ions are contained keeping the total energy and angular
momentum almost constant, the double radial peak in the neutron production
rate can appear without creation of the deep double potential well.
Measurements of strongly localized potential well profiles in an inertial
electrostatic fusion neutron source Abstract: Direct measurements of localized electric fields have been
made by the laser induced fluorescence (LIF) method using the Stark effect in
the central cathode core region of an inertial electrostatic containment
fusion (IECF) neutron (proton) source. These are expected to have various
applications, such as luggage security inspection, non-destructive testing,
land mine detection and positron emitter production for cancer detection,
currently producing continuously about 107 n/s D-D neutrons. Since
1967, when the first fusion reaction was successfully proved to have taken
place in a very compact IECF device, potential well formation due to the space
charge associated with spherically converging ion beams has been a central key
issue remaining to be clarified in beam - beam collision fusion, which is the
major mechanism of the IECF neutron source. Many experiments, although
indirect, have been done so far to clarify the nature of the potential well,
but none of them has produced definitive evidence. The results found by the
present LIF method show a double well potential pro le with a slight dip for
ion beams with relatively larger angular momenta, whereas for ions with
smaller angular momenta, a much steeper potential peak develops.
FUSION REACTIVITY CHARACTERIZATION OF A SPHERICALLY CONVERGENT ION FOCUS Abstract: The deuterium - deuterium (D-D) fusion reaction rate in a
spherically convergent ion focus is observed to significantly exceed the rate
predicted by a collisionless flow model. However, a careful consideration of
ion-neutral collisions and the trapped neutral density in the cathode account
for the extra reactivity without invoking anomalous ion trapping in the
converged core region. This conclusion is supported by proton collimation
measurements, which indicate that the bulk of the observed reactivity
originates outside the core region. In addition, a classical flow model, where
charge exchange collisional effects on the ion and fast neutral distributions
are included, provides fusion rate estimates that are quantitatively
consistent with the observed D-D fusion neutron production rate.
Convergence, electrostatic potential, and density measurements in a
spherically convergent ion focus Abstract: Unique measurements of the basic plasma-flow characteristics
in a low pressure (less than 53 mPa H2) spherically convergent ion
focus are obtained using high-voltage (less than 5 kV) emissive and double
probes. The radial plasma potential distribution agrees with a collisionless,
recalculating, space-charge-limited current model. Flow convergence increases
with voltage and neutral pressure and decreases with cathode grid wire spacing
and current. Core radii within 4–5 times the ideal geometric limit are
measured, and the observed core sizes are consistent with predictions from a
multipass orbit model which includes asymmetries in the accelerating potential
well. A virtual anode is observed in the converged core region, and no
evidence for multiple potential well structures in the core is found.
Measurements of the core ion density ~nic;1015 m23! are consistent with simple
flow convergence models.
SELF MAGNETIC INSULATION OF PULSED ION DIODES Abstract: Pulsed ion diodes magnetically insulated by their own feed
currents can be treated in a manner similar to that used for applied field
diodes. The self insulated diode has the advantages of easy construction and
automatic confinement of the magnetic field to the accelerating gap. On the
other hand, the energy that produces the magnetic field is utilized
inefficiently. With models for the ion current density, it is possible to
calculate the optimum electrode shapes of ion diodes to produce a spherical
focus. In this application it is shown that the pinched electron diode may not
be the most advantageous self insulated geometry.
Non-Linear Dynamics of Non-Neutral Plasmas Abstract: An expanding or contracting non-neutral plasma without an
external magnetic field is investigated. In certain situations the density and
temperature rise to many times their initial values in a short time, followed
by an equally sharp fall. The plasma shows no Landau damping.
Alternate Fusion: Continuous Inertial Confinement Abstract: We argue that alternate fusion approaches should be pursued
if 1) They do not require magnetic confinement superior to tokamaks; 2) Their
physics basis may be succinctly stated and experimentally tested; 3) They
offer near-term applications to important technical problems; and
4) Their cost to proof-of-principle is low enough to be consistent with budget
realities. An approach satisfying all of these criteria is presented, based on
continuous inertial confinement. E such an approach, the inertia of a
nonequilibrium plasma produces concentrations of plasma density.
Recent theoretical developments indicate that fusion gain of order unity or
greater may be produced in a system as small as a few mm radius! Confinement
is that of a nonneutralized plasma. A pure electron plasma with a radial beam
velocity distribution is absolutely confined by an applied Penning trap field.
Spherical convergence of the confined electrons forms a deep virtual cathode
near T = 0, in which thermonuclear ions are absolutely confined at useful
densities. We examine the equilibrium, stability, and classical relaxation of
such systems. A sketch of immediate and long-term experimental opportunities
is given.
Spherical Nonlinear and Rotating
Waves Abstract: We establish the existence of time-periodic solutions of semi-linear wave
equations on the unit sphere in R3. The problem has been studied previously in
(1982, V. Benci and Fortunato, Ann. Mat. Pura Appl. 132, 215 242) using
variational techniques. Our results here are much sharper: We employ delicate
methods of bifurcation theory (1979, H. Kielho fer, J. Math. Anal. Appl. 68,
408 420; 1987, H. Kielho fer and P. Ko tzner, J. Appl. Math. Phys. 38, 201
212) combined with well-known group-theoretic ideas to find branches of
small-amplitude solutions. Precise spatio-temporal patterns of solutions are
uncovered as a by-product of the analysis. Moreover, in certain cases we prove
the existence of global solution branches (in the sense of P. Rabinowitz).
Measurements of ion energy distributions by Doppler shift spectroscopy in an
inertial-electrostatic confinement device Abstract: Doppler shift spectroscopy was carried out on the discharge
in a spherically symmetric inertial-electrostatic confinement system.
This enabled the ion energy distributions, types, and densities of ionic
species to be determined. A weakly ionized hydrogen radio-frequency
discharge was used as the ion source for two spherical and concentric
electrostatic grids. The inner and outer grids were the cathode and
anode, respectively. It was found that the ion energy distribution
consisted of a non-Maxwellian directional component, as well as a spatially
isotropic Maxwellian distribution. The directional component consisted
of three broadened energy peaks belonging to H+3 (20%),
H+2 (60%), and H+ (20%). The ions had
energies approximately 20% of the cathode potential. The temperature (in
electron-volts) of the Maxwellian distribution was approximately 15% of the
cathode potential.