摘要:

Ever since 1958, when Oscar Anderson observed copious neutrons emanating from a “magnetically self-constricted column of deuterium plasma,” scientists have attempted to develop the simple linear pinch into a fusion power source. After all, simple calculations show that if one can pass a current of slightly less than 2 million amperes through a stable D-T plasma, then one could achieve not just thermonuclear break-even, but thermonucleargain. Moreover, several reactor studies have shown that a simple linear pinch could be the basis for a very attractive fusion system. The problem is, of course, that the seemingly simple act of passing 2 MA through a stable pinch has proven to be quite difficult to accomplish. The pinch tends to disrupt due to instabilities, either by them=0(sausage) orm=1(kink) modes. Curtailing the growth of these instabilities has been the primary thrust of z-pinch fusion research, and over the years a wide variety of formation techniques have been tried. The early pinches were driven by relatively slow capacitive discharges and were formed by imploding a plasma column. The advent of fast pulsed power technology brought on a whole new repertoire of formation techniques, including: fast implosions, laser or field-enhanced breakdown in a uniform volume of gas, a discharge inside a small capillary, a frozen deuterium fiber isolated by vacuum, and staged concepts in which one pinch implodes upon another. And although none of these have yet to be successful, some have come tantalizingly close. This paper will review the history of this four-decade long quest for fusion power. ©1997 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.53836

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Magnetically driven z-pinch liners coupled with z-pinch plasma formation schemes may make the achievement of controlled fusion conditions in the laboratory possible in a shorter time frame and at much lower cost than with any other approach. ©1997 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.53833

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In our previous computational modeling of deuterium-fiber-initiated Z-pinches intended for ohmic self-heating to fusion conditions, instability-driven expansion caused densities to drop far below those desired for fusion applications; such behavior has been observed on experiments such as Los Alamos’ HDZP-II. A new application for deuterium-fiber-initiated Z-pinches is Magnetized Target Fusion (MTF), in which a preheated and magnetized target plasma is hydrodynamically compressed, by a separately driven liner, to fusion conditions. Although the conditions necessary for a suitable target plasma—densityO(1018 cm−3),temperature O(100 eV), magnetic field O(100 kG)—are less extreme than those required for the previous ohmically heated fusion scheme, the plasma must remain magnetically insulated and clean long enough to be compressed by the imploding liner to fusion conditions, e.g., several microseconds. A fiber-initiated Z-pinch in a 2-cm-radius, 2-cm long conducting liner has been built at Los Alamos to investigate its suitability as an MTF target plasma. Two-dimensional magnetohydrodynamic modeling of this experiment shows early instability similar to that seen on HDZP-II; however, when plasma finds support and stabilization at the outer radial wall, a relatively stable profile forms and persists. Comparison of experimental results and computations, and computational inclusion of additional experimental details is being done. Analytic and computational investigation is also being done on possible instability-driven cooling of the plasma by Benard-like convective cells adjacent to the cold wall. ©1997 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.53834

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Quasistatic Z-pinches formed “on axis” and magnetically confined by a current layer larger than a critical current (>1.5 MAfor deuterium) are supposed to undergo radiative collapse providing high energy density thermal plasmas. Z-pinches created from solid fibers do not well couple to the necessarily high power drivers due to lacking initial conductivity and compressibility resulting in fast global plasma expansion and current leaks. Therefore experiments starting from plasmajets (ne⩽1023 m−3,Te≈1 eV) have been performed using two different drivers, namely the terawatt pulseline KALIF (2 MV, 900 kA) and the fast condenser bank SPEED 1 (200 kV, 900 kA) in order to investigate driver-load coupling with different initial power conditions. The main results of this study are: (i) plasmajets show much better initial coupling than fiber experiments, (ii) there is a critical limit of the reduced electrical field(E/n≈10−16 Vm2)above which fast plasma erosion and decoupling takes place preventing pinch formation and (iii) plasma loads need high initial densities(ne⩾1024 m−3)in order to well couple to terawatt drivers providing pinch electric fields above107 V/m.A conductive, dense and narrow plasma column is a necessary condition for an efficient energy transfer from the driver to the load. Whether or not this is sufficient to induce radiative collapse still remains to be experimentally demonstrated. ©1997 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.53837

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The main long term objectives of the DZP Project at Imperial College are to achieve radiative collapse from cryogenic hydrogen fibres, to study Z-pinch conditions relevant to controlled fusion, and to study the basic plasma physics processes. Initial experiments have been conducted on carbon fibres using both the IMP (250 kA) and MAGPIE (1.5 MA) generators. Recently cryogenic deuterium fibres have also been employed. A wide range of diagnostics has been developed including short pulse laser interferometry, schlieren and Faraday rotation, as well as optical and X-ray streak and framing pictures. We have made a special study of the transient(∼1 ns)intense X-ray bright spots and their bifurcation, and found good agreement with a 2-D MHD simulation with ionisation and recombination included. The magnetic field and current distribution have been measured in the coronal plasma showing that over 90&percent; of the circuit current is flowing in the pinch. A current prepulse has led to a much more uniform and more intense X-ray emission during the main current pulse. Schemes are being explored for non-linear saturation of instabilities using sheared axial flow, large ion Larmor radius and axial magnetic field. ©1997 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.53895

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The Staged Z Pinch couples energy to a target plasma, dynamically in stages. The present UCI experiment provides stable, multishell z pinches at 1.2 MA and 1 &mgr;s implosion time. Test-stand studies of an exploded-fiber target indicate that the fiber core is not ionized, due to current channeling in the high conductivity ablated plasma. ©1997 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.53838

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The present work deals with a comparative study in a compressional gas embedded Z-pinch inH2and inD2are presented. The use ofH2andD2allows discharges with the same electrical properties, but different dynamics. Pressures of1/3,1/6and3/70 atmwere used to carry out the experiments. The pinch is initiated by a focused laser pulse, which is coaxial with a cylindrical DC microdischarge. This configuration results in a double column pinch at early times, which as current rises, coalesces into a single column becoming a gas embeddedcompressionalZ-pinch. The maximum electron density achieved on axis is greater than twice the expected value from the filling pressure, in contrast with a traditional gas embedded pinch. The expansion rate is reduced to a third of the observed value for the single channel laser initiated gas embedded pinch. This observation is consistent with a central current channel in the composite pinch. The experimental results, electron density at the centre and lower expansion rate, confirm the high degree of compression achievable with the composite preionization scheme. ©1997 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.53855

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

For a pinch under equilibrium, the Pease-Braginskii current limit sets the ceiling when the ohmic heating rate is balanced by the bremsstrahlung loss rate. Under a dynamical condition. Shearer showed that, when the pinch current exceeds the Pease-Braginskii limit, the difference in ohmic heating and bremsstrahlung loss rate could lead to the phenomenon of radiative contraction, producing a plasma structure of ultra high energy density. The work was extended by Haines and Robson independently to describe the conditions for radiative collapse. These analytical results show that under certain circumstances, a high temperature pinch can be self-compressed to an extremely high density, limited only by photon self-absorption or electron degeneracy. In this paper, we present an analysis on the radiative collapse formalism including the effect of an external circuit. It is shown that the degree of contraction is governed by the intrinsic rate of energy delivery to the system. Two expressions are derived which define the ultimate pinch dimension with the plasma parameters and that of the electrical circuit. ©1997 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.53913

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The results of a cryogenics fibre maker which extrudes fibres continuously are presented. The fibre maker is based on a simple concept of differential temperature. Two reservoirs are connected in cascade and are kept at different temperatures. The first reservoir is connected to an external gas line supply (the gas that will made the fibre) and is used to liquefy the gas. The second reservoir is colder that the first and the liquid that comes from the first reservoir is frozen and later is used to form the fibre. The pressure of external gas supply in the first reservoir is used to extrude the fibre. The system is cooled by a two stage closed cycle refrigerator, which uses liquid helium as a working fluid. The nozzles used to extrude the fibre are made of stainless steel capillary with diameters between 50 &mgr;m and 250 &mgr;m, with a length of 2 mm. The use of a system with two independent temperatures, permits to control the extrusion rate of the fibres and to produce the fibres continuously. Using this system, hydrogen deuterium, nitrogen and argon fibres of various diameters were extruded. ©1997 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.53914

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A series of experiments have been carried out on MAGPIE (Mega Ampere Generator for Plasma Implosion Experiments) usingCD2fibre loads. Diameters between 50 &mgr;m and 200 &mgr;m were used. The generator was operated at a voltage of 1.4 MV, peak current of 1.1 MA, 150 ns rise time and with a stored energy of 215 kJ. The effect of reversing the polarity of the generator on the neutron emission was studied. An average anisotropy in the neutron emission of 1.2 (end-on to side-on) was obtained in the case where the end-on measurement was taken with a detector located behind the anode. When the initial polarity was reversed (the end-on detector, now being behind the cathode) the anisotropy increased to 1.7. This is a novel observation and requires a theoretical model that explains the acceleration of ions in both directions. Correlation between the fibres diameters and the neutron yield will be discussed. The neutron energy was measured using the time of flight technique. Three plastic scintillators were located at different positions in relation to the fibre. Neutron energies up to 4.8 MeV were measured at 45 degrees from the pinch axis in the anode direction. This, together with the detection of hard x-ray emission, indicates a beam-target reaction as the mechanism responsible for the neutron production. A deuteron beam energy of 2.6 MeV was inferred from these results. This is consistent with the electron beam energies inferred from the hard x-ray emission in a similar experiment. ©1997 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.53844

出版商:AIP    

年代:1997

数据来源: AIP