Showing papers in "Journal of Fusion Energy in 1989"

Design for a high power-density Astron reactor

Abstract: A liquid lithium blanket surrounding the plasma volume is described. The liquid lithium flows along magnetic flux tubes at a high speed. There is no vacuum wall between the blanket and the plasma. The E-layer of relativistic particles within which the plasma is confined serves as a vacuum wall protecting the plasma from the lithium vapor, which is continuously produced at the surface of the blanket, by ionizing the lithium atoms and ejecting the same along open magnetic lines. The heat load at the surface of the blanket generated by 14 MeV neutrons can be several hundred MW per square meter.

Selective energy neutron source based on the D-Li stripping reaction

Abstract: A proposal is made on a version of the deuterium-lithium stripping (the FMIT)-type neutron source enhanced with its potential suitability for resolving complex neutron energy dependence in irradiation effects on materials. Some attractive features of such an accelerator-based source are skimmed out which cover the limitations fatal in the conventional means. The flexibility of controlling the quality and quantity of neutrons and the closer accessibility toin-situ- type experimentation are stressed as essential for the advanced studies on either interpretation of complex phenomena or innovating new materials compatible with specific neutron environments. A suggested conceptional design specification includes the selectivity of energy from 5, 10, and 14 MeV, and the maximum fluence of about 0.5–1×1022 n/cm2/year which can create damage of a typical candidate fusion reactor material by around 10 dpa. The concept is stressed to be reasonable and a realistic optionregarding the maturity of underlying technology, financial feasibility, and timing.

Beam plasma neutron sources based on beam-driven mirror

Abstract: The design and performance of a relatively low-cost, plasma-based, 14-MeV D-T neutron source for accelerated end-of-life testing of fusion reactor materials are described in this article. An intense flux (up to 5×1018 n/m2·s) of 14-MeV neutrons is produced in a fully-ionized high-density tritium target (n e ≈ 3×1021 m−3) by injecting a current of 150-keV deuterium atoms. The tritium plasma target and the energetic D+ density produced by D0 injection are confined in a column of diameter ⩽ 0.16 m by a linear magnet set, which provides magnetic fields up to 12 T. Energy deposited by transverse injection of neutral beams at the midpoint of the column is conducted along the plasma column to the end regions. Longitudinal plasma pressure in the column is balanced by neutral gas pressure in the end tanks. The target plasma temperature is about 200 eV at the beam-injection position and falls to 5 eV or less in the end region. Ions reach the walls with energies below the sputtering threshold, and the wall temperature is maintained below 740 K by conventional cooling technology.

Need for and requirements for a neutron irradiation facility for fusion materials testing

Abstract: The construction and operation of an intense 14-MeV neutron source is essential for the development and eventual qualification of structural materials for a fusion reactor demonstration plant (DEMO). Because of the time required for materials development and the scale-up of materials to commercial production, a decision to build a neutron source should precede engineering design activities for a DEMO by at least 20 years. The characteristic features of 14-MeV neutron damage are summarized including effects related to cascade structure, transmutation production, and dose rate. The importance of a 14-MeV neutron source for addressing fundamental radiation damage issues, alloy development activities, and the development of an engineering database is discussed. For these considerations, the basic requirements and machine parameters are derived.

Option for spallation neutron sources

Abstract: Spallation reactions are a very important option for efficient neutron sources appropriate for fusion materials testing. An “option of this option” is the EURAC concept, which makes use of short-term accelerator technology in the cheapest way and is proved to provide the needed neutron flux to verify fast experiments on fusion materials performance. Its flexible conception allows an optimum combination of very high fluxes of about 1016 n/cm2/s, with decreasing fluxes along the testing zones in enough volume to perform the correct irradiations. With this assumption, the rate effect can be perfectly analyzed together with the end-of-life conditions assumed in the structural material of the future fusion environments. The possible negative effects of the high-energy neutrons in the Spallation spectrum have been taken into account, concluding their non-significance in the desired damage parameters. The EURAC concept can also be considered in light of other purposes like incineration processes,μ production, and, with the appropriate booster, high-flux cold neutron source.

Spallation neutron sources: Basics, state of the art, and options for future development

Abstract: The paper outlines the physics of the spallation reaction and the resulting rules of thumb with respect to neutron yield, heat deposition, and energy distribution. Technical problems and performance expectations are discussed on the basis of two high beam power spallation neutron source projects, namely, the German SNQ Project (not funded) and the Swiss SINQ Project (under construction). Since both of these projects were designed mainly for thermal neutron scattering application, emphasizing the production of a high flux of moderated neutrons, an alternative conceptual design is presented which, while still allowing the extraction of cold and thermal neutron beams, also offers the opportunity of placing samples into positions where the neutron spectrum has changed only very little due to transport in matter. The anisotropy of the high-energy neutron field can be taken advantage of to select, to some extent, how much of the high energy component will be seen by the specimens. No technical design concept exists so far for a spallation neutron source for fusion materials test purposes, and more detailed studies would be required to assess its value and usefulness. However, a source for combined use for different purposes seems to be feasible without too many compromises.

A high-flux accelerator-based neutron source for fusion technology and materials testing

Abstract: Advances in high-current linear-accelerator technology since the design of the Fusion Materials Irradiation Test (FMIT) Facility have increased the attractiveness of a deuteriumlithium neutron source for fusion materials and technology testing. This paper discusses the conceptual design of such a source that is aimed at meeting the near-term requirements of a high-flux high-energy International Fusion Materials Irradiation Facility (IFMIF). The concept employs multiple accelerator modules providing deuteron beams to two liquid-lithium jet targets oriented at right angles. This beam/target geometry provides much larger test volumes than can be attained with a single beam and target and produces significant regions of low neutron-flux gradient. A preliminary beam-dynamics design has been obtained for a 250-mA reference accelerator module. Neutron-flux levels and irradiation volumes were calculated for a neutron source incorporating two such modules, and interaction of the beam with the lithium jet was studied using a thermal-hydraulic computer simulation. Approximate cost estimates are provided for a range of beam currents and a possible facility staging sequence is suggested.

Measurements and analysis of transmitted spectra from LOTUS fission-suppressed hybrid blanket driven by D-T neutrons

Abstract: The neutron spectra transmitted across a fission-suppressed hybrid blanket and its components, driven by a low intensity 14 MeV Haefely neutron generator, were measured with a 2″×2″ NE213 detector at LOTUS facility. These experiments have been analyzed with 2D and 3D codes DOT3.5 and MCNP, respectively. The spectral integrals between 15 to 1 MeV show good agreement among the 2D, the 3D, and the NE213 for 15 cm lead, 18 cm beryllium, and 25 cm graphite slabs. However, there are large discrepancies for 6.2 cm stainless steel and 15 cm lithium carbonate slabs. The assemblies involving two or more of these slabs reflect these tendencies. We observe also considerable disagreement over pointwise spectra for a number of assemblies.

The high-density Z-pinch as a pulsed fusion neutron source for fusion nuclear technology and materials testing

Abstract: The dense Z-pinch (DZP) is one of the earliest and simplest plasma heating and confinement schemes. Recent experimental advances based on plasma initiation from hair-like (10s μm in radius) solid hydrogen filaments have so far not encountered the usually devastating MHD instabilities that plagued early DZP experimenters. These encouraging results along with the debut of a number of proof-of principle, high-current (1–2 MA in 10–100 ns) experiments have prompted consideration of the DZP as a pulsed source of DT fusion neutrons of sufficient strength (SN ⩾ 1019 n/s) to provide uncollided neutron fluxes in excess ofIw= 5–10 MW/m2 over test volumes of 10–30 liters or greater. While this neutron source would be pulsed (100s ns pulse widths, 10–100 Hz pulse rate), giving flux time compressions in the range 105–106, its simplicity, near-term feasibility, low cost, high-Q operation, and relevance to fusion systems thatmay provide a pulsed commercial end-product, e.g., inertial confinement or the DZP itself, together create the impetus for preliminary consideration as a neutron source for fusion nuclear technology and materials testings. The results of a preliminary parametric systems study (focusing primarily on physics issues), conceptual design, and cost vs. performance analyses are presented. The DZP promises an inexpensive and efficient means to provide pulsed DT neutrons at an average rate in excess of 1019 n/s, with neutron currents Iw≲10 MW/m2 over volumes Vexp ⩾ 30 liter using single-pulse technologies that differ little from those being used in present-day experiments.

High-intensity 14-MeV cut-off neutron production by the 1 H(t,n) 3 He source reaction

Abstract: A detailed description of neutron production by the1H(t, n)3He source reaction is given. The corresponding angular-dependent yields and spectra are calculated for an incident triton energy of 21 MeV and a thick (totally absorbing) hydrogen target. Since this reaction is proposed for alternative consideration to present concepts of d-lithium fusion materials test facilities, the angular and spectral yields, and the volume-dependent fluxes in a test cell are compared with the equivalent quantities achievable from such facilities involving 35-MeV deuterons incident on thick natural lithium targets.

Impact of high-temperature superconductors on the possibility of radiofrequency confinement of fusion plasma

Abstract: Recent discoveries of superconducting materials that operate at high temperatures may have both technical and economic consequences for magnetic confinement fusion. In addition, however, they could also open up the possibility of plasma confinement by radiofrequency fields. The new, high-temperature superconductors may impact the feasibility of rf confinement in two important ways: (1) higher temperature superconductors should have higher criticalB fields and consequently may allow higher critical electric fields to be sustained in the cavity, thus allowing the necessary confining pressure to be achieved; and (2) the higher temperature superconductors lower the refrigeration power necessary to maintain the superconducting cavity, thus allowing a favorable energy balance.

Fusion neutron test facility requirements for interactive effects in structural and high-heat-flux components

Abstract: A relevant design data base is needed for structural components in near-term and commercial fusion devices. A high-flux, high-fluence fusion neutron test facility is required for testing the failure mechanisms and lifetime-limiting features for first wall, blanket, and high-heat-flux components. We describe here the key aspects of the fusion environment which influence the response of structural and high-heat-flux components. In addition to test capabilities for fundamental radiation-effects phenomena, e.g., swelling, creep, embrittlement, and hardening, it is shown that the facility must provide an adequate range of conditions for accelerated tests to study the limitations on component lifetime due to the interaction between such fundamental phenomena. In high-heat-flux components, testing of the failure mechanisms of duplex structures is shown to require maintenance of an appropriate temperature gradient in the 14-MeV neutron field. Thermal stresses are shown to result in component failure, particularly when the degradation in the thermal conductivity and mechanical properties by irradiation are considered. Several factors are discussed for assessment of the failure modes of the first wall and blanket structures. These are displacement-damage dose and dose rate, the amount of helium gas generated, the magnitude of irradiation and thermal creep, prototypical temperature and temperature-gradient distributions, module geometry, and external mechanical constraints.

The reversed-field-pinch (RFP) fusion neutron source: A conceptual design

Abstract: The conceptual design of an ohmically heated, reversed-field pinch (RFP) operating at ∼5-MW/m2 steady-state DT fusion neutron wall loading and ∼124-MW total fusion power is presented. These results are useful in projecting the development of a cost effective, low-input-power (∼206 MW) source of DT neutrons for large-volume (∼10 m3), high-fluence (3.4 MW yr/m2) fusion nuclear materials and technology testing.

Reversed field pinch, compact toroids, and dense Z-pinch

Abstract: The tokamak is the primary plasma confinement device, under development around the world, as a source for magnetic fusion energy. The reversed field pinch, compact toroids, and dense Z-pinch are frequently referred to as 'alternates', meaning that they are different from the tokamak but candidates, ultimately, as confinement devices for energy-producing plasma. These alternates are of interest in some cases because they offer potential advantages in a reactor embodiment (e.g., reduced magnetic field requirements). In other cases, the interest to the national program is primarily because of some specialized application, such as the potential of the Z-pinch as a neutron source. In all cases, the plasma physics insights gained through study of these devices will be important to the evaluation of plasma fusion broadly. In fact, the different view of the same fundamental physics when applied in tokamaks can provide insights and advances that prove to be critical for tokamak advancement.

Neutron-Imaging Technique for Monitoring High-Temperature Plasma Dynamics

Abstract: A preliminary design for the adaptation of a pinhole experiment (PINEX) technique to the monitoring of the dynamics of high-temperature plasmas is described. Specifically, this imaging technique uses a thick aperture, an efficient radiation converter, and highly intensified television cameras to provide real-time viewing of radiation sources, such as the neutron emissions from d-d and d-t fusion reactions in controlled thermonuclear research devices. The neutron emission strengths,R ∼ 51015 n/sec, recently achieved at the Tokamak Fusion Test Reactor (TFTR) and the Joint European Torus (JET) should be sufficient for 3 to 6-cm spatial resolution and 10 to 100-msec time resolution using such a system. Such information should be useful for on-line optimization of the plasma and for quantitative evaluation of its performance.

Design principles for efficient muon production in muon-catalyzed fusion reactors

Abstract: The two major schemes for a fixed-target muon production system in muon-catalyzed fusion reactors are analyzed and compared using Monte Carlo simulation techniques. Starting with a careful optimization of the pion production target we next consider the complete system where pion conversion losses and muon losses in the target and the pressure vessel are taken into account. A simple but realistic design for the pion-muon converter is introduced. Problems and inefficiencies are identified to provide a basis for future inventions.

Tritium breeding analysis of a tokamak magnetic fusion production reactor

Abstract: With three-dimensional modeling and neutron transport analysis, a tokamak with a low technology blanket containing beryllium was found to have a tritium breeding ratio of 1.54 tritons per DT neutron. Such a device would have a net tritium production capability of 9.1 kg/yr from 450 MW of fusion power at 70% capacity factor.

High beta and/or high field tokamaks and stellarators

Abstract: This paper discusses high beta aspects of the stellarators and tokamak reactors and the need to understand the MHD equations involved. 7 refs., 3 figs.

Compact Tokamak Ignition Concepts

Abstract: The title of this session is "A Panel Discussion on Compact Tokamak Ignition Concepts." Figure 1 illustrates the reason we are interested in the concept of compact ignition tokamak concepts. What we did here is to plot cost versus performance for recently built and planned machines, assuming Goldston scaling. The shaded areas show the principal advantage that we see with compact ignition concepts. There seems to be confirmation that you do get higher performance with a given cost in the compact devices. The disadvantage is that you suffer in terms of reduced access and perhaps some limitations on pulse length that may not be applicable for the particular goals that we have in mind for the ignition device. Figure 2 shows a list of physics issues having to do with alpha particles. This is taken from MFAC Panel 14, which looked at the idea of a compact ignition tokamak. A check mark indicates that the issue is going to be dealt with; a dash indicates that it will be explored. What you see in Fig. 2 is that a compact ignition tokamak can resolve many of the alpha-particle issues for fusion and contributes to almost all of the other tokamak issues, with the exception being a full exploration of burning plasma physics. Finally, it should be noted that it is our intent to carry out such an experiment as a national project with the full support of the fusion community. Whatever it is that we do in the way of a compact ignition tokamak, it is going to take all of us