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[...]if advanced physics performance could be realized as recent experimental innovations from DIII-D, AUG and other tokamaks suggest, a compact high field tokamak reactor can be realized. Besides providing a viable path to fusion demo, the ITER experience is invaluable for the design of all future tokamak reactors. [...]it postulates liquid metal air-driven pistons, with highly efficient energy recovery, to arrive at a low gain fusion power plant with 40 MW net output power.

In this work, a Serpent 2 neutronics model of the Wendelstein 7-X (W7-X) stellarator is prepared, and an response function for the Scintillating-Fibre neutron detector (SciFi) is calculated using the model. The neutronics model includes the simplified geometry for the key components of the stellarator itself as well as the torus hall. The objective of the model is to assess the 14.1 MeV neutron flux from deuteron-triton fusions in W7-X, where the neutrons are modelled only until they have slowed down to 1 MeV energy. The key messages of this article are: demonstration of unstructured mesh geometry usage for stellarators, W7-X in particular; technical documentation of the model and first insights in fast neutron behaviour in W7-X, especially related to the SciFi: the model indicates that the superconducting coils are the strongest scatterers and block neutrons from large parts of the plasma. The back-scattering from e.g. massive steel support structures is found to be small. The SciFi will detect neutrons from an extended plasma volume in contrast to having an effective line-of-sight.

In October 2003, Dr. Raymond Orbach, Director of the Department of Energy’s Office of Science, issued a charge to the Fusion Energy Sciences Advisory Committee (FESAC) “to identify the major science and technology issues that need to be addressed, recommend how to organize campaigns to address these issues, and recommend the priority order for these campaigns.” The sections in this report document the results of the Panel’s work. The first two sections describe the concepts of the overarching themes, topical scientific questions, and campaigns. The next six sections (Sections 3–8) describe in detail the six scientific campaigns. Section 9 describes some important enabling research activities necessary for the campaigns. Sections 10–12 describe the overarching themes, which provide a crosscutting perspective of the activities in the six campaigns. Finally, the Panel’s recommendations are set forth in Section 13. The charge letter to the panel is provided as Appendix A; the FESAC response letter is provided as Appendix D.

Reduction of particle and heat fluxes to plasma facing components is critical to achieve stable conditions for both the plasma and the plasma material interface in magnetic confinement fusion experiments. A stable and reproducible plasma state in which the heat flux is almost completely removed from the material surfaces was discovered recently in the Wendelstein 7-X stellarator experiment. At the same time also particle fluxes are reduced such that material erosion can be mitigated. Sufficient neutral pressure was reached to maintain stable particle exhaust for density control in this plasma state. This regime could be maintained for up to 28 seconds with a minimum feedback control.

This report was prepared by a Working Group at the request of the U.S. Department of Energy, Office of Fusion Energy Sciences in 1997. The report addresses technical opportunities for mutually beneficial collaboration between the United States and other international fusion research programs. A number of outstanding opportunities are discussed.

A radially scanning small-angle CO(,2) laser scattering system was designed and built to study driven radio frequency (RF) waves in the steady-state Advanced Concepts Torus (ACT-1). The well characterized multispecies hydrogen plasma (H(,1)('+), H(,2)('+), H(,3)('+)), with low neutral pressure and warm ions, is a convenient medium for the study of finite ion Larmor radius (FLR) effects. Two types of waves, the ion Berstein wave (IBW) and lower hybrid wave (LHW), are investigated. Ion Berstein waves, existing because of the inclusion of FLR terms in the wave dispersion relation, are launched at frequencies below the n('th) ion cyclotron harmonic (f = n(omega)(,ci)/2(pi), n = 2,3,4) and studied through their density (laser) and potential (probe) fluctuations. Detailed dispersion curves are mapped out, showing the highest harmonic FLR effects yet observed. A new nonintrusive method for measuring hydrogen ion temperature, using externally launched IBW as test waves detected by laser scattering, is demonstrated. This technique does not require knowledge of T(,e) or n(,e) to obtain T(,i). Application of this technique to large, hot tokamak plasmas is discussed. Lower hybrid waves are studied near the lower hybrid resonance, i.e., in the frequency range 1(, )<(, )(omega)/(omega)(,LH) < 3. Resonance cones are detected with the laser system, and wave K(,(PARLL))-spectra are measured both by scanning the scattering k-vector (k(,(PERP))) with fixed plasma conditions, and by sweeping the density while holding k(,(PERP)) constant. In this manner, the effects of antenna phasing and electron Landau damping on the LHW k(,(PARLL))-spectrum in the plasma are observed. High levels of low frequency turbulence are seen to destroy the laser resonance cone signal. Extensive two-dimensional plasma parameter profiling shows the importance of planar wave-fronts to aid detection of the low (absolute) level RF waves with laser scattering. Power scaling shows nonlinear effects associated with background neutral ionization, and buckling of plasma profiles. Finally, FLR effects are observed on LHW trajectories, both by probe and laser, with periodicity (omega)(,ci) in the range 4 < (omega)/(omega)(,ci) < 8, when 1(, )<(, )(omega)/(omega)(,LH) < 2. These effects are highly sensitive to plasma and antenna parameters, and can be qualitatively understood with a wave trajectory code including magnetized warm ion terms.