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Notes: The total abundance of secondary ion current detected from a heavy ion beam probe (proportional to nσeff ) is a function of the electron temperature through the collision cross section. n and Te can be separated by probing the same volume with two different ion species or monitoring two different charge states produced from the same ion. Measurements at Rensselaer (RENTOR) have demonstrated the technique by using a single detector system to look at Cs++ and Cs+++ on successive plasma shots. Data from EBT-S has shown a sensitivity to electron energies up to 1 MeV, but accurate determination of bulk temperatures is limited to a few hundred volts. Two new analyzers have been installed on RENTOR to demonstrate the capability of providing Te profiles during a single shot. Calibration of these measurements requires a detailed accounting of all input beam ions, reaction products, and sample volumes.

Notes: Heavy ion beam probes for reactor-size plasma devices will require beam energies of approximately 10 MeV. Although accelerator technology appears to be available, beam deflection systems and parallel plate energy analyzers present severe difficulties if existing technology is scaled in a straightforward manner. We propose a different operating mode which will use a fixed beam trajectory and multiple cylindrical energy analyzers. Development effort will still be necessary, but we believe the basic technology is available.

Notes: Heavy-ion beam probing generally consists of passing a beam of 1+ ions through a plasma imbedded in a magnetic field. Secondary ions with higher ionization levels are produced by ionizing collisions with the plasma electrons. Detection of the secondary ions with a small-aperture electrostatic energy analyzer allows continuous fluctuation measurements of the plasma density and space potential with both spatial and temporal resolution. Spatial resolution is the order of 0.1 cm3 and temporal resolution is presently electronics limited to ∼1 μs. The energy of the probing beam is determined primarily by the requirement that the secondary ion must escape from the plasma. Typical beam energies extend from 10 to 500 keV. The range of plasma densities that have been investigated is 1012 cm−3〈ne〈1014 cm−3. At the higher densities, beam attenuation becomes a serious problem. Higher beam energies provide better penetration of the magnetic field, and reduced beam attenuation. Heavy-ion beam probes were first used to measure a coherent density fluctuation on a hollow cathode arc in 1969, and soon afterward to measure the space potential. Since then beam probes have been used to measure the space potential and fluctuations in both density and space potential for plasmas with varying magnetic geometries. There is continuing development work to study the feasibility of using beam probes to measure magnetic fluctuations and magnetic field structure. Sensitivity for measuring density and potential fluctuations is best demonstrated by what is the most sophisticated beam probe to date: the 500-keV system on TEXT. For broadband measurements (50–250 kHz), the TEXT beam probe has demonstrated a sensitivity to space potential fluctuations of 2 V (rms), and resolution for ñe/ne of 10−3.Recent measurements on both ISX-B and TEXT have demonstrated the capability of obtaining simultaneous ñ and cursive-phi˜ measurements at three separate locations in the plasma. For some locations the sample volumes are poloidally separated and S(kθ, w) can be estimated for both ñ and cursive-phi˜. This permits evaluation of the net electrostatic-fluctuation-induced particle flux. Some of the problems still being encountered with present beam probes are the nonideal behavior of the energy analyzer, cross talk between ñ and cursive-phi˜ for high-wave-number fluctuations, the effect of finite sample volume and sample volume spacing on the evaluation of k spectra, simultaneous measurement of two components of the k vector, probing of the complex 3-D magnetic fields, and extension of the measurements to higher-energy beam probe systems.

Notes: Recent applications of heavy-ion beam probes on such devices as the TEXT tokamak have shown the importance of increasing the capabilities of both the beam injection and detection systems. To this end we have investigated a new solid-state ion detector that will substantially improve spatial resolution. The application of the diagnostic technique on substantially larger devices will also require new electrostatic energy analyzer geometries, which are also under investigation.

Notes: Initial design studies of a heavy-ion beam probe that would be capable of accessing the full plasma cross section of Texas Experimental Tokamak upgrade showed that it would require a 2-MeV Tl+ beam. Such a beam probe would have an estimate sensitivity for measuring broadband potential fluctuations of 2 V rms, an accuracy for measuring potential profiles of ±40 V, and a resolution for measuring normalized broadband density fluctuations of 0.1%.

Notes: This article reviews digital spectral analysis techniques that yield experimental insight into plasma turbulence. Methods to quantify the statistical properties of the fluctuations and to measure the particle and heat flux caused by electrostatic fluctuations are presented. Furthermore, analysis techniques to study the nonlinear coupling process of turbulence and the redistribution of energy among the different modes are discussed. The impact of the analysis techniques on fusion research is demonstrated with experimental results collected with Langmuir probes, heavy-ion beam probes, and laser scattering in the tokamak TEXT. Special emphasis is given to the characterization of the wavenumber distribution and the correlation lengths in all toroidal directions, including a first measurement of k(parallel) in a tokamak.

Notes: Digital complex demodulation techniques are used to generate time-varying auto- and cross-power spectra which, in turn, are useful in characterizing the time-frequency characteristics of nonstationary plasma fluctuation data. The approach is illustrated with fluctuation data measured with a heavy-ion beam probe on the TMX experiment.

Notes: Broad bandwidth (60 kHz ≤f≤500 kHz), long wavelength (k¯θ≤2 cm−1) density fluctuation measurements were made using a heavy ion beam probe on the Texas Experimental Tokamak (TEXT) [K. W. Gentle, Nucl. Technol./Fusion 1, 479 (1981)]. Fluctuation amplitudes and correlation length scalings do not correspond to linear or quasilinear drift wave theory. Power-weighted root-mean-square (rms) wave number estimates are much lower (〈k¯θ〉rmsρs≤0.1, ρs=[miTe]1/2/eB) than quasilinear theoretical expectations (k¯⊥ρs∼0.3). Core results indicate strong turbulence with a wave number spread, Δk∼k¯ at fixed frequency f, consistent with strong turbulence predictions, while edge results can be considered consistent with weak turbulence. In between the core and edge (0.6≤r/a≤0.8) is a transition region. © 1995 American Institute of Physics.

Notes: Fluctuations in electric potential, electron pressure, and their relative phase have been measured in the RENTOR tokamak [Phys. Rev. Lett. 55, 2417 (1985)] using a heavy ion beam probe. Between 70 and 200 kHz, pressure fluctuation levels of p˜/p∼0.04 and potential fluctuation levels of eφ˜/Te=0.08–3 have been observed. The phase angle between the pressure and potential fluctuations is approximately 25°. The heat transport by the observed fluctuations is not enough to account for the observed heat loss at the plasma edge. The RENTOR results are compared with measurements on the TEXT (J. Forster, Ph.D. thesis, Rensselaer Polytechnic Institute, 1987) and ISX-B [Phys. Rev. Lett. 59, 1301 (1987)] tokamaks and with drift wave and rippling mode theories.