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  • AIP Publishing  (4)
  • 1
    In: Physics of Fluids B: Plasma Physics, AIP Publishing, Vol. 2, No. 6 ( 1990-06-01), p. 1300-1305
    Abstract: Measurements of the toroidal rotation speed vφ(r) driven by neutral beam injection in tokamak plasmas and, in particular, simultaneous profile measurements of vφ, Ti, Te, and ne, have provided new insights into the nature of anomalous transport in tokamaks. Low-recycling plasmas heated with unidirectional neutral beam injection exhibit a strong correlation among the local diffusivities, χφ≊χi & gt;χe. Recent measurements have confirmed similar behavior in broad-density L-mode plasmas. These results are consistent with the conjecture that electrostatic turbulence is the dominant transport mechanism in the tokamak fusion test reactor tokamak (TFTR) [Phys. Rev. Lett. 58, 1004 (1987)], and are inconsistent with predictions both from test-particle models of strong magnetic turbulence and from ripple transport. Toroidal rotation speed measurements in peaked-density TFTR ‘‘supershots’’ with partially unbalanced beam injection indicate that momentum transport decreases as the density profile becomes more peaked. In high-temperature, peaked-density plasmas the observed gradient scale length parameter ηtoti=d ln Ti/d ln ne correlates reasonably well with predictions of the threshold for exciting ion-temperature-gradient-driven turbulence (ITGDT), as would be expected for plasmas at marginal stability with respect to this strong transport mechanism. In L-mode plasmas where ITGDT is expected to be too weak to enforce marginal stability, ηtoti exceeds this threshold considerably. However, preliminary experiments have failed to observe a significant increase in ion heat transport when ηtoti was rapidly forced above ηc (the threshold for exciting ITGDT) using a perturbative particle source, as would have been expected for a plasma at marginal stability.
    Type of Medium: Online Resource
    ISSN: 0899-8221
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1990
    detail.hit.zdb_id: 2130787-8
    detail.hit.zdb_id: 648023-8
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  • 2
    In: Physics of Fluids B: Plasma Physics, AIP Publishing, Vol. 2, No. 6 ( 1990-06-01), p. 1287-1290
    Abstract: Magnetohydrodynamic (MHD) activity within three zones (core, half-radius, and edge) of TFTR [Plasma Physics and Controlled Nuclear Fusion Research 1986 (IAEA, Vienna, 1987), Vol. 1, p. 51] tokamak plasmas are discussed. Near the core of the plasma column, sawteeth are often observed. Two types of sawteeth are studied in detail; one with complete, and the other with incomplete, magnetic reconnection. Their characteristics are determined by the shape of the q profile. Near the half-radius the m/n=3/2 and 2/1 resistive ballooning modes are found to correlate with a beta collapse. The pressure and the pressure gradient at the mode rational surface are found to play an important role in stability. MHD activity is also studied at the plasma edge during limiter H modes. The edge localized modes (ELM’s) are found to have a precursor mode with a frequency between 50–200 kHz and a mode number m/n=1/0. The mode does not show a ballooning structure. While these instabilities have been studied on many other machines, on TFTR the studies have been extended to high pressure (plasma pressure greater than 4×105 Pa) and low collisionality [vi*(a/2) & lt;0.002, ve*(a/2) & lt;0.01].
    Type of Medium: Online Resource
    ISSN: 0899-8221
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1990
    detail.hit.zdb_id: 2130787-8
    detail.hit.zdb_id: 648023-8
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  • 3
    In: Physics of Fluids B: Plasma Physics, AIP Publishing, Vol. 3, No. 8 ( 1991-08-01), p. 2270-2276
    Abstract: A variety of experiments have been performed on the TFTR tokamak [Wilson et al., Plasma Physics and Controlled Nuclear Fusion Research 1988 (IAEA, Vienna, 1989), Vol. 1, p. 691] utilizing ion cyclotron range of frequencies (ICRF) heating. Of special interest has been the insight into plasma performance gained by utilizing a different heating scheme other than the usual neutral beam injection (NBI). Utilizing ICRF heating allows control over the power deposition profile independent of the plasma fueling profile. In addition, by varying the minority concentration the power split between ion and electron heating can be varied. Confinement has been examined in high recycling gas fueled discharges, low recycling supershot plasmas, and peaked density pellet fueled discharges. Global confinement is found not to be affected by the method or localization of plasma heating, but the calculated local diffusivities vary with the power deposition profile to yield similar global values. In addition, sawtooth stabilization observed with ICRF heating has been investigated and found to occur in qualitative agreement with theory. ICRF sawtooth stabilized discharges exhibit peaked temperature and density profiles and have a safety factor q that appears to fall well below unity on axis.
    Type of Medium: Online Resource
    ISSN: 0899-8221
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1991
    detail.hit.zdb_id: 2130787-8
    detail.hit.zdb_id: 648023-8
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  • 4
    Online Resource
    Online Resource
    AIP Publishing ; 2023
    In:  Review of Scientific Instruments Vol. 94, No. 6 ( 2023-06-01)
    In: Review of Scientific Instruments, AIP Publishing, Vol. 94, No. 6 ( 2023-06-01)
    Abstract: A radium-223 ion beam was delivered to an experiment from the electron cyclotron resonance ion source, ECR2, at the Argonne Tandem Linac Accelerator System (ATLAS). The radium-223 material was in a nitrate salt form within a vial, prior to being converted to a usable sputter sample. The sputter sample was produced using a new sample preparation method, where the radium nitrate was dissolved into a solution and pipetted onto pressed aluminum powder. This sample was then allowed to dry, distributing the radium-223 material throughout the sputter sample. Ion source operation using the radium sputter sample is described with the operating parameters listed. The intensity and energy requirements for this ion beam were 1 × 106 particles/s and 1.07 GeV, respectively. Because the intensity is relatively low compared to most experiments at ATLAS, previously developed accelerator mass spectrometry methods were used Scott et al. [Rev. Sci. Instrum. 87, 02A732 (2016)] to avoid the need for tuning of the low-intensity beam of interest. Handling of the radium material, as well as loading and unloading of the sputter sample from ECR2, required collaboration with Health Physics. Procedures were used and dry runs were carried out before, during, and after the experiment to ensure the safety of the workers. The processes used and lessons learned are described within.
    Type of Medium: Online Resource
    ISSN: 0034-6748 , 1089-7623
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2023
    detail.hit.zdb_id: 209865-9
    detail.hit.zdb_id: 1472905-2
    SSG: 11
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