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Divertor detachment may be essential to reduce heat loads to magnetic fusion tokamak reactor divertor surfaces. Yet in experiments it is difficult to control the extent of the detached, low pressure, plasma region. At maximum extent the front edge of the detached region reaches the X-point and can lead to degradation of core plasma properties. We define the 'detachment window' in a given position control variable C (for example, the upstream plasma density) as the range in C within which the front location can be stably held at any position from the target to the X-point; increased detachment window corresponds to better control. We extend a 1D analytic model [1] to determine the detachment window for the following control variables: the upstream plasma density, the impurity concentration and the power entering the scrape-off layer (SOL). We find that variations in magnetic configuration can have strong effects; increasing the ratio of the total magnetic field at the X-point to that at the target, ${{B}_{\times}}/{{B}_{t}}$ , (total flux expansion, as in the super-x divertor configuration) strongly increases the detachment window for all control variables studied, thus strongly improving detachment front control and the capability of the divertor plasma to passively accommodate transients while still staying detached. Increasing flux tube length and thus volume in the divertor, through poloidal flux expansion (as in the snowflake or x-divertor configurations) or length of the divertor, also increases the detachment window, but less than the total flux expansion does. The sensitivity of the detachment front location, z h , to each control variable, C, defined as $\partial {{z}_{h}}/\partial C$ , depends on the magnetic configuration. The size of the radiating volume and the total divertor radiation increase $\propto {{\left({{B}_{\times}}/{{B}_{t}}\right)}^{2}}$ and $\propto {{B}_{\times}}/{{B}_{t}}$ , respectively, but not by increasing divertor poloidal flux expans, Wolfson Foundation (Royal Society Wolfson Research Merit Award), Research Councils UK (EPSRC grant number EP/I501045), Research Councils UK (grant number EP/I501045)

Scaling laws for the transport and heating of trace heavy ions in low-frequency magnetized plasma turbulence are derived and compared with direct numerical simulations. The predicted dependences of turbulent fluxes and heating on ion charge and mass number are found to agree with numerical results for both stationary and differentially rotating plasmas. Heavy ion momentum transport is found to increase with mass, and heavy ions are found to be preferentially heated, implying a mass-dependent ion temperature for very weakly collisional plasmas and for partially ionized heavy ions in strongly rotating plasmas., United States. Dept. of Energy. Office of Fusion Energy Sciences (Fusion Energy Sciences Postdoctoral Fellowship), United States. Dept. of Energy (Grant DE-FG02-91ER-54109)

The effect of small deviations from a Maxwellian equilibrium on turbulent momentum transport in tokamak plasmas is considered. These non-Maxwellian features, arising from diamagnetic effects, introduce a strong dependence of the radial flux of cocurrent toroidal angular momentum on collisionality: As the plasma goes from nearly collisionless to weakly collisional, the flux reverses direction from radially inward to outward. This indicates a collisionality-dependent transition from peaked to hollow rotation profiles, consistent with experimental observations of intrinsic rotation., United States. Dept. of Energy. Office of Fusion Energy Sciences (Postdoctoral Fellowship), United States. Dept. of Energy (Grant DE-SC008435), United States. Dept. of Energy. Office of Science (Contract DE-AC02-05CH11231)

Using theoretical arguments, a simple scaling law for the size of the intrinsic rotation observed in tokamaks in the absence of a momentum injection is found: The velocity generated in the core of a tokamak must be proportional to the ion temperature difference in the core divided by the plasma current, independent of the size of the device. The constant of proportionality is of the order of 10 km·s[superscript -1]·MA·keV[superscript -1]. When the intrinsic rotation profile is hollow, i.e., it is countercurrent in the core of the tokamak and cocurrent in the edge, the scaling law presented in this Letter fits the data remarkably well for several tokamaks of vastly different size and heated by different mechanisms., United States. Dept. of Energy (DEFC02- 04ER54698)