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The physics of tokamak start-upa)
a)Paper UT3 1, Bull. Am. Phys. Soc. , 340 (2012).
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View: Figures


Image of FIG. 1.
FIG. 1.

The neutral hydrogen total ionization cross-section versus electron energy. Note that σ vanishes below 13.6 eV peaks near 30 eV and then decreases.

Image of FIG. 2.
FIG. 2.

The Paschen curve of breakdown voltage, V, between parallel plates separated by a distance d at pressure p for hydrogen. Note that there is a minimum pd for which breakdown occurs and above that minimum, V increases approximately linearly such that for fixed separation E/p is approximately constant.

Image of FIG. 3.
FIG. 3.

The number of new electrons per unit length of path for an electron in a gas, the first Townsend coefficient, α is not a simple function E/p, but α/p is.

Image of FIG. 4.
FIG. 4.

The cooling rate due to impurity radiation, assuming coronal equilibrium is plotted as a function of electron temperature peaks below 20 eV for low Z impurities.

Image of FIG. 5.
FIG. 5.

Fast-framing camera images show the C emission at various times during the start-up of DIII-D assisted by 2nd harmonic X-Mode ECRH. The caption below each frame shows the time in ms, I in kA, and the loop voltage at that time. Reprinted with permission from G. L. Jackson , Phys. Plasmas , 056116 (2010). Copyright 2010, American Institute of Physics.

Image of FIG. 6.
FIG. 6.

Phases of plasma evolution with ECRH assisted plasma start-up. The first frame shows the ECH power (red), applied toroidal electric field (green), and I (black) versus time. The 2nd and 3rd frames show the D emission and intensity of the visible bremsstrahlung, respectively. The 4th frame has the line average density of vertical views at 1.48 m (black), 1.94 m (red), and 2.1 m (green). The bottom frame is the electron temperature measured by electron cyclotron emission. Reprinted with permission from G.L. Jackson , Fusion Sci. Technol. , 27 (2010). Copyright 2010 The American Nuclear Society.

Image of FIG. 7.
FIG. 7.

Fast camera image of plasma in EAST just after breakdown. The bright plasma and metallic surfaces make interpretation of the plasma location uncertain. Reprinted with permission from J. A. Leuer , Fusion Sci. Technol. , 48 (2010). Copyright 2010 The American Nuclear Society.

Image of FIG. 8.
FIG. 8.

The first 3 successful discharges on EAST. Note that previous attempts had all resulted in I falling from about 35 kA to zero before 0.1 s. Reprinted with permission from J. A. Leuer , Fusion Sci. Technol. , 48 (2010). Copyright 2010 The American Nuclear Society.

Image of FIG. 9.
FIG. 9.

Comparison of evolution of a discharge initiated with a large-bore (red) with one grown from a smaller aperture (blue) such that q95 reaches its flattop value early and approximately constant after 0.05 s. Note that the factor of two difference in internal inductance (l) at the start of plasma current flattop.

Image of FIG. 10.
FIG. 10.

Results of ray-tracing done for EBW on MAST. Note that because the incoming O-Mode ECH beam is launched from below the midplane towards the polarizing reflector at the midplane, the outgoing X-Mode ECH is mostly above the device's midplane. This vertical imbalance is exploited to produce co-current drive as described in the text.

Image of FIG. 11.
FIG. 11.

The radial field in MAST is used to move the plasma centroid up before closed flux surfaces are formed so that so the majority of the X-Mode ECH and EBW are below the plasma midplane and produces co-current drive. Moving the plasma down as I increases to form closed flux puts the EBW above the plasma midplane and produces co-current drive. The red-dashed curve with constant vertical field demonstrates that the current is not driven by flux from the vertical field. The blue curves indicate a case with the vertical field increased as I is increased to maintain better position control. Reprinted with permission from V. F. Shevchenko , Nucl. Fusion , 022004 (2010).

Image of FIG. 12.
FIG. 12.

The main components of the NSTX CHI system discussed in the text. The fast, color camera images on the right show the plasma growing into the vessel in time. The green color is due to Li emission.

Image of FIG. 13.
FIG. 13.

The plasma current in kA for a discharge initiated with CHI and further ramped with induction (blue) is compared to a reference inductive-only discharge from the NSTX 10YR data base that reached 1 MA in a shorter time than other discharges (black). At 120 ms, the solenoid flux used by both discharges is the same.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: The physics of tokamak start-upa)