SWIP. 托卡马克位形优化. 高庆弟. 核工业西南物理研究院 成都. 1. Plasma shaping. Elongation is beneficial to plasma confinement by increasing the current holding capacity . Triangularity is beneficial to supresion some MHD instabilities Quadrangle shaping showing evidence to modify ELMs (DIII-D).
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EFIT code developed in GA has been used widely in the would for the plasma shaping control
Determination of the plasma boundary for the single null divertor plasma in HL-2A
Reconstructed boundary at 320ms for 2898 shot. (+ and + denotes the filament and the centroid of plasma current respectively. X point position (Xr=1.552m, Xz=-0.451m), the position of strike point Zi=-0.780m (inner), Zo=-0.812m (outer), the plasma geometric center (Rg=1.652m, Zg=-0.069m), the plasma current centroid (Rc=1.664m, Zc=0.007m), plasma minor radius ap= 0.380m, elongation k=1.085)
Plasma shaping in HL-2A divertor plasma in HL-2A
(c) divertor plasma in HL-2A
Fig.2.1 Magnetic geometry of (a) a plasma with a nearly circular cross – section, (b) a plasma with the X point moving inward (D-shape, k95=1.08, 95=0.44), (c) a plasma with modest elongation (elongated D-shape, k95 = 1.21, 95 = 0.41).
The triangularity variation with respect to the flux coordinate is dependent on the plasma current profile, but for both hollow and peaked current profiles it decreases rapidly at the plasma boundary region while moving towards the plasma center
Fig.2.2 Triangularity of the D-shaped plasma, versus the flux surface for the cases of hollow current profile (full line) and peaked current profile (dotted line).
2. Optimization of the plasma current profile coordinate is dependent on the plasma current profile, but for both hollow and peaked current profiles it decreases rapidly at the plasma boundary region while moving towards the plasma center
Dispersion relation in the LH frequency domain coordinate is dependent on the plasma current profile, but for both hollow and peaked current profiles it decreases rapidly at the plasma boundary region while moving towards the plasma center
wci << w <<wce
f = w/2p ≈ 107 109 1011 Hz (l ~ 10 cm)
Ray tracing for LH waves coordinate is dependent on the plasma current profile, but for both hollow and peaked current profiles it decreases rapidly at the plasma boundary region while moving towards the plasma center
n||0: injected value; q = rBtor/RBpol
3 Fokker-Planck analysis coordinate is dependent on the plasma current profile, but for both hollow and peaked current profiles it decreases rapidly at the plasma boundary region while moving towards the plasma center
An electron kinetic equation can be written as
The wave diffusion operator is the 1-D divergence of the RF induced flux:
where Dql is the quasi-linear diffusion coefficient, and here it signifies a sum over all waves in existence on a flux surface, with the appropriate powers and velocities. A simple sum is used, which means that we assume there are no interference effects.
with the collisional diffusion and drag coefficient given by
In solving for fe we set , because the time for equilibration between RF power and the electron distribution is short compared with the time for plasma to evolve. Then the solution for fe is an integral in velocity space,
LH waves can drive a fast electron tail
Fig.1.1 Waveforms of the plasma current I Eder,p, loop voltage Vp, the NBI power PNB, and the LH wave power PLH
Fig.1.2 Magnetic geometry of the discharge
Fig.1.3 (a) The temporal evolution of LH wave driven current profile, and (b) q profiles at different times for the sustained RS discharge
Fig.1.4 (a) Waveforms of the plasma currents I profile, and (b) q profiles at different times for the sustained RS dischargep, ILH, IBS, INB, and IOH and (b) their profiles at t=1.0s for the sustained RS discharge
Fig.1.5 The ion temperature T profile, and (b) q profiles at different times for the sustained RS dischargei (full line), and magnetic shear s (dotted line) versus x
Fig.1.6 Time traces of a quasi-stationary RS discharge: (a) LHCD efficiency, CD and non-inductive current fraction, (b) the H-factor, H98(y,2) and normalized beta, N, (c) the locations of the minimum q (full line) and the minimum i (dotted line), (d) the central plasma temperatures (Ti, Te).
The double transport barrier is indicated by two abrupt decreases of the ion heat diffusivity, of which the two minima are located near the shear reversal point, min 0.55, and near the plasma edge, 0.95, respectively. The elevated heat diffusivity between the two minima separates the two barriers.
Fig.2.3 Profiles of q and ion heat diffusivity, i (at t=1.0s) for the elongated D-shape plasma.
Fig.2.4 Profile of ion temperature and the ion temperature gradient, Ti (at t=1.0s).
In the DB discharge the plasma confinement is enhanced, and decreases of the ion heat diffusivity, of which the two minima are located near the shear reversal point, normalized beta, N and H-factor, H98(y,2) are higher than in the RS configuration with L-mode edge(see Fig.1.6)
Fig.2.5 Time traces of an RS discharge with double transport barrier: (a) normalized beta, N, (b) H-factor, H98(y,2), (c) locations of the double transport barrier (two dotted lines), and location of the shear reversal point (full line). The fainter lines indicate the results of the RS with L-mode edge.
Profile control by ECH+LHCD decreases of the ion heat diffusivity, of which the two minima are located near the shear reversal point,
Employing LHCD for large-scale q(r) control in a low-density plasma ofne =1.01019m-3 and Ip = 400kA, BT = 2.43T is considered. The target plasma is heated by EC of 0.48MW + 0.47MW lunched from 2 gyrotrons. By adjusting the polar lunch angle the EC power from 2 gyrotrons deposits around r = 0.2 and r = 0.3 respectively.
The q-profile has a little change in the ECH phase. To control the current profile, 0.5 MW LH power in the current drive mode (the multi-junction antenna phasing =90) is injected. As the LH wave deposition primarily governed by a nonlinearity between the LH power deposition profile and the electron temperature profile, the q-profile adjusts slowly, and the safety factor between r=0.0 and r=0.7 evolves gradually to the new quasi-steady values on the resistive time scale.
FIG. 8 Temporary evolution of q at various flux surfaces.
After the current profile is fully relaxed, the decreases of the ion heat diffusivity, of which the two minima are located near the shear reversal point, q values of r = 0.0-0.6 constrict to a narrow range of 1.0-1.3 (Fig. 6), and a q-profile with weak shear region extended to x=0.6 and qa=3.21 is established. It is sustained until LHCD is turned off. Though the q-profile in the weak shear region is not as flat as that in the discharge controlled by ECCD, the absolute value of the magnetic shear s[(dq/dr)(r/q)] is rather low.
FIG. 9 (a) q-profiles, and (b) absolute value of magnetic shear versus r at various times, (c) Te-profiles at t=0.4s (Ohmic phase ),and t=1.3s, thin black line indicating electron heating power.
Fully non-inductive current drive decreases of the ion heat diffusivity, of which the two minima are located near the shear reversal point,
Current profile at t = 1.4s: total plasma current jp (full line), ohmic current joh (thin full line), LH driven current jlh (dotted line), and EC driven current jecr (dashed line).
FIG. 10. (a) Ti – profile, (b) Te – profile (fainter line indicates the location of LH wave deposition), (c) q – profile. the case of NBI heating only at t=0.9s; the case of the NBI+LH heating at t=1.2s
FIG. 3.5 (a) Electron temperature profiles during LH heating at t=0.9s ( ), and before LH heating at t=0.65s ( ). The fainter thin line indi-cates the location of LH absorption; (b) Electron thermal conductivity profile at t=0.9s. (c)q-profile at t=0.9s .
For comparison, the above Ohmic plasma (Te>Ti) is heated by the sameLH wave scheme only to establish hot electron scenario.
Fig. 4 Temporal evolution of Ti0 (blue line), and Te0 (purple lines). Full lines indicate hot ion mode (NBI+LH heating), and dotted lines indicate hot electron mode (LH heating only)
FIG. 12. Temporal evolution of Ti(0), scenario of preferentially dominant electron heating. Electron tempera-ture increases significantly. In contrast to the large increment of the electron temperature, the ion temperature only has a small change (dotted lines in Fig. 4).
RS plasma;non-RS plasma
FIG. 13. Temporal evolution of Ei,
RS plasma; non-RS plasma
A comparison for the ion confinement is made between the RS and non-RS discharge: RS discharge - the LH wave is injected with slightly asymmetric spectrum ( = 170); non-RS discharge - the LH wave is injected with purely symmetric spectrum ( = 180), in this case the q-profile with negative shear could not be formed since the off-axis current driven by the LH wave is not sufficient.
The energy variation of the injected particles can be described with fairly accuracy by the following energy loss equation when
With W in eV, the rate of the beam energy loss is
If we consider beam particles of energy W which undergo complete therma-lization, then the average fraction of the total energy given up by the beam particles, which goes into the thermal ions of the plasma, is
Fig. 2 Average fraction of beam energy that goes into the thermal ions, F_ion, versus time, full line: Pbi/(Pbi+Pbe); dotted line: Fi
Fig. 3 (a) NBI heating power, and (b) NBI power losses versus time. Pbi is the NBI power that goes into ions, Pbe the NBI power that goes into electrons, Pbth the power from thermalization of the beam ions, Pcx the NBI power lost by charge-exchange, Pshin the NBI power shone through, Porb the orbit loss power of the beam ions, and Pie the power loss by electron-ion coupling inside the ion-ITB.
Plasma equilibrium in a tokamak with current hole versus time. P
Experimental results in JT-60U
Experimental results in JET
The rotational transform, versus time. P
The flux renormalization equation,
The usual hoop force balance equation,
The ellipticity equation,
An versus time. Pn/m = 0/1 resistive kink mode become unstable when the negative current creates a zero in the poloidal field (e. i. q is infinitive).This instability removes the negative current in the center and flattens the central current profile to zero