Chapter 11: The Heating and Current Drive Systems of the FTU

“…No further effect associated with the N spectrum is expected because the launched one is unchanged for all of our data (N 0 = 1.82) and the very weak dependence of η CD on N 0 (see [2]) levels out possible different upshifts. No distortion either of the launched spectrum can occur in the coupling process, since FTU has a conventional LH launching grill [28], where the injected power passes only once through a waveguide and does not interact at all with the adjacent ones, differently from a multijunction.…”

Section: The Basic Experimental Findingmentioning

confidence: 99%

“…It may only lead to a slightly optimistic evaluation of the layer transparency since it underestimates the strength of the angular scattering, while it almost leaves the frequency broadening unaffected. Here we can always attribute a single value only, N 0 = 1.82, to the N spectrum supplied by the LH launcher since its width is very narrow ( N (FWHM) = 0.56) [23]. (4) Plane geometry is assumed for the layer, and the regions inside LCMS are neglected since there the fluctuation amplitude is 10 −2 [36] against ∼0.2-0.3 of the SOL, which means a weight ∼50-100 times smaller, being the scattering intensity ∝ (δn e /n e ) 2 (see equation ( 1)).…”

Section: The Model Validation and The Collection Of The Relevant Datamentioning

confidence: 99%

“…This approach clearly needs both the average and turbulent features of the SOL plasma crossed by the LH waves to be known in detail. Our set of dedicated Langmuir probes allows this if only one LH power gyrotron is fed, out of the six that equip FTU [23], for a total coupled power P LH ∼ 320 kW. Using only one gyrotron also helps in studying the frequency spectrum of the back-scattered LH radiation.…”

Section: Introductionmentioning

confidence: 99%

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Lower hybrid current drive efficiency in tokamaks and wave scattering by density fluctuations at the plasma edge

Ridolfini¹,

Apicella²,

Calabrò³

et al. 2011

Nucl. Fusion

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The turbulence in the scrape-off layer (SOL) plasma of FTU is characterized in order to assess its effect on the current drive efficiency of the lower hybrid (LH) waves. Amplitude, frequency and perpendicular wave vector of the fluctuations are measured for a variety of the main plasma conditions in front of the LH antenna together with the temperature and density in the SOL and used as inputs for the linear scattering theory of the LH waves developed many years ago. This theoretical model can account for both the frequency spectral broadening of the LH pump and the variations of the driven current, inferred by the perpendicular fast electron bremsstrahlung signals. The fraction of the LH power that is then deduced to be effective for current drive appears to be well related to the calculated optical thickness τ of the SOL. It drops as low as 40% as τ increases, consistent with the model prediction. Possible ways to control the SOL optical depth are investigated and a clear relation of the fluctuation level with the collisionality is found.

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“…If the same ECH is launched perpendicularly to the toroidal direction power a remarkably weaker ITB is obtained, whereas even sawteeth reappear and no ITB is built in on-axis co-ECCD [14]. The ECCD configuration is obtained by setting the toroidal angle of the ECH beam in the range 0˚(⊥B T ) ± 30˚by means of the launching mirrors, through which the beam can be focused at a height between ±0.2 m onto the equatorial plane, approximately [15]. Figure 1 shows that an almost full CD ITB (loop voltage, V loop < 0.2 V, ohmic (OH) current I OH < 20% of the total) is sustained for the whole duration of the ECH pulse at n e0 > 1.3 × 10 20 m −3 (n e0 /n GW ≈ 0.9) and e − temperature T e0 > 5 keV.…”

Section: High-density Itb Formation and Main Characteristicsmentioning

confidence: 99%

High density internal transport barriers for burning plasma operation

Ridolfini¹,

Barbato²,

Buratti³

et al. 2005

Plasma Phys. Control. Fusion

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A tokamak plasma with internal transport barriers (ITBs) is the best candidate for a steady ITER operation, since the high energy confinement allows working at plasma currents (I p ) lower than the reference scenario. To build and sustain an ITB at the ITER high density ( 10 20 m −3 ) and largely dominant electron (e − ) heating is not trivial in most existing tokamaks. FTU can instead meet both requests, thanks to its radiofrequency heating systems, lower hybrid (LH, up to 1.9 MW) and electron cyclotron (EC up to 1.2 MW). By the combined use of them, ITBs are obtained up to peak densities n e0 > 1.3 × 10 20 m −3 , with central e − temperatures T e0 ≈ 5.5 keV, and are sustained for as long as the heating pulse is applied (>35 confinement times, τ E ). At n e0 ≈ 0.8 × 10 20 m −3 T e0 can be larger than 11 keV. Almost full current drive (CD) and an overall good steadiness is attained within about one τ E , 20 times faster than the ohmic current relaxation time. The ITB extends over a central region with an almost flat or slightly reversed q profile and q min ≈ 1.3 that is fully sustained by off-axis lower hybrid current drive. Consequent to this is the beneficial good alignment of the bootstrap current, generated by the ITB large pressure gradients, with the LH driven current. Reflectometry shows a clear change in the turbulence 0741-3335/05/SB0285+17$30.00 © 2005 IOP Publishing Ltd Printed in the UK B285 B286 V Pericoli Ridolfini et al

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Chapter 11: The Heating and Current Drive Systems of the FTU

Cited by 24 publications

References 14 publications

Chapter 12: FT3 - An Experiment to Study Burning Plasma Physics Issues in Deuterium Plasmas

Chapter 12: FT3 - An Experiment to Study Burning Plasma Physics Issues in Deuterium Plasmas

Lower hybrid current drive efficiency in tokamaks and wave scattering by density fluctuations at the plasma edge

High density internal transport barriers for burning plasma operation

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