Validation of the ITER-relevant passive-active-multijunction LHCD launcher on long pulses in Tore Supra

Abstract

A new ITER-relevant lower hybrid current drive (LHCD) launcher, based on the passive-active-multijunction (PAM) concept, was brought into operation on the Tore Supra tokamak in autumn 2009. The PAM launcher concept was designed in view of ITER to allow efficient cooling of the waveguides, as required for long pulse operation. In addition, it offers low power reflection close to the cut-off density, which is very attractive for ITER, where the large distance between the plasma and the wall may bring the density in front of the launcher to low values. The first experimental campaign on Tore Supra has shown extremely encouraging results in terms of reflected power level and power handling. Power reflection coefficient <2% is obtained at low density in front of the launcher, i.e. close to the cut-off density, and very good agreement between the experimental results and the coupling code predictions is obtained. Long pulse operation at ITER-relevant power density has been demonstrated. The maximum power and energy reached so far is 2.7 MW during 78 s, corresponding to a power density of 25 MW m−2, i.e. its design value at f = 3.7 GHz. In addition, 2.7 MW has been coupled at a plasma–launcher distance of 10 cm, with a power reflection coefficient <2%. Finally, full non-inductive discharges have been sustained for 50 s with the PAM.

Design and testing of a 5GHz TE10–TE30 mode converter mock-up for the lower hybrid antenna proposed for ITER

“…The LH launcher design presently foreseen for ITER is a passive-active multijunction (PAM), which has been successfully validated on FTU [4] at 8 GHz and on Tore Supra [5,6] at 3.7 GHz. The nominal refractive parallel index n excited by the coupling structure has been determined from integrated simulations of propagation and absorption of LH waves in ITER for several scenarios.…”

WEST Physics Basis

“…The ITERrelevant PAM launcher, on the other hand, has its optimum operating range close to the cut-off density (1.7 × 10 17 m −3 at f = 3.7 GHz) and is therefore more suitable for operating in conditions with large plasma-launcher distance or with steep edge density gradients [24].…”

Recent progress on lower hybrid current drive and implications for ITER

“…2. This launcher is characterized by very low reflected power from the plasma (2% to 6% of the input power) [17], even at a distance from the last closed flux surface (LCFS) of 10 cm in or during fast supersonic molecular beam injections mimicking ELMs in L-mode plasma [18]. A total of 11.4 GJ of accumulated energy has been coupled to the plasma in 2011 with the PAM launcher, which was powered by the old-generation klystrons (400 kW/klystron).…”