Passive Active Multijunction Concept Research Articles

Manufacturing process and tests of a lower hybrid passive active multi-junction launcher for long pulse experiments on Tore-Supra

A new Passive Active Multijunction (PAM) Lower Hybrid heating and Current Drive (LHCD) launcher, has been successfully manufactured and tested on Tore-Supra (TS). The design and the fabrication of this new actively cooled launcher based on the PAM concept, as the present ITER LHCD design, is a major component of the TS CIMES project (Components for the Injection of Matter and Energy in Steady-state), and will play a key role in the TS near term program. To achieve 1000 s pulses with a power flux of 25 MW/m 2 the PAM launcher has been designed for steady state (CW) operation (active cooling) with the objective of coupling 2.7 MW of LHCD power to the plasma at 3.7 GHz with a parallel index N ∥ = 1.7 ± 0.2. The launcher has achieved its qualifications tests, i.e. low power Radio Frequency measurements, vacuum and hydraulic leak tests, and has been installed on Tore-Supra tokamak in September 2009. It is commissioning on plasma started a month later, quickly achieving its design performance of 2.7 MW on a 35 s pulse. After a technical description of the PAM, this paper presents an overview of the project phases (RF optimization, manufacturing and qualification) and concludes with the first experimental results of the PAM.

3D electromagnetic analyses during plasma disruption for the Tore Supra lower hybrid passive active multi-junction launcher

A Passive Active Multijunction (PAM) Lower Hybrid heating and Current Drive (LHCD) antenna has been installed on Tore Supra in 2009. The design and the fabrication of this antenna based on the passive-active multijunction concept is a major part of the CIMES project (components for the injection of mater and energy in steady-state) on Tore Supra. The antenna made of copper and stainless steel has to withstand important electromagnetic forces due to eddy currents during plasma disruption. 3D electromagnetic analyses have been performed with the ANSYS code to calculate the eddy currents and the electromagnetic forces.

Coupling characteristics of the ITER-relevant lower hybrid antenna in Tore Supra: experiments and modelling

A new concept of lower hybrid antenna for current drive has been proposed for ITER (Bibet et al 1995 Nucl. Fusion 35 1213–23): the passive active multijunction (PAM) antenna that relies on a periodic combination of active and passive waveguides. An actively cooled PAM antenna at 3.7 GHz has recently been installed on the tokamak Tore Supra. This paper summarizes the comprehensive experimental characterization of the coupling properties of the PAM antenna to the Tore Supra plasmas. In this paper, the electromagnetic properties of the antenna are measured at a reduced power (<1 MW) to allow a systematic comparison with linear wave coupling theory and the associated modelling based on the linear ALOHA code. In a wide range of edge electron densities at the antenna aperture (spanning a factor 20 from 0.5 × nc to 10 × nc where nc is the slow wave density cut-off, nc = 1.7 × 1017 m−3 at 3.7 GHz) and antenna phasing, the ALOHA simulations reproduce the experimental results observed on Tore Supra. In addition, reduced power reflection coefficients (<5%) are measured at a low edge density, close to nc, i.e. in the range 0.5–3 × nc. Measurement and analysis with ALOHA of the antenna–plasma scattering matrices provide explanation of the good coupling properties of the PAM antenna close to nc by highlighting the crucial role of the slow wave intercoupling between active and passive waveguides through the plasma edge. This detailed validation of the coupling modelling is an important step towards the validation of the PAM concept in view of further optimizing the electromagnetic properties of the future ITER antenna.

Toward a LHCD system for ITER

Abstract On ITER, the LH system aims at supplying 20 MW CW for controlling the q-profiles in partially and fully non-inductive steady-state operation (9 MA). The designed LH system relies on a transmitter made of 24 5 GHz 1 MW klystrons linked to one antenna based on the passive active multijunction (PAM) concept, via a 60 m long oversized circular transmission line. Through a common European effort including several associations (CEA, ENEA, UKAEA, IST, TEKES and IPP-CZ) many outstanding problems have been solved: coupling has been achieved on JET in a physics scenario similar to ITER, a PAM has been tested with success on the FTU plasma. The reliability of LH for long pulse operation has been ascertained on Tore Supra. In order to routinely realise long pulse operation (1000 s), the Tore Supra LH system is being refurbished within the CIMES project framework where the transmitter is to be equipped with 16 klystrons 700 kW 1000 s at a frequency of 3.7 GHz. A new LH launcher based upon the PAM concept has been studied, designed and is actually under realisation.

The test of a PAM launcher on FTU: The first step toward the LHCD launcher for ITER

The 20 MW, 5 GHz, LHCD system for ITER aims mainly at controlling the q-profiles in partially (hybrid regime at IP = 12 MA) and fully non-inductive steady-state operation (IP = 9 MA). In the last few years several European associations have given their contribution to the solution of many prominent problems on the road to the design of an efficient and reliable system. LH coupling has been achieved on JET in physics scenarios relevant for ITER, while the reliability of the LH for long pulse operation has been ascertained on Tore Supra. A downscaled prototype of the Passive Active Multijunction (PAM) launcher presently proposed for ITER, has successfully demonstrated on FTU its good coupling characteristics, power handling capability and current drive efficiency. An ITER relevant launcher, based on the PAM concept is presently under construction to be installed on TORE SUPRA to investigate the technological solutions (materials, cooling, etc.) envisaged for this launcher.

Overview of the ITER-FEAT LH system

LH is considered to be used in ITER-FEAT steady-state scenario thanks to its highest current drive efficiency in the plasma outer part. The design of a 5 GHz, 20 MW CW LH system has been realised. That relies on a transmitter of 24 1-MW klystrons, and a circular oversized 60-m long transmission line feeding an antenna, based on the passive active multijunction concept. In order to have a high reliability, the power density is limited to 33 MW/m 2. After the system description, the results of different studies are given: RF computation, launcher coupling properties, thermal analysis, mechanical stress caused by disruption, neutron activation, acceleration of electrons in the antenna near field.