Maintenance and preparation of the 3.7 GHz LHCD system for WEST operation

Léna Delpech,Arthur Armitano,Paul Bienvenu,Joelle Achard,Marc Prou,J Hillairet

doi:10.1051/epjconf/201715703009

Abstract

The generator for the 3.7 GHz Lower Hybrid Current Drive (LHCD) system on Tore Supra consists of 16 klystrons capable of delivering 600kW/1000s each on plasma. Such a powerful installation needs to be operated on a regular basis in order to preserve the specifications of the klystrons in terms of output power and pulse duration. This has been of particular importance during the long shutdown between the last Tore Supra campaign in 2011 [1] and the start of LHCD experiments on WEST in 2017. The TH2103C klystrons have been operated on matched load once a year during the shutdown. A reduction of 14% of the available RF power for the experimental program is found, which is partly due to the loss of one klystron. Another important aspect of the maintenance procedure is to maintain the knowledge of the operating team at a good level. This paper describes the procedure and tests performed during six years of shut-down. It also summarizes the technical problems encountered and the consequences on the test schedule, and highlights the importance of maintaining such large plants in operating condition during shutdowns.

Highlights

The complete refurbishment of the Tore Supra tokamak into WEST tokamak equipped with a divertor dedicated to test Plasma Facing Components (PFC) for ITER, took place from 2011 to 2016 [2]
WEST Lower Hybrid Current Drive (LHCD) generator composed of 16 powerful klystrons (700kW/1000s on matched load and 600kW/1000s on plasma) was upgraded in 2009-2010 (Fig 2)
The LHCD system is mandatory for sustaining long pulse operation in WEST and essential for testing the PFC-technology for ITER in the framework of the WEST project

Summary

Introduction

The complete refurbishment of the Tore Supra tokamak into WEST tokamak equipped with a divertor dedicated to test Plasma Facing Components (PFC) for ITER, took place from 2011 to 2016 [2]. Lower Hybrid Current Drive (LHCD) heating system is one of the main heating to maintain long pulse operation and to ensure the power flux on the PFC targets is reached [3] [4]. The maintenance has allowed keeping the klystrons operational, and the tests revealed that some parameters of the tubes evolved and sometimes some serious failures appeared. The traceability over the years of the state of the klystrons and the plant is essential as well as to maintain operator’s skill maintenance. The tests and target to maintain the plant in good operating condition are described and explained. The paper summarizes the evolution of the 16 klystrons parameters during 6 years of shutdown in section 2 and in section 3, it highlights the main failures the operators had to face

Klystrons maintained in operational conditions

Six years of shutdown: overview of the LH generator maintenance and failures

Findings

Conclusion