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

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

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

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

Validation of 500-kW/1000-s operation of 5-GHz klystron for KSTAR LHCD system

In this study, a klystron for the KSTAR lower hybrid current drive (LHCD) system was developed as a prototype for a 5 GHz, 500 kW CW operation that is aimed to meet the requirement of the ITER LHCD system as well. Before the 2012 KSTAR campaign, the prototype klystron was validated only for 350 kW CW operation. The weakest part of the klystron for 500 kW CW operation was the RF output window failure due to a thermal stress caused by the temperature gradient. The klystron was equipped with two RF windows, each of which should transmit 250 kW power. Prior to the full performance test of the klystron, the performance of the test RF windows that were identical to those mounted on the klystron was tested with half of the klystron's full power. The temperature increase in the test RF windows was monitored using an IR camera. The temperature difference, Delta T-ce, between the center and edge of the test window at 250-kW 1000-s transmitting power was predicted to be 23 degrees C, which is smaller than the safe Delta T-ce, which is 50 degrees C according to the manufacturer. Based on the result of the test window measurement, 500-kW 1000-s operation of the klystron was conducted successfully. The klystron output power characteristics depending on the phase of load reflection VSWR 1.4:1 were investigated. The klystron generated stable power on a load VSWR of 1.4:1 at various phases. The output power at the worst phase was 380 kW. Details of the IR-imaging setup are discussed and the results obtained are presented.11Nsciescopu

Operational domain for the new 3MW/1000s ECRH System on WEST

International audienc

Developing high performance RF heating scenarios on the WEST tokamak

International audienceHigh power experiments, up to 9.2 MW with LHCD and ICRH, have been carried out in the full tungsten tokamak WEST. Quasi non inductive discharges have been achieved allowing to extend the plasma duration to 53s at medium density (ne=3.7×10 19 m-3). Apart few pulses post-boronization, the plasma radiation is rather high (Prad/Ptot~50%) and is dominated by W. This fraction does not vary as the RF power is ramped up and, against expectations, it is quite similar in ICRH and/or LHCD heated plasmas. Hot L mode plasmas (Te(0)>3keV) with a confinement time following the ITER L96 scaling are routinely obtained, confirming the weak aspect ratio dependence of this scaling law. Tungsten accumulation is generally not an operational issue on WEST. Nonetheless, 25% of the of the discharges are affected by a rapid collapse of the central electron temperature which occurs when a slight decrease of Te leads to enhanced radiation causing flat or hollow current profiles. To this respect LHCD-only discharges are compared to ICRH and ICRH/LHCD discharges

Developing high performance RF heating scenarios on the WEST tokamak

International audienceHigh power experiments, up to 9.2 MW with LHCD and ICRH, have been carried out in the full tungsten tokamak WEST. Quasi non inductive discharges have been achieved allowing to extend the plasma duration to 53s at medium density (ne=3.7×10 19 m-3). Apart few pulses post-boronization, the plasma radiation is rather high (Prad/Ptot~50%) and is dominated by W. This fraction does not vary as the RF power is ramped up and, against expectations, it is quite similar in ICRH and/or LHCD heated plasmas. Hot L mode plasmas (Te(0)>3keV) with a confinement time following the ITER L96 scaling are routinely obtained, confirming the weak aspect ratio dependence of this scaling law. Tungsten accumulation is generally not an operational issue on WEST. Nonetheless, 25% of the of the discharges are affected by a rapid collapse of the central electron temperature which occurs when a slight decrease of Te leads to enhanced radiation causing flat or hollow current profiles. To this respect LHCD-only discharges are compared to ICRH and ICRH/LHCD discharges

Developing high performance RF heating scenarios on the WEST tokamak

International audienceHigh power experiments, up to 9.2 MW with LHCD and ICRH, have been carried out in the full tungsten tokamak WEST. Quasi non inductive discharges have been achieved allowing to extend the plasma duration to 53s at medium density (ne=3.7×10 19 m-3). Apart few pulses post-boronization, the plasma radiation is rather high (Prad/Ptot~50%) and is dominated by W. This fraction does not vary as the RF power is ramped up and, against expectations, it is quite similar in ICRH and/or LHCD heated plasmas. Hot L mode plasmas (Te(0)>3keV) with a confinement time following the ITER L96 scaling are routinely obtained, confirming the weak aspect ratio dependence of this scaling law. Tungsten accumulation is generally not an operational issue on WEST. Nonetheless, 25% of the of the discharges are affected by a rapid collapse of the central electron temperature which occurs when a slight decrease of Te leads to enhanced radiation causing flat or hollow current profiles. To this respect LHCD-only discharges are compared to ICRH and ICRH/LHCD discharges

Developing high performance RF heating scenarios on the WEST tokamak

International audienceHigh power experiments, up to 9.2 MW with LHCD and ICRH, have been carried out in the full tungsten tokamak WEST. Quasi non inductive discharges have been achieved allowing to extend the plasma duration to 53s at medium density (ne=3.7×10 19 m-3). Apart few pulses post-boronization, the plasma radiation is rather high (Prad/Ptot~50%) and is dominated by W. This fraction does not vary as the RF power is ramped up and, against expectations, it is quite similar in ICRH and/or LHCD heated plasmas. Hot L mode plasmas (Te(0)>3keV) with a confinement time following the ITER L96 scaling are routinely obtained, confirming the weak aspect ratio dependence of this scaling law. Tungsten accumulation is generally not an operational issue on WEST. Nonetheless, 25% of the of the discharges are affected by a rapid collapse of the central electron temperature which occurs when a slight decrease of Te leads to enhanced radiation causing flat or hollow current profiles. To this respect LHCD-only discharges are compared to ICRH and ICRH/LHCD discharges