RF heated wall conditioning discharges in JT-60U

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Abstract

In series of experiments in 2000 and 2008, helium wall conditioning discharges by ECRF heating (ECH) were extensively studied in JT-60U with BT = 3.6 T and PECRF  2.5 MW. Homogeneous ECH conditioning discharges were reproducibly obtained by applying the horizontal field as large as 0.2% of BT. It was found that the horizontal field is effective to extend He plasma toward high field side from the fundamental resonant surfaces of ECH. The ECH wall conditioning discharge with PECRF = 2.5 MW and tpulse = 1.5 s was applied after the plasma disruption with W = 3.3 MJ and the successful recovery of the current ramp-up with 0.5 V/m of ohmic electric field was obtained.

Introduction

In order to reduce impurity influx to the core plasmas and to control particle recycling level, first wall conditioning by the hydrogen and helium discharges, such as glow discharge cleaning (GDC) and Taylor discharge cleaning (TDC) are widely used in fusion devices [1]. Here, TDC utilizes tokamak discharges with short pulse, low power but high repetition rate [1]. The typical plasmas for TDC have parameters of Ip = 50 kA, BT = 0.7 T and tpulse = 20 ms and those plasmas are repeated every 3–5 s in JT-60U. Here Ip, BT and tpulse are the plasma current, toroidal field and pulse length, respectively. For the control of the recycling level, TDC with helium gas (He TDC) is applied for 3–7 min between the experimental discharges in JT-60U.

However, GDC cannot be utilized due to the stationary toroidal field in superconducting tokamaks, such as ITER and DEMO. There is also restriction on the applicable voltage on the superconducting poloidal coils and the toroidal electric field must be below 0.3 V/m. TDC plasmas would not break down in such low electric field conditions.

In order to address these issues, wall conditioning techniques using ion cyclotron range of frequency (ICRF) heating have been investigated in high toroidal field (BT) conditions in TEXTOR [2], TORE SUPRA [3] and EAST [4]. There have been no study about wall conditioning using electron cyclotron range of frequency (ECRF) heating in BT conditions in tokamaks, while few studies using RF heating by electron cyclotron resonance had been carried out in low BT (∼0.05 T) [5], [6].

This paper presents particle recycling controls by helium conditioning discharges using ECRF heating (ECH) in high BT conditions in JT-60U.

Section snippets

Production of ECH wall conditioning plasmas

In experimental campaign to investigate RF heated wall conditioning discharges in 2000, a few trials of wall conditioning discharges using ICRF heating and lower hybrid range of frequency (LHRF) heating with reduced toroidal field (BT = 0.73 T) and a series of wall conditioning discharges using ECRF heating system[7] with high BT (BT = 3.65 T) were carried out.

ECRF heating (ECH) wall conditioning plasmas have been produced in the same experimental sequence with the tokamak discharges in JT-60U. The

Summary and discussions

In series of experiments in 2000 and 2008, wall conditioning discharges under high BT = 3.6 T were investigated by using the 110 GHz ECRF system of JT-60U.

Homogeneous He plasmas for wall conditioning were reproducibly obtained with the fundamental ECH when the horizontal field (0.5% of BT strength) was applied in 2000. It was found that 2.4 Pa m3 of He gas puff was optimum in terms of homogeneous plasma and the maximum H2 outgas amount with PECRF = 0.59 MW and tpulse = 1 s. With PECRF = 1.27 MW and tpulse = 1 s,

References (12)

  • J. Winter

    J. Nucl. Mater.

    (1989)
  • H.G. Esser

    J. Nucl. Mater.

    (1997)
  • E. Gauthier

    J. Nucl. Mater

    (1997)
  • J.S. Hu

    J. Nucl. Mater.

    (2008)
  • Y. Sakamoto

    J. Nucl. Mater

    (1980)
  • K. Ushigusa

    Fus. Eng. Des.

    (1999)
There are more references available in the full text version of this article.

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