Theoretical and experimental studies of runawayelectrons in the TEXTOR tokamak

Theoretical and experimental studies of runaway electrons in tokamaksand their mitigations, particularly the recent studies performed by a group of theHeinrich-Heine University Düsseldorf in collaboration with the Institute of Energy and Climate Research of the Research Centre (Forschungszentrum) of Jülich are reviewed. The main topics focus on (i) runaway generation mechanisms, (ii) runaway orbits in equilibrium plasma, (iii) transport in stochastic magnetic elds, (iv )diagnostics and investigations of transport of runaway electron and their losses in low density discharges (v) runaway electrons during plasma disruptions, and (vi) runaway mitigation methods. The development of runaway diagnostics enables the measurement of runaway electrons in both the centre and edge of the plasma. The diagnostics provide an absolute runaway energy resolved measurement, the radial decay length of runaway electrons and, the structure and dynamics of runaway electron beams. The new mechanism of runaway electron formation during plasma disruptions is discussed

Runaway electron studies in TEXTOR

The evolution of runaway electrons in disruptive plasmas in TEXTOR is determined by observing the synchrotron radiation (hard component E > 25 MeV) and by measuring the runway electrons with an energy of a few MeV using a scintillator probe. Disruptions are initiated by a massive argon gas injection performed by a fast valve. The observed runaway beam of the high energy component (synchrotron radiation) fills about half of the diameter of the original plasma. The beam is smooth and shows no indication of filamentation. The initial conditions are in all cases very similar. The temporal development of the runaway electrons, however, is different: one observes cases with and without subsequent mode excitation and other cases in which the hard runaway component survives the apparent end of the runaway plateau. Several methods are applied to remove the runaway electrons including massive gas injection from two additional valves of different sizes as well as external and internal ergodization by inducing a tearing mode. The mitigation is only marginally successful and it is clearly found that the runaways in disruptions are substantially more robust than runaways created in stationary, low density discharges

Structure of the runaway electron loss during induced disruptions in TEXTOR

The loss of runaway electrons during an induced disruption is recorded by a synchrotron imaging technique using a fast infrared CCD camera. The loss is predominantly diffuse. During the “spiky-loss phase”, when the runaway beam moves close to the wall, a narrow channel between the runaway column and a scintillator probe is formed and lasts until the runaway beam is terminated. In some cases, the processed images show a stripe pattern at the plasma edge. A comparison between the MHD dominated disruptions and the MHD-free disruption is performed. A new mechanism of plasma disruptions with the runaway electron generation and a novel model which reproduces many characteristic features of the plasma beam evolution during a disruption is briefly described

Influence of radiation on changing the energy of runaway electrons during tokamak disruptions

Playwright: Bertolt Brecht Director: Susan Hargrave Scene: Donamarie Reeds Costume: Elizabeth M. Poindexter Lighting: Kenneth R. Dorst Academic Year: 1982-1983https://scholarworks.sjsu.edu/production_images/2204/thumbnail.jp