Spectra Analysis of Runaway Electron Synchrotron Radiation for the Recent East Runaway Experiment

Abstract

The energy of disruption generated runaway electrons can reach as high as tens of megaelectronvolt and they can cause a serious damage of plasma-facing-component surfaces in large tokamaks like International Thermonuclear Experimental Reactor (ITER). The synchrotron radiation diagnostic allows a direct observation of such runaway electrons and an analysis of their parameters and promotes the safety operation of present day large tokamaks and future ITER. Only this diagnostic will be applied in ITER. In the paper detail analysis of the synchrotron radiation spectra of runaway electrons for the recent Experimental Advanced Superconducting Tokamak (EAST, Institute of Plasma Physics of Chinese Academy of Sciences) experiment parameters has been presented. The calculations are carried out on the base of precise expression for synchrotron radiation spectral density. They make more precise spectra analysis of the previous paper by Zhou R.

Measurements of runaway electron synchrotron spectra at high magnetic fields in Alcator C-Mod

“…(SOFT also determines zero contrib ution to the spectra from REs on-axis.) Coupling the TPM with SOFT (figure 15(c)) is better at matching experiment, but only for later times t = 0.85-1.00 s. Earlier times t = 0.75-0.80 s are opposite the experimental trend, and the 21) in [20] was used as a better approximation for P(λ, p, t). time evolution of the 'slope' is not monotonic, unlike the measured data.…”

“…2.7-7.8 T) will increase the power lost per electron by almost an order of magnitude. From the spectral power density of an arbitrarily-moving charge as formulated in [19], the synchrotron power spectrum-hereafter referred to as P(λ, p, t) = dP synch /dλ (W m −1 )-was calculated for a toroidal magnetic geometry in equation (15) of [20]. The relative changes in spectra for increasing energy E and B are shown in figure 4.…”

“…Using TPM data on the magnetic axis and brightness formula B (4) produces spectra completely unlike experiment, as seen in figure 15(b). One explanation for this is that an asymptotic expansion of P(λ, p, t), given by equation ( 21) in [20], is used to compute the spectra, as the full calcul ation becomes increasingly computationally-intensive for such low energies. More importantly, as seen in figure 5, synchrotron emission from REs on the magnetic axis is never directly viewed by the spectrometer, so emission from REs on other flux surfaces must be considered.…”

“…Figure 4. Synchrotron power spectraP(λ) [16,20] are plotted over the visible and near-infrared ranges for two cases: (a) At a constant B = 5.4 T, the RE energy is varied among 20 MeV (solid), 30 MeV (dotted), and 40 MeV (dot-dashed); and (b) at a constant RE energy E = 30 MeV, B is varied among 2.7 T (solid), 5.4 T (dotted), and 7.8 T (dot-dashed). The pitch p ⊥ /p = 0.1 is held constant for both cases, and the spectra have been re-scaled by the factors given to highlight change in spectral shape.…”

“…For six times during the 7.8 T discharge: comparisons of (a) experimental normalized brightness spectra to synthetic data from (b) on-axis TPM data input into B (4), and (c) TPM data from all surfaces input into SOFT. Note that in (b), equation (21) in[20] was used as a better approximation for P(λ, p, t).…”