Solar flares are known to release a large amount of energy into accelerating electrons. Studying small timescale (≤2s) fluctuations in nonthermal X-ray flux offers the opportunity to probe the nature of those acceleration mechanisms. By comparing the durations, differences in timing between energy bands, and the periodicity of these spikes against the relevant timescales called for by various acceleration mechanisms, a test for each mechanism’s validity can be made. This work details the analysis of fast fluctuations in Fermi Gamma-ray Burst Monitor (Fermi GBM) data from two M9.3 class solar flares that occurred on SOL2011-07-30 and SOL2011-08-04. This study shows the usefulness of Fermi GBM data as a means of examining these small timescale spikes and presents a rigorous method of identifying, counting, and measuring the temporal properties of these subsecond X-ray spikes. In the two flares examined we found spikes to primarily occur in spans of 60–100 s in the impulsive phase. The relative spike intensity averaged between 6% and 28% when compared to the slowly varying component of the X-ray flux. The average spike durations were 0.49 and 0.38 s for the 2 flares. The spike duration distribution for the SOL2011-08-04 flare was found to follow a power law with a −1.2 ± 0.3 index. Of the three spiking intervals identified, only one was found to have a periodicity, showing significant power at the 1.7 ± 0.1 Hz frequency.

The present status of feedback systems to counteract unwanted beam motion and coupled-bunch beam instabilities in the BESSY II storage ring is reviewed.

This paper presents an overview of the bunch-by-bunch feedback kickers designed for the BESSY II storage ring. Simulation results for the longitudinal kicker cavity and for the transverse stripline kicker are discussed.

Abstract. The commissioning of the high-brilliance synchrotron light source BESSY-II in Berlin started in April 1998. Within the commissioning period, bunch-by-bunch feedback systems to counteract longitudinal and transverse multibunch instabilities will be installed. This paper reviews their design and present status.

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