Darrell L. Judge

Extreme-ultraviolet efficiency measurements of freestanding transmission gratings

We report new, near-normal-incidence, transmission grating efficiency results at selected extreme-ultraviolet wavelengths between 4.5 and 30.5 nm for two transmission gratings, one with a period of 200 nm and the other with a period of 400 nm. These gratings consist of opaque gold bars separated by open spaces that have been produced by photolithography techniques commonly used to produce electronic components. The gold bars and the open spaces are nominally of the same width. Both gratings have a thickness of 470 nm. The transmission efficiency at the central, first, and, when possible, second order of diffraction was measured. In addition, guided-wave phenomena at nonnormal angles of incidence, as well as transmission differences depending on which side of the grating was illuminated, were investigated. The observed guided-wave effects allow one to selectively enhance the transmission of the grating at desired wavelengths, as is realized with a blazed reflection grating.

SEP Temporal Fluctuations Related to Extreme Solar Flare Events Detected by SOHO/CELIAS/SEM

The SOHO CELIAS/SEM measurements of the solar Extreme Ultraviolet (EUV) irradiance in the He II 30.4 nm first-order channel (26–34 nm) are highly sensitive to impacts of Solar Energetic Particles (SEP). A model of the SEM response to a quasi-isotropic SEP fluence allowed us to determine both the range of proton incident energies and the SEM sensitivity to the SEP flux, which has a maximum around 12 MeV. We propose to use high-cadence (15 s) SEM first-order count-rates to analyze the temporal fluctuations of the SEP flux arriving from extreme solar flare events. A comparison of these temporal fluctuations for the July 14, 2000, October 28, November 2, November 4, 2003, and January 20, 2005 events shows that the most intense high-frequency RMS variations of the first-order count-rates at the time when SEPs started to arrive, were associated with the January 20 event. These high-frequency variations are produced by packets of SEPs. Two (plus and minus) first-order SEM detectors with the distance between them of about 62 mm allow us to analyze the spatial coincidences and temporal distribution of SEP related signals at 1 AU. The largest temporal separation of the SEP packets is observed at the time when the packets start to arrive. RMS fluctuations (variances) for all analyzed events do not follow the photon noise ( √ N) in assumption of the Poisson or normal distribution but correlate (R = 0.999) with the speed at which the SEP flux grows. If the found correlation is confirmed on a larger statistical data base, it may allow the prediction of the SEP flux growth profile by analyzing the RMS amplitudes for the initial phase of the SEP impact.

A study of the effect and consequence of solar cycle variation on low-energy galactic cosmic rays using Pioneer 10 H Lyman α data as a solar cycle proxy

The correlation of the 1981–1990 (∼ 23 to ∼ 50 AU) data of three instruments, the ultraviolet photometer (UV), the charged particle instrument (CPI), and the trapped radiation detector (TRD), on board Pioneer 10 is investigated. The reduction of the data necessary for applying a fast Fourier transform (FFT) algorithm is described. A cross correlation function between the hydrogen Lyman a backscattered radiation, used as a solar cycle proxy, and the cosmic ray fluxes is obtained from the FFT algorithm. The time lag in the anticorrelation function between the galactic cosmic rays and the Lyman α line is used to determine the distance to the solar wind termination shock (75 AU), under the assumption that the cosmic ray modulation boundary for low-energy particles and the termination shock are coincident. The ratio of the upwind termination shock distance to the downwind shock distance is determined to be 2/3 using the Voyager 1 position in 1996.