R. Kallenbach

Solar wind measurements with SOHO: The CELIAS/MTOF proton monitor

The proton monitor, a small subsensor in the Charge, Element, and Isotope Analysis System/Mass Time-of-Flight (CELIAS/MTOF) experiment on the SOHO spacecraft, was designed to assist in the interpretation of measurements from the high mass resolution main MTOF sensor. In this paper we demonstrate that the proton monitor data may be used to generate reasonably accurate values of the solar wind proton bulk speed, density, thermal speed, and north/south flow direction. Correlation coefficients based on comparison with the solar wind measurements from the SWE instrument on the Wind spacecraft range from 0.87 to 0.99. On the basis of the initial 12 months of observations, we find that the proton momentum flux is almost invariant with respect to the bulk speed, confirming a previously published result. We present observations of two interplanetary shock events, and of an unusual solar wind density depletion. This large density depletion, and the correspondingly large drop in the solar wind ram pressure, may have been the cause of a nearly simultaneous large increase in the flux of relativistic magnetospheric electrons observed at geosynchronous altitudes by the GOES 9 spacecraft. Extending our data set with a 10-year time span from the OMNIWeb data set, we find an average frequency of about one large density depletion per year. The origin of these events is unclear; of the 10 events identified, 3 appear to be corotating and at least 2 are probably CME related. The rapidly available, comprehensive data coverage from SOHO allows the production of near-real time solar wind parameters that are now accessible on the World Wide Web.

Isotopic composition of solar wind neon measured by CELIAS/MTOF on board SOHO

We present first results taken from the high-resolution mass time-of-flight spectrometer (MTOF) of the charge, element, and isotope analysis system (CELIAS) experiment on board the Solar and Heliospheric Observatory (SOHO) spacecraft launched in December 1995, concerning the abundance ratios of neon isotopes in the solar wind. We obtain the isotopic ratios 20Ne/22Ne = (13.8 ± 0.7) and 20Ne/21Ne = (440 ± 110), which agree with the values obtained from the Apollo foil solar wind experiments and which have been derived from measurements of solar particles implanted in lunar and meteoritic samples.

Kinetic properties of solar wind minor ions and protons measured with SOHO/CELIAS

Using observations of the Charge Time-of-Flight(CTOF) charge and mass spectrometer of the Charge, Element and Isotope Analysis System (CELIAS), and of CELIAS/proton monitor on board the Solar and Heliospheric Observatory (SOHO), we present an overview of speeds and kinetic temperatures of minor ions and protons in the solar wind near solar minimum, covering the Carrington Rotations 1908 to 1912. In the case of a collision-dominated solar wind the speed of minor ions is expected to be lower or equal to the speed of the protons, and all species are expected to have equal temperatures. On the other hand, minor ions can be accelerated and heated by wave-particle interaction. In this case, equal thermal speeds of all species are expected. CTOF data allow the determination of the kinetic parameters of various ions with high accuracy and with high time resolution. The mean O6+ speed of the observed period is 390 km s−1. The speeds of Si7+ and Fe9+ correlate well with O6+, the linear correlation coefficient being 0.96 or higher. Our results also indicate that silicon and iron tend to lag behind oxygen with a speed difference of ∼20 km s−1 at 500 km s−1. At the same time, the kinetic temperature of the ions under investigation exhibit the well-known mass proportionality, which is attributed to wave-particle interactions. During the period of low solar activity in consideration, many cases are observed where the kinetic temperature is extraordinarily low (104 K for O6+).

Origin, Injection, and Acceleration of CIR Particles: Observations

This report emphasizes new observational aspects of CIR ions revealed by advanced instruments launched on the Ulysses, WIND, SOHO, and ACE spacecraft, and by the unique vantage point of Ulysses which carried out the first survey of Corotating Interaction Region (CIR) properties over a very wide range of heliolatitudes. With this more complete observational picture established, this review is the basis to consider the status of theoretical models on origin, injection, and acceleration of CIR particles reported by Scholer, Mann et al. (1999) in this volume.

Doubly-resonant second-harmonic generation in β-barium-borate

Abstract We describe a versatile tunable continuous wave ultraviolet source for spectroscopy. An angle-tuned β-barium-borate frequency doubler is placed inside a doubly resonant build-up cavity. By compensating for double refraction, this scheme provides efficient second harmonic generation in a pure TEM00 mode.

Iron freeze‐in temperatures measured by SOHO/CELIAS/CTOF

The CELIAS particle experiment on SOHO contains the Charge Time Of Flight (CTOF) mass spectrometer which measures the ionic and elemental composition of minor ions in the solar wind. In this paper we present iron freeze-in temperatures derived with a time resolution of 5 min. They indicate that some of the filamentary structures of the inner corona observed in Hα survive in the interplanetary medium as far as 1 AU.

A frequency-stabilized titanium sapphire laser for high-resolution spectroscopy

Abstract A single-frequency Ti:sapphire laser has been stabilized to a reference cavity with the simple side-of-fringe locking technique and a piezo-controlled mirror as compensating element. A frequency stability of 1 kHz rms with respect to the locking etalon is obtained. This Ti:sapphire laser, optimized for 972.5 nm, will be used for two-photon excitation of the 2S–4S transition in atomic hydrogen.

Elemental composition of the January 6, 1997, CME

Using solar wind particle data from the CELIAS/MTOF sensor on the SOHO mission, we studied the abundance of the elements O, Ne, Mg, Si, S, Ca, and Fe for the time period around the January 6, 1997, coronal mass ejection event (CME). In the interstream and coronal hole regions before and after this event we found elemental abundances consistent with the expected abundance patterns of the respective flow regimes. However, during the passage of the CME and during the passage of the erupted filament, which followed the CME, we found that the elemental composition differed markedly from the interstream and coronal hole regions before and after this event. During the passage of the CME and the passage of the erupted filament we found a mass-dependent element fractionation, with a monotonic increase toward heavier elements. We observed Si/O and Fe/O abundance ratios of about one half during these time periods, which is significantly higher than for typical solar wind.

Charge exchange of low energy particles passing through thin carbon foils: Dependence on foil thickness and charge state yields of Mg, Ca, Ti, Cr and Ni

Abstract We experimentally investigate charge exchange of ions passing through thin carbon foils of 1.1–10 μg/cm 2 thickness at incident energies from 0.5 to 5 keV/u. At such low energies usually only the charge exchange processes occurring at the back surface determine the final charge state of the emerging projectiles. However, for some elements we observe a significant foil thickness dependence which cannot be explained by current theoretical models. Possible reasons for this thickness dependence are discussed in this paper. We further present new data on charge state yields for Mg, Ca, Ti, Cr and Ni.

A blue dye laser with sub-kilohertz stability

Abstract We have stabilized the frequency of a commercial ring dye laser operating in the blue near 486 nm with an internal electro-optic modulator, using optical heterodyne detection of phase-modulated light reflected from a reference cavity. With a servo bandwidth of 10 MHz, the short-term stability has been reduced below 1 kHz. Frequency doubling of this laser will provide highly monochromatic 243 nm radiation for high resolution spectroscopy of the two-photon hydrogen 1S–2S transition.