Invited talks - Abstracts
(titles link to presentations)

 


ACKERMAN

Fiber Optic Technology for Antenna Remoting
Edward Ackerman and Charles Cox

Because of its very low attenuation and dispersion properties, telecommunications-grade single-mode optical fiber allows the signals collected by multiple antenna elements to be processed in one location, which, depending on the signal bandwidth, can be a distance a few or many kilometers away. We review the state of the art in analog fiber-optic link technology to assess the extent to which it can serve this role in radiophysics applications such as the Frequency Agile Solar Radiotelescope (FASR). We show the performance and cost of fiber-optic links that have been designed for antenna remoting applications in recent years, and project performance and cost estimates for antenna remoting links in the FASR.

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ASCHWANDEN

Time Scales of Solar Flare Phenomena
Markus J. Aschwanden

We discuss physical time scales of (1) particle acceleration, (2) injection, (3) propagation, (4) trapping, and (5) precipitation that all play a role in the particle kinematics and resulting radio emission during solar flares. Besided the fast time scales of particle kinematics we discuss also the slower MHD time scales that are relevant for chromospheric evaporation, filament eruption, CME evolution, in the context of related radio emission and the modulation of it. The physical time scales of particle kinematics and the resulting frequency-time drift rates pose constraints on the time and frequency resolution of the Frequency-Agile Solar Radiotelescope (FASR) and on the science this instrument is capable to perform.

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BASTIAN

Science with FASR and strawman specifications (PDF)
Tim Bastian

The Frequency Agile Solar Radiotelescope (FASR) is a telescope concept currently under study in the United States. It is envisaged to be a Fourier synthesis telescope designed to perform broadband imaging spectroscopy over an extremely broad frequency range (~0.1-30 GHz). The frequency, temporal, and angular coverage and resolution of the instrument will be optimized for the many and varied radio phenomena produced by the Sun. This talk will review the primary science drivers of the instrument and the instrument they imply. These include solar energetic phenomena, space weather studies, coronal magnetic fields, and studies of the "thermal" Sun. A "strawman" telescope will be presented and several outstanding technical issues will be outlined.

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BASTIAN

EVLA
Tim Bastian

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BASTIAN

FASR Antenna Size and Configuration
Tim Bastian

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BASTIAN
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FASR Science Drivers (Summary Session)
Tim Bastian

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BENZ

Coherent burst emission
Arnold O. Benz

The radio emission of solar flares at decimeter wavelengths includes a variety of emission processes of a plasma thought to have a high beta. Very intense coherent emissions are observed at wavelengths longer than about 3 cm. They are caused by plasma instabilities driving various wave modes that in turn may emit observable radio waves. Particularly important are type III bursts, caused by electron beams exciting Langmuir waves. Their trace in the corona points back to the acceleration region of the electrons. Less known are radio emissions from trapped electrons driving loss-cone unstable waves, suspected for type IV bursts. These types of coherent radio emission give clues on the geometry and plasma parameters near the acceleration region.

More speculative are emissions that are directly produced by the acceleration process. A possible group of such phenomena are narrowband, short peaks of emission. Narrowband spikes are seen sometimes at frequencies above the start of metric type III events. There is mounting evidence for the hypothesis that these spikes coincide with the energy release region. Much less clear is the situation for decimetric spikes, which are associated with hard X-ray flares. More frequently than spikes, however, there is fluctuating broadband decimetric emission during the hard X-ray phase of flares. The use of these coherent radio emissions as a diagnostic tool for the primary energy release requires a solid understanding of the emission process. At the moment we are still far away from an accepted theory. Complementary observations of energetic electrons and the thermal coronal background in EUV lines and soft X-rays can put coherent emissions into context and test the different emission scenarios. In combination with other wavelengths and their imaging by FASR would provde exciting possibilities for the diagnostics of the acceleration process.

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BOGOD

Future plans and technical developments for the RATAN-600 telescope
V.Bogod

Today RATAN-6000 is working like solar dedicated instrument, carrying out daily observations during last 5 years. We continue to develop its parameters for solar study. Multi-azimuths mode of observations with 4 minutes cadence during 4 hours is already realized. It allows us to improve telescope opportunities for study of temporal evolution and multi-wave mapping of solar active regions. New spectral analyzer is under development. .
Examples of observations of solar objects with fine spectral and temporal characteristics are presented. Future main technical and observational parameters of the telescope are discussed.

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BRADLEY
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Broad Bandwidth Feeds for Reflector Antennas (PDF)
R. Bradley

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BROSIUS

Coronal Diagnostics With Coordinated Radio and EUV/Soft X-Ray Observations (PDF)
Jeffrey W. Brosius

I will provide a brief review of what we have learned about the solar corona from existing coordinated radio and EUV (or soft X-ray) observations. Results from these earlier studies will be used to help focus on coronal diagnostics that can be performed with similar coordinated observations involving FASR, as well as to recommend FASR instrument requirements.

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CANE

Meter wavelength radio bursts and what we still don't know (PDF)
Hilary Cane

This talk will be a brief review of what is known about meterwave radio bursts, followed by some new results on type III bursts and some suggestions for FASR.

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DE BOER

Antennas from an ATA Perspective (PDF)
David R. DeBoer

As antenna farms are currently being developed to provide low-cost high-performance radio telescopes, the physical structure of the antenna is a critical cost/performance component that does not yield to Moore's law. The ATA is developing an offset Gregorian design that utilizes inexpensive, accurate and essentially self-supporting reflectors made by a proprietary "hydroforming" process that are basically placed on a pipe in the field. This talk will describe the ATA antenna and discuss other efforts in developing low-cost reflectors.

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EMERSON

Technical goals
Darrel Emerson

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ENOME

Nobeyama Perspective on Calibration (PDF)
Shinzo Enome

A specific review on calibration is described with a perspective on Nobeyama Radioheliograph and with some comments a strawman design of FASR.

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ERICKSON

Active Balun/Dipole Development for the Low Frequency Array (PDF)
K. P. Stewart, W. C. Erickson, Brian C. Hicks

We are developing and testing active baluns and electrically short dipoles for possible use as the primary wideband receiving elements in the Low Frequency Array (LOFAR) for long wavelength radio astronomy in the 10 to 100 MHz frequency range. Two dipoles, with dimensions scaled approximately by a factor of three, have been built and tested. The antenna temperatures varied from about 25 % to 100 % of the average brightness temperature of the Galactic background. With these parameters it is easy to make the amplifier noise levels low enough that final system temperature is dominated by the Galactic background.

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ESCOFFIER
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Correlators (PDF)
Ray Escoffier

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FISHER

Spectral requirements and interference excision (PDF)
Rick Fisher

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FLEISHMAN

Requirements for spectral and temporal resolution to study kinetic processes in solar plasma
G.D.Fleishman

Solar radio bursts with narrow spectral bandwidth and short time scales are discussed. The main question of interest within the report is what temporal and spectral resolution is required to study various kinetic processes in the solar plasma quantitatively. The considered processes are quasilinear relaxation of unstable electron distributions, nonlinear wave-wave interactions, effects of wave dispersion in the corona, Raman scattering of radio waves on low-frequncy waves. New possibilities of the background plasma and fast particle diagnostics with high temporal, spectral and spatial resolution are discussed.

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GARY

Phase A Study Activities and Workshop Goals
Dale E. Gary

FASR is now in a Phase A study whose goals include defining the important science FASR is expected to address, prioritizing the science, and seeking design options for the instrument that address the science within the cost constraints. This FASR Science Definition workshop provides an opportunity to engage the scientific community in the science definition and design process, and to start a dialog between the scientists and engineers. The goals of the workshop include laying out the broad science that can be addressed through radio observations, discussing what important science may be missing from our current thinking, and refining the instrumenta specifications needed to meet the science goals. Most importantly, we seek to prioritize the science so that when compromises in the design must be made due to cost or complexity constraints, we can ensure that the most meritorious science is retained.

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GARY

OVSA Experience of Relevance to FASR
Dale E. Gary

OVSA uniquely shares features envisioned for FASR, specifically frequency-agile interferometry. The multi-frequency interferometry approach provides some interesting and potentially useful simplifications in approach to calibration, and also raises some potential difficulties that need to be considered in any calibration scheme. The simplifications involve making use of the linear frequency dependence of many sources of phase instability (atmosphere, temperature changes, effective cable lengths), to resolve lobe ambiguities. The difficulties involve the precision needed for interchannel calibration within a band. We briefly discuss some of these issues, illustrated with OVSA data.

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GARY

Site Issues for FASR
Dale E. Gary

One of the goals of the Phase A study is to begin the investigation of potential sites for FASR. Here we briefly describe some of the criteria by which site selection should be made, and discuss some of the progress made to date on identifying potential sites.

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GARY
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Future Activities for FASR
Dale E. Gary

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GELFREIKH

Bremsstrahlung diagnostics of coronal magnetic fields (PDF)
G.B.Gelfreikh

The basic equation of the transfer of the radio waves in anisotropic collisional plasma are considered to get some formula used to determine the longitude component of the magnetic field. The cases of transparent and optically thick plasma are analyzed. The results of measuring magnetic fields in the solar atmosphere are illustrated as based on observations made with the radio heliograph Nobeyama and the reflector type telescope RATAN-600. The studied plasma structures include: sunspots, faculae, coronal loops, coronal holes, arches connected with CME. The technical reqiuirements to a solar radio telescope used to coronal magnetography based on polarization-spectral analysis of the thermal bremsstrahlung are discussed. High sensitivity in measuring low degree of polarization seems to be the main source of limits in the problem. Some perspectives of usage FASR for the analysis of the coronal magnetic structures based on observations of their thermal bremsstrahlung are discussed.

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GOPALSWAMY

Radio observations of coronal mass ejections
N. Gopalswamy

Coronal mass ejections (CMEs) have been traditionally observed in white light using coronagraphs. Requirement of an occulting disk in coronagraphs renders the detection of Earth-directed CMEs very difficult. One has to resort to non-coronagraphic observations such as radio, X-ray and EUV to detect Earth-directed CMEs. Furthermore, inner coronal imaging at these wavelengths is the only way to study the early evolution of CMEs. In this talk, I discuss the observability of CMEs at radio wavelengths, heavily drawing from the observations of the Nobeyama and the Clark Lake radioheliographs. In particular, I will discuss how the CME substructures could be imaged at radio wavelengths.

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HUDSON

The Yohkoh observations of solar flares
H. S. Hudson

The Yohkoh mission provided comprehensive views of solar flares based upon soft X-ray and hard X-ray imaging plus spectroscopy. This paper reviews the decade of Yohkoh observations, emphasizing the implications of the observations for flare models in the context of FASR capabilities. The discussion touches also on CMEs as viewed in the low corona, since flare and CME effects are often inseparable in the Yohkoh observations.

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HURFORD

The RHESSI - FASR Connection (PDF)
G. J. Hurford

The RHESSI mission has a great deal in common with FASR, in terms of both overlap in their scientific objectives and in the characteristics of their data. Scientifically, a central component of each mission is the use of imaging spectroscopy for the study of thermal and nonthermal electrons in solar flares. Observationally, both use Fourier transform imaging for achieving these objectives. Both missions are striving to reach out to a user community that is not necessarily familiar with these techniques. Finally, both offer the user exceptional flexibility in selecting the time, energy and spectral resolution with which to analyse the data. After establishing these points, this paper reviews the RHESSI 'experience' as seen from the user's perspective and discusses the extent of its relevance to FASR.

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HURFORD

Solar Calibration Strategies
G. J. Hurford

The purpose of this paper is to suggest the range of calibration strategies that might be employed to enable FASR to achieve its scientific objectives. An overview of calibration requirements is presented with some emphasis on the influence of the solar-oriented and multi-frequency nature of the instrument. Tradeoffs associated with different phase calibration strategies that might be employed are described for alternative configurations which do and do not include large antennas.

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KASSIM

Thoughts on LOFAR/FASR Synergy (PDF)
Namir Kassim

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KELLER

FASR and the Quiet Sun (PDF)
Christoph U. Keller

While active regions are a prime target for FASR observations, FASR will also contribute to our knowledge of the quiet sun, in particular through precise temperature measurements and potentially through magnetic field measurements. I will review current problems in understanding the quiet sun from the perspective of a solar physicist who is mostly working with optical telescopes.

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KERDRAON

Special Issues in low frequency solar radio observation
A. Kerdraon

I will present instrumental constraints due to low-frequencies (lower than ~1GHz) observations of solar radio-emissions. Specifics constraints come mainly from the variability of the signal and very strong interferences. They have a strong impact on the analog and digital sub-systems, including the correlator.

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KRUCKER

Coronal heating and microbursts (PDF)
Sam Krucker

I will discuss radio microbursts observed in the quiet corona and their relation to coronal heating. What will we learn from FASR observations of quiet Sun microbursts?

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LEE

Radio Studies of Solar Flares
Jeongwoo Lee

Solar flare radiation at centimeter wavelengths is dominated by incoherent gyrosynchrotron emissions. They provide unique diagnostic tools for high energy electrons and magnetic fields, which become more powerful with increasing spectral capability of the radio instrument used with. This talk focuses on some recent progress made primarily using the Owens Valley Solar Array (OVSA) in collaboration with X-ray, EUV, and H-alpha observations to understand acceleration, magnetic trapping, and collisional precipitation of electrons during solar flares. The results demonstrate advantages of a multi-frequency radio observation as a stand-alone diagnostic tool in solar flare study as well as a powerful ground-based tool supporting the space observations.

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PICK

Flares, CMEs and Interplanetary Disturbances
Monique Pick

Coronal Mass Ejections are now identified as an important link between activity at the Sun and its effect in the Earth environment. We present a synthesis of results on the initiation and development of Coronal Mass Ejection events using coordinated observations from space and from ground-based instruments. The emphasis is placed on radio spectral and imaging data. Rather sophisticated CME models, involving multiple magnetic flux systems are now developed; it is shown that radio observations can bring important constraints in these CME models. The origin of energetic electrons detected in the interplanetary medium and their association in particular with flare /CME events are briefly discussed. The source of imaging data used in these studies was the Nancay radioheliograph (NRH) which records quasi-simultaneously 5 to about 10 frequency images in a limited frequency range. This is one of the major limitation for these studies. FASR will provide multiple images across a broad frequency range and will be a powerful tool to understand the relationship between CME’s, solar surface activity, flares and particle origin. Finally, some results on the association between interplanetary transient disturbances detected in the vicinity of the Earth and CME’s are presented. Disk observations, in particular radio observations provide the identification of the solar source of the CME’s. Investigating the properties of these solar sources is a necessary step for understanding the origin of geo-effective events. Here again this is important to cover a broad frequency range as it will be obtained with FASR.

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RYABOV

Coronal Magnetography from Quasi-Transverse Propogation (PDF)
Ryabov, B.I.

The technique of coronal magnetography based on the analyses of quasi-transverse (QT-) propagation of microwaves in the low solar corona and some coronal magnetograms are briefly reviewed. The technique itself is quite powerful, yet it requires some efforts to improve the determination of the distance between the microwave source and the coronal region of QT-propagation of the microwaves. Some recommendations for the FASR design are specified for the radio measurements of the fields of 1 - 300 Gauss to be completed.

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SHIBASAKI

Flare imaging observations by the Nobeyama Radioheliograph
Kiyoto Shibasaki

Imaging observations of thermal and non-thermal sources of solar flares by the Nobeyama Radioheliograph (NoRH) are presented. NoRH is a solar dedicated radio interferometer operating at 17 and 34 GHz since 1992. Plasma cloud motions and non-thermal electron propagation features will be presented as movies. Flare geometry and dynamics observed by NoRH are used to identify the cause of solar flares. Based on these observations and the solar flare scenario, I will discuss the instrumental requrements for FASR to push further the current knowledge of particle acceleration, plasma heating and ejection associated with solar flares.

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SMOLKOV

Future plans and technical developments for the Siberian Solar Radio Telescope
A.T.Altyntsev, V.V.Grechnev, B.B.Krissinel, S.V.Lesovoi, V.P.Maksimov,
G.Ya.Smolkov, V.G.Zandanov and A.M.Uralov

How and for what, in which conditions was created the Siberian Solar Radio Telescope (SSRT). Short description and current modernization of SSRT. New scientific tasks and technical requirements to SSRT. An ways for technical developments for SSRT.

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WHITE

Radio Observations of Gyroresonance Emission from Coronal Magnetic Fields
S. White

The use of gyroresonance emission to study coronal magnetic fields will be reviewed and its implications for FASR design will be discussed.

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WHITE

FASR at low frequencies
S. White

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