ASTRID (Aarhus STorage RIng in Denmark) is a particle storage ring at Aarhus University, Aarhus, Denmark. ASTRID was designed, constructed and is operated by ISA (Institute for Storage Ring Facilities in Aarhus), a Danish National Facility where research is carried out in Physics, Chemistry, Materials Science, Laboratory Astrophysics and Biology using accelerators and storage rings.

ASTRID as it looked in 1989 just after the construction of the ring had finished and before any beamlines had been built.

Designs for ASTRID started in 1985.[1] The original concept for the ring was to store low-energy heavy ions for laser spectroscopic and laser cooling experiments and for atomic collision studies[2]. It was soon realised during the design phase that it would also be possible to store energetic electron beams in the ring and therefore ASTRID could operate as a synchrotron radiation (SR) source, providing photons in the UV to soft x-ray region. In 1988 the Natural Sciences Faculty at Aarhus University was awarded 16.7 M DKK for establishing an Instrument centre in Synchrotron Radiation Research, thus forming ISA. By late 1989 ASTRID was operating in ion storage mode with the first experiments being carried out on laser cooling a stored beam of Li+ ions to 1 mK .[3]
ASTRID as it looks now

Electrons were first stored in ASTRID in 1991 and by this time two beamlines had been constructed to make use of the synchrotron light, a surface science beamline (SX700) and an x-ray microscope (XM). Ion storage in ASTRID dominated in the early 90s, with many successful experiments storing both positive and negative ions ranging in mass from 1 (hydrogen atom) to 840 (carbon 70 cluster). Meanwhile the synchrotron radiation based research at ISA was expanding, and by 1995 ASTRID was operated 50% of the time in ion storage mode and 50% for synchrotron radiation. With the construction of the Electrostatic Storage Ring for Ions, at Aarhus (ELISA) in 1998, and an increasing demand for synchrotron radiation (by 2000 there were 7 beamlines on ASTRID using the light source), the ion storage runs were gradually reduced, until finally in 2005 ASTRID operated in ion storage mode for the last time. Since then ASTRID has been operating in electron storage mode producing synchrotron radiation throughout the year, with 3 or 4 electron runs, separated by shutdown periods for maintenance and development of the ring.

In December 2008, a contract was awarded to design and build ASTRID2, a 46 meter storage ring which will be built adjacent to ASTRID. Rather than having an electron beam which decays over time, ASTRID2 will be continually "topped up" by a feed from ASTRID, allowing nearly constant current.[4] It is expected to be completed by the end of 2011. It will generate synchrotron radiation to provide a tunable beam of light, expected to be of "remarkable" quality, with wavelengths from the ultraviolet through to soft x-rays.
[edit] Technical details for electron storage.
ASTRID schematic

The ASTRID storage “ring”, with a circumference of only 40 m, is actually a square, formed by four sets of two 45 degree dipole bending magnets. There are eight pairs of quadrupole magnets used for horizontal and vertical focusing of the electrons and eight pairs of sextupole magnets for chromaticity correction. Electrons are injected via a septum magnet into the ring from a 100 MeV race-track microtron in 4-5 mA pulses, and captured by a 105 MHz RF system which bunches and accelerates the electrons as they pass through the RF cavity. Many of these pulses of electrons are accumulated at 100 MeV to reach more than 180 mA of current in the ring, which then is accelerated to 580 MeV with negligible loss of beam. The lifetime of a stored beam at 160 mA is 100 to 120 hours.

Technical parameters

The table below shows the typical operating parameters for ASTRID when running in electron storage mode.
Parameter Value
Maximum Energy 580 MeV
Max. Current (2005) 286 mA
Typical Stored Current 180–220 mA
Lifetime (at 160 mA) 100–120 hours
Horizontal emittance 0.14 mm mrad
RF Frequency 104.9 MHz
No. of bunches 14
SR critical energy 0.38 keV
Dipole rigidity 1.9 Tm
Quadrupole max gradient 6.7 T/m

Beamlines on ASTRID

There are eight operational SR beamlines on ASTRID. The characteristics of these beamlines are summarised in the table below and their location shown in the schematic drawing. Please follow the links in the table for further information and descriptions of the individual beamlines.
The ASTRID beamlines[5] Station Source Spectral Range (λ)[nb 1] Resolving power Typical flux
(1010 photons/sec) Applications
eV nm gratings
SGM 1[6] Bending magnet 30–650 1.9–41 3 5,000–14,000 2 Surface Science
SX700[7] Bending magnet 6–700 1.8–205 2 200–2,500 1 Surface Science
XRM[8] Bending magnet 410–830 1.5–3.0 0 2,000 2 X-Ray Microscopy, Imaging
MIYAKE[9] Undulator 15–180 6.9–83 1 2,000 20 Atomic and Molecular Physics
SGM 2[10] Undulator 12–40 31–105 1 10,000–20,000 20 Atomic and Molecular Physics
SGM 3[11] Undulator 8–150 8.3–155 3 15,000 20 Surface Science
UV 1[12] Bending magnet 1.5–12 105–830 2 1,000–5,000 20 CD Spectroscopy, Photobiology, UV Spectroscopy
CD 1[13] Bending magnet 1.8–9.9 125–700 1 <500 100 CD Spectroscopy

^ Conversions between eV and nm are italicized.

See also

Synchrotron Radiation Source


^ "ASTRID - The Aarhus Storage Ring, R. Stensgaard, Physica Scripta T22, p315-317 (1988)". Retrieved 2009-02-01.
^ "Laser cooling of stored ions in ASTRID: a storage ring for ions and electrons, J. S. Hangst, et al, Nuc. Inst. Meth. Phys. Res. B 68(1-4) p17-22 (1992)". Retrieved 2010-03-30.
^ "Laser cooling of a stored ion beam to 1 mK, J. S. Hangst et al.". 1991. p. 1238. doi:10.1103/PhysRevLett.67.1238.
^ "ASTRID2 – The ultimate synchrotron radiation source". Retrieved 2009-01-31.
^ SGM 1
^ SX700
^ SGM 2
^ SGM 3
^ UV 1
^ CD 1

External links

The ISA website
ISA page for the ASTRID facility
ISA page for the ASTRID 2 facility
Department of Physics and Astronomy, Aarhus University

Physics Encyclopedia

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