Lecture on Targets
A. Introduction
scattering exp., gas target, storage ring
B. Basics on Vacuum, Gas Flow etc
pumps, molecular flow & tubes, T-shaped storage cell
C. Integration of Gas Targets into Storage Rings
requirements on beam optics and vacuum systems
D. Summary
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Lecture on Targets
– additional material
Traditional Nuclear Physics Scattering experiment
Beam from (Tandem) accelerator directed on a thin foil target, e.g. thin Carbon
foil covered with a layer containing the target atoms under study. Versatile
method to study Energy Levels and Structure of Nuclei throughout the periodic
system!
Today, the technology of targets is a very diverse field, ranging from highpower production targets for secondary beams (e.g. pions, anti-protons) to
radioactive targets and gas targets (e.g. spin polarized).
Our focus is on “Gas Targets for Storage Rings”.
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Gas Target in a Storage Ring
The basic principle of storage ring experiment is shown schematically. In order to
minimize Coulomb losses at the target, it is placed at the center of a low-beta
section, where the acceptance angle is high.
Electron Cooling (or Stochastic Cooling) may be used in order to compensate for the
energy loss and beam blow-up by the target. In this way, storage times of several
hours can be accomplished.
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T-shaped Storage Cell in a Storage Ring
Sketch of the FILTEX-Target
(Rathmann, Steffens, Zapfe et al.,
1992).
The FILTEX experiment
demonstrated „Spin Filtering“ of an
ion beam for the first time, i.e.
polarizing a circulating beam by
spin-dependent attenuation on an
internal target (spin-filtering of
neutrons had been demonstrated in
the 1960‘s by Shapiro et al in
Dubna).
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T-shaped Storage Cell in a Storage Ring
View into FILTEX
scattering chamber
(under vacuum!)
- center: T-shaped
target cell
- right: cell support
and panel of cryo
pump
- background:
permanent sextupole
magnet for focusing a
polarized hydrogen
beam into the cell
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FILTEX Experiment at the TSR Heidelberg
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Polarized H&D Gas Target for HERMES
HERMES experiment: Deep-inelastic electron scattering at 27.5 GeV
Located in the electron ring of the HERA ep-collider (1992 – 2007) at DESY, Hamburg
Top view:
HERA ep-collider
Protons 920 GeV
Electrons 27.5 GeV
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HERMES Target at HERA
view along beam direction
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Design of the HERMES Target Cell
Cell optimized for operation in an
electron storage ring
Conducting surface with smooth
variation of cross section avoids
excitation of wake fields!
System of W collimators for
protection against beam and SR
Cooled via cooling rails by cold He
gas to 60-100K
75mm Al walls with Drifilm coating
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Cooler Synchrotron COSY (FZJ)
p, d with momenta up to 3.7 GeV/c
• internal experiments –
with circulating beam
• external experiments –
with extracted beam
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ANKE Target
Storage cell (top, bottom) and ABS (right) with
target chamber and central dipole (blue).
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Overview PAX Target
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PAX Target
Cell walls made up by very thin teflon
foils. Movable to provide large cell
opening during beam injection!
Top right: b-function in the
target region (blue: horizontal,
red: vertical)
Right: Arrangement of quadrupole lenses (yellow) and special
low-b quadrupoles (blue)
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Conclusions
 Targets are part of a (fixed target) Scattering Experiment. There is a
large variety of different techniques for making the optimum target for a
particular experiment.
 Modern scattering experiments are often performed in Storage Rings
with phase space cooling. They require windowless Gas Targets in order to
limit energy loss and beam blow-up.
 Scattering of spin-polarized particles is studied at COSY (FZJ) in order
to learn about the spin-dependence of the strong force. For these
experiments, spin-polarized beams and targets are required.
 Spin-polarized gas targets for storage rings are based on the T-shaped
storage cell, into which a beam of polarized atoms is injected. In this way,
a triangular density of the polarized gas (e.g. hydrogen or deuterium)
along the straight beam tube can be produced, resulting in a much higher
areal density as compared with the atomic beam itself.
 For more details see Review Article!
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Der Spin, die Wünschelrute
in den Händen des Physikers
frei nach E. W. Otten (Mainz)
File of target review
paper (48 p.) available
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Thank You!
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