Lecture on Targets A. Introduction scattering exp., gas target, storage ring B. Basics on Vacuum, Gas Flow etc pumps, molecular flow & tubes, T-shaped

Lecture on TargetsA. Introduction scattering exp., gas target, storage ring

B. Basics on Vacuum, Gas Flow etcpumps, molecular flow & tubes, T-shaped storage cell

C. Integration of Gas Targets into Storage Rings

requirements on beam optics and vacuum systems

D. SummaryBatumi 14.08.2012 1E. Steffens "Lecture on Targets"

Lecture on Targets – additional material

Batumi 14.08.2012 2E. Steffens "Lecture on Targets"

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 high-power 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”.

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.

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).

T-shaped Storage Cell in a Storage Ring


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


FILTEX Experiment at the TSR Heidelberg


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:

Protons 920 GeV Electrons 27.5 GeV

HERA ep-collider

HERMES Target at HERA view along beam direction


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

75m Al walls with Drifilm coating

Cooler Synchrotron COSY (FZJ)


p, d with momenta up to 3.7 GeV/c

• internal experiments – with circulating beam • external experiments – with extracted beam

ANKE Target


Storage cell (top, bottom) and ABS (right) with target chamber and central dipole (blue).

Overview PAX Target


PAX Target


Right: Arrangement of quadru-pole lenses (yellow) and special low- quadrupoles (blue)

Cell walls made up by very thin teflon foils. Movable to provide large cell opening during beam injection!

Top right: -function in the target region (blue: horizontal, red: vertical)

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!

Der Spin, die Wünschelrute

in den Händen des

Physikers

frei nach E. W. Otten (Mainz)


File of target review paper (48 p.) available

Thank You!



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Documents

Lecture on Targets A. Introduction scattering exp., gas target, storage ring B. Basics on Vacuum, Gas Flow etc pumps, molecular flow & tubes, T-shaped