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The source-sample stage of the new two-dimensional angular correlation of annihilation radiation spectrometer at Technische Universität München
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10.1063/1.4801454
/content/aip/journal/rsi/84/4/10.1063/1.4801454
http://aip.metastore.ingenta.com/content/aip/journal/rsi/84/4/10.1063/1.4801454
View: Figures

Figures

Image of FIG. 1.
FIG. 1.

Schematic overview of the ACAR spectrometer. (a) Total view of the spectrometer, including detectors. The baseline of the Anger cameras is 16.5 m in order to achieve the desired angular resolution. (b) Cut-view of the central assembly. The cold finger of the cryostat is fed into the sample chamber from below. (c) Detailed cut-view of the source-sample chamber with the custom-built pole piece assembly. Sample and source are positioned symmetrical with respect to the pole pieces.

Image of FIG. 2.
FIG. 2.

Magnetic field configuration. FEM simulation of the magnetic flux density inside the sample chamber. Between the two pole pieces a region with a homogeneous field is created. Sample and source are placed inside this region for optimal positron transport.

Image of FIG. 3.
FIG. 3.

Magnetic field configuration. Measured magnetic field in sample plane. The sample position is located on the plateau in the center. The flux density decreases rapidly outside the pole piece configuration.

Image of FIG. 4.
FIG. 4.

Dependence of the magnetic flux density at the sample position on the electric current through the coils. At a current of I coil ≈ 45 A the soft iron is beginning to saturate.

Image of FIG. 5.
FIG. 5.

Calculated positron momentum distribution on the sample, obtained by a Monte-Carlo simulation. For high flux densities almost the full spectrum is mapped onto the sample.

Image of FIG. 6.
FIG. 6.

Measured beta efficiency in comparison with the expectation derived from the simulation. The measured values exceed the expectation indicating that positrons which are emitted into the upper half-space are effectively reflected downwards onto the sample by the Ta reflector.

Image of FIG. 7.
FIG. 7.

Dependence of the spot diameter on the magnetic flux density at the sample position for two arbitrary orthogonal axis.

Image of FIG. 8.
FIG. 8.

Contour plot of the ACAR spectrum of single crystalline α-quartz.

Image of FIG. 9.
FIG. 9.

Horizontal cut through the ACAR spectrum along p y = 0.

Image of FIG. 10.
FIG. 10.

Vertical cut through the ACAR spectrum along p x = 0.

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/content/aip/journal/rsi/84/4/10.1063/1.4801454
2013-04-18
2014-04-23
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: The source-sample stage of the new two-dimensional angular correlation of annihilation radiation spectrometer at Technische Universität München
http://aip.metastore.ingenta.com/content/aip/journal/rsi/84/4/10.1063/1.4801454
10.1063/1.4801454
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