Measurements of the emittance and current density profile of the beam produced by the ATA injector Page: 3 of 18
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into a corresponding number of beamlets. The mask slot pattern shown in Fig.
2 was chosen to facilitate the alignment of the TV axis to the slot axis and
to simplify the fabrication of the mask. The beamlets pass through a drift
region of approximately 23 cm in which they freely expand. They then pass
through a range thin aluminum foil and excite a fast phosphor deposited on the
foil back. Using front surface mirrors the image created by the beamlets is
relayed to a gated TV/comDuter system which records and analyzes the image.
A sketch of the optics containing a definition of the angles and lengths
is given in Fig, 3. In this schematic the maximum angle that can pass through
the slot is shown. The instrument is only useful if the measured width is
considerably less than 2 W. For this instrument the slots have a width of
0.051 cm and the carbon is 1.27 cm thick. The slot acceptance angle 6k is
0.04 radians and W zquals 0.92 cm. This places a limit on the maximum
normalized emittance that can be measured by this instrument^r^ Y/2) of
approximately 0.6 for the parameters of this experiment. The slots are
located 1.35 cm apart. As a consequence, if the beam emittance is too large
to be measured with this instrument, the images of the slots at the phosphor
The TV image is generated by the electrons passing through a cadmium doped
ZnS phosphor deposited on the back of a 0.025 cm aluminum sheet. The phosphor
has a time decay of less than one nanosecond. Four holes located
symmetrically on a 3 cm radius circle about a center hole are used to
determine size in the TV image.
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Fessenden, T.J. Measurements of the emittance and current density profile of the beam produced by the ATA injector, report, June 27, 1983; [Livermore,] California. (digital.library.unt.edu/ark:/67531/metadc1100317/m1/3/: accessed September 25, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.