THE FINAL MECHANICAL DESIGN, FABRICATION, AND COMMISSIONING OF A WIRE SCANNER AND SCRAPER ASSEMBLY FOR HALO-FORMATION MEASUREMENTS IN A PROTON BEAM Page: 3 of 4
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The peak heat flux that the wire is exposed to is
1400 kW/cm2. The peak heat flux occurs for the beam
parameters of a 1-mm rms size, 100-mA current, a
20-microsecond pulse length, and a beam repetition rate
of 1 Hz. The predicted pseudo-steady-state peak
temperature for the wire under these conditions is 1717 K
(1444 0C). The limiting temperature is 1800 K (1527 0C)
where the onset of thermionic emission is believed to
occur. Actual testing of the wire early on in the
experimenting verified that the thermionic emission
temperature is indeed near 1800 K. Figure 2 is a plot of
the predicted wire temperature where the beam on and off
pulsing effect can be seen by the temperature rising and
falling in step with the beam repetition rate.Figure 2: Predicted Wire Temperatures
2.2 Mounting of the Sensing Wire
A key part of the assembly is the mounting of the 33
micron wire onto the inner movable frame. A small
spring-loaded subassembly was designed to grasp the wire
and hold it in place for making wire scan measurements.
The requirements for the holding subassembly are: i) grip
and hold the wire with no slippage, ii) maintain electrical
conductivity in the wire circuit, iii) prevent the wire from
sagging due to thermal expansion, and iv) electrically
isolate the wire from the support frame. A spring loaded
clamp was designed to grasp the wire. Figure 3 is an
illustration of the clamp mechanism. The clamp consists
of a tapered two-jawed collet, a matching tapered collar, a
compression spring, a retaining ring, and a dielectric
housing. The dielectric housing is made of Vespel [3].
The Vespel holder is bolted to the inner movable frame.
The Vespel holder provides both mechanical support and
electrical isolation. Two mounting clamp subassemblies
are used on each measuring axis to hold one wire in place.
A signal wire of the wire scanner assembly is soldered
directly to the collar of the clamp assembly in order to
carry the wire scan signal to the detection electronics.
Collar Compression Spring
ColleWire
Dielectric housing R-a
retaining Ring
Figure 3: Spring-Loaded Clamp
The wire is mounted into two clamps that are fastened
to the inner movable frame of the scanner assembly by
first threading the wire into the collet with the spring load
relaxed. The collar is slid into place on the collet in order
to grip the wire. The collet-wire-collar combination is
pressed lightly against the spring, and the wire is threaded
into the opposite facing clamp assembly. This spring
compression will determine the preload that is placed on
the wire. The wire is fixed in the second clamp by
repeating the same process as was used on the first clamp.
The end of the wire protruding from the back end of the
each clamp is trimmed off. The wire is now properly
mounted in the assembly.
3 THE BEAM SCRAPER
3.1 The Scraper Analysis and Design
The peak target heat flux that the scraper is intended to
be exposed to is 610 kW/cm2. The peak predicted
temperature for the scraper is 493 0C. The peak predicted
stress is 31 MPa. The beam interaction region of the
scraper oscillates between minimum values and these
peaks as the beam is pulsed on and off. This creates a
fatigue loading situation. The scraper design has been
tested in a high heat flux application, and was found to be
able to maintain its integrity in excess of 180,000 cycles
[4]. This number of cycles allows for ample halo testing
in the LEDA lattice. Figure 4 illustrates the scraper
design.
" Mp~oFigure 4: Beam Halo Scraper
3.2 The Scraper Fabrication
A scraper is fabricated by first machining the copper
body and graphite face plates. The copper body is brazed
to the stainless steel cooling tubes in the first braze of the
process. Next, the graphite face plates are brazed onto the
scrapers. Although only one face intercepts the proton
beam two graphite face pieces are brazed on to the
scraper. Two graphite pieces are brazed on to balance the
bending loads placed on the scraper during the brazing
cool-down cycle and prevent permanent warping of the
scraper. Final machining is done on the scraper to create
sharp edges on the beam intercepting portion, and remove
excess graphite.1800
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VALDIVIEZ, R.; MARTINEZ, F. Z. & AL, ET. THE FINAL MECHANICAL DESIGN, FABRICATION, AND COMMISSIONING OF A WIRE SCANNER AND SCRAPER ASSEMBLY FOR HALO-FORMATION MEASUREMENTS IN A PROTON BEAM, article, April 1, 2001; New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc724200/m1/3/: accessed April 17, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.