Effects of grids in drift tubes Page: 4 of 5
This article is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided to Digital Library by the UNT Libraries Government Documents Department.
The following text was automatically extracted from the image on this page using optical character recognition software:
was machined from single 1mm thickness tungsten plate
by a CNC wire cutting EDM. The width of the grid facing
to the beam direction is 0.2 mm. The connection points
between the tungsten quadrants and the springs were
brazed but one connection point was remained free. At the
installation, this remained free connection point makes
easier the process. The edge of the free spring snaps into
the hollowed edge of the quadrant. Figure 3 shows the
installed grid onto a mockup drift tube.
In the cavity design stage, Micro Wave Studio was
used for the RF simulation. To obtain the detailed 3D
information, we used TOSCA-OPERA assuming a
static electric condition including the fine structures of the
grids. Only one gap was analyzed, although the real
buncher has two gaps those are apart 3/2 #3A. The used 3D
model is shown in Fig. 4. Generally, the gap field is
expressed as a 3D expansion, however, in this report we
used 2D Fourier expansion which is built-in the OPERA
post processor since the 2D image is sometimes easier to
understand the field deformations. The expansion is
A cylindrical coordinate system is defined as 'z axis =
beam axis.' So the field components are expressed as Er,
EB, Ez. The coefficients were derived from the field along
the yellow circle indicated in the figure. The radius of the
circle is 7 mm from the beam axis which is just inside of
the apexes of the grid's pattern.
or' -aO -40
Figure 4: 3D model for OPERA
The inner diameter and gap length are 32 mm and 10
mm. The edge of the tube are rounded by r = 3 mm and
the grid's face started at z = +3.1 mm position. The
distance between two facing grids is 16.2 mm. In this
analysis, the gap voltage is assumed as 100 V.
Transit time factor
Figure 5 shows longitudinal electric field strengths at r
= 7 mm, b0 component of Ez along the beam axis, with
and without grids. The dotted lines include RF phase
change assuming a 750 keV proton beam. At z = 0
position, the RF phase of cosine is zero. At the tail of the
fields, the induced voltage has negative value around z =
15-30 mm. If the cavity employs 6A/2 gap interval, these
negative effect could be avoided, since the /12 = 30
6x0 - ((O -- -
W/O end --
- - - 0 1 s
- - W/O3 pd, RP -
I r -
-40 20 0 20
Figure 5: Longitudinal field strength (r = 7mm).
TTF can be derived by comparing the solid curves and
dotted curves at the certain phase (the graph shows zero
phase angle). The obtained values are summarized in
Table 1: Transit time factors
On axis With grids 63.50 %
Without grids 50.14%
r=7 mm With grids 72.28 %
Without grids 57.03 %
The grids enhance the TTF about 26 %.
-26x00 _ - - - - - - - - - - -
-40 -30 -20 -10 (I mlm 10 20 30
Figure 6: Transverse field strength (r = 7mm).
bo component of Er represents focusing and defocusing
force. Figure 6 shows the component. The dotted lines
include the RF phase angle of -90 at z = 0 position. The
integrated values along the axis with grid and without
Here’s what’s next.
This article can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Article.
M., Okamura & Yamauchi, H. Effects of grids in drift tubes, article, May 20, 2012; United States. (https://digital.library.unt.edu/ark:/67531/metadc841256/m1/4/: accessed April 19, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.