Transcript 27} FETS Meeting 9March11 RFQ Flattening Groove

Engineering Solution to
Modulation-Induced Field Tilt
• Modulations affect field flatness of RFQ
• Moving from one end of RFQ to the other:
Modulation Depth UP  Capacitance DOWN  Frequency UP  Voltage DOWN
• Can counteract this by varying bulk inductance
• Can do this by changing quadrant radius, but this
affects how you join sections together
• Equivalent, preferred method: cut grooves in walls
• Now, all sections have same quadrant radius, but
each section has its own groove depth
• This makes all sections have same frequency,
despite modulations, so flattens field in full 4m
Frequency of Cells When Cavity
Sections Have Different Quadrant Radii
Simplified 4m Test Model Replicating
Effects of Modulations on Voltage
Simplified 4m Model
Ideas 1
Using the same
smaller radius of
44.1 throughout and
using a radius to
increase the internal
volume.
Advantage:
Would allow use of
large custom cutter
for bulk of profile.
Disadvantage:
How to join new
radius to large radius
without introducing
sharp corners.
Disadvantage with
this design is need
for many passes of
ball nose cutter
An alternative
is.........
Best design by far
from a machining
point of view.
Still needs ball nose
to make profile but
flat can be made
more conventionally.
Scott’s calcs should
still hold true.
BUT now we have
introduced an
asymmetry which
bring the dipole
modes closer?
Ideas 2
Bottom of flat cut-out
is perfectly flush with
bottom of already-cut
circle.
0mm
Only corners of flat
need cutting in.
Bottom of flat is
definitely cut in by a
small amount.
3mm
Narrow flat, cut quite
deep.
6mm
If square cut used, linear change in
frequency with cut depth
Easier to use ball-ended cutter
Large version
Using diam 25 ball nose cutter
Cutter
Small version
Using same diam 25 ball nose cutter
Ideas 3
Section 1 & 2 (first 50cm) have 44.1mm
quadrant radius with no cut
Ball cut depth = 2.55mm normally
into wall for Section 2 (last 50cm)
‘Depth’ defined as
normal cut into wall
Ball cut depth = 4.1mm normally
into wall for Sections 3 & 4
‘Depth’ defined as
normal cut into wall
Modulations with Cavity Frequency
Corrected Using Grooves in Wall
Cell 220 (in last 50cm of Section 2)
Uncorrected Frequency = 324.121 MHz
Corrected Frequency = 323.276 MHz
Cell 307 (in Section 4)
Uncorrected Frequency = 324.664 MHz
Corrected Frequency = 323.111 MHz
Non-linear change in area of circular cut
makes non-linear frequency dependence
Question from Pete: “Ahhhh.... But machining here affects the relative ‘sticky-out-ness’ of
the tuners! Is this a problem?”
NO! We’ll deal with it. If these cuts into the wall make the field 70% flatter than if no
cuts were made, then the tuners won’t be needed as much anyway.
Sections 1 & 2 (first 50cm) need no groove cut into wall.
Section 2 (last 50cm) needs a 2.55mm deep groove cut into wall.
Sections 3 & 4 need a 4.1mm deep groove cut into wall.
Looking from high energy end........
Looking from section 2 to 1........
Small step at junction of section 2 to 3........
Keep cutback same distance
from cooling pocket
COOLING
CHANNEL