PEP-II IR2 LER BPM Button Pulling Mechanism

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PEP-II IR2 LER BPM Button Pulling Mechanism
October 25, 2006 Nadine Kurita, Michael
Kosovsky, and Nick Reeck
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Motivation

• Low Energy Ring (LER) Beam Position Monitor (BPM)
  feedthroughs are experiencing button heating

Button
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Motivation, Contd

• BPM feedthroughs cannot easily be replaced, as
  they are welded into the chambers
• To replace, every chamber would need to be
  removed. Then each feedthrough would need to be
• Ground off the chamber
• Replaced with a new BPM feedthrough
• Electron beam welded into chamber
• Cost and time prohibitive need an alternate
  solution

Weld
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Purpose

• The purpose of the button puller is to remove the
  BPM buttons from the existing vacuum chambers
  without removing the chambers (in situ).
• Remaining 2.4 mm pin functions as new button

CHAMBER
BPM
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Access

• Nearly every BPM chamber has a bellows on at
  least one end of the chamber.
• The bellows can be removed to give chamber access.

BPM Location
Bellows
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Access

• There is approximately 4 (101.6 mm) between the
  chambers available for the mechanism to be
  inserted into the chamber when the bellows is
  removed.

4 Gap
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Assembly Sequence
Borescope
Collet
Handles
Locking Screw
Anchor
Shafts
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How It Works

• The collet is carefully positioned below the
  button
• The borescope is used to guide the collet into
  position

Button
Collet
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How It Works, Contd

• With the collet in position, the cam shaft is
  activated by rotating the cam handle.

Cam Handle
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How It Works, Contd
The cam shaft transforms the rotational motion
into translational motion. The cam shaft
consists of two cams that are lagging 90 deg to
each other. The inner cam operates the Collet
the outer cam operates the Outer Plunger,
PF-343-650-14.
Collet
Cam Shaft
Outer Plunger
Outer Plunger Cam
Collet Cam
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Lab Testing

• Prior to use in the tunnel, we verified operation
  in the lab.
• Worked exactly as intended
• Did not break a single pin in 10 button pulls

Borescope Image
Inserting puller into the chamber
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In the Tunnel

• BPM distance from the end of the chamber varies
  from 3 to 72.
• Alignment with button tricky, often time-consuming

CHAMBER
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Pin Breakage

• On average, one pin in every 4 feedthroughs is
  broken. Fractures may occur due to
• Pre-existing cracks in the pin (brittle fracture)
• Slight misalignment of button puller
• Cold welding of the button to the pin
• In every case, fracture occurs at diameter change
  in pin (the logical fracture site)

Pin Fracture Site
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Progress

• GREEN Completed location
• RED Yet to be pulled
• As of Monday, October 23
• 97 out of 117 buttons pulled (83)
• 26 out of 97 buttons pulled broke the pin (27)

2032
2082
2164
3132
1162
2056
2112
2142
2182
3041
3052
3072
3102
3149
3184
3172
IP
2052
2122
3112
3182
2022
2062
2092
2152
2172
2185
3062
3042
3082
3142
3162
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PEP-II LER Arc BPM Replacement
PEP-II BPM Retrofit Update October 25, 2006 Nick
Reeck Nadine Kurita
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Existing LER Arc BPM Feedthrough
15mm Button
Housing
Ceramic Disc (or Glass)
Pin
SMA Jack
Cross section of existing BPM (SA-342-601-26)
with parts labeled
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Option 1 Pull Button, Leave Pin

• Pull off 15mm button, leave the pin as a 1.4mm
  button

• Pros
• Simple
• Cheap
• Cons
• May lose some resolution, especially in single
  bunch, single pass

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Option 2 Press Fit

• Pull off 15mm button, press on a 7mm button

• Pros
• On Site modification (slight radioactivity a
  concern)
• Good electrical contact
• More robust that old buttons
• Cons
• Button press largely trial and error, have to
  measure buttons and pins to .0001
• Lots of SLAC labor

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New BPM Feedthrough

• Remove old BPM feedthrough, install new BPM
  feedthrough

• Pros
• Better thermal conductivity (Boron Nitride disc)
• Very robust
• Excellent electrical contact
• Less SLAC labor
• Cons
• More expensive

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New BPM Design
Borosilicate Glass
One-Piece Button and Pin
Laser Welds
Boron Nitride Disc
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Photos of New Design
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Electropolishing the Moly

• Purpose Smooth surface cracks to reduce stress
  concentration points
• We wish to reduce or eliminate the failure mode
  seen in IR-2 BPM feedthroughs
• As can be seen in these photos, electropolishing
  is effective

3 Minutes
1 Minute
Before
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Electropolish Fixture

• Made a fixture to hold the parts during
  electropolish (700 parts electropolished to
  date).
• Prevents pins from being electropolished rough
  surface likely helps glass adhesion during firing

Electropolish Fixture
Molybdenum Button / Pins
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Bakeout

• First 44 BPM feedthroughs were placed in a can
  for bakeout
• Vac shop could not get the can to pump down
• XPS Results marginally clean parts, but high
  vapor pressure contaminants
• Magnesium, sodium, calcium, sillicate, carbon
• Add up to 36 atomic percent of surface
  composition
• BPM feedthroughs were cleaned at SLAC
  (degreased), put back in can for bakeout on
  Thursday, October 19
• Still somewhat dirty, having trouble pumping down
• As of Monday, October 23 we do not have RGA data

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Installation Schedule (estimate)
Arc 1 11/3 11/10
Arc 11 12/7 12/14
IP
Arc 9 12/1 12/7
Arc 3 11/10 11/17
Arc 7 11/24 12/1
Arc 5 11/17 11/24
(Assumes 2 crews, 2 weeks to complete each arc)
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Questions?
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Phases of Operation

• Once the collet is in position, there are four
  phases during one shaft handle rotation.
• One complete shaft rotation is necessary to pull
  the button

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Phase 1

• 0-90 degrees The Collet is being inserted into
  the .04 radial gap and engaged with the BPM
  button. The Outer Plunger is dwelling.

Outer Plunger
Collet
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Phase 2

• 90-180 degrees The Collet is dwelling in the
  inserted position. The Outer Plunger is moving
  upward to force the collet fingers tightly around
  the button.

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Phase 3

• 180-225 degrees The Collet, with the engaged
  BPM Button, travels a half stroke (4mm) downward.
  Hence, the BPM button is being removed (pulled
  from the BPM pin). The Outer Plunger is dwelling
  in the upward position, preventing the Collet
  from disengaging from the BPM button.

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Phase 3, contd

• 225-270 degrees The Collet, with the engaged
  BPM Button, travels the rest of the stroke (4mm)
  toward chamber center plane. The Outer Plunger is
  dwelling in the inserted position.

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Phase 4

• 270-360 degrees The Collet, with the removed
  BPM Button, is dwelling in the lower position.
  The Outer Plunger is moving towards the chamber
  center plane to its lower position.

• So, one 360 degree rotation of the shaft handle
  removes one BPM button.

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Disassembly

• The mechanism is then disassembled. The BPM
  button and the mechanism are removed from the
  chamber.

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Mechanical Design (cont.)

• To remove the next BPM Button the cycle is
  repeated.
• The mechanism is rotated 180 degrees about the
  vertical axis to remove the right versus the left
  BPM buttons
• The mechanism is rotated 180 degrees about the
  horizontal axis to remove the top versus the
  bottom BPM buttons.

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BPM Pull Status
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Installation Schedule

• Delivered
• October 11 45 units
• October 20 150 units (195 total)
• To Be Delivered
• October 27 150 units (345 total)
• November 8 150 units (495 total)
• November 15 150 units (645 total)
• November 22 150 units (795 total)
• November 29 105 units (900 total)

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XPS Results