S1 Entry Ticket: Pre-Synchronous Session Diagnostic (Capstone)

Scenario: "The Week After Maintenance"

R1-A was taken out of service last week for a comprehensive maintenance session. The following work was performed:

1. R1-P-RP oil was changed (pump oil had been in service for 8 months)
2. The foreline (R1-L-FL) was replaced because the original tubing had developed a dent. The replacement tubing was sourced from workshop stock: 16 mm internal diameter, 1.0 m long, with one 90-degree bend. The original foreline was 25 mm internal diameter, 0.6 m long, and straight.
3. The chamber flange O-ring was replaced with a new Viton O-ring from sealed stock
4. R1-FLT-EXH was replaced with a new filter element
5. The chamber interior was wiped down with isopropanol cleaning solvent

After maintenance, the system was reassembled and returned to service on Monday morning. The first pump-down produces the following data:

Pump-down data:

Rate-of-rise test (isolated at 0.20 mbar, R1-V-ISO closed, R1-V-VENT closed, pump off):

Additional evidence:

• R1-G-BX reads 949 mbar (normal atmospheric variation)
• R1-P-RP sounds normal, oil sight glass shows clean fresh oil at the correct level
• R1-FLT-EXH exhaust is clean — no visible oil mist
• R1-P-RP tested independently at its own inlet: reaches 0.008 mbar in 4 minutes (within specification)
• The new chamber O-ring appears correctly seated in its groove
• The isopropanol cleaning was performed with the chamber open and the solvent was allowed to "air dry" for approximately 10 minutes before the chamber was closed

Entry Question 1: Phase Analysis (M03 Integration)

Compare the viscous flow phase to the molecular flow phase. Is only one phase affected, or are both? What does this comparison tell you about the location and nature of the problem?

Your answer:

Entry Question 2: Rate-of-Rise Interpretation (M02 Integration)

Examine the rate-of-rise values in the table above. Is the rate constant or decreasing over time? What type of gas source does this pattern indicate — a leak or outgassing?

Given the maintenance activities performed, identify at least two specific sources that could produce this gas load pattern.

Your answer:

Entry Question 3: Pump Assessment (M06)

The pump reaches 0.008 mbar independently. The system stalls at 0.20 mbar.

What does this 25-fold gap between pump capability and system performance tell you? Is the pump a contributing factor to the problem?

Your answer:

Entry Question 4: Foreline Analysis (M03 Integration)

The replacement foreline (16 mm bore, 1.0 m, one bend) replaced the original (25 mm bore, 0.6 m, straight). Without calculations, describe the effect of each change (diameter, length, bend) on conductance, and explain which flow regime is most affected. Could this foreline change alone explain the full performance degradation?

Your answer:

Entry Question 5: Multi-Factor Diagnosis

This scenario likely has more than one contributing factor. Based on all the evidence, rank the following hypotheses and explain your reasoning:

• Hypothesis A: Foreline conductance reduction from the replacement tubing
• Hypothesis B: Solvent residue outgassing from the isopropanol cleaning
• Hypothesis C: New O-ring outgassing (fresh elastomer off-gassing)
• Hypothesis D: Pump failure

For each hypothesis, state whether the evidence supports, contradicts, or is neutral. Identify at least one discriminating test for each.

Your answer:

Entry Question 6: Capstone Escalation Note

Write a 3-sentence escalation note for the maintenance supervisor: (1) what was observed, (2) what the evidence indicates (including what has been ruled out and what contributing factors remain), and (3) what additional information would help clarify the situation (include at least 3 UNKNOWN items that require further evidence to resolve).

Your answer:

S2 Worked Example: Entry Ticket Model Answer

Entry Question 1 — Model Answer

Both phases are affected, but to different degrees. The viscous flow phase is slightly slower than reference (1.2 mbar at 1.5 min vs the expected 1.0 mbar at 1.5 min) — this suggests a modest conductance reduction that affects even the high-pressure phase, consistent with the narrower replacement foreline. The molecular flow phase is severely degraded (stalled at 0.20 mbar vs the normal 0.05 mbar at 8 minutes).

The fact that both phases are affected points to a conductance issue (the foreline) that impacts all pressures. But the disproportionate impact on the molecular flow phase tells us there is an additional factor: in molecular flow, conductance depends on geometry alone (M03) and scales with the cube of diameter, making the narrower foreline far more restrictive.

Additionally, the molecular flow phase is where surface gas load dominates — and the cleaning solvent and new O-ring introduce extra gas load that the already-restricted foreline cannot remove efficiently. Multiple factors are likely compounding.

Entry Question 2 — Model Answer

The rate-of-rise values provided in the data table show a clearly decreasing pattern: 0.080, 0.060, 0.040, 0.024 mbar/min over the 10-minute observation. This is the outgassing (depleting source) pattern — not a constant-rate leak.

Given the maintenance activities, two specific gas load sources that could produce this pattern:

1. Isopropanol solvent residue: The chamber was wiped with isopropanol and allowed only 10 minutes to "air dry." Isopropanol evaporates quickly at atmospheric pressure but can be absorbed into surface micro-porosity on stainless steel and into the new O-ring elastomer. Under vacuum, this trapped solvent outgasses as a significant gas load — particularly heavy initially (high vapour pressure), depleting over hours as the solvent inventory is exhausted.

1. New Viton O-ring outgassing: Fresh elastomer O-rings contain absorbed atmospheric gases, moisture, and residual manufacturing compounds. A new O-ring outgasses more heavily than a conditioned one — the outgassing rate decreases as the ring is exposed to repeated pump-down cycles. This contributes a moderate, slowly depleting gas load.

Both sources are consistent with the decreasing rate-of-rise pattern and the maintenance history.

Entry Question 3 — Model Answer

The pump reaches 0.008 mbar at its own inlet — well within its rated specification. The system stalls at 0.20 mbar — 25 times higher.

This gap proves definitively that the pump is NOT the problem. The pump has ample capability that is not reaching the chamber.

The gap is attributable to two factors: (1) the replacement foreline's reduced conductance limits how much of the pump's speed is delivered to the chamber (M03 effective pumping speed), and (2) the elevated gas load from solvent residue and O-ring outgassing adds gas that the already-restricted effective pumping must overcome. The pump is healthy — the bottleneck is between the pump and the chamber.

Entry Question 4 — Model Answer

Diameter reduction (25 mm to 16 mm): In molecular flow, conductance scales approximately with the cube of the diameter. The 36% reduction in diameter (25 to 16 mm) reduces molecular flow conductance dramatically — a rough estimate suggests approximately 75% reduction from diameter alone. In viscous flow, the effect is present but less severe because viscous flow conductance also depends on pressure (higher pressure means higher conductance), partially offsetting the geometric restriction.

Length increase (0.6 m to 1.0 m): Conductance decreases inversely with length. The 67% increase in length reduces conductance by approximately 40% (independent of the diameter effect). Longer tubes mean more wall collisions for molecules, randomising their direction and increasing the fraction that bounce back toward the chamber.

Added bend (one 90-degree elbow): Each bend forces molecules to collide with the elbow wall, further randomising their direction. In molecular flow, where there is no bulk gas stream to carry molecules around corners, bends are particularly costly. The bend adds an effective length increase and a directional randomisation penalty.

Most affected regime: Molecular flow is most affected because conductance in molecular flow depends entirely on geometry. In viscous flow, the pressure-dependent component of conductance partially compensates for geometric restrictions.

Could the foreline alone explain the full degradation? Partially, but probably not entirely. The foreline reduction explains the slow molecular flow phase and the modest viscous phase delay. But the rate-of-rise test shows a high initial outgassing rate (0.080 mbar/min) that is above what geometry alone would produce — the solvent and O-ring gas loads are additional contributing factors.

If the foreline were the only problem, the rate-of-rise would be lower (the chamber's normal outgassing would be the only source). The elevated rate-of-rise points to additional gas load on top of the conductance restriction.

Entry Question 5 — Model Answer

Multi-factor conclusion: The most likely diagnosis is a combination of Hypotheses A and B as the dominant factors, with C as a minor contributor. The foreline conductance restriction limits how fast gas can be removed (a permanent geometry problem that will not improve with time). The solvent residue adds a large but temporary gas load.

Together, they compound: the restricted foreline cannot remove the elevated gas load efficiently, producing the stall at 0.20 mbar. As the solvent depletes over multiple cycles, performance will partially improve — but the conductance restriction will prevent full recovery until the foreline is replaced.

Entry Question 6 — Model Answer

"R1-A is stalling at 0.20 mbar following last week's maintenance (normal base: 0.05 mbar in 8 minutes); both viscous and molecular flow phases are slower than reference, R1-P-RP reaches 0.008 mbar independently (pump eliminated as a cause), and a rate-of-rise test shows a high but decreasing rate (0.080 to 0.024 mbar/min). The evidence indicates two contributing factors — the replacement foreline (16 mm bore, 1.0 m, one bend vs original 25 mm bore, 0.6 m, straight) has severely reduced molecular flow conductance, and solvent residue from the isopropanol cleaning (only 10 minutes air-dry time) is producing elevated outgassing — while pump failure and a true leak are eliminated by the independent pump test and the decreasing rate-of-rise pattern respectively. UNKNOWN: (1) whether original-specification foreline tubing is available in maintenance stock, (2) whether the solvent residue is confined to the chamber surfaces or has also been absorbed into the new O-ring elastomer (repeated cycling would reveal this), and (3) whether any other connections were disturbed during maintenance that might contribute a small additional leak masked by the outgassing — a follow-up rate-of-rise test after the solvent depletes would reveal any constant-rate component."

S3 Worked Example: Situation Report

Scenario Context (Facilitator-Provided During Synchronous Session)

R1-A has been returned to service after the foreline was restored to original specification. The solvent residue has been depleted through five pump-down cycles over two days. The system is now on its sixth pump-down.

R1-G-CH reads 0.07 mbar at 10 minutes into the pump-down and is still dropping slowly. The operator is uncertain whether the system is recovering as expected or whether a residual problem remains.

Model Situation Report

System: R1-A State: ROUGHING (R1-V-ISO open, R1-V-VENT closed, R1-P-RP running) Time: 14:20

Observation: R1-G-CH reads 0.07 mbar at 10 minutes into pump-down. R1-G-BX reads 949 mbar. Viscous flow phase completed in approximately 90 seconds (normal).

The pump-down below 1 mbar is slower than the historical 8-minute reference but significantly improved from the 30-minute stall at 0.20 mbar seen before the foreline replacement.

R1-P-RP sounds normal. R1-FLT-EXH exhaust is clean.

Oil sight glass shows clear amber oil at the correct level. No unusual odour.

Interpretation: The system is in the molecular flow regime at 0.07 mbar. The restored foreline (original 25 mm bore, 0.6 m, straight) has recovered most of the conductance that was lost. The remaining 0.02 mbar above normal base (0.07 vs 0.05 mbar) is consistent with the new O-ring still conditioning — fresh Viton outgasses slightly more than a conditioned ring.

Over the next several days of daily pump-down cycling, this should decrease toward normal. The five prior pump-down cycles appear to have depleted the bulk of the solvent residue (the system no longer stalls and the rate of approach to base pressure is close to normal).

Comparison to expected: Logbook reference: 0.05 mbar at 8 minutes. Today: 0.07 mbar at 10 minutes.

The system is approximately 85% recovered. The remaining gap is small and consistent with O-ring conditioning — not a new problem.

Unknowns — Evidence Needed:

1. UNKNOWN: Will the system reach 0.05 mbar if given additional pump-down time? Continued monitoring over the next 10 minutes would clarify this.
2. UNKNOWN: Is the rate of pressure decrease still declining (approaching base pressure), or has it levelled off (approaching a stall)? R1-G-CH readings at 2-minute intervals would distinguish between these two patterns.
3. UNKNOWN: Has the new O-ring's outgassing rate decreased compared to the first pump-down cycle two days ago? A comparison of today's molecular flow pump-down rate to the Day 1 post-foreline-replacement data would indicate whether conditioning is progressing.
4. UNKNOWN: If the system does not reach 0.05 mbar within 20 minutes, a rate-of-rise test would help check for any constant-rate component that might indicate a small leak masked by the earlier outgassing.

Escalation: "R1-A roughing in progress — sixth pump-down since foreline restoration. Currently at 0.07 mbar at 10 minutes, compared to the post-maintenance stall at 0.20 mbar. System is recovering as expected.

Slightly above the historical 0.05 mbar base — consistent with new O-ring conditioning. Monitoring to confirm base pressure recovery. If the system stalls above 0.06 mbar after 20 minutes, further investigation would be warranted."

S4 Worked Example: Evidence Brief

Scenario Context

Following the full investigation of R1-A's post-maintenance performance problem, all evidence has been collected and corrective actions have been taken. This evidence brief documents the complete investigation for the maintenance record.

Model Evidence Brief

System: R1-A State during investigation: ROUGHING (stalled at 0.20 mbar), then ISOLATED (rate-of-rise test) Investigation: Post-maintenance performance assessment — capstone multi-factor diagnosis

State Call: Initially ROUGHING — R1-V-ISO open, R1-V-VENT closed, R1-P-RP running. Then ISOLATED for rate-of-rise. Confirmed by valve positions and gauge readings.

Observed Evidence:

• Viscous flow phase slightly slow (1.2 mbar at 1.5 min vs normal 1.0 mbar) — both phases affected
• Molecular flow phase severely degraded — stalled at 0.20 mbar vs expected 0.05 mbar
• Rate-of-rise: decreasing (0.080 to 0.024 mbar/min) — outgassing pattern, not a leak
• Pump independent test: 0.008 mbar — pump within specification
• Foreline geometry changed: bore reduced from 25 to 16 mm, length increased from 0.6 to 1.0 m, one bend added
• Chamber cleaned with isopropanol, air-dried 10 minutes — potential solvent residue source
• New Viton O-ring installed — potential minor outgassing source
• R1-FLT-EXH replaced — clean exhaust, no visible oil mist
• Fresh pump oil — correct level, clear

Plausibility Check: The pump reaches 0.008 mbar independently, confirming the pump is not the problem. The 25-fold gap between pump capability (0.008 mbar) and system performance (0.20 mbar) with no leak detected (decreasing rate-of-rise) points to two compounding factors: reduced conductance (the foreline) and elevated gas load (solvent residue). The viscous flow phase delay is consistent with a conductance restriction that affects all pressures, while the molecular flow phase is disproportionately affected (cube-of-diameter dependence in molecular flow + additional gas load).

Hypotheses (ranked):

Resolution:

1. Foreline replaced with original specification (25 mm bore, 0.6 m, straight) — conductance restored
2. Five pump-down cycles performed over two days — solvent residue depleted
3. System now reaching 0.07 mbar at 10 minutes (sixth cycle) — recovering toward normal
4. Expected full recovery to 0.05 mbar within several additional days as O-ring conditions

UNKNOWN — Evidence Needed:

1. Whether the system will reach exactly 0.05 mbar or settle at a slightly elevated base — continued monitoring will confirm
2. Whether the dented original foreline can be repaired or must be permanently replaced — investigate stock of 25 mm tubing
3. Whether the 10-minute solvent air-dry procedure is sufficient or whether a longer drying time (or vacuum-assisted drying) would have prevented the elevated outgassing — this question remains open pending further evidence from the current recovery cycle

Escalation Note: "Post-maintenance investigation on R1-A complete.

Two primary causes identified: (1) replacement foreline with degraded geometry (16 mm bore, 1.0 m, one bend) caused a severe conductance bottleneck, and (2) insufficient solvent drying after isopropanol cleaning produced elevated outgassing. Pump verified healthy. No leak found.

Corrective actions taken: foreline restored to original specification, solvent depleted through repeated pump-down cycles. System is recovering — currently at 0.07 mbar (sixth cycle), expected to return to 0.05 mbar as the new O-ring conditions. It remains to be confirmed whether the maintenance SOP adequately specifies original foreline dimensions and minimum solvent drying time."

S5 Worked Example: Sector Lens Output

Scenario Context

Using the capstone multi-factor scenario, the student applies the thin-film coating sector lens. This is the final sector lens of the course, integrating all six modules.

Model Sector Lens Output

Base scenario: R1-A post-maintenance performance degradation — conductance bottleneck from replacement foreline compounded by solvent residue outgassing, stalling at 0.20 mbar (normal: 0.05 mbar).

Sector: Thin-Film Coating

Sector Lens Application:

In a thin-film coating production environment, this multi-factor failure would have cascading consequences:

• Process impact: Thin-film coating requires base pressures typically between 10^-3 and 10^-6 mbar before process gas introduction. A system stalling at 0.20 mbar is 200 to 200,000 times above the required base pressure. No coating process could proceed. More critically, the solvent residue outgassing introduces hydrocarbon contamination — volatile organic compounds that would co-deposit with the coating material, producing defective films with poor adhesion, optical haze, and compositional impurities. Even if the pressure were somehow acceptable, the contamination would not be.

• Root cause analysis discipline: In a coating facility, the two errors that caused this failure — substituting a non-specification foreline and insufficient solvent drying — would be treated as non-conformances requiring formal corrective action reports. Maintenance procedures in coating environments specify exact component dimensions, materials, and process steps precisely to prevent this class of problem. "Close enough" tubing and "it looked dry" solvent procedures are unacceptable in precision manufacturing.

• Pump-down cycle time: In a production coating tool running multiple cycles per shift, the conductance restriction would extend every pump-down cycle. Even partial recovery through solvent depletion leaves a permanently slower molecular flow phase until the foreline is corrected. Over a production week, the cumulative throughput loss from extended pump-downs could represent significant lost production value.

• Contamination carryover: The solvent residue does not just affect one pump-down cycle. In a coating tool, the volatile organics co-deposit with coating material on both the substrate and the chamber walls. Subsequent pump-downs release this contamination from the chamber walls, creating a carryover effect that persists for many cycles. In semiconductor fabrication, a chamber contaminated with organic residue may require a full cleaning and reconditioning procedure (potentially including bake-out) before it can be returned to production — a process that can take days.

• Multi-factor awareness: This scenario demonstrates a critical lesson for coating facility technicians: system problems are often multi-factor. The foreline conductance and the solvent residue contributed simultaneously. A technician who fixes only the foreline would see partial improvement and might declare the problem solved — missing the solvent contribution. A technician who only waits for the solvent to deplete would see improvement but never reach normal base pressure — because the conductance restriction is permanent. Comprehensive diagnosis requires identifying ALL contributing factors, not just the most obvious one.

Sector-Specific Escalation: "Post-maintenance investigation on R1-A identified two simultaneous failure modes with direct relevance to thin-film coating quality: (1) replacement foreline with non-specification geometry caused a conductance bottleneck preventing adequate base pressure, and (2) insufficient solvent drying introduced hydrocarbon outgassing into the chamber environment. In a coating application, either factor alone would be sufficient to produce defective films. Together, they would halt production entirely.

Corrective actions implemented: foreline restored to specification, solvent residue depleted. Questions that remain open: (a) whether the maintenance SOP adequately specifies exact component dimensions with sign-off requirements, (b) whether current solvent cleaning procedures specify sufficient drying time or a vacuum-assisted drying protocol, and (c) whether a pre-production qualification pump-down (with rate-of-rise verification) is specified after any maintenance that opens the chamber or replaces gas-path components."

S6 Reading List

Use these references to deepen your understanding of the concepts covered in Module 6. They are organised by topic and include section references for quick navigation.

How to Use This List:

• Start with Milne, Chapters 4-5 for a narrative introduction to pump types and operating principles — this maps directly to Lessons 2 and 3
• Read Varian, Chapters 6-8 for the most practical treatment of pump performance, oil management, and system-level pump integration — this is the most directly relevant resource for Module 6
• Reference Pfeiffer, Sections 3.1-3.5 for detailed pump specifications and turbo pump principles — useful for understanding the numbers behind pump performance
• Browse the KJLC/ORNL deck, slides 200-280 for visual reinforcement of pump mechanisms and system integration concepts

KJLC/ORNL Deck — Slide Guide for Module 6:

End of Assessment Content — Module 6