Question 1 — Question 1

During roughing on R1-A, R1-G-CH drops from 950 mbar to 5 mbar in 3 minutes. The operator notes the first 2 minutes brought the pressure to about 1 mbar, while the last minute only brought it from 1 mbar to 5 mbar — wait, that is backward. Looking at the log again: 950 to 1 mbar took about 90 seconds, and 1 to 0.1 mbar took another 5 minutes. What best explains the difference in pump-down speed between these two phases?

• A. The pump is losing efficiency as it heats up during operation
• B. The first phase removes bulk gas in viscous flow where the pump works efficiently; the second phase involves surface gas sources and the transition to molecular flow, both of which reduce pumping effectiveness
• C. The gauge switches to a different measurement mode below 1 mbar
• D. The isolation valve is partially closing as pressure drops

Question 2 — Question 2

R1-G-CH on R1-A reads 0.08 mbar after extended pumping. The pump manufacturer's datasheet states the pump's ultimate pressure is 0.01 mbar. The system is clean and a rate-of-rise test confirms no leak (decreasing rate). What is the most likely reason R1-G-CH cannot reach the pump's rated ultimate pressure?

• A. The Pirani gauge cannot read below 0.08 mbar
• B. The pump is defective and not meeting its specifications
• C. Conductance limitations between the chamber and the pump — the foreline, isolation valve, or other components in the gas path restrict flow, reducing the effective pumping speed at the chamber
• D. The chamber is too large for this pump

Question 3 — Question 3

Which of the following correctly describes the relationship between mean free path and flow regime?

• A. Mean free path increases as pressure increases, leading to viscous flow
• B. Mean free path increases as pressure decreases; when the mean free path exceeds the system dimensions, the flow transitions from viscous to molecular
• C. Mean free path is constant regardless of pressure
• D. Mean free path only matters in high-vacuum systems above 10^-6 mbar

Question 4 — Question 4

On R1-A, the foreline (R1-L-FL) has an internal diameter of 25 mm. A technician suggests that replacing it with a 12 mm diameter tube of the same length would save space. In molecular flow, what approximate impact would this have on the foreline conductance?

• A. Conductance would decrease by about half (proportional to diameter)
• B. Conductance would decrease by about a factor of four (proportional to diameter squared)
• C. Conductance would decrease dramatically — by roughly a factor of nine or more — because in molecular flow, conductance scales approximately with the cube of the diameter
• D. Conductance would not change because molecular flow depends only on pressure

Question 5 — Question 5

R1-A is being roughed from atmospheric. At 10 mbar (R1-G-CH reading), the pump is efficiently pulling gas through R1-L-FL. At 0.05 mbar, the same foreline now appears to limit the pump-down. What has changed about the foreline between these two pressure readings?

• A. The foreline has physically narrowed
• B. The foreline has developed a leak
• C. The flow regime has changed — at 10 mbar the foreline is in viscous flow with high, pressure-dependent conductance; at 0.05 mbar it is in molecular flow where conductance is lower and fixed by geometry alone
• D. The pump has become weaker at lower pressures

Question 6 — Question 6

A technician observes two pump-down curves for R1-A on different days. Day 1: 950 to 0.05 mbar in 8 minutes (normal). Day 2: 950 to 1 mbar in 90 seconds (same as Day 1), but 1 to 0.05 mbar takes 20 minutes instead of the usual 6.5 minutes. What is the most significant difference between Day 1 and Day 2, and what category of cause does it suggest?

• A. The pump has degraded — it took the same time for bulk removal but much longer for fine vacuum
• B. The viscous flow phase is identical (pump and bulk gas removal are normal), but the molecular flow phase is extended — this pattern suggests increased surface gas load (water, contamination) rather than a pump or conductance problem
• C. A conductance bottleneck has developed that only affects low-pressure performance
• D. The gauge is behaving differently on Day 2

Question 7 — Question 7

In a thin-film coating system based on R1-A architecture, the chamber must reach 0.001 mbar before the coating process can begin. The system consistently stalls at 0.05 mbar. An engineer measures the pump's ultimate pressure directly at the pump inlet (with no foreline or valve attached) and finds it reaches 0.0005 mbar. What does this comparison tell you?

• A. The pump is defective because it should reach the same pressure when connected to the chamber
• B. The pump is performing to specification — the factor-of-100 gap between the pump's capability (0.0005 mbar) and the chamber pressure (0.05 mbar) confirms a severe conductance limitation in the path between pump and chamber
• C. The gauge on the chamber is miscalibrated
• D. The thin-film coating process is incompatible with this pump

Question 8 — Question 8

On R1-A, the pump-down from 950 mbar is observed. R1-G-CH drops to 500 mbar in 15 seconds, to 100 mbar in 30 seconds, to 10 mbar in 60 seconds, and to 1 mbar in 90 seconds. Between 950 and 1 mbar, what flow regime dominates and why is the pump-down so rapid?

• A. Molecular flow — molecules move faster at high pressure
• B. Viscous flow — gas molecules collide frequently and flow collectively toward the pump, allowing efficient bulk gas removal driven by the large pressure differential
• C. Transition flow — the system is between viscous and molecular
• D. Turbulent flow — the high gas velocity causes turbulence

Question 9 — Question 9

R1-A is at 0.05 mbar after a normal pump-down. The operator isolates the system (R1-V-ISO closed) and records: 1 min → 0.07 mbar, 3 min → 0.09 mbar, 5 min → 0.10 mbar, 10 min → 0.11 mbar. The rate of rise is decreasing. However, the operator also notes that the normal base pressure for this system is 0.05 mbar and the rate-of-rise values are typical. Considering Module 3 concepts, why does the rate of rise slow down over the 10-minute test?

• A. A leak is gradually sealing itself
• B. The gauge loses sensitivity as pressure rises
• C. Outgassing is a diffusion-limited process — surface molecules desorb quickly, but deeper molecules take longer to reach the surface, so the gas release rate decreases over time; additionally, as chamber pressure rises, the driving force for desorption decreases
• D. The isolation valve is not fully closed

Question 10 — Question 10

A vacuum system has the following components in series between the chamber and the pump: a 40 mm bore isolation valve, a 25 mm diameter foreline (1 metre long), and the pump inlet (40 mm diameter). In molecular flow, which component most likely limits the overall conductance of the path?

• A. The pump inlet, because it is the last component
• B. The isolation valve, because valves always have the lowest conductance
• C. The 25 mm diameter, 1 metre long foreline — its combination of narrow diameter and long length gives it the lowest conductance of the three components
• D. All three components contribute equally

Question 11 — Question 11

During a discussion about R1-A performance, a colleague states: "We should upgrade to a bigger pump — the current pump is too small to reach the pressures we need for thin-film coating trials." R1-G-CH stalls at 0.08 mbar; the pump specification says it should reach 0.01 mbar. What is the most technically accurate response?

• A. Agree — a bigger pump is always the best solution for lower base pressure
• B. Before upgrading the pump, verify whether the current pump reaches its rated 0.01 mbar at its own inlet; if it does, the gap is a conductance limitation, and a bigger pump will not solve the problem without also addressing the foreline and valve restrictions
• C. Disagree — pumps have no effect on base pressure
• D. The pump size is irrelevant because the gauge cannot read below 0.08 mbar

Question 12 — Question 12

On the R1-A pump-down curve, the pressure region from approximately 1 to 0.01 mbar is sometimes called the "transition region." What is transitioning in this range?

• A. The pump is transitioning from one speed to another
• B. The gauge is transitioning between measurement modes
• C. The gas flow regime is transitioning from viscous flow (molecule-molecule collisions dominate) to molecular flow (molecule-wall collisions dominate)
• D. The chamber material is transitioning from one thermal state to another

Question 13 — Question 13

An R1-A operator records two pump-down attempts. Attempt 1: reaches 0.05 mbar in 8 minutes (normal). Attempt 2 (one hour later, same conditions): reaches 0.05 mbar in 7 minutes. What does the improvement in Attempt 2 most likely indicate?

• A. The pump has warmed up and is more efficient
• B. The first pump-down removed surface water and gas; the second pump-down encounters less surface gas load because there was insufficient time at atmosphere for full re-adsorption between attempts
• C. The atmospheric pressure changed
• D. A leak sealed itself between attempts

Question 14 — Question 14

In a thin-film coating production environment, the chamber must cycle between atmospheric pressure (for loading substrates) and 0.005 mbar (for coating) multiple times per shift. From a flow-regime perspective, why is the design of the foreline and pumping path critical in this application?

• A. The foreline must be long to allow the gas to cool before reaching the pump
• B. Each cycle requires transitioning through viscous, transition, and molecular flow regimes; the foreline must have sufficient conductance in the molecular flow regime to allow rapid achievement of the low base pressure — a bottleneck that barely matters during rough pumping becomes the dominant limitation at coating pressures
• C. The flow regime does not matter in production environments
• D. The foreline only matters during venting, not during pump-down

Question 15 — Question 15

An operator notices that R1-A takes significantly longer to pump from 0.5 mbar to 0.05 mbar than it did three months ago. The pump-down from 950 to 1 mbar is unchanged. No contamination or leak is found. The pump meets its ultimate pressure specification when tested independently. What should be investigated?

• A. The chamber has developed micro-porosity
• B. A conductance degradation in the path between chamber and pump — possible causes include a partially obstructed foreline (debris, corrosion, constriction), a valve that no longer opens fully, or a fitting that has been replaced with a smaller bore component
• C. The pump needs a larger motor
• D. The atmospheric pressure at Selkirk has changed

Question 16 — Question 16

On R1-A, R1-V-ISO is an angle valve connecting the chamber to the foreline. If the valve were replaced with a valve that has a 50% smaller bore (internal passage), what would be the primary effect on pump-down performance?

• A. No effect — the pump determines the pump-down speed
• B. Pump-down would be slower at all pressures equally
• C. Pump-down would be significantly slower at low pressures (molecular flow) where the reduced bore severely limits conductance, but relatively unchanged at high pressures (viscous flow) where conductance is less sensitive to the restriction
• D. The pump-down would be faster because the smaller valve creates a higher velocity gas jet

Question 17 — Question 17

A student writes the following in their diagnostic report: "The pump-down is slow. Possible causes include: a small foreline, a restricted valve, dirty chamber surfaces, a weak pump, and a leak. All five are equally likely." Using Module 3 diagnostic principles, what is the primary weakness of this analysis?

• A. This is excellent — comprehensive and thorough
• B. This is adequate — it covers all possibilities
• C. This is weak — it fails to rank the hypotheses or identify a leading bottleneck based on evidence; effective diagnosis names one most likely cause supported by the specific observations (where the pump-down stalls, whether the pump meets spec independently) rather than listing five equal possibilities
• D. This is wrong because there are actually ten possible causes

Question 18 — Question 18

R1-A is pumping down. At 0.5 mbar, the operator notes that R1-G-CH is still dropping but very slowly. They record: 0 min → 0.50 mbar, 5 min → 0.30 mbar, 10 min → 0.18 mbar, 15 min → 0.12 mbar, 20 min → 0.09 mbar. Is this pump-down progressing normally, and what flow regime characterises this pressure range?

• A. Abnormal — pressure should drop linearly over time; this is molecular flow
• B. Normal — the decreasing rate of pressure drop is expected as surface gas load diminishes and the system is in or approaching molecular flow where pumping is less efficient; the system is progressing toward base pressure
• C. Abnormal — the pressure should have reached 0.05 mbar by 10 minutes
• D. Normal — this is viscous flow and the pump is working at maximum efficiency

Question 19 — Question 19

In the context of R1-A, explain why a foreline bend (elbow fitting) reduces conductance more in molecular flow than in viscous flow.

• A. Bends create turbulence that only exists in molecular flow
• B. In viscous flow, the gas flows collectively and can navigate bends with moderate loss; in molecular flow, molecules travel in straight lines between wall collisions — a bend forces additional wall collisions that randomise direction, and some molecules bounce back the way they came, significantly reducing net throughput
• C. Bends do not affect conductance in either flow regime
• D. Bends only matter in the transition regime

Question 20 — Question 20

R1-A is being evaluated for use in a thin-film coating trial. The current system reaches a base pressure of 0.06 mbar. The coating process requires 0.005 mbar. The system data shows: the pump's rated ultimate is 0.005 mbar (measured at the pump inlet); the foreline (R1-L-FL) is 25 mm diameter and 1.5 metres long with two 90-degree bends; R1-V-ISO has a 20 mm bore. Based on Module 3 principles, what does this evidence identify as the primary factor preventing the system from reaching the required base pressure?

• A. The pump lacks sufficient capacity and needs replacement
• B. Adding a second pump in parallel would resolve the gap
• C. The conductance bottleneck is the primary factor — the narrow, long foreline with bends and the undersized valve bore are severely limiting effective pumping speed at the chamber in molecular flow; the pump already meets the target pressure at its own inlet, so the gas path geometry is the limiting element
• D. The system cannot be used for thin-film coating under any circumstances

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