Vacuum-Vacuum Pump-Lecture Slides, Slides of Hydraulic Structures and Machines

Download Vacuum-Vacuum Pump-Lecture Slides and more Slides Hydraulic Structures and Machines in PDF only on Docsity!

Vacuum Basics & PumpsVacuum Basics & Pumps

Liu, UCD Phy250-1 NanoFab

2

I. VacuumI. Vacuum

1 atm= 760 torr = 1.0132 bar = 1.013x

Pa = 14.7 psi^5

Rough Vacuum (RV)

1 torr – 760 torr

Medium Vacuum (MV)

(^10) - torr – 1 torr

High Vacuum (HV)

(^10) - torr – 10 (^) torr-

Ultrahigh Vacuum (UHV)

<10 - torr^

Liu, UCD Phy250-1 NanoFab

4

Vacuum CircuitVacuum Circuit

Vacuum conductance:

C (^) (liter/sec)

Vacuum impedance:

Z

Gas flow (Throughput):

Q=(P

1 2 -P

)C

In series: Analogous to electrical conductance

In parallel:

i^ ∑^ = ∑= i

total i i

total C

C Z

Z 1

1

i^ ∑^ = ∑= i

total ii^

total C

C Z

Z 1

1

Liu, UCD Phy250-1 NanoFab

5

Conductance of a Straight TubeConductance of a Straight Tube

2

128

2

L (^1) PP (^4) D

C

≈ η π

Molecular flow^ Viscous flow

L D

M Tk

C B 3

(^621) π ≈

air @ RT

)( )](

(^10) [

sec)/

(

cm 4 L cmD

literC^ ≈

air @ RT

)( )](

(^10) [

sec)/

(

cm 3 L cmD

literC^ ≈

Maximize (^) D , minimize

(^) L , avoid bending

Liu, UCD Phy250-1 NanoFab

7

Contamination &Contamination & Outgassing

Outgassing

Black list of high vapor pressure elements: Mg, Yb, Li, Sr, Sb, Ca, Bi, BaBr, I, Hg, S, Cs, Rb, K, P, Se, Cd, Na, As, Zn, Te,

Outgassing Dry NBakeoutChoice of materials (^2) venting

Electron / plasma bombardment of chamber inner surfaceCoating of getter material (Ti, Nb…)

Liu, UCD Phy250-1 NanoFab

8

Clean Surface LifetimeClean Surface Lifetime

Surface impact rate

sec

/

0 )

( 2

2 cm^21

torrP ×× BTmk P

≈ ≈ π

Surface with 1 monolayer of gas Assuming a sticking coefficient of 1, time to cover a clean

)

( 104 torr 6 P × − ≈

P= 10

torr, lifetime-^

(^) ~ 4 sec

torr,^

~ 6 min

torr,^

~ 11 hr

Liu, UCD Phy250-1 NanoFab

10

IIA. Roughing: Rotary Vane PumpIIA. Roughing: Rotary Vane Pump

(Gas Transfer)(Gas Transfer)

(^10) -2 Single-stage torr^

(^10) -3 Dual-stage torr^

Foreline trap: copper gauze, molecular sieve, LNOil: lubricant, coolant, sealant, contamination Speed: 1-100 cfm

2

Venting;

Exhaust;

Vibration

Liu, UCD Phy250-1 NanoFab

11

Roughing: Sorption PumpRoughing: Sorption Pump

(Gas Capture)(Gas Capture)

- 10^

torr-^

Drawback:Oil free, no moving parts Gas selective- difficulty w/ inert gasesNeed regeneration

Liu, UCD Phy250-1 NanoFab

13

Roughing: Rotary Lobe PumpRoughing: Rotary Lobe Pump

(Gas Transfer)(Gas Transfer)

(^10) -4 Gas transfer Roots torr when backed^

Handle high gas loads

Liu, UCD Phy250-1 NanoFab

14

10 -2 Gas transfer Scroll Roughing: Other Dry PumpsRoughing: Other Dry Pumps

torr

12-25 cfm

(^10) -3 Gas transfer Screw torr^

May handle aggressive gases30-320 cfm

Liu, UCD Phy250-1 NanoFab

16

High Vacuum:High Vacuum: Turbomolecular

Turbomolecular Pump

Pump

(Gas Transfer)(Gas Transfer)

-^

torr-^

Gas selective: difficulty w/ HCrossover P: ~ 1000 mtorr50 L/s - 3500 L/s

(^2) , He

Easy w/hydrocarbon

BearingsOften verticalHigh speed, screen Magnetically levitatedCeramic

Liu, UCD Phy250-1 NanoFab

17

High Vacuum:High Vacuum: Cryo

Cryo Pump

Pump

(Gas Capture)(Gas Capture)

(^10) -9 Closed-cycle He cryocompressor Cryo-condensation + cryo-sorption torr or better^

Regeneration & replacementGas selective: difficulty w/ HeCrossover P: ~ 200 mtorrNo backing neededAny orientation

Liu, UCD Phy250-1 NanoFab

19

Chemical reaction w/ Ti (getter) + burial (ion implantation) Reactive gases

All gases

torr^

Low throughputGas selective: difficulty w/ inert gasPermanent magnet: ionization; heavyClean, bakeable, vibration-freeAny orientationCross over P: ~<1mtorr

Liu, UCD Phy250-1 NanoFab

20

HV Pump ComparisonHV Pump Comparison