Vacuum System (Synchrotron Light Source)

Vacuum System(Synchrotron Light Source)

J. R. ChenSynchrotron Radiation Research Center

Hsinchu 30076, Taiwan

The Fourth OCPA Accelerator School, Aug. 2, 2006

Vacuum SystemI. Introduction (Vacuum and Pressure Units)II. Considerations on Accelerator Vacuum

SystemIII. Vacuum System Design ConsiderationsIV. Outgas, Pumping and Pressure DistributionV. Vacuum Components and ReliabilityVI. Case Study

Introduction

A. VacuumB. Pressure Units

Vacuum

Vacuum: an environment with a pressure < 1 atm

Low Vacuum : 760 – 25 torrMedium Vacuum: 25 – 10-3 torr High Vacuum (HV): 10-3 – 10-6 torrVery High Vacuum: 10-6 – 10-9 torrUltra High Vacuum (UHV): 10-9 – 10-12 torrExtreme High Vacuum (XHV): < 10-12 torr

Pressure unitsPressure: force per unit of area

Pa: Newton/m2 (SI unit), 1 Newton = 1 kg-m-sec-2

bar: (kg/cm2), 106 dyne/cm2, 1 dyne =1 g-cm-sec-2

mbar: milli-bar, 10-3 bar, 103 dyne/cm2

Torr: mm-Hg (at 0℃)

1 torr = 1.333 mbar = 133.3 Pa ≒ 1.316 × 10-3 atm1 Pa = 10-2 mbar ≒7.5 × 10-3 torr ≒ 9.869 × 10-6 atm1 atm ≒ 760 torr ≒1013 mbar ≒ 1.013 × 105 Pa

Pressure

PV= nRT

“Pressure” is equivalent to “number density”.

Number density (at room temperature):at 1 Torr, N ~ 3.2 x 1016 molec./cm3

at 10-10Torr, N ~ 3,200,000 molec./cm3 !!

Considerations on Accelerator Vacuum System

A. Accelerator Vacuum SystemB. Vacuum Related Beam Considerations

Accelerator Vacuum System

--- to provide a comfortable path for the particle beam (to increase the beam lifetime and also the beam quality)

--- to provide a clean environment for the critical components (to keep their high performance)

--- a vacuum system contains vacuum chamber, pumps, gauges, valves, mechanical and electrical feedthroughs, the related control units, and many other subsidiary components.

Vacuum Related Beam ConsiderationsA. Beam Lifetime Issues

Pressure: scatteringIon/Dust Trapping: scattering

B. Beam Stability IssuesMechanical Stability: Beam OrbitBeam Duct Cross section: ImpedanceChamber Material: Frequency ResponseIon Effects: Beam Lifetime, Beam Size and Emittance(Electron Clouds: Beam Size and Emittance)

Beam Lifetime and Beam Size Issues

The less the gas molecules density

▼

the less the interactions between the particle beams and the gas molecules

▼

the less the blow up of the beam bunch and also the less the beam loss.

The less the gas molecules density

▼

the less the interactions between the particle beams and the gas molecules

▼

the less the blow up of the beam bunch and also the less the beam loss.

Beam lifetime (electron rings)

τ-1 = τT-1 + τRGS

-1 +τion-1

τ: Beam lifetime (in general,τT <τRGS<τion)τT : Touschek LifetimeτRGS : Residual gas lifetimeτion : Ion-trapping lifetime

τRGS-1 = τBS

-1 + τNS-1 +τee

-1

τBS : Bremsstrahlung-scattering lifetimeτNS : Nuclear-scattering lifetimeτee : Electron-electron-scattering lifetime

(in general, τNS < τBS <<τee)

Bremsstrahlung-scattering lifetime

τBS-1 = c σBS N = c(ρ/X0)W

where X0: radiation length of the residual gas (g - cm-2)ρ : density of the residual gas (g - cm-3), c : velocity of light (3x1010cm-sec-1)W = 4/3 ln(γ /△γ)–(5/6), probability to loss energy > △γ, γ = Ee /mec2

ρ = MP/24500× 760 at room temperatureM: mass of the residual gas (a.m.u.)P: pressure (torr)

Ref: J. Kouptsidis and A. G. Mathewson, DESY report, DESY 76/49, 1976.

Bremsstrahlung-scattering lifetime

Assume △γ /γ =1%

τBS-1 = 8539 MP/ X0 sec-1 = 3.1× 107 MP/ X0 hr –1

M/X0 = Σi (M/ X0)i

36.119.437.335.945.534.242.558X0

444028181616121MCO2ArCOH2OCH4OCH

Nuclear-scattering lifetime

τNS-1 = [c1(E2A0

2/Pβ0)(1/<β>)]x-1

+ [c1(E2A02/Pβ0)(1/<β>)]y

-1

whereC1 : 1.0× 10-7 hr- GeV -2- nTorr-1

E : electron energyP : pressure (nTorr)A0: limiting aperture (min.[vacuum chamber, dynamic aperture])β0 : Betatron function at the limiting aperture<β> = ∫ringβ ds/L, average betatron function

Ref: H. Wiedemann, “Coulumb scattering and vacuum chamber aperture,” SSRL-ACD-NOTE, Dec.13,1983.

Assume: d= 5 cm, < β> = 10mτEN

-1 = c σEN N = 3x 1010 × 4π × [(2.8 x 10-13)2Z2/ γ2θmax

2] × (6× 1023/24500) × (P/760)= 1.4 × 105 (Z2/E2)P hr-1

τEN-1 = c σEN N

σEN = 4πr2Z2/ γ2θmax2

θmax = (d/2)/< β>

where,r : classical electron radius

= 2.8 x 10-13 cmZ: atomic numberγ = Ee/meC2

d: diameter of vacuum chamber< β>: average betatron function

Electron-electron-scattering lifetime

τee-1 = c σee N

whereσee : electron-electron scattering cross section

= 5.0 × 10-25 (Z/γ)(γ/ △γ) (cm2)Z: atomic number of the residual gasN = 3.2 × 1016 P (# of molecules/cm3), at RTP : pressure (Torr)

Beam Stability IssuesMechanical stability: as stable as possible

vibration or thermal expansion of vacuum chambers movement of Magnets or BPMs

Beam Orbit ChangeBeam duct cross section: as smooth as possible

abrupt change of cross section wake fieldInduce Beam Instability (and the lost energy could also heat up vacuum components)

Chamber material and thickness: Frequency ResponseAC or pulse magnetic field Eddy current

Shielding or Changing the Original Magnetic Field and Heating the vacuum Chamber

Vacuum System Design Considerations

A. Basic Vacuum IssuesB. System Operation Issues

Vacuum System Design Considerations

A. Basic Vacuum Issues1. How to reduce pressure2. How to overcome thermal problems

B. System Operation Issues1. How to keep a precise mechanical structure even after

baking 2. How to reduce the impact from the stringent environment

(radiation, humidity, dust, etc.)3. How to protect the vacuum system in case of an

accident

Basic Vacuum Issues

--- How to reduce pressurereduce outgassing rate (material, sealing, treatment) effective pumping configuration

--- How to reduce thermal problemsincrease thermal conductivity (material, direct cooling)absorbers, grazing incident, differential heat removal (low Z material), cooling system

System Operation Issues

--- How to protect the vacuum system in case of an accidentdevice self protection (IP, IG), electrical or pneumatic actuated valves, reliable vacuum interlock system (e.g. PLC), redundant sensors, reliable utility systems (e.g. compressed air and cooling water systems)

--- How to reduce the impact from the stringent environment high radiation resistance material, installation under clean room conditions, to avoid the condense of water vapor, and to prevent the contact with humid air (e.g. with isolation coatings, to avoid corrosion)

--- How to keep a precise mechanical structure even after baking careful dimension control during machining and welding, rigid fixed points (at BPMs, heavy components, critical positions), bellows and flexible supports, pre-displacement so as to have an optimized-force condition for some critical components during baking, to use springs to reduce the load of heavy components

Outgas, Pumping and Pressure Distribution

A. Outgas1. Thermal outgas2. Photon-induced desorption

B. Pumping and Pressure Distribution1. Throughput, Conductance and Effective Pumping Speed2. Pumping Configurations3. Pressure Distribution4. Pumps

In order to get a lower pressure in the UHV range, it is much more effective to reduce outgassing rate than to increase pumping speeds.

P = Q / Swhere

P: pressureQ: outgassing rate S: pumping speeds

Thermal desorption1. Qth ~ exp(-Ed/kT)

Ed--- surface binding energy of the desorbed gask --- Boltzmann constant (8.6x10-5eVK-1)T --- temperature (°K)

2. Qth : a) mechanism: surface desorption and diffusionb) can be effectively reduced by the treatments of chemical cleaning and

in-situ bakingc) water vapor is the major outgas before baking, hydrogen is the major

outgas after bakingd) Elastomers and the materials with high vapor pressure are not

recommended for an UHV system.

Photon-stimulated desorption, PSDe—beam Synchrotron Radiation Photo-electron Gas molecules

I d/dt (d2N(ε)/dIdε) Y(hv)F(θ) 2η

Qpsd = I ×∫d/dt (d2N(ε)/dIdε)Y(ε)F(θ) dε × 2ηY↓, F(θ)↓, η↓ Qpsd ↓(normal incident, θ =90º F(θ) minimum)

where, I: beam current (mA) Y(ε): photoelectron yield (# of electrons/ # of photons) for aluminum, Y(ε) ≒ 2.61 ε-0.94 10eV< ε≦ 1560eV

≒ 441.9 ε–1.13 1560eV< ε < 10keVη: desorption coefficient (# of molecules /# of electrons) F(θ) ≒ sin-1/2 θ

Ref: A.G. Mathewson et al., KEK report, KEK-78-9, (1978).

Qpsd = I ×∫d/dt (d2N(ε)/dIdε)Y(ε)F(θ) dε × 2η≒ 8.6 ×1017 I E εc

-1/3 Y(εc ) F(θ) 2 η

whered/dt (d2N(ε)/dIdε)≒1.51 ×1014 ρ/E2 (ε/εc )-2/3, for ε≦ε c

≒0 for ε > ε c

I: beam current (mA)E: electron beam energy (GeV)ε c : critical photon energy = 2.21 ×103 I E3/ρF(θ) ≒ sin-1/2 θ

ρ: bending radius (m)for aluminum, Y(εc ) = (0.41 - 1.66 εc

-0.6) hv ≦ 1560eV= (1 - 216.2 εc

-0.6) hv > 1560eV

Throughput is the volume of gas at a known pressure and temperature that pass a plane in a known time.

Throughput = Outgassing rate (if no absorption in the path)

Q = P’(ch)S’(ch) = P(pump) S(pump)= C (P’(ch) – P(pump))

C : conductance of the tube (unit: l/s)= function of geometry, independent of pressure for the molecular flow regime

1/S’(ch) = 1/S(pump) + 1/CS’(ch) : effective pumping speed at the chamberC : conductance of the tube

It is useless to use a large pump with a narrow tube!

Throughput, Conductance andEffective Pumping Speed

Pumping

Pumping Configurations

The conductance of the beam duct in an accelerator is always very small so that special pumping configurations are necessary to meet the stringent low pressure requirements.

a) Distributed Pumpingb) Localized Pumping

Insertion Device Chamber (extremely conductance limited)

(Distributed pumping) (NEG Strip / NEG coating)

Insertion Device Chamber (extremely conductance limited)

(Distributed pumping) (NEG Strip / NEG coating)

Heavy Gas Load

Ante-chamber + Localized Pumping

Heavy Gas Load

Ante-chamber + Localized Pumping

Conductance Limited Area

Discrete Absorber + Localized Pumping

Conductance Limited Area

Discrete Absorber + Localized Pumping

IP NEG

IP

IP

IP

IP

NEG

NEG

NEG

DIP

DIP

DIP

TMPIP

NEG

Distributed Ion Pump

TMP (commissioning)IP+NEG (normal operation)TMP (commissioning)

IP+NEG (normal operation)

Pressure Distribution

Si Pi = Qi + Ci(Pi-1 – Pi ) + Ci+1(Pi+1 – Pi )

Ref: D.C. Chen et al., J. of Vac. Soc. of ROC 1(1), 24(1987).

Pump considerations

a) pumping speedsb) preferred gasesc) ultimate pressured) oil free e) vibration freef) micro-dust freeg) failure safe (or interlocked)h) long lifetime and maintenance free

Pumps

a) Mechanical Pumpsb) Sputter ion pumps c) Getters (NEG, TSP)

(NEG: Non-evaporable getter, TSP : Ti-sublimation pump)

d) Adsorption pumpe) Cryo-pump

NEG

Turbomolecular Pump (TMP)

Titanium Sublimation Pump (TSP)

Non-Evaporable Getter(NEG)

Sputter Ion Pumpgas molecule

electron

N S

magnet

magnet

ion Ti cathode

Sputtered-Ti Sputtered-Ti gas molecule(trapped)

Magnet field

N S

Ti cathode anode (cell)

Vacuum Components and Reliability

A. Vacuum Chamber Material and TreatmentB. Sealing TechniqueC. ValvesD. BellowsE. Mechanical feedthroughF. Electrical feedthroughG. Special components

Vacuum Chamber Material(& thermal absorber)

UHV Considerations--- low defect (to avoid virtual or real leak)--- low outgassing rate, low vapor pressure--- easy machining, easy welding (increase reliability)--- bakable

High Thermal Load Considerations--- high thermal conductivity--- grazing incident (to reduce thermal density)--- differential heat removal, the first layer with low Z material

Surface Treatments

1. chemical cleaning2. in-situ baking3. glow discharge cleaning4. surface coating5. high temperature degas

Sealing Technique

• Welding, Tungsten Inert Gas (TIG), metal-to-metal• Brazing, between two different materials, metal-to-

ceramics, different metals,• E-beam welding • Flange sealing, Con-Flat Flange, O-ring, Helicoflex,

metal wires (e.g. indium wire, aluminum wire, etc.)

• leak check, He-gas mass spectrometerLeak rate unit: Torr-L-sec-1, Pa-m3-sec-1, atm-cc-sec-1

Valves

• Gate Valves, Angle Valves, Variable Leak Valves, Fast Closing Valves

• All metal valves and O-ring valves

• Considerations:leak tight, tunability, response time, baking temperature, type of actuation, mechanical reliability and lifetime

Bellows

• Flexibility, expansion/suppression dimension• Rf sliding fingers (touch force, flexibility)• Thermal conductivity• Mechanical reliability (strength and lifetime)

• How to fix ? or free suspended (vacuum force!!)

Mechanical Feedthrough

Applications:scrapers, screen monitors, rf tunners, front-end and beam line components, etc.

Considerations:Stroke, Precision, Heat removal (thermal contact and cooling), Mechanical Reliability (wearing and lifetime)

Electrical Feedthrough

Applications:beam position monitors, stripline monitors, excitation electrodes, gauges, pumps, etc.

Considerations:Frequency response, HV range, Current rangeRadiation induced damage (corrosion, degrade of contact or insulation)

Special Components

• RF bridge• Be-window• Ceramic chambers• Glass- and ceramic-windows

Case Study

A. TLS Vacuum System1. Vacuum Chamber Fabrication and Treatments2. System Installation and Operation

B. TPS Vacuum System Design(Lessons learned from the TLS vacuum system)

TLS Vacuum System

Vacuum Chamber Fabrication and Treatments1. Aluminum vacuum chambers2. Oil-less Fabrication Process3. Low Impedance Structure

System Installation, Operation, and Commissioning4. Oil-less and Effective Pumping System5. Low-Dust Treatments6. Vacuum Safety Interlock System

A. Vacuum Chamber Fabrication1. Aluminum vacuum chambers2. Oil-less Fabrication Process3. Low Impedance Structure

B.System Installation and Operation4. Oil-less and Effective Pumping System5. Low-Dust Treatments6. Vacuum Safety Interlock System

The TLS Vacuum System

Aluminum vacuum chambers

Aluminum Components(B-chamber, S- chamber, flanges, gaskets, bellows, BPMs, etc.)

Aluminum TIG WeldingAl-Al and Al-S.S. Seals with Al Gaskets

(between two chambers or components)(no transition material was used)

Co-extruded or Co-machined Cooling Channels

Oil-less Fabrication Process

A. Bending ChambersOil-less numerical control machining in an ethyl-alcohol environmentDegreased cleaning

B. Straight ChambersExtrusionDetergent + Acid + DI water ultrasonic cleaning

Low Impedance Structure

1. Smooth Cross Section(main chamber: 38mm-H x 80mm-W)

2. Gate Valves, Bellows, Flange Gaps shielded with rf bridges

3. Smooth Transitions in Cross Sections4. Port with small holes or slots5. Long Slots with a Large Width to Height Ratio

(in B-chamber for extraction SR to beamlines)

Oil-less and Effective Pumping System

1. Oil-less pumps were adoptedsorption pump, dry pump (membrane pump + molecular drag pump), magnetic bearing turbo-molecule pump, sputter ion pump, and non-evaporable getters

2. The pump locations and pumping speeds determined by computer simulations

3. “Localized” pumping + distributed ion pump in the bending chamber

4. Heavy dynamic gas loads mainly evacuated out of the vacuum system (by the TMPs) in the beginning of commissioning

Low-Dust Treatments

1. Welding and pre-assembly in clean rooms.2. Clean booths were used during installation3. Ion pumps turned on after baking (at ~10-8 torr)4. Slow venting (if necessary)5. Low IP voltage (HV ~ 3kV)

1) NC Machiningwith Ethyl Alcohol

2) Dimension CheckAfter Machining

3) Surface Cleaning4) DIP Installation

5) Welding in Clean Room

6) Deformation Check After Welding

7) Leak Test8) Pre-assemblyIn Lab

9) Installation in the Tunnel

TLS Vacuum System (Fabrication)

8880

38 44

80

60

17

17

21.5

13

171

174

Standard S-Chamber

ID-Chamber for EPU5.6, U5, U9 Undulators

B-Chamber

ID-Chamber for Wiggler(W20)

4.16 m

10 mm

TLS Vacuum System (Fabrication)

S.S. Taper

(1) Al Beam duct (Extruded)

Al/SS Bimetal adaptor

(4) Flatness Check

(5) TIG Welding on the other side (with Al beam duct installed in SW6)

(2) TIG welding on one side (3) Leakage Check

SW6

11 mm inner height

Temperature of beam duct ~ 100 K

TLS Vacuum System (Cold Chamber)

ID-Chambers for Superconducting Wiggler SWLS (2002), SW6 (2003), IASW x3 (2005-6)

8622 Ah1). Accumulated Beam Dose : ~ 8622 Ah

1993.07 ~ 2005.11 (12 years)Yearly operation hour: ~5000-5500 hours

TLS Operation Results (Beam Dose)

-- About 100 hour (~2%) of the users’ time was lost in a year.-- Less than 2% of the failures (< 2 hours in a year) was

attributed to the vacuum failure.-- The most popular items of the vacuum failures are

utility related components.

0

200

400

600

1996 1997 1998 1999 2000 2001

Year

Hou

r

PSBoosterRFControlMagnetVacuumUtilitySafetyOtherTotal

Machine Failure Hours

TLS Operation Results (Reliability)2). High Reliability: Vacuum Failure < 2 hr/ year

a) P/I vs. Beam Dose

27 hoursat 200 mA

SW6

Installation of New Devices W20

EPU,U5U9

SWLS

SRF cavity

1×10-10

Pa/mA

TLS Operation Results (Beam Cleaning)

b) I τ vs. Beam Dose

Busy with Installation Work

EPU5.6 U5

U9 SWLS SW6SRF Cavity

Replace newKicker Chambers

Top-up300 mA

W20

P/I vs. time

The data of P/I and I ·τ scattered due to frequent installation of new devices.

Lesson Learned from TLS -1

1) Beam Cleaning Interrupted by New ID Installations

Homework to Design the TPS (Lesson-1)

Q1: Beam Cleaning Interrupted by New ID Installations, How to Avoid?

A1:1) -- Most of the ID-chambers are to be fabricated and installed before

the TPS is commissioned, to prevent the vacuum from being frequently broken and to allow the beam dose on the ID-chamber to be accumulated effectively.

-- Some ID-chambers will be unavailable at the commissioning of the TPS, they will be cleaned in a photon beam line before installation.

2) Effective pumping system is necessary for the ID-Chamber.-- NEG strip is to be installed in a side-channel of the beam duct as a

distributed pumping. The arrangement is effective to reduce the potential effects caused by the drop off of the NEG powders in the beam channel.

-- Some other pumps (e.g. Ion Pump) are required to remove the inert gases and methane, which the NEG cannot do.

0 200 400 600 800 1000 1200 1400-0.08-0.06-0.04-0.02

0 200 400 600 800 1000 1200 14000.51.01.52.0

0 200 400 600 800 1000 1200 14002425262728

0 200 400 600 800 1000 1200 14000

100200

Beam Position

mm

m in

BPM Displacem ent

um

Vac-cham ber Tem p

Tem

p (C

)

Beam Current

mA

The expanded vacuum chamber moves the components touched or connected to it. The force transferred to the girder, to the magnets and then to the beam orbit.

Lesson Learned from TLS -2

2) Effect of the Movements of Vacuum Chambers

Movement of the vacuum chamber, sensitivity to water temp.: ~10 μm / ℃Movement of the girder (~0.3μm/℃) and BPM (~1μm/℃)Induced beam orbit drift: ~10-30 μm / ℃

Homework to Design the TPS (Lesson-2)

A2:For vacuum chambers: 1) Independent supports fixed directly to the ground.2) A 3mm gap between the magnet and vacuum chamber.3) The vibration caused by water flow must be suppressed. A

heavy chambers is helpful to reduce the vibration amplitude.

Q2: Effects of the Movements of Vacuum Chambers,How to Reduce?

Lesson Learned from TLS -3

3) Vacuum Pressure and RF Impedance Need be Better

1) Pumping slots RF impedance

2) Gas molecules & ions> 1,000,000/cm3 !! (@0.1nTorr)

Vacuum Related Beam Instabilities

SGV完全開啟與不完全開啟影像

SGV完全開啟(機構撐開) SGV不完全開啟(機構未撐開)

RF fingers撐開 RF fingers未撐開

RF Fingers 撐開影像

RF Fingers 撐開機構

RF Fingers 撐開機構

故障!RF Fingers 撐開影像

RF Fingers 略彎曲影像

Al Bellows (R6S6) 影像

PT100Thermal sensor

HeaterRF contactCu sheet

RF Fingers

Q3: Vacuum Pressure and RF Impedance Need be Better,How to Improve?

Homework to Design the TPS (Lesson-3)

1) A large B-chamber can confine more PSDs locally. 2) It is easier to design with more pumps and also with a

differential pumping structure in a large B-chamber to benefit the ante-chamber design, which is good in reducing the number of gas molecules (and ions) in the beam channel.

5 mA3: A large B-chamber with ante-chamber structure.

(BPM-chamber: 70mm*13mm，Left side: SGV, Right side: ID )

Fixed end of RF fingers

Movable end of RF fingers

Movable end of RF fingers

Homework to Design the TPS (Lesson-3)

4) In addition to the chambers and pumping ports, the bellows, flange gap, gate valve, tapers, BPMs, and other monitors will be carefully designed to reduce the impedance.

1/4~ 0.3nTorr~1.3nTorrPressure increase (design value)

atη= 1x10-5 molec./ e

1x~1x10-6~1x10-6Q (for one cell)

1/4 (1/2)

lesssame

more

4x

Remark

7.520Bending Angle of Dipole Magnet (deg.)

92.8%77%Percentage of the synchrotron light inside the B- chamber

|Z/n| (Chamber/Total)

Pump ports per cellNominal Pumping Speed (per cell)

Beam Duct Material

QTot atη= 1x10-5 molec./e (Torr*l/s)Beam current (mA)Beam energy (GeV)

Parameter

10 (off axis)13 (on axis)

~2.4x10-5~5.9x10-6

AluminumAluminum

~ 4000 L/s~ 4000 L/s

0.003/0.00850.012/0.0163

4002003.01.5TPSTLS

TPS Vacuum

1) The thermal problem is reduced by designing a larger B-chamber, so that the crotch absorber in the B-chamber is farer away from the source point. The criteria are met by a B-chamber with ~ 5 m long.

2) By using stepped surfaces (to keep a smaller photo electric yield) and fins in the cooling channel enables the maximum temperature of the aluminum chamber surface to be reduced from ~196°C to ~109°C.

Steppedsurfaces

fins in the cooling channel

~196 °C~109 °C

3 GeV, 400 mA, ~ 22 W/mm2 at L = 3.3 m (from BM source)

Saw tooth (0.4 mm / 2 mm-step)

Crotch-1

Crotch-2

Homework to Design the TPS (Lesson-4)

Vacuum Safety Interlock System

• device self protection or alarm (IP, IG, TMP)• electrical or pneumatic actuated valves• reliable vacuum interlock system (e.g. PLC)• redundant sensors• reliable utility systems (e.g. compressed air and cooling

water systems)• Thermal problem protections