Vacuum System
(Synchrotron Light Source)
J. R. Chen
Synchrotron Radiation Research Center
Hsinchu 30076, Taiwan
The Fourth OCPA Accelerator School, Aug. 2, 2006
Vacuum System
I.
II.
Introduction (Vacuum and Pressure Units)
Considerations on Accelerator Vacuum
System
III. Vacuum System Design Considerations
IV. Outgas, Pumping and Pressure Distribution
V. Vacuum Components and Reliability
VI. Case Study
Introduction
A. Vacuum
B. Pressure Units
Vacuum
Vacuum: an environment with a pressure < 1 atm
Low Vacuum :
Medium Vacuum:
High Vacuum (HV):
Very High Vacuum:
Ultra High Vacuum (UHV):
Extreme High Vacuum (XHV):
760 – 25 torr
25 – 10-3 torr
10-3 – 10-6 torr
10-6 – 10-9 torr
10-9 – 10-12 torr
< 10-12 torr
Pressure units
Pressure: 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 atm
1 Pa = 10-2 mbar ≒7.5 × 10-3 torr ≒ 9.869 × 10-6 atm
1 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 System
B. 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 Considerations
A. Beam Lifetime Issues
Pressure:
Ion/Dust Trapping:
scattering
scattering
B. Beam Stability Issues
Mechanical Stability:
Beam Orbit
Beam Duct Cross section:
Impedance
Chamber Material:
Frequency Response
Ion Effects:
Beam Lifetime, Beam Size and
Emittance
(Electron Clouds:
Beam Size and Emittance)
Beam Lifetime and Beam Size Issues
The
The less
less the
the gas
gas molecules
molecules density
density
▼
▼
the
the less
less the
the interactions
interactions between
between the
the
particle
particle beams
beams and
and the
the gas
gas molecules
molecules
▼
▼
the
the less
less the
the blow
blow up
up of
of the
the beam
beam bunch
bunch
and
and also
also the
the less
less the
the beam
beam loss.
loss.
Beam lifetime (electron rings)
τ-1 = τT-1 + τRGS-1 +τion-1
τ: Beam lifetime (in general,τT <τRGS<τion)
τT : Touschek Lifetime
τRGS : Residual gas lifetime
τion : Ion-trapping lifetime
τRGS-1 = τBS-1 + τNS-1 +τee-1
τBS : Bremsstrahlung-scattering lifetime
τNS : Nuclear-scattering lifetime
τee : 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 temperature
M: 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
C
12
O
16
CH4 H2O CO Ar
16
18 28 40
CO2
44
M
H
1
X0
58 42.5 34.2 45.5 35.9 37.3 19.4 36.1
Nuclear-scattering lifetime
τNS-1 = [c1(E2A02/Pβ0)(1/<β>)]x-1
+ [c1(E2A02/Pβ0)(1/<β>)]y-1
where
C1 : 1.0× 10-7 hr- GeV -2- nTorr-1
E : electron energy
P : pressure (nTorr)
A0: limiting aperture (min.[vacuum chamber, dynamic aperture])
β0 : Betatron function at the limiting aperture
<β> = ∫ring β ds/L, average betatron function
Ref: H. Wiedemann, “Coulumb scattering and vacuum chamber aperture,” SSRLACD-NOTE, Dec.13,1983.
τEN-1 = c σEN N
σEN = 4πr2Z2/ γ2 θmax2
θmax = (d/2)/< β>
where,
r : classical electron radius
= 2.8 x 10-13 cm
Z: atomic number
γ = Ee/meC2
d: diameter of vacuum chamber
< β>: average betatron function
Assume: d= 5 cm, < β> = 10m
τEN-1 = c σEN N
= 3x 1010 × 4π × [(2.8 x 10-13)2Z2/ γ2 θmax2] × (6× 1023/24500) × (P/760)
= 1.4 × 105 (Z2/E2)P hr-1
Electron-electron-scattering lifetime
τee-1 = c σee N
where
σee : electron-electron scattering cross section
= 5.0 × 10-25 (Z/ γ)( γ/ △ γ) (cm2)
Z: atomic number of the residual gas
N = 3.2 × 1016 P (# of molecules/cm3), at RT
P : pressure (Torr)
Beam Stability Issues
Mechanical stability: as stable as possible
vibration or thermal expansion of vacuum
chambersÎ movement of Magnets or BPMs
Î Beam Orbit Change
Beam duct cross section: as smooth as possible
abrupt change of cross sectionÎ wake field
ÎInduce Beam Instability (and the lost energy could also
heat up vacuum components)
Chamber material and thickness: Frequency Response
AC or pulse magnetic fieldÎ Eddy current
ÎShielding or Changing the Original Magnetic Field and
Heating the vacuum Chamber
Vacuum System Design Considerations
A.
B.
Basic Vacuum Issues
System Operation Issues
Vacuum System Design Considerations
A. Basic Vacuum Issues
1. How to reduce pressure
2. How to overcome thermal problems
B. System Operation Issues
1. 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 pressure
reduce outgassing rate (material, sealing, treatment)
effective pumping configuration
--- How to reduce thermal problems
increase 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 accident
device 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. Outgas
1. Thermal outgas
2. Photon-induced desorption
B. Pumping and Pressure Distribution
1. Throughput, Conductance and Effective Pumping Speed
2. Pumping Configurations
3. Pressure Distribution
4. 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/S
where
P: pressure
Q: outgassing rate
S: pumping speeds
Thermal desorption
1. Qth ~ exp(-Ed/kT)
Ed--- surface binding energy of the desorbed gas
k --- Boltzmann constant (8.6x10-5eVK-1)
T --- temperature (°K)
2. Qth :
a) mechanism: surface desorption and diffusion
b) can be effectively reduced by the treatments of chemical cleaning and
in-situ baking
c) water vapor is the major outgas before baking, hydrogen is the major
outgas after baking
d) Elastomers and the materials with high vapor pressure are not
recommended for an UHV system.
Photon-stimulated desorption, PSD
e—beam ÎSynchrotron Radiation ÎPhoto-electron Î Gas molecules
I
Î d/dt (d2N(ε)/dIdε) Î Y(hv)F(θ) Î 2η
Qpsd = I ×∫d/dt (d2N(ε)/dIdε)Y(ε)F(θ) dε × 2η
Y↓, F(θ)↓, η↓ Î Qpsd ↓(normal incident, θ =90ºÎF(θ) minimum)
where,
I: beam current (mA)
Y(ε): photoelectron yield (# of electrons/ # of photons)
10eV< ε ≦ 1560eV
for aluminum, Y(ε) ≒ 2.61 ε-0.94
≒ 441.9 ε–1.13 1560eV< ε < 10keV
η: 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
where
d/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/ρ
F(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, Conductance and
Effective Pumping Speed
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/C
S’(ch) : effective pumping speed at the chamber
C : conductance of the tube
It is useless to use a large pump with a narrow tube!
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 Pumping
b) Localized Pumping
Heavy
HeavyGas
GasLoad
Load
Î
ÎAnte-chamber
Ante-chamber++Localized
LocalizedPumping
Pumping
IP
NEG
DIP
NEG
IP
DIP
NEG
IP
DIP
Conductance
ConductanceLimited
LimitedArea
Area
Î
ÎDiscrete
DiscreteAbsorber
Absorber++Localized
LocalizedPumping
Pumping
NEG
IP
IP
Insertion
InsertionDevice
DeviceChamber
Chamber(extremely
(extremelyconductance
conductancelimited)
limited)
Î
Î(Distributed
(Distributedpumping)
pumping)(NEG
(NEGStrip
Strip/ /NEG
NEGcoating)
coating)
TMP
TMP(commissioning)
(commissioning)
Î
Î IP+NEG
IP+NEG(normal
(normaloperation)
operation)
TMP
IP
NEG
Distributed Ion Pump
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 speeds
b) preferred gases
c) ultimate pressure
d) oil free
e) vibration free
f) micro-dust free
g) failure safe (or interlocked)
h) long lifetime and maintenance free
Pumps
a) Mechanical Pumps
b) Sputter ion pumps
c) Getters (NEG, TSP)
(NEG: Non-evaporable getter, TSP : Ti-sublimation pump)
d) Adsorption pump
e) Cryo-pump
Î
Î
Î
Î
Î
NEG
Turbomolecular Pump (TMP)
Titanium Sublimation Pump (TSP)
Non-Evaporable Getter
(NEG)
gas molecule
N
Sputter Ion Pump
S
Ti cathode
electron
anode (cell)
Magnet
field
magnet
ion
N
Ti cathode
S
Sputtered-Ti
magnet
Sputtered-Ti
gas molecule
(trapped)
Vacuum Components and Reliability
A.
B.
C.
D.
E.
F.
G.
Vacuum Chamber Material and Treatment
Sealing Technique
Valves
Bellows
Mechanical feedthrough
Electrical feedthrough
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.
2.
3.
4.
5.
chemical cleaning
in-situ baking
glow discharge cleaning
surface coating
high temperature degas
Sealing Technique
• Welding, Tungsten Inert Gas (TIG), metal-to-metal
• Brazing, between two different materials, metal-toceramics, 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 spectrometer
Leak 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 range
Radiation induced damage (corrosion, degrade of contact
or insulation)
Special Components
•
•
•
•
RF bridge
Be-window
Ceramic chambers
Glass- and ceramic-windows
Case Study
A.
B.
TLS Vacuum System
1. Vacuum Chamber Fabrication and
Treatments
2. System Installation and Operation
TPS Vacuum System Design
(Lessons learned from the TLS vacuum system)
TLS Vacuum System
Vacuum Chamber Fabrication and Treatments
1. Aluminum vacuum chambers
2. Oil-less Fabrication Process
3. Low Impedance Structure
System Installation, Operation, and Commissioning
4. Oil-less and Effective Pumping System
5. Low-Dust Treatments
6. Vacuum Safety Interlock System
The TLS Vacuum System
A. Vacuum Chamber Fabrication
1. Aluminum vacuum chambers
2. Oil-less Fabrication Process
3. Low Impedance Structure
B.System Installation and Operation
4. Oil-less and Effective Pumping System
5. Low-Dust Treatments
6. Vacuum Safety Interlock System
Aluminum vacuum chambers
Aluminum Components
(B-chamber, S- chamber, flanges, gaskets, bellows,
BPMs, etc.)
Aluminum TIG Welding
Al-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 Chambers
Oil-less numerical control machining in an ethyl-alcohol
environment
Degreased cleaning
B. Straight Chambers
Extrusion
Detergent + 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 Sections
4. Port with small holes or slots
5. Long Slots with a Large Width to Height Ratio
(in B-chamber for extraction SR to beamlines)
Oil-less and Effective Pumping System
1.
2.
3.
4.
Oil-less pumps were adopted
sorption pump, dry pump (membrane pump + molecular
drag pump), magnetic bearing turbo-molecule pump,
sputter ion pump, and non-evaporable getters
The pump locations and pumping speeds determined by
computer simulations
“Localized” pumping + distributed ion pump in the
bending chamber
Heavy dynamic gas loads mainly evacuated out of the
vacuum system (by the TMPs) in the beginning of
commissioning
Low-Dust Treatments
1.
2.
3.
4.
5.
Welding and pre-assembly in clean rooms.
Clean booths were used during installation
Ion pumps turned on after baking (at ~10-8 torr)
Slow venting (if necessary)
Low IP voltage (HV ~ 3kV)
TLS Vacuum System (Fabrication)
4) DIP Installation
3) Surface Cleaning
2) Dimension Check
After Machining
1) NC Machining
with Ethyl Alcohol
5) Welding
in Clean Room
9) Installation
in the Tunnel
8) Pre-assembly
In Lab
7) Leak Test
6) Deformation Check
After Welding
TLS Vacuum System (Fabrication)
88
80
Standard S-Chamber
38
44
80
B-Chamber
60
4.16 m
ID-Chamber for EPU5.6,
U5, U9 Undulators
174
13
17
171
ID-Chamber for Wiggler
(W20)
17
21.5
10 mm
TLS Vacuum System (Cold Chamber)
ID-Chambers for Superconducting Wiggler
SWLS (2002), SW6 (2003), IASW x3 (2005-6)
(1) Al Beam duct (Extruded)
(2) TIG welding on one side
(3) Leakage Check
(4) Flatness Check
11 mm inner height
Al/SS Bimetal adaptor
S.S. Taper
(5) TIG Welding on the other side (with Al beam duct installed in SW6)
Temperature of beam duct ~ 100 K
SW6
TLS Operation Results (Beam Dose)
1). Accumulated Beam Dose : ~ 8622 Ah
1993.07 ~ 2005.11 (12 years)
Yearly operation hour: ~5000-5500 hours
8622 Ah
TLS Operation Results (Reliability)
2). High Reliability: Vacuum Failure < 2 hr/ year
600
PS
Booster
RF
400
Hour
Control
Magnet
Vacuum
200
Utility
Safety
0
Other
1996
1997
1998
1999
2000
2001
Total
Year
Machine Failure Hours
-- 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.
TLS Operation Results (Beam Cleaning)
Installation of
New Devices
a) P/I vs. Beam Dose
EPU,U5 SWLS
W20
U9 SW
6
SRF cavity
1×10-10
Pa/mA
b) I τ vs. Beam Dose
27 hours
at 200 mA
Lesson Learned from TLS -1
1) Beam Cleaning Interrupted by New ID Installations
The data of P/I and I ·τ scattered due
to frequent installation of new devices.
Busy with Installation Work
Replace new
Kicker Chambers
W20
EPU5.6
U5
SRF Cavity
U9
P/I vs. time
SWLS
SW6
Top-up
300 mA
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.
Lesson Learned from TLS -2
2) Effect of the Movements of Vacuum Chambers
mA
200
100
0
Temp (C)
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.
28
27
26
25
24
B eam C urrent
0
um
mm
-0.02
-0.04
-0.06
-0.08
400
600
800
1000
1200
1400
V ac-cham ber T em p
0
2.0
1.5
1.0
0.5
200
200
400
600
800
1000
1200
1400
B P M D isplacem ent
0
200
400
600
800
1000
1200
1400
B eam P osition
0
200
400
600
800
1000
1200
1400
m in
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)
Q2: Effects of the Movements of Vacuum Chambers,
How to Reduce?
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.
Lesson Learned from TLS -3
3) Vacuum Pressure and RF Impedance Need be Better
Vacuum Related Beam Instabilities
1) Pumping slotsÆ RF impedance
2) Gas molecules & ions
> 1,000,000/cm3 !! (@0.1nTorr)
SGV完全開啟與不完全開啟影像
SGV完全開啟(機構撐開)
RF fingers撐開
SGV不完全開啟(機構未撐開)
RF fingers未撐開
RF Fingers 撐開機構
RF Fingers 撐開影像
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
Heater
RF contact
Cu sheet
PT100
Thermal sensor
RF Fingers
Homework to Design the TPS (Lesson-3)
Q3: Vacuum Pressure and RF Impedance Need be Better,
How to Improve?
A3: A large B-chamber with
ante-chamber structure.
5m
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.
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.
Movable end
of RF fingers
Movable end
of RF fingers
Fixed end of RF fingers
(BPM-chamber: 70mm*13mm，Left side: SGV, Right side: ID )
TPS Vacuum
Parameter
TLS
TPS
Remark
Beam energy (GeV)
1.5
3.0
Beam current (mA)
200
400
QTot atη= 1x10-5 molec./e (Torr*l/s)
~5.9x10-6
~2.4x10-5
4x
Q (for one cell)
~1x10-6
~1x10-6
1x
Beam Duct Material
Aluminum
Aluminum
Bending Angle of Dipole Magnet (deg.)
20
7.5
Percentage of the synchrotron light
inside the B- chamber
77%
92.8%
more
Nominal Pumping Speed (per cell)
~ 4000 L/s
~ 4000 L/s
same
Pump ports per cell
13 (on axis)
10 (off axis)
less
Pressure increase (design value)
atη= 1x10-5 molec./ e
~1.3nTorr
~ 0.3nTorr
1/4
|Z/n| (Chamber/Total)
0.012/0.0163
0.003/0.0085
1/4 (1/2)
Homework to Design the TPS (Lesson-4)
3 GeV, 400 mA, ~ 22 W/mm2 at L = 3.3 m (from BM source)
~196 °C
Stepped
surfaces
fins in the
cooling channel
~109 °C
Saw tooth (0.4 mm / 2 mm-step)
Crotch-1
Crotch-2
1) The thermal problem is reduced by designing a larger
B-chamber, so that the crotch absorber in the Bchamber 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.
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