Large Systems Commissioning
Large Systems Commissioning
Kirsten Zapfe, DESY
CAS Vacuum in Accelerators
Platja D`Aro, May 21, 2006
Outline
z
Introduction
z
Pump Down and Leak Check
z
Components Check
z
Bake Out
z
Interlocks/Safety
z
Cryogenic Systems
z
First Beam
z
Concluding Remarks
Introduction
z
Accelerator vacuum system
beam intensity
beam lifetime
beam stability
static pressure
dynamic pressure
beam pipe aperture
material
rf shielding
Introduction
Commissioning
system meets the needs and
expectations of the user
required performance accessible with
Introduction
verification of system
performance
pressure
residual gas composition
outgassing
pump down times
conditioning time
preparation for standard
operation
functionality
safety
remote operation
add equipment
Introduction
Premises for “smooth”
commissioning
proper planning
overall system design
choice of materials and
manufacturing techniques
choice of vacuum equipment
specifications
vacuum controls
availability of continuous
monitoring and data logging
quality control
design and manufacturing of
components
handling procedures
cleaning
testing
installation
Introduction
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Large systems
zlength
znumber of components
zcomplexity
Example
zLEP
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27 km circumference
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~ 2700 bellows
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~ 7000 feedthroughs
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~ 2200 pick-up connections
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~ 700 gauges
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130 sector valves
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520 roughing valves
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1900 sputter ion pumps
z
13.000 flanged connections
TTF/FLASH
DESY
Pump Down and Leak Check
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Proper fixture of components
z
loose/fixed points
zbellows
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Pressure decay
¬
first hints for leak
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check with RGA or pressure rise method
z
Leak Check
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gross check p < 10
-4mbar
zfine check p < 10
-6mbar
z
flanged connections, ceramics, feedthroughs, windows
z
equipment
z
mobile pump station with leak detector/RGA
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systematic work necessary
zswitch of sputter ion pumps
¬
avoid spoiling with He in case of leak
Pump Down and Leak Check
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Conditioning of vacuum system without beam
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activation of titanium sublimation pumps
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activation of NEG pumps
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Observe behavior of pressure
¬
repeat leak check if necessary
LEP
O. GröbnerHERA
Bake Out
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System check
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equipment (heaters, thermocouples, cabling)
zfunctionality
¬
reliable attachment of sensors
zheating process (
Δ
T/time, …), automation
zinterlock
z
power failure
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failure of equipment
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pressure rise/leak
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Cooling of critical components
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magnets, monitors, etc.
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During bake out
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avoid large temperature gradients
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check movement of components due to heating
zobserve pressure for leaks
vacuum chamber
magnet
Components Check
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Vacuum equipment
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correct allocation
z
components
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cables
¬
electronics
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display on computer
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functionality of pumps, gauges, valves, etc.
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Vacuum control
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remote operation of components
zfunctionality
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add/improve handling options
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modify/integrate additional parameters
Components Check
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Movable elements
(collimators, diagnostics, …)
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correct path length
zend switches
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remote operation
¬
check for pressure increase during movements
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Special equipment of experiments
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e.g. gas inlet systems
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Final alignment
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be careful shifting components
under vacuum
¬
temporarily unfixed components
Interlocks/Safety Checks
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Self safe operation of system
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failing of equipment (pumps, gauges)
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Vacuum interlocks
¬
closing of valves
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pressure increase
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failing of equipment (pumps, gauges)
zswitching off equipment
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Fast shutters/delay lines
TTF/FLASH
prepare adequate tools for
check-out in advance
Interlocks/Safety Checks
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Beam interlocks
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linear accelerator
¬
stop beam production
zstorage rings
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dump beam
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Different modes of beam operation
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injection
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user beam lines
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Interlocks connected to other systems
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diagnostics
zexperiments
Cryogenic Systems
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Superconducting magnets
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beam pipe partially surrounded by liquid helium
e.g. Tevatron, HERA, RHIC, LHC
Cryogenic Systems
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Superconducting accelerating structures (cavities)
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cavities = beam pipe surrounded by liquid helium
e.g. Tristan, LEP, CEBAF, TTF/FLASH, XFEL, …
beam vacuum system (2K)
coupler vacuum system (RT) insulating vacuum system
TTF, XFEL
Cold Beam Vacuum Systems
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Leak check of final connections
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flanges, in-situ welds
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no leak check under cold conditions possible
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extreme care necessary, e.g. integral leak check
Beam lines movable
Plug-in module
Beam lines fixed Cold bore
Cooling tubes Beam screen
Cooling tube exit pieces
Cold Beam Vacuum Systems
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Pressure before cool down
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permanent pumps (e.g. sputter ion pumps)
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HERA: p ~ 10
-6mbar
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no active pumping after pump down
Cold Beam Vacuum Systems
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Cool down
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beam pipe = cryo pump
¬
pressure drop
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Measure integral leak rate and wall coverage
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release of gas during warm up measured with RGA
HERA
RT
¬
4.5 K
Insulating Vacuum Systems
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Segmentation
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distance of vacuum barriers has increased with time
z
HERA
¬
20 m
z
RHIC
¬
500 m
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LHC
¬
200 m
¬
larger distance = increased complexity for commissioning
L H C AR C : CR Y O G E N IC A N D IN S U L A T IO N VA C U U M BA S E L IN E D E S IG N
A B A B A B A B A B A C D A B A B A B A B A B A B A
Insulatio n V acu um sectorization:
M agnet vacuum barriers Jum per vacuum barriers Cryogenic line vacuum barriers
C old-m ass sectorization:
Bus-bar plugs Safety relief valves C ooldow n and fill valves
QR L vacuum jacket
M agnet vacuum vessel
TTF/XFEL
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Pump down
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equipment
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start with large roughing pumps
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sufficient mobile pump stations necessary
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initial pump down dominated by large amounts of water
from super insulating foils
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be prepared for frequent maintenance of roughing pumps
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eventually flushing with N
2Insulating Vacuum Systems
Insulating Vacuum Systems
Example
10 days
first pump down takes a long time
RHIC
D. Hseuh et al.
Insulating Vacuum Systems
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Leak check of air leaks
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equipment
¬
sufficient granularity important
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leak detectors at mobile pump stations and/or directly attached to tank
¬
base pressure usually not sufficient for RGA
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gauges
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He background in tunnel may be significant
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leaks from cryogenic He supply lines
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no exhaust line for roughing pumps
¬
HD as alternative to He as tracer gas
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dead time could be significant
zlarge leaks are not exceptional
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at high pressure small leaks are not detectable
z
needs to repair large leaks first
Insulating Vacuum Systems
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Leak check of air leaks (cont’d)
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O-rings
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permeation determines detection limit for leaks
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permeation takes time
¬
might simulate leak due to delay
in signal
dead time 10 s He at t=0
Insulating Vacuum Systems
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Leak check of process lines
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equipment
z
same as for leak check of insulating vacuum
¬
leak detectors/gauges
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sufficient He compression in case of He leaks necessary
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with insulating vacuum pumped down
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pump out process lines
¬
background level
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pressurize one line after the other
e.g. HERA: 15 bar He
Insulating Vacuum Systems
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Leak check of process lines (cont.)
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leak location
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often not easy to find
¬
sufficient diagnosis mandatory
¬
profile of He signal
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vent insulating vacuum, open sliding sleeves,
check welds, etc.
¬
pressurized with sniffer
¬
pressurized with vacuum tight fixtures
locating and repairing He leaks
-difficult and time consuming effort
Insulating Vacuum Systems
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Cool down
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check for movement of components due to
shrinkage of materials
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pressure drop
z
10
-3mbar required before cool down
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10
-6mbar required for routine operation
¬
remove part of mobile pump stations
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check for condensation/freezing of water
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thermal bridges
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monitoring of He signal
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leaks from process lines
¬
locate after warm up
¬
cold leaks
HERA
4.5 K
Insulating Vacuum Systems
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Leaks which can not be localized or repaired
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He leaks
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inside magnets, cavities, …
¬
add pump stations at insulating vacuum
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air leaks
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flanges on insulating tanks, …
¬
glue, rubber mastic …
HERA
4.5 K
Insulating Vacuum Systems
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Observe also beam vacuum
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during leak check of process lines
zduring cool down
¬
direct leaks from (liquid) He
at sc. cavities/ sc. Magnets
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leaks against insulating vacuum
¬
combined leaks:
process lines
¬
insulating vacuum
¬
beam vacuum
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less critical if leak against insulating vacuum
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not so nice
¬
He leaking into beam vacuum
¬
supply sufficient pumping speed for He
e.g. sputter ion pump with enhanced He pumping speed
e.g. charcoal (RHIC)
First Beam
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First passage of beam …
… possible reasons if the beam does not pass
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closed valves
z
obstacles, e.g. rf fingers
z
…
z
proper functioning of magnets, etc.
z
Check heating of components
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proper rf-shielding
First Beam
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Beam life time
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Beam-gas effects
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Pressure behavior
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thermal heating
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photon-induced desorption
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Conditioning of vacuum with beam
z
cleaning of surface
¬
beam scrubbing
LEP
O. GröbnerConcluding Remarks
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Sufficient time for systems tests necessary
z
installation of vacuum system is one of the final steps of accelerator installation
ztime slot often reduced due to delays of preceding steps
z
pump down can not really be speed up
Commissioning
(final) proof of correct
layout
design
manufacturing and
installation
proper planning of commissioning
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