V. Parma (organizer), Thomas Hott (local host) +
Stefan Choroba, Wolf Dietrich Moeller, Bernd Petersen, Stephan Simrock, Elmar
Vogel, Hans Weise (DESY) +
S. Calatroni, O. Capatina, E. Ciapala, R. Garoby, F. Gerigk, S. Weisz (CERN)
Purpose : learn about SRF technology from
TESLA, ILC and XFEL.
Agenda: Tuesday 08 September 2009
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12:30 |
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12:40 |
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13:00 |
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13:25 |
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13:50 |
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14:15 |
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14:40 |
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15:05 |
Coffee (15') |
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15:20 |
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15:45 |
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XFEL data:
- 2.1 km long
5.3 m diameter + 3 km beam lines with 5 tunnels 4.5 m diameter.
- 2 straights
with a slight angle at the end of the accelerator, laser-straight tunnel =>
small slope ~ 30 m below ground.
- Klystrons in
the tunnel every ~ 100m.
- Suspended
cryomodule.
- Pulsed cables
under the floor. 1.5 km long Other cables are on the
side wall.
Two injectors
for maximum availability
Produces light
pulses at 10-50 fs
Planning: Start
of construction at the beginning of 2009. End in 2012. Start of Physics
commissioning in 2015
Facility for
physics: 103 shorter pulse than usual with 1010 the brightness
of best synchrotron.
DESY: 1400
employees (including post-docs + visiting scientists).
4
departments (1 for Accelerators).
XFEL today: ~
120 FTE/year. Will go up to 450
PETRA-3
modification and FLASH are still mobilizing a significant number of staff.
Accelerator
consortium coordinated by DESY.
XFEL GmbH is a
separate entity, which is based on European rules and which is independent of DESY.
Around
50% of the accelerator (~500 MÛ) in-kind contributions (DESY itself providing many).
Work Packages for
pieces of equipment.
Accelerator Module (12.2 m) is based on
experience from TESLA/ILC/É
Will build 3
prototypes from 3 companies (100 in total).
Cryomodules
will be assembled in Saclay and shipped to DESY where they will be high power
tested.
Applying
European rules for Call for Tenders.
Chinese built
cryomodule delivered.
Work in CEA
will be done by industry at Saclay, under CEA supervision.
Production
rate: 1 module per week. 20 days for assembling one module. Infrastructure is
in construction.
Test
transported a full module between Saclay and Hamburg and found some troubles which will be resolved.
No conditioning
or processing (Helium, HPP) after final assembly ÒIf there is field emission
after assembly, you have to live with itÓ (W.D. Moeller).
Recently issued
final specifications for mechanical fabrication and cavity treatment.
So far the
final treatment for all cavities was always done at DESY. Last year an EP
facility was installed at ACCEL and first cavities were treated there. For the
series production the complete chemical treatment will be done by industry.
Main companies
for building cavities: ZANON and Research Instruments (ACCEL).
These companies
will be provided by DESY-made measurement devices (eddy currents scan, optical
inspection, RF measurements, tuning of dumbbells and of full cavities
É).
Needed 30
pre-series cavities. Niobium procurement took ~ 1 year.
Units of 4
cavities will be sent to DESY and vertically tested (in their He tank) 4 by 4. In
ÒAMTFÓ Accelerator Module Test Facility
Gradient &
field emission (as measured externally from X-rays) are specified. Then they
will be sent to Saclay where the bad ones will be discarded and returned.
The gradient
selected is compatible with 90 % production yield. Expect ~ 20 MV/m Freedom is
left to the companies to choose either EP or BCP (rough polishing is done by
EP)
RF power
coupler is from LAL Orsay. Conditioning will be at Orsay.
Detailed
assembly and test procedures prepared for the tuner.Installation
into the tunnel will be with the waveguide-system already mounted on the
modules.
Still to
develop is an automated slow flow venting system for cryomodules in the tunnel.
The injector is
~ copy of FLASH Linac.
Magnets with
resistive conduction cooled leads.
A tunnel
mock-up has been constructed to test installation procedures.
Main difference
with previous projects: much more coordination to meet safety rules (Pressure vessel
tests, É), CE certifications + complexity of working
with non-European partners.
Offers to host CERN
people for a significant period of time to help learn engineering practice.
XFEL will have 800
cavities - 120 kW/cavity - 23.6 MV/m average gradient.
Power needs: 3.9
MW for 32 cavities
5.2 MW RF source
(10 % loss + 15 % reserve)
10
Hz rate (up to 30 Hz but limited by average RF power of klystron 250 kW).
Modulator Hall
---- Accelerator tunnel (klystrons + pulse transformer) linked by 10 kV pulsed
cables.
Tunnel:
klystrons on the floor + suspended cryomodules.
~30
modulators in a single hall (football range size).
3 prototype 10 MW MBKs developed by THALES, TOSHIBA and CPI.
Fit for tunnel
installation: 2.9m long, 0.6 m diameter.
e.g. TOSHIBA E3736H – 10 MW at
118.8 kV + 129.5 A
it was stressed that prototype
klystrons must be tested at full duty cycle (which is not always possible at
the manufacturer). DESY discovered problems when going beyond the duty cycle
that was tested at the factory (Thales).
Only vertical
klystrons tested so far, horizontal needed in machine
Bandwidth
~ 2 MHz. Total weight ~ 3 tons (including pulse transformer).
Hoping for a
price < 0.5 MEuros/unit.
DonÕt expect
more than 60% efficiency from klystrons
Voltage
stability +- 0.5% required to achieve the required
phase stability (0.01 deg).
Simple bouncer
modulator provides this without problem
The LLRF needs
this stability to get the required 0.01 degree RF
precision & reproducibilty
Pulse
transformer is 2.6 m long x 1.4 m high.
1.57 ms flat
top at 120 kV with bouncer to get flatness. IGCT switches.
Alternative
solutions: PSM solution by Thomson Multimedia which provides regulation within
the pulse + failure tolerance. Same price and volume than the
bouncer type.
0.5 – 1
MEuros price range. Much more costly than the klystron
Pulse
transmission via cables tested successfully over the distance needed
RF
distribution:
- 32 cavities /
klystron (8 cavities/cryomodule)
- asymmetric shunt tees + 1 splitter for 2 cavities.
- 1 circulator
for each cavity.
- 1 phase
shifter (mechanical with remote control) for each cavity. (May manage to do
without).
- Klystrons are
10 MW able, but the need at the start is for 5.2 MW! Hidden agenda is to one day get 35 MV/m cavities.
- Adjustable RF
couplers (Qext: 1e6 - 1e7) to allow for very different modes of operation
(remotely controlled).
Requirements:
phase stability <0.01 degrees (20 fs) and better at some places of the injector
(everything included). Of the order of 0.1
degree along the accelerator length.
100 fs can be
achieved with coax transmission, 10 fs with fibre
É high power phase shifters / cavity + variable couplers.
Hardware ATCA-based.
Installed in the accelerator tunnel, in a shielding enclosure. Each rack has
its own temperature control.
Closed loop
bandwidth is up to 60 kHz. Gain 300
ÔDegradedÕ mode
of operation available if problems, feedforward only, no RF feedback
Klystron
characteristics is corrected in open loop (no klystron loop is felt necessary, based on
FLASH experience).
Using Titanium
and Niobium, because soldering technology is well mastered.
Niobium quality
of todays market is very good. Only 5-10% of the
material is rejected after careful scanning of incoming sheet (specified)
Discussion
on heat processing. 800C is chosen for hydrogen degassing. Higher temperatures (1400C) for Nb
purification are no longer needed with todayÕs quality of the raw niobiumÉ
Company put a
lot of efforts in providing pure material that helps avoid high temperature
treatment and provide good welding on the equator.
NbTi flanges
are used, they also go in the furnace at 800C. Flat
flanges with Al diamond seal, commercial. The titanium He tank is welded
afterwards
Copper plated stainless
steel bellows in-between cavities. Aluminium vacuum joints.
2 industrial
studies have been made and published on the assembly of full cryo-modules
(BABCOCK, ACCEL)
Details about
assembly are available in 2 industrial studies on the XFEL site.
Basic design is
based on TESLA technology.
Cavities are
filled with He-2 from 2 phase tube. Gas from each
cavity is returned by large gas return pipe. Tube size limits warm-up speed. 1
week cool down / warm up.
Cavities are
fixed with Invar rods to avoid movements during temperature changes. Cavities
are aligned warm. It was tested with a wire-system that the transverse
positions remain stable during cooldown. For the series production there will
be no longer the provisions for a wire measurement.
According to
the pressure vessel code cavities have to be tested at 6 bar.
This was done without seeing any plastic deformation. However, the cavity was
slightly detuned afterwords.
3 posts hold
the He return pipe.
1
manual (cold) valve at each end of a cryomodule. No valve between cavities.
Assembly
of cavity string in clean room.is with bolts and screws, including cold part of
couplers.
Then string is
closed and moved out of clean room and assembled onto the support pipe.
Magnetic shield
is then installed.
RF tuning of
cavity cells is done at warm in the companies building the cavities.
Ò Q-diseaseÓ
sometimes happens because of H2 in solution in the niobium, which
precipitates into hydrides (which are normal conducting) during cooldown if
process is slow (precipitation is diffusion dominated). Often avoided by fast
cooling from 150 K down to 4 K. Not possible at XFEL, but felt not necessary
because of the quality of nowadays Nb and a 800 C heat
treatment of the cavities. Q-disease can be checked by
keeping a cavity at 100K for several hours. If the resulting Q is lower
the cavity has Q-disease.
RF couplers
have 2 windows. No contamination during assembly in cryomodule.
Alignment
tolerance for quads: +-0.3 mm and +-3 mrad. for
cavities: +-0.5 mm
Building an
Accelerator Module Test Facility capable to exercise 3 modules simultaneously.
Duration of
test for 1 module: 12 days +-3.
Design pressure
for the cavities (He tanks) is 4 bars.
Even tested with a safety margin of 1.4 giving no plastic deformation.
It is a lot of pain
to exchange a cryomodule. 2 weeks for warm-up É for total of 6 weeks.
No spares but 8
extra-cryomodules installed in the beam path and nominally not powered.
The only
difficulties where found in some of the first modules: tuners (wrongly operated),
He feed throughs, and leaks between beam pipe and insulation vacuum. In later
modules these problems did no longer occur.
Cryogenics
tasks: 816 cavities @ 1.3 GHz, 40 cavities @ 3.9 GHz, 92 cryomodules in
operation, 8 idle.
Operation
schedule of 2-3 years without warm-up. Availability > 99%.
All cryo-pipes are
within the cryomodule.
String
connection box between 12 cryomodules (about 150 m) with vacuum barrier.
Heat < 20 W/cryomodule.
Pressure differences
in the vapour return line will be greater in SPL and may limit the cryomodule length
Feedthroughs
at the location of each magnet.
Checked effect
of different incident scenarios on a full size cryomodule.
Only
degradation obtained with catastrophic loss of cavity/beam vacuum to ambient
air.
Propagation of
air through the beam tube takes ~ 4 s, which allows for protection of the other
modules by a valve.
=> layout of safety valves (2K circuit: 2 DN150 SVs at both
ends of the linac - 5K/8K/2.2 K
safety valves at each string connection box - 40/80 K safety valves at both linac ends).
Maximum
Credible Incident: much less stored energy than in LHC => LHC-like event
very unlikely. But consequences could be much more severe because of suspension
to the ceiling. => installed much more release
valves.
GRP limits the cool down and
warm up time (due to alignment).
Cavities dressed supplied by
manufacturers. Mechanical Alignment reference w.r.t. electrical axis is made in industry. Then references transfer
to cavities flanges. These are the referentials for alignment during assembly
of string to GRP.
Cool-down (warm up) time: 1
week.
Alignment during
cool-down warm up changes.
Quad:+or-0.3mm
precision.cavity quite less.
Cryomodule cold testing:
~10days each.
Breaks: first protos helium
leaks: weld Ti vessel, or 2-phase welding, no leak at operation. Cold tuner electronics feedthrough broken.
Design pressure 4 bars,
safety valves 2 bars absolute. 1.4x4 is the test pressure.
Replacement of cryomodule is
not foreseen during an operation run. But in case: 2 weeks warm up,
intervention, then 1 week for cool down. 8 built-in ÒspareÓ cryomodules out of
100 cryomodules! No real spares for the moment.
1 cryoplant.9-10 cryo strings for a total of 1.7 km
length. Vacuum barriers at each sting connection box.
Each SCB is about 3 m long. 150m sectorisation of insulation
vacuum. Helium supply
Low pressure is 31mbar and .K
Up to 20 W per cryomodule only then wavy behavior
expected.
Reused one existing Hera 4.5 K plant upgraded with 2K
cold box. Similar to one LHC box,
but 2 refrigerators used in parallel.
Vacuum Valves foreseen every 150 m (cell) at
connection boxes but still under discussion. Then fast warm
valves in the CWT zones. MCI being analysed by WUT
Poland.
Cooldown pressure 1.3-1.4 bars abs. not to open safety
valves at 4 bars.
Note: stratification of helium vapors in GRP gives
visible alignment modifications.
Beam vacuum pumping ports at every cryomodule, at the
bellows-cryostats interconnections. No ion pumps
TM pumps for insulation vacuum
High power coupler:
- average power: 1.9 kW
- High power
processing 1 MW at reduced pulse length 1.3 mS 2 Hz. Done
two at a time,
- Looking at design of RF processing
system.- Variable coupling (adjustable from the
outside of the module) Qext 1e6 – 1e7.
- Double window
system: 1 cold + 1 warm.
- Horizontal.
- Bias on inner
conductor against multipacting.
- Cylindrical
ceramics with TiN coating.
- S.steel parts
including bellows are copper plated (galvanic)
- Region
between the two ceramics pumped by SPI plus sublimation pump
Modified at
Cornell to operate at higher average power with more cooling on the inner
conductor and other minor changes.
Power Coupler
was operated in 1 case up to 600 kW because of detuning. No problem recorded.
Beam line HOM absorber: ceramic absorber cooled at 70 K. 1 at the end of
each cryomodule.
Only plain
bellows, without RF screen, even along the beam pipe (between cavities and
between modules). Bellows are nevertheless a critical part of design, and all
copper plated
HOM coupler couples to the lower frequency range. Considering improved
feedthroughs from JLab with better thermal conductivity. Feature
due to the presence of the notch filter which must be superconducting.
One per cryomodule
Tuner: The Saclay type tuner was adopted (not the blade
tuner, which is foreseen for the ILC), resolution: 1 Hz/step - 800 kHZ slow range – 1 kHz fast range.
Mechanical
lever arm design. With stepping motor and piezo elements.
Piezo stroke at
cold is 10-20 % of room temperature.
Important: If the step motor of the tuner fails and
the cavity needs to be detuned because of cavity problems, then the machine has
to be stopped for replacement of the cryomodule.
Bunch
compressor transforms 50 A peak current into 5 kA! Linearization of time vs energy dependency with 3rd harmonic.
RF couplers are
on alternating sides of the beam pipe. ~ scaled copy
of 1.3 GHz device.
Also used in
FLASH but with less voltage (19 MV instead of 40 MV).
Alignment
+-0.5 mm to keep transverse blow-up at ~ 5%.
INFN will build
the cavities for XFEL.
Cryogenic pipes will be flanged.
Agenda : Wednesday 09 September 2009
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09:00 |
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09:30 |
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10:30 |
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12:00 |
Lunch (1h00') |
Role: technical
coordinator.
Total budget 1000
MEuros – German contribution 560 MEuros.
Mission of
Technical Coordination: coordinate and supervise the overall systems
integration into the final facility (including Civil Engineering).
Need to define:
what shall be built, by who and how (qualityÉ).
Need for clear
links between TC and WPs. Change management is a responsibility of the TC.
Presently
defining a Work Breakdown Structure.
In
a transition phase. In the process of organizing the project, which is not along the usual
DESY practice.
Systems
integration is based on 4 pillars:
- (accelerator) section coordination,
- 3D/CAD
integration
- Installation
workflow coordination,
(e.g. infrastructure cabling and piping will take 1 yearÉ)
Machine
installation will take 99 weeks after infrastructure installation.
- Reviewing:
Conceptual Design Review, Design Review, PRR followed by fabrication/tendering.
Project Life-cycle
Management. Based on ÒTeamcenter EnterpriseÓ.
Set-up and
resource profile very similar to what happens in industry for unique products.
Using EDMS
platform to store/manage information for lifespan of 30++ years.
Project phase:
Prototyping/industrialization with very distributed project team.
Need for
managing complexity of collaboration, coordination, communicationÉ
Building unique
products: no reference processes.
Collaboration
partners rely on their own design and simulation environments. Contribute to
PLM on casual basis.
Users are
involved in several projects in different roles.
User acceptance
is key to success.
Discussion:
quality assurance is not specified at the level of DESY.
Civil
Engineering:
3 construction sites.
Try to convince
contributors to immediately use the tool.
Standard tool
for commenting/correcting is Adobe Acrobat Professional.
English is
enforced, except for Civil Engineering because of German Law and because of the
implication of local workers.
Project
follow-up is done with MS-Project Professional.
3D CAD QA team
checks consistency of the documents/drawings received, look for conflicts and
requests follow-upÉ
Discussion:
standardizationÉ Know it is mandatory. Expect it to happen as part of the
review process before tendering.
Representing
physical parts: e.g. cavity (efficient/ clear web interface).
Next challenge:
extension to a full cryomodule.
Comment: ~ CERN
MTF process.
Process industrialization.
Set of
documents/instructions for every item.
Visit to CMTB
FLASH hall and Tunnel mock-up
- Cavities
tuned before He tank fitted.
- Warm cavity measurement
& adjustment gives the correct frequency when cold
- Heat
treatment has no effect on frequency
- No frequency
drifts in early operation, i.e. after initial cool-down warm-up cycles