Transcript Visit to CERCA - LHC Machine Advisory Committee

Plan for Collimator Beam
Commissioning & Phase 2 Plans
R. Assmann, CERN/AB
13/06/2008
for the Collimation Project
LHC MAC
Slides, data and input provided by
O. Aberle, A. Bertarelli,
C. Bracco, F. Caspers,
J. Coupard, A. Dallocchio,
W. Hoefle, Y. Kadi, L. Lari,
R. Losito, A. Masi, E. Metral,
R. Perret, S. Perrolaz,
V. Previtali, S. Redaelli,
T. Weiler, AB/BDI (R. Jones et al),
…
RWA, LHC MAC 6/08
1) Production and Installation
All collimator locations under vacuum. Good end of a long race…
RWA, LHC MAC 6/08
Jaw Flatness (Ring & TL)
Total: 148 jaws
1.2 m
360 MJ proton
beam
Flatness better than many feared. Out of tolerance collimators were
placed in locations with more relaxed tolerances, meaning larger beta
(limited sorting). Enough collimators for tightest places (40 mm).
RWA, LHC MAC 6/08
Minimum Collimation Gap (Ring)
Total: 32 TCSG, 30 TCT
TCSG
(fiber-reinforced
graphite)
TCT
(tungsten)
High precision collimators produced adequate for LHC conditions!
Note: No time to discuss here production problems with a few CERN collimators.
Important: Readiness for 2008 run and parameters is ensured.
RWA, LHC MAC 6/08
2) Hardware Commissioning and
Residual Problems
• Collimator beam commissioning is only efficient if a thorough and
successful hardware commissioning is done before (sort out as many
issues without beam as possible). Therefore summarized here…
• Hardware commissioning procedure published and approved.
• MTF system is set up.
• Collimator HWC comes after vacuum commissioning (bakeout). Request
from vacuum group to perform bakeout without water in collimator.
• 80% of collimators have completed hardware commissioning. Now
working on getting all data into MTF.
• About 2 weeks still needed for completion of tunnel work.
• Fully integrated into LHC schedule. Frequent shifts and adjustments to
access conditions (cooldown has priority)…
• Present scheduled end of collimator HWC: July 7th.
RWA, LHC MAC 6/08
Last Collimator Commissioning Schedule
RWA, LHC MAC 6/08
New Issue: Lifetime of Rail System
Cage
Connected
to movable
jaw
velocity: v/2
Rail
Rail
velocity: v
fixed
Two rails per axis.
Rollers
Pressed together to
support jaw weight
(pre-load).
Without grease.
Outside of vacuum.
RWA, LHC MAC 6/08
New Issue: Lifetime of Rail System
Cage
Connected
to movable
jaw
velocity: v/2
Rail
Rail
velocity: v
fixed
Cage “creeps”
too fast in
collimators from
early series
production.
Random effect.
Not seen in tests
for prototype
collimator (32,000
cycles).
Stop not in all
collimators 
cage can get
damaged.
Rollers
RWA, LHC MAC 6/08
Seen in lab
during controls
tests.
Collimator Creeping
Collimator
Cage type
Orientation
Creeping
expected
[mm/km]
Maximum
creeping
observed
[mm/km]
Creeping
observed
[mm/cycle]
1 cycle = 60 mm
TCS
Inox
Vertical
~5
278
16.7
TCS
Inox
Horizontal
~5
20
1.2
TCS
Aluminum
Vertical
~5
53
3.2
TCT
Aluminum
Vertical
~5
10
0.6
Statistical behavior and reason for increased creeping not
understood.
Studies ongoing in CERN mechanical engineering group
(TS/MME).
Creeping not an issue for collimator lifetime if cage is
adequately stopped (demonstrated 22,000 cycles, all but 28 first
collimators equipped following production issues).
RWA, LHC MAC 6/08
Roller Cage Summary
•
No problems in 2008 run to be expected based on lifetime data available
presently. Several collimators now used for cycling tests (originally restricted to
50 cycles to keep lifetime) and reached > 20,000 cycles.
•
10 collimators (early production) with lifetime of about 1-2 nominal years (first
problems towards end of 2009 run?).
•
15 collimators (early production) with lifetime of about 10 nominal years.
•
All other collimators conform with specified lifetime of > 20 years (> 22,000
cycles).
•
We are very lucky that we found this problem in the lab and not in the tunnel with
beam. If not fixed, we will adjust operational procedures to known weakness:
minimum number of cycles, avoid using collimators with inox cage, …
•
Preparing to retrofit stops for 28 collimators before end of July. We have
good hope that this will succeed, solving this new issue. Now (June 12)
validated for 2,500 cycles (factor 8 improvement: 1 y  8 y). Cycling ongoing…
RWA, LHC MAC 6/08
3) Controls Readiness and Remote
Commissioning
• Collimators are fully operational after HWC (single collimator). Lifetime
problem not an issue for the first year and will anyway be fixed at latest in
the shutdown.
• Low, middle and top level software is operational with most required
features.
• Allows to generate movement functions versus time for any collimator:
– Specify setting in number of sigma.
– From database information (later including beam-based calibration) generate
settings in mm (take into account local beta, emittance, local orbit, calibration
data).
• As the first collimators have become available, functionality has been
remotely commissioned for ensembles of collimators. Many single
collimators must work as a coherent system!
RWA, LHC MAC 6/08
For Fun…
Example:
Remote, functiondriven movement of
collimator jaw (10 min).
Remote reading of jaw
position in tank
reference system with
LVDT’s.
What does this
read???
Initially in 2008: Control 88 collimators for the two beams (~ 400 DOF)!
RWA, LHC MAC 6/08
First 7 Collimators in IR3: Remotely
Executing 30 min Ramp Function
Position
Realistic LHC ramp functions generated for 7 collimators
in IR3. Executed synchronously (software trigger used:
timing signal not available).
Different absolute settings due to local beta function and
different types of collimators (families). Automatically
generated at top level application.
Jaw and gap positions surveyed independently of motor
drivers with 10 sensors per collimator.
RWA, LHC MAC 6/08
Gap
Jaw Position Error:
Requested - Measured
7 IR3 collimators: 14
jaws with 28 sensors.
Example interlock level
Remotely controlled
from CERN control
room.
width of
human hair
Demonstrated: (1) Accurate jaw positioning. (2) Synchronous movement.
(3) Precise position readout and survey (collimator and machine protection).
RWA, LHC MAC 6/08
Problem: Magnetic Interference on LVDTs of TI2
Collimators (TCDIV.29012 and TCDIH.29050)
See last MAC!
The resistive magnets
(5KA peak current)
current cables in TI2
generate a magnetic
field that perturbs the
LVDTs collimator
nominal behavior
RWA, LHC MAC 6/08
The position drift follows the
magnet’s current cycle. Drift of up to
150 um have been experienced.
Reproduced in lab. Shields tested…
Countermeasures Applied for
TCDIV.29012 and TCDIH.29050
Installation of a magnetic shielding to reduce the
external magnetic field on the LVDTs
60% reduction of the LVDTs excitation
voltage as best trade-off between magnetic
interference reduction and reading accuracy
reduction (the standard deviation of most
LVDT’s is still below 1 um)
The LVDT deviation is now below 50 um (apart from one LVDT. A better shielding strategy is under study).
Axes
position
25 mm
10 mm
0 mm
LU
(um)
12
40
30
Dp LD
(um)
8
12
15
Dp RU
(um)
40
40
40
Dp RD
(um)
12
25
25
Dp Gu
(um)
18
14
15
Dp Gd
(um)
10
20
15
Dp
Axes
position
25 mm
10 mm
0 mm
LU
(um)
6
14
100
Dp LD
(um)
45
50
30
Dp RU
(um)
3
12
4
Dp RD
(um)
12
10
10
Dp Gu
(um)
20
40
12
Dp Gd
(um)
1
30
20
Dp
Magnetic Interferences summary for collimator TCDIV.29012 Magnetic Interferences summary for collimator TCDIH.29050
RWA, LHC MAC 6/08
Problem: Overshoot on the Position Reading after
Large Displacement
As consequence of the long cables capacitance between
LVDT’s and conditioning electronic a phenomenon of
reading overshoot has been remarked. The overshoot
can reach more than 100 um after a displacement of
40 mm. The recovery time can reach several
minutes.
The phenomenon has been reproduced
(even if not yet understood..) in the lab
and different scenarios have been
tested. The figure refers to a 70 mm
displacement
Countermeasure:
Again at half excitation
voltage the overshoot is
reduced by a factor 4.
RWA, LHC MAC 6/08
Collimator Interlocks
•
Two checks agreed (10 position sensors/collimator):
1) Measured position and gap at a given time checked versus allowed
position versus time (already implemented into low level controls).
2) Measured gap at a given energy (beta) versus allowed gap for this energy
(beta). Keep this as simple as possible.
a)
Energy and beta function from timing signal.
b)
Work ongoing for implementation by end of June.
•
Working on MP check procedure for commissioning this (run special
automatic cycle to trigger interlocks).
•
Note temperature, state-driven and BLM interlocks in and close to
collimators have also been defined (not reported here).
RWA, LHC MAC 6/08
Position Interlock Test TCDI2905
Example showing that
interlock logic works
(low level controls).
Once interlock (“dump
limit”) is reached jaw
movement is stopped.
At the same time
interlock generated 
any beam would be
dumped.
Can decide later to relax
(e.g. “just stop
movement but do not
dump”).
RWA, LHC MAC 6/08
Position Interlock Check Procedure
(automatic verification of position interlocks)
20
MPlimit +
MPlimit -
CPlimit +
CPlimit -
Jaw 1 US set
Jaw 1 DS set
Jaw position [mm]
15
10
5
0
-5
Interlocks generated
-10
0
10
20
30
40
50
Time (arbitrary unit)
RWA, LHC MAC 6/08
60
70
80
90
4) Plan for Beam Commissioning
• By start of beam operation (much is already there – see previous slides):
– Collimators fully operational.
– Controls system ready for driving collimators following any function.
– Controls system ready for setting any warning and interlock levels safely
(MCS).
– MP functionality fully working by commissioning jaw position interlocks already
without beam.
– Collimator safety (closest devices to beam) ensured by temperature interlocks
and interlocks on BLM rates next to collimators.
– Other systems operational (BIC, MCS, BLM, Timing incl. E signal), especially
relative reading of BLM’s close to collimators. BLM’s already working.
• Beam commissioning plan then means:
– Decide what collimators to use when and at what settings.
– Beam-based calibration of collimators (input to functions).
RWA, LHC MAC 6/08
Reminder: Beam-Based Calibration of
Collimators
• Not reported in detail since the status is the same as in December:
– Method has been worked out (based on Tevatron/RHIC/HERA experience).
– Method has been tested and realistic accuracy established with the LHC
prototype collimator in the SPS (see past reports).
– Machine conditions for calibration defined (up to few nominal bunches at top
energy). See report in December.
– Full set-up is lengthy: 6 shifts of about 8 hours. Faster if only updating,
checking calibration.
• Agreed goal is to have automatic beam-based calibration (as
TEVATRON) available for 2009 run:
– Hardware connections prepared (collimators – BLM’s).
– Wok package in AB/CO group. Further SPS tests this year.
• No more details here this time to avoid repetition… Note: big expected
impact from collimation upgrade in phase 2 (much better)!
RWA, LHC MAC 6/08
Collimator Operational Modes
• For simplification, several modes defined:
– Mode 1: Primary collimators and protection collimators only.
– Mode 2: Primary collimators, absorbers and protection collimators.
– Mode 3: Full 2008 system (5 instead of 11 secondary collimators in IR7 per
beam).
– Mode 4: Full phase 1 system, as installed for 2009.
• Settings, performance reach and tolerances defined for each mode.
• Realistic assumptions for efficiency:
– Factor 2-3 margin for BLM thresholds and uncertainties in FLUKA.
– Factor ~10 reduction in cleaning efficiency with realistic imperfections (shown
in PhD thesis of Chiara Bracco).
• Master table for collimator commissioning, defining settings for
various operational stages. A few examples in next slides…
RWA, LHC MAC 6/08
Commissioning Table: Settings
Here listed for nominal settings
(b*=0.55m): tightest gaps and
tolerances.
Settings in normalized sigmas for
every collimator family.
Converted into mm with the tools
described before.
RWA, LHC MAC 6/08
Commissioning Table: Performance
RWA, LHC MAC 6/08
Comm. Table: Optimized Ramp Settings
Just one out of 3 fully calculated ramp cases shown here. Used also for b*.
For each case settings, performance reach and tolerances calculated (not fully shown).
Our basis for placing LHC collimators.
Too many numbers  some figures for visualization…
RWA, LHC MAC 6/08
Collimators Closed with Relaxed
Tolerances During Energy Ramp
with imperfections
Transient b beat: 10%
Orbit:
0.3 s
Collimator:
0.4 s
RWA, LHC MAC 6/08
40%
1.2 s
1.6 s
Collimators Closed with
Tight Tolerances During Ramp (Nominal)
with imperfections
Transient b beat:
Orbit:
Collimator:
RWA, LHC MAC 6/08
10%
0.3 s
0.4 s
10%
0.3 s
0.4 s
Performance Reach 7 TeV
(Nominal Settings)
Work on imperfections to approach ideal performance reach (40% of nominal intensity)!
Here assume peak loss rate of 0.1% per second. If lower, higher intensity can be reached!
RWA, LHC MAC 6/08
The Collimation Plan on One Slide
1.
2.
3.
4.
Pilot bunch:
a)
Start with primary collimator only and protection elements.
b)
Keep open during first ramps and close as we learn about the ramp.
c)
Bring in additional collimators and test ramp functions & stability.
d)
End of ramp compatible with b* = 11 m.
43 bunches and/or squeeze to b* = 2 m:
a)
Use full installed system, according to collimator hierarchy.
b)
Close during ramp with optimized ramp settings (maximum tolerances).
c)
Squeeze without closing collimators (end of ramp compatible with b* = 2 m).
156 bunches and/or squeeze to b* = 0.55 m:
a)
Close collimators to nominal settings and tight tolerances.
b)
Squeeze with tight collimator settings. Compatible with b* = 0.55 m.
75 ns running (push intensity and luminosity):
a)
Reduce imperfections (machine & collimators) and improve machine stability.
RWA, LHC MAC 6/08
Summary Beam Commissioning
•
All collimation locations under vacuum. HWC well advanced: scheduled to be
completed July 7th. Residual problems being addressed (“cage creeping”).
•
A strong team has been trained for collimator commissioning. See results from
various team members presented. Try to learn as much as possible from
Tevatron, HERA and RHIC and adapt to LHC (no simple copy possible).
•
Installed collimators are precision devices, as specified. Remote commissioning of
collimator ensembles has started (7 collimators remote controlled and surveyed
over 30 min to 30 mm, the width of a human hair).
•
An extensive collimator table has been worked out for the beam commissioning:
takes into account performance reach, realistic imperfections, defines used
collimators, their settings and tolerances for different energies and intensities.
•
Plan has been established, minimizing number of complications at given time
(first ramp, first squeeze without collimator movements, …).
•
Time to get the beam…
RWA, LHC MAC 6/08
CERN Plan for Phase 2 Collimation
RWA, LHC MAC 6/08
Reminder: Constraints Phase 1
• Strict constraints in 2003 for phase 1 system:
– Availability of working collimation system for beam start-up (2007 originally)
– Robustness against LHC beam (avoid catastrophic problems)
– Radiation handling (access for later improvements)
– No modifications to SC areas (due to short time and problems with QRL)
• Compromises accepted:
– Limited advanced features (e.g. no pick-ups in jaws).
– Risk due to radiation damage for fiber-reinforced graphite (electical + thermal
conductivity changes, dust, swelling, …). Kurchatov data shows factor 4-5 changes with
irradiation in various important parameters.
– Steep increase in machine impedance due to collimators.
– Excellent cleaning efficiency, however, insufficient for nominal intensity.
RWA, LHC MAC 6/08
The Phase 2 Path
•
Due to LHC extrapolation in stored energy and predicted limitations in phase 1
system:
The LHC collimation system was conceived and approved during its
redesign in 2003 always as a staged system.
•
Phase 1 collimators will stay in the machine and will be complemented by
additional phase 2 collimators.
•
Significant resources were invested to prepare the phase 2 system upgrade to the
maximum extent.
•
Phase 2 does not need to respect the same constraints as the phase 1
system.
•
The challenge we put to ourselves: Improve
beyond phase 1!
RWA, LHC MAC 6/08
at least by factor 10
Constraints: Phase 2
• Strict constraints in 2003 for phase 1 system:
– Availability of working collimation system for beam start-up (2007 originally)
– Robustness against LHC beam (avoid catastrophic problems)
– Radiation handling (access for later improvements)
– No modifications to SC areas (due to short time and problems with QRL)
• Phase 2 constraints:
– Gain factor ≥10 in cleaning efficiency.
– Gain factor ≥10 in impedance.
– Gain factor ≥10 in set-up time (and accuracy?).
– Radiation handling.
– Sufficient robustness, also against radiation damage.
RWA, LHC MAC 6/08
Phase 2 Collimation Project
• Phase 2 collimation project on R&D has been included into the white
paper, thanks to strong support by CERN top management :
– We set up project structure in January. Key persons in place.
– Budget requested and allocated.
– Manpower request for white paper post sent.
– We are gaining momentum. Emphasis now on technical progress…
• FP7 request EUCARD with collimation work package:
– Overall marks very high (14.5/15.0).
– Expect that this will fly and make available significant additional resources
(enhancing white paper money).
– Remember: Advanced collimation resources through FP7 (cryogenic
collimators, crystal collimation, …).
• US effort (LARP, SLAC) is ongoing and we are well connected (not
reported here). Expect first basic prototype results before EPAC.
RWA, LHC MAC 6/08
General Work Plan
• So far 6 meetings for phase 2 specification (R. Assmann). In parallel
collimator design meetings going on in TS/MME (A. Bertarelli)
• Overall work plan:
– Define general directions until July 08.
– Prepare conceptual design until October 08.
– Discuss conceptual design and organize project details in November 08.
– Testing of hardware in 2009/10 (lab and beam tests).
• Time plan will be affected by start of LHC beam operation (highest priority
to make phase 1 collimation system work).
• However, once LHC intensity is limited (see previous slides) time will be
short (prepare now!).
• Note: Phase 2 locations in IR3 might initially be used for installing
temporary betatron cleaning to live with electronics problems in IR7
(study for combined betatron/momentum cleaning for LHC ongoing  not reported here).
RWA, LHC MAC 6/08
Concept to Realize Improvement
on Phase 2 Timescale
•
Factor 10 efficiency for protons and ions (work Thomas Weiler/Ralph Assmann):
– Place metallic, advanced phase 2 collimators (efficiency study by Chiara Bracco). 2-3
complementary development paths in CERN and US (SLAC rotatable design).
– Place cryogenic collimators into SC dispersion suppressor (use missing dipole space).
– Different material for primary collimators (to be evaluated).
•
Factor 10 in set-up time (and accuracy?):
– Integration of pick-ups into collimator jaws for deterministic centering of jaws around
circulating beam. Support from BI group (R. Jones et al).
– Gain accuracy due to possibility to redo for every fill (avoid reproducibility errors fill to
fill).
•
Factor 10 in impedance:
– No magic material yet (factor 2 seems possible). Pursue further the various advanced
ideas! Work by Elias Metral and Fritz Caspers. Tests ongoing.
– Rely to some extent on beam-based feedback. Work by Wolfgang Hoefle.
– Open collimators or use less collimators with improved efficiency (see above) and
increased triplet aperture (phase 1 triplet upgrade), if feedback cannot stabilize beam.
RWA, LHC MAC 6/08
1) Concept for Improving Efficiency
• Fundamental problem:
– Particle-matter interactions produce off-momentum particles in straight
cleaning insertions (both p and ions). These are produced by different basic
physical processes that we cannot avoid (single-diffractive scattering,
dissociation, fragmentation).
– No dispersive chicane after collimation insertion: Off-momentum particles get
lost in SC magnets after first bend magnets downstream of straight insertion.
• Conceptual solution (no decisions taken – under study):
– Reduce number of off-momentum particles produced (phase 2 primary and
secondary collimators).
– Install collimators into SC area, just before loss locations to catch offmomentum particles before they get lost in SC magnets.
– Might be beneficial to install around all IR’s, for sure in IR3 and IR7.
– Elegant use for space left by missing dipoles!
RWA, LHC MAC 6/08
Collimator
Schematic Solution Efficiency
Warm cleaning insertion
(straight line)
Off-momentum particles
generated by particlematter interaction in
collimators
RWA, LHC MAC 6/08
SC bend dipole
(acts as spectrometer)
Ideal orbit (on
momentum)
SC quad
(acts as
collimator)
Collimator
Schematic Solution Efficiency
Warm cleaning insertion
(straight line)
Off-momentum particles
generated by particlematter interaction in
collimators
SC bend dipole
(acts as spectrometer)
SC quad
Ideal orbit (on
momentum)
Add cryogenic collimator, using
space left by missing dipole
(moving magnets)
RWA, LHC MAC 6/08
Change in Layout of DS
3 m to left
3 m to right
No longitudinal displacement.
Moves inwards by 3 cm.
Layout and optics checked with MADX. No problem for the optics and survey seen.
Optics change (move of Q7) small even without optics rematch. More careful work
is required. Note, that impact on infrastructure was not checked yet!
RWA, LHC MAC 6/08
Proton Collimation Efficiency with Phase 2 Cu
Collimators and Cryogenic Collimators
99.997 %/m  99.99992 %/m
Inefficiency reduces by factor 30 (good for nominal intensity). Lower losses in the
experimental collimators (background). Should also work for ions.
Caution: Further studies must show real feasibility of this proposal (energy deposition,
heat load, integration, cryogenics, beam2, … ). Just a concept at this point.
Cryogenic collimators will be studied as part of FP7 with GSI in Germany.
RWA, LHC MAC 6/08
Zoom into DS downstream of IR7
quench level
Impact pattern on
cryogenic collimator 1
RWA, LHC MAC 6/08
Impact pattern on
cryogenic collimator 2
2) Concept for Improving Set-Up
• Standard method relies on centering collimator jaws by creating beam
loss (touching primary beam halo with all jaws).
• Procedure is lengthy (48h per ring?) and can only be performed with
special low intensity fills for the LHC.
• Big worries about risks, reproducibility, systematic effects and time lost for
physics (integrated luminosity).
• Tevatron and RHIC must rely on collimator calibration and optimization
performed at the start of each physics run.
• LHC can only do better if non-invasive methods are used (no touching
of primary beam halo and no losses generated):
– integration of pick-ups and loss measurements into jaws.
RWA, LHC MAC 6/08
Schematic 1
RWA, LHC MAC 6/08
Schematic 2
1) Center jaw ends around beam by zeroing difference signal from pair
of pickups (not touching beam halo  no or very low losses.
RWA, LHC MAC 6/08
Schematic 3
2) Put the same gap at both ends as measured from jaw position (phase
1 feature).
RWA, LHC MAC 6/08
Collimator - BPM Study
• No time for detailed studies and simulations this year. Will start next year.
• In the meanwhile implement “best guess” electrodes into mechanical
design.
• Crucial help from BI group (R. Jones et al). Engineering design driven by
TS in phase 2 collimation project.
• Ansatz: Implement some reasonable buttons, build a prototype and test
with beam how well it works (improve then with second generation design).
• Needed for high intensity: Should not be too difficult to reach much better
accuracy than with collimator beam-based alignment method.
• Will still require knowledge of local beta function. Can in principle be
evaluated with movable BPM buttons. However, chance to measure with
global methods regularly (1000 turn small kicks).
RWA, LHC MAC 6/08
Engineering Design for Prototype
RWA, LHC MAC 6/08
Electrode Design
RWA, LHC MAC 6/08
Improvements Beyond Phase 2
• We should not forget these advanced directions because we might need
to have them at some point to advance LHC intensity.
• Time scale is beyond phase 2 collimation (2011/2).
• Several advanced directions have been proposed but are too early for
starting engineering design now. They are pursued as longer term
improvements:
– Crystal collimation, waiting for successful results from Tevatron and SPS.
– Non-linear collimation.
– Hollow electron beam lens.
– Laser collimation.
• Partly funded through FP7 proposal.
RWA, LHC MAC 6/08
Conclusion Phase 2
• Within the last months we have gained quite a bit in knowledge: thanks to
many colleagues for their support in very busy times.
• Based on this work we can hopefully propose a big step forward for
LHC collimation, evolving the existing system with relatively modest
modifications (no new magnets). Concept being evaluated for:
– Factor 30 in efficiency (AP OK, check with energy deposition studies).
– Factor 50 in setup time, some factor in accuracy.
– Factor 2 in impedance, hope to stabilize with feedback, use increased
aperture after phase 1 triplet upgrade, trade-off with efficiency.
– Higher radiation robustness.
• Feasibility will now be addressed in more detail. The LHC tunnel is very
constrained and we might encounter showstoppers.
• Important milestone: Review of conceptual design with parallel
development paths in late autumn 2008.
RWA, LHC MAC 6/08