**Review**

**of**

**The ATLAS ID evaporative cooling system**

**CERN, 14^th^** June 2000

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[Distribution:]{.underline} EB Members, TC Members, Members of the ID
steering group, All participants mentioned in the report.

# Purpose of the review

Wednesday 14.6.2000 there was an internal ATLAS Inner Detector review of
the small scale evaporative system setup in the cooling lab. The review
was limited to the system aspects and did not include results of the
structure tests, except that the structures were used as load and their
temperatures were monitored to verify that the system operated
correctly.

The purpose was :

-   review the results obtained with the small scale setup (studies of
    system performance at startup, stop, sudden load variations, varying
    loads from standby to 100%).

-   review of baseline system, including cooling services and control.

-   identify key issues yet to be studied.

-   review the phase two program leading up to the FDR in January 2001.

The report is written in three parts :

A)  The external parts and overall concept.

B)  The internal system, the cooling services.

C)  The phase II plans.

# Review committee.

E.Anderssen (LBNL), G.Gilchriese (LBNL), M.Olcese (Genova), R.Apsimon
(RAL), E.Perrin (Geneva), D.Greenfield (RAL), J.Godlewski (Cracow),
W.Witzeling (CERN), G.Bachy (CERN).

Ex-officio : G.Tappern (RAL), S.Stapnes (Oslo), M.Tyndel (RAL), L.Rossi
(Genova).

# Background.

In the ID TDR April 1997 both the SCT and PIXEL groups presented binary
ice as the baseline cooling, but the PIXEL group also presented an
evaporative system (both systems low pressure).

The LHCC review in the summer 1997 strongly recommended an aggressive
approach to material reduction in the ID - pointing to the cooling
system as one area for saving.

The cooling review in Sept./Oct. 1997 concluded:

-   Fluorinert should replace water for use in the cooling systems for
    the different sub-detectors

-   The committee has a distinct preference for the evaporative systems
    for the following reasons :

-   it has lower material budget

-   the cooling medium is much safer

-   the consequences of a leak are less dramatic

-   there are less components so reliability should be higher

-   the routing of pipes is simpler and more likely to fit into the
    available space

-   The committee also recommended that the teams should combine
    resources and propose one evaporative system and pursue studies of
    such a system.

The Pixel TDR in May 1998 showed a C~4~F~10~ evaporative cooling system
as baseline and a very important material reduction compared to binary
ice. The SCT changed to monophase fluorinerts and also participated in
the evaporative program.

Compared to monophase fluorinerts the material savings are also
substantial:

0.4 % Χ~o~ for the PIXELs - per layer, even more for the B-layer (above
0.6 %).

0.05 - 0.1 % Χ~o~ for the SCT - per layer.

In addition there are changes (positive or negative) depending on
pipe-dimensions, pressures, heating blocks, manifolding versus
capillaries and insulation thickness (several of these influence
services space as well as material).

In the Spring 1999 both the SCT and PIXEL groups increased their power
budgets for the FE electronics by 50%.

The phase I evaporative programme for the SCT and PIXEL was nevertheless
concluded with a cooling review in May 1999, confirming the evaporative
systems of the PIXEL and SCT detectors. A regulated system with input
capillaries as demonstrated in the small scale review today was then
presented. While the SCT already at that point suggested use of C~3~F~8~
, the PIXEL group officially changed to C~3~F~8~ in the fall 1999.

The CORE cost of the evporative system is 710 000 CHf and the next
critical milestones are the FDR and PRR in the January/April 2001. These
milestones are largely driven by the delivery of the first system to
Oxford in the fall 2001.

# The external system and overall concept.

**Observations :** A small scale system which performed well and in a
predictable way under many different conditions have been demonstrated
and presented.

**Main conclusion :**

The reviewers all expressed that the system shown worked well and that
they believe it can be made to work as a large system.

**Concerns :**

Resources for the next steps; in particular engineering manpower.

System complexity, reliability, operation complexity and need for
experts during operation.

A complete new costing needed.

## Recommendations :

Move ahead with development of the complete evaporative cooling system.

Produce complete project plan for the project (both phase II and
production).

Identify more manpower for the project.

Improve operational specifications (pressures, transient modes, delta T
versus delta p in stave, failure modes); consistency across the SCT and
PIXEL systems.

Develop model so that the system performance can be predicted and
compared against data obtained with prototypes.

Define and cost pre-cooling system if used.

Use current system to develop and test the simplest possible
configuration for the final system (more tests might be needed). In
general the system and operation should be kept as simple as possible.

Perform radiation tests of the components, even though problems are not
expected.

# The internal system, the cooling services.

**Observations :** The system was demonstrated with pre-cooling and no
heating in return path. Results were also shown without pre-cooling and
large heaters (200% of normal load) in the return. In both cases the
cooling performance of the system was stable.

Most likely the services area will increase compared to the current
layout, but further work is needed to optimise the services with the new
grouping of services.

**Main conclusion :** Not conclusive with respect to the services but
several of the implementations shown could work.

**Concerns :**

Large heaters, their operation, temperature and safety.

Complicated control loops between temperatures of the return, mass-flow
regulations and heater power.

Resources (engineering).

Active insulation not well tested.

Space and layout of services.

**Recommendations :**

The ID cooling group should as soon as possible propose an engineered
cooling services layout which keep the temperatures above the dew point
(15 degrees to be safe) and below 25 degrees outside the active or
passive insulation, justified by measurements and calculations.

Use the simplest and safest solution that does the job.

Identify/clarify responsibilities for this part of the system, design
and implementation.

# Phase II.

**Observation :** The plans are well advances and the structures are
being prepared. The components are identified. Timescale driven by
delivery of the first system to Oxford (SCT assembly) in Sept 2001.

**Main conclusion :** The phase II work to move ahead as soon as
possible.

**Concerns :**

The engineering support and documentation must be improved.

Resources (manpower mostly) not sufficient.

Structure measurements, including long term tests, will need to continue
in parallel adding to the manpower problem.

**Recommentation :**

Move ahead with purchase of key components (compressor and regulators).

Define test-program (tests to be performed and conditions to be
explored - as various geometrical orientations, thermal cross-talks,
active heating, failures).

Identify manpower (include in costing if it has to be paid for as part
of the project).

Identify responsible for services part of the system - in an attempt to
increase the manpower involved.

The phase II system should be as close as possible to final system
(identical in for all key elements), also the services part. Again,
chose the simplest solutions for the implementation based on the results
from the small scale tests (minimal heaters and simple control loops).

As a part of the project plan the phase II programme must be detailed,
as well as structure tests on the parallel system (test-needs for the
next year to be specified by the SCT and PIXEL groups).

Identify additional tests (material studies, irradiation studies).

# 7. Summary of main conclusion

Move ahead with the system as shown.

Use simplicity and safety as important guideline for further technical
choices related to the services configuration and control aspect.

Develop complete project plan for phase II and production.

Improve resource situation quickly, in particular engineering manpower.

Re-cost system as important increases compared to CORE have been
identified.

# 8. Acknowledgements

The reviewers would like to thank the participants in the review, in
particular Gregory Hallewell and Vaclav Vacek, for the impressive effort
put into the preparing the system, and to demonstrate and present it
during the review. Their effort is very much appreciated.

# Appendix I: Format and agenda

**9:00-12:00 :** Demonstration in the lab with the cooling group, seeing
the system in action under varying conditions.

**13:30-14:00 :** In 40-RD-10 Pre-meeting of reviewers.

**14:00-17:00 :** In 40-RD-10 (this meeting is open).

This will be followed by 3 hours of presentations of the small scale
system and its performance.

The following will be covered (informal and with reasonable time for
discussions):

-   History and background

-   Postmortem of the Counter Current Heater Exchanger tests.

-   Description of the May setup in the lab.

-   Results from the tests early May.

-   Description of the current setup (shown in the morning).

-   Results (mostly demonstrated in the morning, some additional
    comments).

-   Description of a baseline system with regulated input / output for
    each channel (as tested).

-   Phase (2) plans - some comments.

An outline of the above (results as of the IDSG 12.05.00) is available
on :

[http://edmsoraweb.cern.ch:8001/cedar/doc.info?document_id=111369&version=1]{.underline}

(all above G.Hallewell and V.Vacek)

-   The services associated to the cooling (space limitations and first
    estimates).

(G.Tappern)

**17:00-18:30 :** Closed session for the reviewers.

The transparencies shown can be found : pointer to be included.