some thoughts about qd0 in the tunnel lau gatignon

Some thoughts about QD0 in the tunnel

Lau Gatignon

Not a complete list, just to trigger discussions


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Why QD0 inside detector? L* = 3.5 m gives potentially largest luminosity This is the most challenging in terms of QD0 strength,

stabilization and integration difficulties If you can make this solution plausible, all other

solutions should a fortiori be possible L* = 8 m seemed to be ruled out because of unrealistic

prealignment constraints (2 mm) Therefore we concentrated on this solution for the

Conceptual Design Report. Note: 4 QD0 magnets are needed

L.Gatignon, 27-01-2012


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Why QD0 in the tunnel? The double QD0 support tube plus anti-solenoid eats up a significant

part of the forward acceptance in the case of shorter L*. The shorter L* is different for CLIC_SiD and CLIC_ILD, leading to severe

complications for either MDI or BDS. End-coils allow to shorten the detector length to 12 (= ± 6) m,

therefore L* = 6 m can be considered instead of 8 m. For L* = 6 m the pre-alignment tolerance becomes 8 mm, (almost) ok.

Also the radiation environment is easier for stabilisation and alignment Stabilization becomes easier, as well as the anti-solenoid

and many integration issues. (Therefore more realistic to reach Lnom?) Only 2 QD0 magnets are needed (same L* by definition)



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So the questions areHow much luminosity does one loose (on paper)?How much acceptance can one gain (on paper)?How serious is the luminosity loss with respect to the

difficulties to keep it stable inside the detector environment, i.e. are thereeffective luminosity losses due to such issues for the short L* ?

What is the net balance between luminosity and acceptance in terms of the physics reach?These questions deserve proper answers !



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What are the steps

What is the potential gain in acceptance, i.e. which systems have to be maintained in the detector region and can they be moved

How much luminosity do we loose, what are the QD0 and QF1 parameters: gradient, length, aperture, co-habitation with spent beam

Once the new detector acceptance has been defined, the physics can decide what luminosity loss can be tolerated.

MDI

BDS

LCD



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More in practical terms for Step 1 (MDI)

How large must the anti-solenoid be, keeping in mind that it must cover the spent beam as well. Note that QD0 is no longer there to shield the main solenoid field in this region.

Must the IP feedback remain inside the detector, and if so, where?

Is there a better location for Beamcal and LumicalThe vacuum system is probably simplified, but do we need

valves inside the detector volume and what is their position and size. Does the vacuum pressure requirement change with the longer lever arm?



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More about step 1

Do we still need a pre-isolator and, if so, should it be modified?

Are there impacts on the backgrounds, e.g. does the argument for a thick vacuum tube remain valid?

Are the arguments for radiation shielding still valid, do we still need PAC-rings?

How do we have to modify the integration studies for the pre-alignment?



8 L.Gatignon, 27-01-2012

Lever arm

SpaceRadiation

Forces

Integration

DetectorDetector


9 L.Gatignon, 27-01-2012

A starting point (for discussion)?


10 L.Gatignon, 27-01-2012


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Final remarks

The LCD work depends on the conclusions for the acceptance in the L* = 6 m solution

The BDS work is significant amount of work, it is important and will take too long to have us waiting for this

On the other hand, in my view there is nothing that prevents us from starting the MDI bit!

Many of the ongoing studies remain useful for both the short and longer L* solutions.


some thoughts about qd0 in the tunnel lau gatignon

Documents

qd0 magnets

tunnel2why qd0

terms of qd0 strength

double qd0 support tube

detector environment

detector length

detector region

new detector acceptance