# Presentation: 842614

## ICARUS next

- Some aspects of the **cryogenics** for a **large LAr TPC detector**

- Elio Calligarich

- Yale - July 2006

## Few historical remarks.

- The R&D program for a LAr TPC started at CERN in 1985. The first “large” detector, **2 m****3**, was realized and used up to 1993, to develop the major items concerning the ***detection of the ionizing particles*** and the ***reconstruction of the interaction events***.
- Then, a program has begun in Pavia ***to enlarge the TPC*** volume. A first **10 m****3** device was activated and later, **two twin detectors** (2* “***T300***”) of about **270 m****3** **each** were constructed.
- One of them was **successfully tested** in summer 2001 in a ***100 days run***. More then ***20.000 cosmic rays interactions*** have been collected and studied.

- Elio Calligarich

- Yale - July 2006

## The species evolution...

- Elio Calligarich

- Yale - July 2006

## ... and then the last step: T300.

- Cryostat (half-module)-T300

- View of the inner detector

- Readout electronics

- Elio Calligarich

- Yale - July 2006

## About the T300 dimensions.

- To develop and to demonstrate such a large LAr TPC it was decided to construct it** at ground level** and then to move to the underground site.
- The chosen dimensions were **those** **maximum admissible** with respect the transfer of the apparatus.
- 	The “bottle neck” was the **dimensions of the Laboratories doors**.

- Elio Calligarich

- Yale - July 2006

## Moving to the LNGS

**Moving to the LNGS**

***(December 2004)***

- Elio Calligarich

- Yale - July 2006

## Benefits of a modular structure.

_**For T600/T1200 detectors**_
- 	*The so designed “modular structure” offers ****many benefits**** **(also some “serendipity effects”).*
- The modularity better fulfill the safety requirements.
- It allows a superior s/n ratio, thanks to the shorter sense wires.
- It allows an _easier activation procedure_ of the detectors**.**
- The modularity also offer the possibility of assembling more modules in parallel, thereby speedup the construction (it was *a very significant opportunity *_*at that time*_).

- Elio Calligarich

- Yale - July 2006

## To activate a large LAr TPC.

- To get operative a TPC detector, a very strict procedure was experienced. It can be summarised as following:
- A very high level cleanliness has to be obtained before filling the cryostat.
- The filling time has to be shorted as much as possible, to limit the Argon darkness through the outgassing.
- The cool down of the apparatus has to be achieved as equally as possible, to reduce the deformations of the vessel and those of the inner detector.

- Elio Calligarich

- Yale - July 2006

## Startup conditions: purity.

**At the start up**, the purity should be taken at least to ~5% of the final needed value *(this last depends by the drift length decided...)**.*
- This purity level gets acceptable the ***recycling time*** before reaching the operative conditions  *(about 2 months, *_*in absence of an external contamination*_*, for a thousands m**3** detector)*.

- Elio Calligarich

- Yale - July 2006

## LAr TPC in operation.

- A **gas phase** purification circuit has to be continuously active. *The circulation rate per hour should be ****~10%**** **of the total volume**.*
- A **liquid phase** purification has to be operating. (ASAP after the start up; it will be used also to amend the possible worst events during the operations). *A practical rate per hour could be at least ****~1%**** **of the total volume*.
- In the sensible volume, the temperature of the LAr has to be maintained uniform, to allow an uniform calorimetric response of the apparatus.

- Three conditions have to be fulfilled for a good TPC efficiency.

- Elio Calligarich

- Yale - July 2006

## T300 purification system.

**LAr** pur. rate  ≤ **2.5 m****3****/h**
**GAr** pur. rate  ≤ **25 m****3****/h/unit**

- Elio Calligarich

- Yale - July 2006

## The trend of the T300 purity

- The LAr is put in the cryostat at a very high purity level (≥ 10 ms mean life); nevertheless the out-gassing pull down the mean life to few μs.

- To reach a appreciable mean life a **10 days** purification full activity have been needed.
**40 days** to reach the target value.

**T300 ELECTRON LIFE TIME**

- Elio Calligarich

- Yale - July 2006

## To keep an uniform temperature.

- The solution implemented for **ICARUS T300** is to use an **Aluminium made vessel****, **to benefit from the **high conductivity** of this metal.
- Then, the vessel is enclosed in** ****a cold shield,** which temperature can be easily and promptly controlled.
- In this way, in a “steady condition”, the **maximum gradient **detected in the liquid was **less then 0.7 °C**.
*The “cold shield” solution can't easily be extended to a wide cryostat.*

- Elio Calligarich

- Yale - July 2006

## The cryostat.

**...****to build up the box**

**...****to realize walls**

- Elio Calligarich

- Yale - July 2006

## The cold shield.

**First thermal Insulation:**
**commercial panel**

**Two external LN****2**** **
**circulation pumps,**
** ****max speed 24 m****3****/hr,**
** ****max head 5 bar**

**Cooling (drawing) panel**

- Elio Calligarich

- Yale - July 2006

## The T300 cool down.

- Elio Calligarich

- Yale - July 2006

## About the inner detector.

**The “inner detector” *****(wires and cabling, HV system, PMs, purity monitors, LAr level meter ...)***** is assembled ****on a stainless steel hyper static structure****, to guarantee an *****high precision and stable geometry*****.**
**The relative contraction, between the structure and the tank (Al), has to be put under control.**
**The structure has to be free to slide with respect the tank, but in the central foot, that is fixed.**

**The ****imaging quality**** is related to the geometrical high precision of the wires chambers.**
**The chambers has to be cooled down, and during this transient could be damaged.**

- Elio Calligarich

- Yale - July 2006

## The hyper static structure.

**An hyper static structure (20 tons of ****stainless steel****) supported by 10 sliding feet (only one is fixed).**

- Elio Calligarich

- Yale - July 2006

## To summarize our experience.

- 	***To get operative a liquid Argon TPC, the following requirements are needed:***
*A very high ****cleanliness**** of the vessel, already **at the start-up phase*.
*A driven* ***cool down ****of the apparatus. It has to be kept at a temperature as**** uniform**** as possible.*
*A* ***quick filling*** *procedure*.
*A* ***gas Ar re-circulation***.
*A* ***liquid Ar re-circulation****.*

- Elio Calligarich

- Yale - July 2006

## Now, for a TPC  “XL”

- Elio Calligarich

- Yale - July 2006

## Why a single large volume?

-   A wide monolithic cryostat will **reduce sensibly the investment cost** for the unitary sensible mass.
- Thanks to the obvious **simplification of the plant**.
- Moreover, **using the current electronic**, a single channel could “read” a LAr volume **10 times larger**:
- The wires could be extended to 16 m, (but pitch 6 mm); ***4 times longer then the actual.***
- The drift length could be extended up to 4 m (or more); ***30% longer then the actual***.

- Elio Calligarich

- Yale - July 2006

## NEVERTHELESS

***	******To enlarge in a significant way the volume some improvements are needed.***
- A method to keep a _wide_ vessel “oxygen free”, **less expensive then the vacuum**, has to be experienced.
- A structure able to support the atmospheric pressure (10 ton m-2) on a extended dimensions has to be very “tough”.
- A method **to reduce the contamination of the Argon** during the **long filling time **has to be implemented.
- The out gassing will affect **the upper portion** of the vessel, i.e. the portion touched by the Argon gas (see later).

- Elio Calligarich

- Yale - July 2006

## Moreover...

- A way to **cool down** **equally as possible:**
- the large cryostat;
- the extended detector structure;
- 	to reduce as possible any mechanical deformations.
- At the end, it’s important to define** the limit beyond which the convective movements of the liquid will downgrade too much the uniformity of the calorimetric detector response.**

- Elio Calligarich

- Yale - July 2006

## To keep a cryostat “oxygen free”.

**To avoid the vacuum phase, a preliminary ****fluxing with ultra high purity gas Argon**** can be considered.**
***EXAMPLE******: ****taking into account a 2000 m**3** cryostat fluxed with ****~40 m******3**** **of ultra-pure gas Argon at standard conditions, three kinds of contamination can be considered****:***
***The residual atmosphere (C******1****** moles)***
***The out-gassing from the inner surfaces and from the traps in the mechanics ( C******2****** moles).***
***The leaks of the cryostat (C******3****** moles).***

*They can be computed as a function of the fluxing time. The used parameters are (about) those evaluated in the T300 test run; but**** *****they can be much better assessed*****.***

- very preliminary

- Elio Calligarich

- Yale - July 2006

## Fluxing rate = 12 l/s

**Fluxing rate = 12 l/s**

- 1 month fluxing time

***After ******one month****** of fluxing, a reduction of a factor ******10******-6****** of the contamination could be reached.****** ***

- Elio Calligarich

- Yale - July 2006

## Some observations.

- 	  After **30 days,** about **31.000 Nm****3** will be fluxed through the cryostat (more or less **15 volumes**) to obtain the needed purification level.
- Operating at higher temperature (~70 °C) we could force the out-gassing process (test are needed!!)
- The fluxing rate (~ 40 m3 h-1) could be easily increased.
- The **“ideal gases”** have been considered (at this stage); with the real ones the result will be different...

- Elio Calligarich

- Yale - July 2006

## A more advanced analysis.

**A FEMLAB-CFD** finite volume analysis is now running.
- Using real gas.
- Looking to the optimization of the input diffusers.
- To evaluate the time needed to reach an adequate purity.
- Used parameters:
- (31.25 m x 8 m x 8 m) volume (»2000 m3)
-  Total GAr flow = 12 l/s = 43.2 m3/h (very conservative!)
-  9 inlets located as in previous figure;
-  Diffusion coefficient = 1.9 x 10-5 m2 s-1 for Air-Ar; !!
-  Perfect mixing between Air and Ar;
-  Initial concentration of Air is about 44.6 mol/m3.

- Elio Calligarich

- Yale - July 2006

## Preliminary study for purging a 2000 m3 LAr TPC.

- Due the very low diffusion speed of the **air in Ar** (few tens of centimeters per hour) only the air is drawn from volume in the first days of purging.

- Preliminary

- Elio Calligarich

- Yale - July 2006

## Purging the cryostat.

- The time needed for purging at
**10 ppb is ~12.5 days** (_6.5 volume changes_)

**Walls outgassing and leaks are**
**not yet considered.**

- Residual contamination (mol/m3)

- Exchanged volume

- Preliminary

**10 ppb after**
**6.5 volume exchanged**

- Elio Calligarich

- Yale - July 2006

## To cool down a wide vessel.

**Before** the filling phase, the cryostat **has to be cooled**, uniformly, to the liquid Argon temperature **(87 K°).**
- Due to the fact that the cold shield technique adopted for ICARUS T300 can’t simply be scaled-up:

- A different way for the cool down
- has to be experienced

- Elio Calligarich

- Yale - July 2006

## A possible cooling method.

- 150 K°

- Too large temperature gradients!

**Temperature field at different times**

**The temperature field ****asymmetries**** ****induce**** convective motion instabilities****.**

- Elio Calligarich

- Yale - July 2006

## A possible alternative.

**To compose a cryostat**

**The cryostat itself acts like a cooler box.**
**The preliminary computations give good results.**

- Elio Calligarich

- Yale - July 2006

## The filling procedure.

**After** the initial cleaning, the cryostat has to be cooled to the LAr temperature. The **pressure has to be maintained** at the atmospheric ones, **injecting ultra-pure GAr**.
- At a specific temperature, the filling has to be started, and it has to be carried on continuously, **as quickly as possible**.
- The outgassing will effect the portion of the vessel touched by the GAr.
- The portion of the cryostat wet by LAr will have a different temperature with respect of the temperature in the gas phase. **Significant mechanical deformations** can be at that time induced: the **same will occur for the mechanical structure.**
- When the level of the liquid will reach an adequate threshold, **the liquid Argon re-circulation has to be activated**.

- Elio Calligarich

- Yale - July 2006

## How quick the filling?

- In the European market about **200 m****3****/day**** ****of LAr could be available** for such an application (*10% of the total production*). The same quantity in US.
- The logistic to collect the cryogenic liquid could reduce the delivery rate to **100 m****3****/day**.
- To fill **2000 m****3** about **125 trucks** have to access the plant, continuously: one each 200 min: _**20 days could be needed**_.

- Elio Calligarich

- Yale - July 2006

## About the input heat.

- A certain amount of input heat*** ***in the cryostat*** is required***, to force the GAr recirculation.
- About the **restrain of the convective movements** in the sensible volume,  the major questions are:
- Does exist a way **to “border”** the convective motions outside the sensible volume?
- Can the sensible volume be kept in a reasonable **“quite condition”** to allow an uniform calorimetric response of the detector?

- Elio Calligarich

- Yale - July 2006

## A possible way for a “self cleaning” cryostat.

- With a good control of the input heat (and then of the convective motions) could be possible to realize a “self cleaning” liquid circuit, collecting the LAr inside a number of **“cleaning boxes”** put on the walls.
- The mass of LAr moved could be adequate.
- Should be an interesting improvement **to avoid an external circulation**.

- Elio Calligarich

- Yale - July 2006

## One more hypothesis to explore...

**Cooler**
**T=~84 K°**

- Input heat

- Elio Calligarich

- Yale - July 2006

## An R&D program.

- Haw to obtain the _initial_ high LAr purity, **without the evacuation of the cryostat**.
- Haw to **control the temperature** of the dewar.
- To contain the gradients during the filling.
- To manage of the convective motions when in operation.
- Haw to manage the Argon purity during the running.
- Will be possible to activate an inside cleaning circuit?

**1. The preliminarily R&D to carry out is:**

**Those develops could be carried out with a small cryostat: with a volume no larger then 40 m****3****.**

- Elio Calligarich

- Yale - July 2006

## More...

**Later**, a wider cryostat (thousands of m3) should be constructed to “certificate“ the new technologies.
- This detector can find place in **Hall B of the LNGS**. The following draws represent a very first approximation of the possible dimensions. The volume could be of the order of **1800 m****3** (about 2500 ton of LAr). Some logistic problems, however, have to be understood and solved.
- It has to be **assembled inside** the tunnel, of course.

- Elio Calligarich

- Yale - July 2006

## Space available in LNGS - HALL B.

*top view*

- Elio Calligarich

- Yale - July 2006

## Cross view.

- Useful area
- 53 m2

- An **horizontal** cylindrical vessel will imply a **~19%** **reduction of **the sensible volume, without a significant benefits in terms of structure cost.

- Useful area
- 43 m2

- Elio Calligarich

- Yale - July 2006

## A different approach.

- Almost all the R&D activity could be carried out with a (larger) cryostat of **about 110 m****3**.
- This choice will be a little bit **more expansive**.
- But, at the end, *an usable detector could be available for the physic*.

- Elio Calligarich

- Yale - July 2006

## Just an exercise...

- Total volume   160 m3
- Active volume 110 m3

*Cross view*

*Lateral view*

*Top view*

- Elio Calligarich

- Yale - July 2006

## CONCLUSIONS.

- An R&D program has to be started to develop **the new techniques** suitable for a large volume (many thousands m3) TPC cryostat. There is the need to study some methods aimed at reaching the following goals :
- To obtain the **preliminary GAr cleaning**.
- To **manage the temperature**** **before and during the **LAr** filling.
- To **manage the input heath**.
- To maintain a good **LAr purity** during the run.
- A small **device (≤ 6 m****3****)** could be used to answer to the first two questions. A device **of ~40 m****3** could to be used to study the last two questions.
- All this R&D develops could be performed in a cryostat of **~110 m****3**.

- Elio Calligarich

- Yale - July 2006

## About the inside structure.

- High tension

- cathode

- PM

- PM

- PM

- 3 planes wire chamber

- Thermal insulation

- Stretching beam

- Race tracks

- Race tracks

- Thermal insulation

- Thermal insulation

- 3 planes wire chamber

**Stretching beam**

- Race tracks

- PM

- Feed trough

- Thermal insulation

**A new mechanical structure, suitable for much more extensive detector, is now in progress.**

- Elio Calligarich

- Yale - July 2006

## Conclusion 2.

**	****At the end, to develop the new technologies, suitable for a ****LAr TPC “XL”**** :**
**An R&D program has to be carried out. We could be use a ****110 m****3**** cryostat****; it could be later used on a ******** ****_x000e_****beam****.**
** ****An operative TPC detector, about ****~1800 m****3**** (~2500 ton) can be realized in Hall B of the LNGS, to demonstrate the effectiveness of a large scale apparatus.**

- Elio Calligarich

- Yale - July 2006

## A conclusive statement.

**Due to**:
- The cool down procedures.
- The needed filling time.
- The cleaning procedures.
- 	it seems, at this stage, **very difficult** to realize a LAr TPC detector with a single volume **of the order of some 10****4**** tons**.
- To move behind the thousands tons **a modular solution seems to be more realistic**.

- Elio Calligarich

- Yale - July 2006