Environmental Control in the CMS Tracker Content: The CMS Tracker environmental protection scheme The active thermal screen The primary feed-through region The buffer region Maintenance-related problems Humidity control and monitoring Dry gas flushing simulations Humidity sensor calibration issues Radiation resistant sensors for the LHC environment Benchmark tests

CMS Tracker Environmental Protection Scheme Zone protected by active screens Service Feed-through Buffer Region Zone protected by passive screens Beampipe Feed-through

Active Screen: Concept Heating foils: produced under customer specs by Rica Industries Insulating layer: Rohacell® panel Cold plate: hot-roll bonded aluminium circuit TOTAL THICKNESS AFTER ASSEMBLY: 13 mm

Examples of Functional Tests Executed on Prototypes HONEY-COMB CARBON FIBER 2 PANELS (variable distance) HOT SIDE COLD SIDE SUPPORT TUBE COOLING COILS Full mapping of the temperature distribution on the outer surface of the Support Tube varying the distance between adjacent panels and the heat dissipated by the LV cables on the inside D = 0 cm D = 16 cm D = 0 cm D = 16 cm ADDITIONAL POWER DISSIPATION FROM INSIDE CABLES (67 W/m2)

Example of Simple Closed-loop Operation

Finalized Thermal Screen Panels Detail of the inlet-outlet region prior to insertion of the pipes First panel positioned inside the Tracker Mock-up

Cold-to-warm Transition and Humidity Protection secondary feed-through region Barrel primary feed-through insulation Buffer region: T > 12 oC Flushed with dry gas (2-3 % RH @ 20 oC) Speeds up the temperature transition of the cold cables Keeps the connectors dry can be equipped with C6F14 sniffers primary feed-through region Endcap primary feed-through Sealing ring WARM TRANSITION COLD

Primary Feed-through Preparation Sequence - 1 Toothed insert First layer of cables laid

Primary Feed-through Preparation Sequence - 2

Primary Feed-through Preparation Sequence - 3

Primary Feed-through Preparation Sequence - 4

Lab Test of a Full-scale Sealing Block Environment @ 75% Rh Full scale sealing block (1 sector) Pipes, cables and optical fibres included Dry environment: No detectable humidity passage through the sealing block

Tests over a Realistic Full-scale 20o Sector Full scale 20o sector including: -TIB/TOB and TEC sealing blocs -Powered cables -Cooled pipes -1 Thermal screen panel -CF sandwich cover Measurements ongoing

The Buffer Region: the Tracker “Bulkheads” PIX main feed-through (to be moulded in place) PIX pipe connectors Integration of the Beampipe and PIX installation rails INDEPENDENT of the TK detectors TEC main feed-through (to be moulded in lab) TEC MSC connectors PIX MSC and OF connectors Environmental separation between PIX and TEC services Integration of the Beampipe support system INDEPENDENT of the TK detectors Creation of a closed volume where dry gas can be “generously” flushed to prevent excess of humidity in front of the TK

Tracker Volume Closing Scheme 1. After the completion of TEC cabling, the closing panels of the outer rings are positioned and sealed 4. The last closing element is the sealing disk around the Beampipe. The supporting scheme require a xyz fixed support in this location and the Beampipe has a shoulder, where the sealing/insulating disk will be connected. A heating sleeve can be integrated in the disk, in order to avoid a sharp thermal transition on the Beampipe wall 3. Following the PIX cabling, the Link elements are extracted, their protection tubes are re-positioned and 4 external shells are placed and sealed. These shells have “sealed holes” for the passage of the light-protecting tubes and of the Proximity sensors and can be thermally insulating 2. After the completion of PIX cabling, the closing panels of the inner rings are positioned and sealed

Cabling Exercises on Bulkhead Mock-ups 1:1 Pixel cabling mock-up 1:1 TEC cabling mock-up

Development of Acceptable Maintenance Models Example of a possible maintenance cycle model Which is a safe limit of the intervention temperature for two long-time interventions to be scheduled after 5 and 7 years of operation in the following model? Year Temperature in operation Time for bake-out Temperature for bake-out Time for maintenance Intervention temperature 1(a) ALWAYS @ +20oC 1(b) -10oC 8 WEEKS @ +20oC 2 3 2 weeks +10oC 4 5 4 weeks Tmaint ? 6 7 8 r = 22cm z = 59cm Fn=3.3x1013 Fp=12.6x1013 Vdep after 500 fb-1 (V) 400 26 Tmaint (oC) For a realistic temperature of intervention (~20oC) 8 weeks are safely allowed

Examples of Possible Maintenance Scenarios - 1 T ≤ -10oC R.H. ≤ 25% Transitional region 1 CMS opened for maintenance No TK maintenance foreseen Condition inside TK as in operation No need of any additional protection TOB TEC TIB PIX Service channels and outer Bulkhead panels opened T ≤ -10oC R.H. ≤ 25% 2 TK maintenance on the service channels and on the TEC connectors TK cooling switched off (Pixel cooling can be on, if needed) Thermal screen active Dry gas flushing (maybe air?) active TOB TEC TIB PIX

Examples of Possible Maintenance Scenarios - 2 T ≤ +10oC R.H. ≤ 5% Conditioned tent TEC TOB TIB 3 Pixel maintenance and/or beampipe bake-out Thermal screen (and TK cooling in case of bake-out) @ +10oC Conditioned tents mounted on the outside Dry air flushing @ (T = +10oC, R.H. = 5%) Silicon Strip TK unaffected T = R.T. R.H. ≤ 5% Conditioned tent 4 Full TK maintenance including TEC removal and access to TOB/TIB TK cooling switched off Thermal screen switched off Conditioned tents mounted on the outside Dry air flushing @ (T = R.T., R.H. < 5%) TOB TIB

Humidity Control and Monitoring Safe condition to be reached Tdew  -35 oC (i.e. RH = 1.35% @ 20 oC) Available dry N2 flow: 25 m3/h for the inertion of the CMS volume Parallel on-going activities: Numerical simulations of drying-out of the Tracker volumes Studies about calibration of humidity sensors Investigations about radiation-resistant humidity sensors Basic studies for calibration of the code parameters and for the comprehension of all phenomena involved Humidity measurement in full-scale models of sub-detector sectors (to start now)

Qualitative study on the flushing optimization for the TOB - 1 OUTLET OUTLET 1 Volume exchange per hour Distribution of the velocity magnitude Computed drying time: 2h INLETS OUTLET OUTLET OUTLET

Qualitative study on the flushing optimization for the TOB - 2 OUTLET 1 Volume exchange per hour Distribution of the velocity magnitude Computed drying time: 3h INLET

Humidity Sensor Calibration Issues - 1 Why / How ? Commercial sensors for humidity measurements : low accuracy without calibration (nominal: 5% Rh at 20°C); No or poor information on below-zero behaviour no information on long time response (drift due to the humidity cycles) Calibration with reference humidity environments Saturated salt solutions can be employed provided that great care is followed (ASTM 104 recommendations) At present, no data are available below zero °C

Humidity Sensor Calibration Issues - 2 First Series of Sensors Analysed Honeywell HIH capacitative sensors Advantages low costs reduced dimensions good accuracy built-in linearisation circuit easy readout Drawbacks not enough radiation hard 10mm

Humidity Sensor Calibration Issues - 3 Theoretical behaviour (manufacturer specifications) Vout=Vsupply (0.62 Rh25 + 0.16) Rh=Rh25 /(1.0546-0.00216*T) Accuracy ±2% Rh Nominal supply 5V Interchangeability ±5% Rh, 0-60Rh%

Humidity Sensor Calibration Issues - 4 Experimental Strategy Procedure Air volumes in contact with saturated salt solutions. Controlled bath temperature (0.5°C) Humidity transient monitoring (48 hour runs) 22 sensors investigated Operating conditions Temperature range (2-23°C) Humidity range (11-96%) Supply voltage range (4.2-5V)

Humidity Sensor Calibration Issues - 5 Example of recorder time history

Humidity Sensor Calibration Issues - 6 Results of the calibration  d (Rh) or 2 sigma dispersion

Humidity Sensor Calibration Issues - 7 Errors and uncertainties E=Error of theoretical estimate with respect to average [Rh%] d (Rh)=uncertainty or interchangeability (20:1) [Rh%]

Humidity Sensor Calibration Issues - 8 Main results of the study Theoretical (manufacturer) curves do not efficiently describe sensor behaviour Sensor uncertainty (interchangeability 20:1): from 2 to 10%, increasing with increasing humidity and with decreasing temperature Error of theoretical estimate with respect to calibration average: from -6%Rh to +30%Rh, depending on Rh and temperature Influence of voltage supply not well predicted It is possible to achieve overall accuracy (interchangeability, Rh effect, supply effect, temperature effect) within ±10% Rh This requires the reduction of the overall calibration data in terms of both humidity and supply voltage by means of a 4 constant equation, as opposed to the nominal one, based on only two. Best accuracy (within ±3% Rh) can be achieved only with individual calibration curves for each sensor

Humidity Sensor Calibration Issues - 9 Examples of (bad) implications STAGED COOL-DOWN PHASE. T = +2 oC RH reading from factory curve = 50%: DP = -7.5 oC From tests: E = 14.2 % [RH], ± d(RH) = ±5.1% [RH] Possible real RH value = 70%: DP = -3 oC MONITORING DURING OPERATION Temperature of the cooling pipe walls: T = -25 oC Sensor positioned in the bulk volume: T = -10 oC RH reading from factory curve = 10%: DP = -34 oC “Small” global reading error: Etot = 20% [RH] Real RH value in the volume = 30%: DP = -23 oC

Humidity Sensor Calibration Issues - 10 Main conclusions of the study Reliable, long-term Rh measurement inside the CMS Tracker require accurate comprehension of sensor behaviour especially at low temperature Once the radiation/magnetic hardness of sensor families of affordable cost and dimensions are demonstrated, saturated salt procedures should be employed to thoroughly characterize the behaviour of the candidates Sensors should be calibrated and tested in a well-controlled environment against different temperature conditions below zero. The use of chilled mirror hygrometers would be highly desirable Long-period experiments (exposure to humidity cycles) should define the drift properties of the selected sensors and provide guidance for their long-term implementation.

Humidity Sensor Calibration Issues - 11 More details... M.Fossa and P.Petagna USE AND CALIBRATION OF CAPACITIVE RH SENSORS FOR THE HYGROMETRIC CONTROL OF CMS TRACKER (CMS note 2003/024) TEMPERATURE INFLUENCE ON HUMIDITY MEASUREMENTS FOR CMS TRACKER CONTROL (CMS note to appear)

Analysis of the Sensor to be Used in LHC - 1 Tracker irradiation levels Inner Tracker: Fluence (cm-2) ~ 1014 Dose:~ 50 kGy Mid- Tracker : Fluence (cm-2) ~ .5x 1014 Dose:~ 50 kGy Outer Tracker : Fluence (cm-2) ~ 1013 Dose:~ 20 kGy The “average” LHC particle is considered to have 200 MeV energy (~2 mips). The PSI irradiations The irradiation took place at the PSI irradiation facility for cancer therapy, OPTIS. The beam current is 2nA giving 12.5x109 particles/(cm2 sec) over a circle of 3 cm diameter, thus resulting to 1.8x109 charged particles/sec. For our required fluence of 1013-1014 charged particles, this means exposure times between 1.5 hrs and 15 hrs. The charged particles were 71 MeV protons. The “average” LHC particle is considered to have 200 MeV energy (~2 mips), while 71 MeV protons are equivalent to 5 mips. This means that for the given fluence, the irradiation dose was higher. The required dose is 100-500 kGy.

Analysis of the Sensor to be Used in LHC - 2 The HMX2000 humidity sensor by Hygrometrix +Vexc R -Vexc Bridge elements R R -Vsig R Stress => Deformation of the bridge Measures humidity +Vsig

Analysis of the Sensor to be Used in LHC - 3 Procedure Three times three samples of HMX-2000 sensors were exposed to the PSI beam. Two sensors on each sample were connected to a data acquisition system. Each set of samples was exposed to the one of the three Tracker irradiation levels; that is, the Inner Tracker, the mid-Tracker and the Outer. The full measuring range (0-100% rh) of the irradiated sensors before irradiation is known. The measuring range will be remeasured after the samples cool down.

Analysis of the Sensor to be Used in LHC - 4 Bridge resistor changes after irradiation Outer barrel irradiation Total resistance change = 2.7% (per resistor 2.4%, 2.7%, 2.4%, 2.4%, 3%) Mid - barrel irradiation Total resistance change = 3.8% (per resistor 3.8%, 3.6%, 3.9%, 3.9%, 3.8%) Inner barrel irradiation Total resistance change = 7.2% (per resistor 7.1%, 7.1%, 7.2%, 7.2%, 7.2%) No sensor died or showed macroscopic changes of behavior after irradiation. The resistors get indeed some deformation through intense irradiation. However, this deformation is well balanced in the bridge. The irradiated sensors will be re-calibrated as soon as available (cooled down)

Benchmark to test the quantitative performance of the simulation Inlet Control volume Humidity measurement Outlet

Typical experimental behaviour Time required to the “dry front” to reach the sensor Tranport dominated phase Diffusion dominated phase

Discrepancy between measurement and simulation (StarCD) First region: very well predicted Second region: very poor forecast

Additional test: a case where diffusion is the main factor Time scale for drying and re-humidifying: typically the same! DRh is the engine!! Measurement point IN OUT Dry flow 2.25 mm gap

BUT: when pure diffusion is involved the simulation is not that bad! Test with NO “cover” Test with “cover”