Thermal Performance of the GLAST LAT Tracker Silvia Rainò INFN-Bari For the Italian GLAST Tracker Collaboration 19/11/2018 Silvia Rainò - 9th IPRD- Siena, 23rd-26th May 2004

Silvia Rainò - 9th IPRD- Siena, 23rd-26th May 2004 Outline The GLAST (Gamma Ray Large Area Space Telescope) Instrument Environmental Tests on the LAT (Large Area Telescope) Tracker: Thermal-Vacuum Test Results Dependence of the Silicon Detectors Performance on Temperature 19/11/2018 Silvia Rainò - 9th IPRD- Siena, 23rd-26th May 2004

Silvia Rainò - 9th IPRD- Siena, 23rd-26th May 2004 The GLAST Observatory Large Area Telescope (LAT) Gamma Ray Burst Monitor (GBM) Spacecraft Launch Vehicle Delta II – 2920-10H Launch Location Kennedy Space Center Orbit Altitude 575 Km Orbit Inclination 28.5 degrees Orbit Period 95 Minutes Orientation +X to the Sun 19/11/2018 Silvia Rainò - 9th IPRD- Siena, 23rd-26th May 2004

Silvia Rainò - 9th IPRD- Siena, 23rd-26th May 2004 The LAT Instruments Tracker GLAST-LAT Performance Tracker Aeff ≈ 8000 cm2 (E > 100 MeV) Angular Res. < 3.50 @ E=100 MeV < 0.150 @ E>10 GeV F.O.V. ≈ 2.4 sr Source Loc. < 0.5’ Energy Resolution < 10% Dead time < 100 s Time Res. ≈ 2 s Power 500 W Grid Thermal Blanket ACD DAQ Electronics Calorimeter Systems work together to identify and measure the flux of cosmic gamma rays with energy 20 MeV ->300 GeV. 19/11/2018 Silvia Rainò - 9th IPRD- Siena, 23rd-26th May 2004

Silvia Rainò - 9th IPRD- Siena, 23rd-26th May 2004 The GLAST LAT Tracker g Read-out cable Carbon fiber side-walls Titanium flexures Multi-Chip Electronics Module (MCM) 16 towers in a 4  4 array 19 stacked carbon fiber panels: trays 18 x,y alternated planes/tower W converter (12 3% r.l., 4 18% r.l.) 2mm gap between x/y oriented SSDs e+ e- 37cm  37cm of active cross section 83 m2 of Si 11500 SSD, ~ 1M channels 19/11/2018 Silvia Rainò - 9th IPRD- Siena, 23rd-26th May 2004

Silvia Rainò - 9th IPRD- Siena, 23rd-26th May 2004 TKR Pictures Tungsten Tray Panel EM Tower final assembly steps Flex cables with thermistors SSDs The tray box MCM 19/11/2018 Silvia Rainò - 9th IPRD- Siena, 23rd-26th May 2004

Tracker detector: construction work-flow 18 Tracker Module Environmental Tests Italy (Alenia Spazio) Module Structure Components SLAC: Ti parts, thermal straps, fasteners. Italy (Plyform): Sidewalls Readout Cables UCSC, SLAC (Parlex) SSD Procurement, Testing SLAC,Japan, Italy (HPK) 10,368 SSD Ladder Assembly Italy (G&A, Mipot) 2592 Tray Assembly and Test Italy (G&A) 342 342 Composite Panel, Converters, and Bias Circuits Italy (Plyform): fabrication SLAC: CC, bias circuits, thick W, Al cores 648 Electronics Fabrication, burn-in, & Test UCSC, SLAC (Teledyne) 19/11/2018 Silvia Rainò - 9th IPRD- Siena, 23rd-26th May 2004

Environmental Tests on TKR Aim of the Environmental Tests on the GLAST TKR Towers is mainly to verify the capability to withstand the conditions expected during launch phases (mechanical tests) and on orbit (thermal/thermal-vacuum tests) Trays Vibration tests & thermal cycles Vibration tests Towers Thermal vacuum cycles: thermal balance This presentation focuses on the results of the THERMAL BALANCE TEST on the EM Tower and on the expected thermal performance of the GLAST Tracker 19/11/2018 Silvia Rainò - 9th IPRD- Siena, 23rd-26th May 2004

EM-Tower: Thermal-balance test Temperature measurements: Thermocouples:  100 placed throughout the tower and MGSE Thermistors: 16 placed two per each flex cable Action: measure the temperature distribution in the tower under predicted orbital operating conditions, by using a combination of 3 tracker power levels (8,10,12 W) and 3 controlled base plate temperatures (20, 0, -15°C). Goal: Correlate GLAST EM TKR Tower internal temperatures with those measured by the Tower cable thermistors and also with those predicted by the Tower thermal math model. 19/11/2018 Silvia Rainò - 9th IPRD- Siena, 23rd-26th May 2004

Test Set-up Thermocouples on the side-walls of the tower Guard shield over the the tower + MLI blanket system to prevent heat losses Thermocouples on the side-walls of the tower TCs MLI blanket covers the tower 19/11/2018 Silvia Rainò - 9th IPRD- Siena, 23rd-26th May 2004

… in the thermal-vacuum chamber Tower Electronics Module Thermal vacuum chamber in Alenia AIT - Rome 19/11/2018 Silvia Rainò - 9th IPRD- Siena, 23rd-26th May 2004

Thermal Balance Test Profile Clean room temperature 22°C Pump down (p=10-6 torr) Start flooding shrouds with LN2 (T=81 K) 25°C HOT BALANCE 20°C MID BALANCE 0°C Recovery LOW BALANCE -15°C 12W 8W 10W 19/11/2018 Silvia Rainò - 9th IPRD- Siena, 23rd-26th May 2004

Silvia Rainò - 9th IPRD- Siena, 23rd-26th May 2004 TB Test Results -1 Node 1: tray 18 (top) Node 5: trays 1/2 Node 4:trays 3/4/5 Node 3: trays 6/7/8/9/10/11 Node 2: trays 12/13/14/15/16/17 Node 6: tray 0 (bottom) The temperature distribution along the tower has been studied dividing it into six nodes. This division allows to create a correlation of the experimental results with the math model. TB1 TB2 TB3 TB4 TB5 TB6 TB7 Balance condition: < 0.2°C/hr Balance duration: 4hr 19/11/2018 Silvia Rainò - 9th IPRD- Siena, 23rd-26th May 2004

Thermistors vs. thermocouples TB Test Results - 2 Thermistors vs. thermocouples Thermocouples (continuous) and thermistors (dashed) 19/11/2018 Silvia Rainò - 9th IPRD- Siena, 23rd-26th May 2004

Silvia Rainò - 9th IPRD- Siena, 23rd-26th May 2004 TB Test Results -3 Average Temperature for each node at the different balance cases T  5  6.5°C between top and bottom trays of the tower 20 °C 0 °C -15 °C 19/11/2018 Silvia Rainò - 9th IPRD- Siena, 23rd-26th May 2004

GLAST TKR Silicon Detectors Performance Signal/Noise dependence on temperature 19/11/2018 Silvia Rainò - 9th IPRD- Siena, 23rd-26th May 2004

SSDs performance simulation A Monte Carlo Code, developed to simulate all the physical processes that occur in Silicon Strip detectors, has been used to evaluate the total number of electron-hole pairs in silicon produced by a MIP, as a function of temperature. The number of e-h pairs has been estimated as a function of temperature. Since Egap slightly decreases as the temperature increases the total number of charge carriers in silicon slightly increases with the temperature. (more details in F.Loparco’s talk… yesterday) 19/11/2018 Silvia Rainò - 9th IPRD- Siena, 23rd-26th May 2004

Pair Production vs Temperature Most probable number of e-h pairs e-h pairs distributions have been fitted with a Landau function Average number of e-h pairs 19/11/2018 Silvia Rainò - 9th IPRD- Siena, 23rd-26th May 2004

Noise sources Thermal noise due to the feedback resistor: i2nf=4KT/Rf P E R Hpre=H1= Vpreamp_out/i input ssd ------- H2= Vout_preamp/Vin preamp - 1st stage of the pre-amplifier is a MOSFET: i2na=0 Electronic noise due to the 1st stage of the pre-amplifier: i2na= 0 v2na = 2.7KT/gm+Af/f Shot noise due to the leakage current: i2nd=2eIL Thermal noise due to the bias resistor: i2nb=4KT/Rb 19/11/2018 Silvia Rainò - 9th IPRD- Siena, 23rd-26th May 2004

Silvia Rainò - 9th IPRD- Siena, 23rd-26th May 2004 RMS Noise Voltage At the shaper output, the rms noise voltage is H1=Vpre/Id Hshaper=Vout/Vpre H2=Vpre/V* Hshaper=Vout/Vpre H2 H1 Hshaper Hshaper detector charge-preamplifier shaper Rd Cd Rf Cf gm gms Rfs Cfs Cc Id Vpre V* Vout 19/11/2018 Silvia Rainò - 9th IPRD- Siena, 23rd-26th May 2004

Noise temperature dependence ENC=1500e- @ T=300K ENC evaluated from the rms noise voltage assuming a front-end overall gain of 115 mV/fC Pre white noise corrisponde al contributo 2.7KT/gm mentre il parallel noise contiene sia il rumore del bias resistor che il contributo della resistenza di feed-back che per il teorema di Miller può essere portata a massa. 19/11/2018 Silvia Rainò - 9th IPRD- Siena, 23rd-26th May 2004

Signal/Noise vs Temperature The signal to noise ratio (S/N) has been evaluated as the ratio between the most probable/average number of electron-hole pairs and ENC. S/N  21.5 @ 300 K MIPs crossing 400 m thick Si Vthreshold: ¼ MIP VMIP (600 mV)  Vth = 150 mV S/N  19 @ 300 K 19/11/2018 Silvia Rainò - 9th IPRD- Siena, 23rd-26th May 2004

Silvia Rainò - 9th IPRD- Siena, 23rd-26th May 2004 Conclusions A detailed study of the mechanical and thermal performance of the GLAST TKR has been done on an Engineering Model Tower before the beginning of the flight production started in April 2004. The results of the Thermal Balance Test have been presented: an average temperature gradient of ≈6°C between the top and bottom of the tower has been found at a nominal tower power level of 10 W confirming the results of the thermal math model The dependence of the detectors performance on the temperature has been studied, by using a Monte Carlo code developed to fully simulate the silicon detector performance. In order to understand the overall performance of the TKR, a complete simulation taking into account the strip geometry, the charge sharing, the impact angles of particles, …. is needed (see M.Brigida talk) 19/11/2018 Silvia Rainò - 9th IPRD- Siena, 23rd-26th May 2004

Silvia Rainò - 9th IPRD- Siena, 23rd-26th May 2004 2007 19/11/2018 Silvia Rainò - 9th IPRD- Siena, 23rd-26th May 2004

Tracker Trays Tray panel Gr/CE Face Sheet Bias-Circuit SSDs Bias-Circuit Structural Panel Converter Foils TMCM Gr/CE Face Sheet C-C MCM Closeout Wall Thermal Boss 1 lb/ft3 Aluminum Honeycomb Core C-C Structural Closeout Wall Tray panel 19/11/2018 Silvia Rainò - 9th IPRD- Siena, 23rd-26th May 2004

End of Mission expectations At the end of mission a total dose of 5 krad (a factor 5 engineering margin is considered); the leakage current per strip increases to Il=94 nA at T0=298 K. ENC  2000 e- @ 300K The S/N ratio decreases from 20 at 250 K to about 4 at 350 K. 19/11/2018 Silvia Rainò - 9th IPRD- Siena, 23rd-26th May 2004

Simulation Parameters Some Parameters used for the SSDs simulation: Il=1.5nA/strip @ 296K Cd=47nF Rb=40M Rf=10G Af=310-12V2 gm=0.7mS 19/11/2018 Silvia Rainò - 9th IPRD- Siena, 23rd-26th May 2004

Front-end electronics Detector Preamplifier Shaper 19/11/2018 Silvia Rainò - 9th IPRD- Siena, 23rd-26th May 2004