Amilkar QuinteroAdvisor: Dr. Marcus Hohlmann

June 18, 20101/41

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The variation of the energy loss around the mean energy loss value is an asymmetric distribution called the Landau distribution

The area density of the medium

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xNx eIeII 00

The atomic photoelectric effect is very important for gaseous detectors development, since X-rays isotopes (~keV) are commonly used to test these detectors.

2

1

cm

E

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4Readout

Detector

Incoming photons

Nucleus

Primary Ionization

Secondary Ionization

Ion

Electron

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Cosmic ray

Atmosphere molecule

Particles

2 Detectors

2 Detectors

High-Z material

Scattering angle

Foil of Kapton coated with copper layers on both sides and chemically pierced.

High voltage is applied across GEM foils so high electric field makes an avalanche of electrons through the holes .

Gas mixture of Argon and CO2 in the volume proportion 70-30.

Spatial resolution ~50m. Triple-GEM configuration

allows foils to hold lower voltage.

Two dimension readout.

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1. Our GEM detectors are based on TERA Foundation detectors design which are an upgraded version of the 30 cm x 30 cm COMPASS experiment GEM detectors.

2. We made minor improvements on the TERA GEM design, notably on the design of frame that support the GEM foils and define space between different GEM foils.

3. Each GEM foil is divided in 12 sectors in order to reduce the discharge probability and its spread over the entire area.

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Courtesy of COMPASS

Validation condition: 500 volts with leakage current less than 5 nA, in Nitrogen (operational voltage ~300 V)

1. Test performed in class 1000 clean room.2. Nitrogen should flow at least five box volumes.3. Test is made before and after framing4. 24 foils were framed.

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Before Framing

After Framing

Average 2 nA

Average 1.3 nA

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1. The frames have been re-designed to reach maximum performance with thermal method for stretching and gluing the foils.

2. The new design also facilitate the alignment of all framed foils during assembly procedure.

3. Inner strips are to maintain the distance between foils.4. Coat the inner parts and put the frames in the oven per 12 hours

at a temperature of 45 0C.

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1. We use the thermal method to stretch the foils.2. We designed the stretching device for 30cm 30cm foils.3. Put it in the oven at 45 0C, in ~20 minutes should be stretched.4. We are the first group to use the thermal method for 30cm 30cm

foils.

1. Glue the frame onto the stretched foil, still in the stretching device, and put them in the oven at 45 0C for 12 hours for the glue to polymerize.

2. Framed foils are re-tested with high voltage.3. GEM 3 must have an slit for the gas system.

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1. The drift cathode is made of a 5 m copper on 50 m Kapton foil 2. Honeycomb structure glued onto the Kapton side as support for

mechanical rigidity.3. Air bubbles must be removed.

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1. A 3 mm frame is glued onto the drift cathode on the copper side that define the drift region of the detector.

2. The extend strip of the cathode is where the HV is applied

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1. The two-dimensional readout consists of two layers of perpendicular copper strips at 400 m pitch separated by 50 m.

2. Like for the drift cathode, we glue the readout board on a honeycomb structure support.

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Courtesy of D. Watts TERA Foundation

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1. We glue together the drift cathode and the 3 framed GEM foils (12 hours for polymerization of the glue).

2. Remove the extra material part

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First two detectors of June 2009

1. Glue the stacked foils on to the readout board.

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1. We coat the side of the assembled detectors to prevent gas leaks and guarantee a good gas tightness

1. The HV board is a voltage divider with 3x12 inputs to equally and independently apply HV to each of the 12 sectors of the 3 GEM foils of one triple GEM detector.

2. The bias current is tested before and after the HV board is attached to the detector to validate its Ohmic behavior (equivalent resistance of 5.42 M).

22/41Disconnected Connected

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HV board

Gas Inlet

Grooves in drift spacer

Slits

Gas Outlet

1. Readout strips for one sector are ganged together to study the entire area, the others sectors are grounded. 2. Mounted Triple-GEM detector for X-ray source test at GDD lab at CERN.3. Energy spectrum obtained with 8.04 keV Cu X-ray , showing a ~ 20% energy resolution (FWHM) (Gaussian fit in blue).

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Argon escape

Photo peak

Gate pulse of ADC

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Around 100,000 muon events were recorded using one sector of the total active area (30cm 5cm) for five hours. We expect ~45,000 counts at sea level, but since Geneva is at 373 m above sea level, more cosmic ray particles are detected.

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The rate of counted X-rays 41.03 kHz at plateau at 3.9 kV

Charge sharing factor kc=1.2228

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COMPASS Result

Average energy to produce ion-electron pair

The current is measured directly from the readout

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Readout

Drift Cathode

Spacers

FR 4 frame

Aluminized Mylar lid

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Disconnected from the detector

Previous result: y = 5.4337x – 17.884

Connected to the detector

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Area 10cm 5cm Rate 40 cpm (50 cpm theoretical value)Applied voltage 4.3 kV

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Area 10cm 5cm Resolution ~60 % (FWHM)Applied voltage 4.3 kV

•Source 55Fe (5.9 keV)•Plateau 4.05 kV

Possible causes: gas mixture, holes shape, bad electric field, energy of the source.

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Eq. I

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The Pre amplifier is an integrator with a 1 pF capacitor

Eq. II

Input signal :-Width: 0.1 s-Height: 0.1 V to 1.5 V

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Eq. I = Eq. II=> Qcal

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Width (s)

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Average: 0.4274 VsStandard Deviation: 0.0237 Vs

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Readout

Honeycomb

GEM foilFR 4 frame

Area 10cm 5cm Rate 20 cpm (50 cpm theoretical value)Applied voltage 4.3 kVNoise level 0.9 VVery sensitive to vibration

Honeycomb lid

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•Assembled 7 detectors, 30cm 30cm active area. Only one shows problems.•Assembly time of one detector is 4 days.•Cosmic rays and Cu X-rays (energy resolution ~20% FWHM) spectrums are reproduced.•Rate plateau shows at 3.9 kV.•Gain ~2 104.

•Standard small detector reproduces cosmic rays and 55Fe X-rays spectrums (energy resolution ~60% FWHM).•The displacement in the plateau of the small detector modify the results obtained with the big chambers. •Honeycomb detector reproduce the cosmic rays distribution but it is very sensitive to vibration.

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55Fe + e- 55Mn + e

Iron 55 decay:

Electron capture

K-shell

5.9 keV

55Mn

K-shell

55Fe