Straw tube Straw tube measurementsmeasurements

Sebastian Bablok, Øystein Sebastian Bablok, Øystein Djuvsland,Djuvsland,

Per Thomas HillePer Thomas Hille

The DetectorThe Detector

A model of the straw tube detector A model of the straw tube detector used for the Outer Tracker in LHCbused for the Outer Tracker in LHCb

16 channels16 channels 1500 V bias1500 V bias Gas mixture: 75% Ar, 15% CHGas mixture: 75% Ar, 15% CH44, 10% , 10%

COCO22

The straw tubeThe straw tube

1500 V

Cathode tube, (5 mm Ø)

Anode wire, Au-plated tungsten (0,025mm Ø)

Gas:75 % Ar15 % CH4

10 % CO2

TestingTesting Test setup for Test setup for

testing the 16 testing the 16 channels one by channels one by oneone

““Only” 2 dead Only” 2 dead channelschannels

Nice soldering points!0

158

The Final setupThe Final setup

Scope trace (average) of Scope trace (average) of output voltage from straw output voltage from straw

tube 15.tube 15.

HypotesisHypotesis

The gas amplification gain depends The gas amplification gain depends on the bias voltage of the straw on the bias voltage of the straw tubes.tubes.

The gain increases at higher The gain increases at higher voltagesvoltages

Test of hypotesisTest of hypotesis

Measure the output signal from the Measure the output signal from the straw tubes for different values of straw tubes for different values of the HV.the HV.

ResultsResults

Conclusion (preliminary)Conclusion (preliminary)

Our observations contradicts the Our observations contradicts the Hypotesis. The gain is independent Hypotesis. The gain is independent of the bias voltage. of the bias voltage.

DiscussionDiscussion

We dont believe in these results, gain We dont believe in these results, gain shoud depend on HV.shoud depend on HV. Implication: We need an ad-hoch hypotesisImplication: We need an ad-hoch hypotesis

Ad hock hypotesis: We used wrong type Ad hock hypotesis: We used wrong type of radioactive source (strontium).of radioactive source (strontium).

We should repeat the measurements We should repeat the measurements again with a monocromatic source again with a monocromatic source (Fe55).(Fe55).

New Gain New Gain measuremenmeasuremen

tsts The output voltage The output voltage

of the straw tubes of the straw tubes was measured for was measured for 1350, 1400, 1450, 1350, 1400, 1450, 1500, 1550 Volt.1500, 1550 Volt.

At 1550 V we could At 1550 V we could also se the escape also se the escape peak.peak.

1350 V 1350 V

1400 V1400 V

1450 V 1450 V

1500 V1500 V

1550 V 1550 V

Escape peak, enlarged Escape peak, enlarged viewview

ResultsResults

All measuremnts fitted with an exponentialFunction.

Only the 4 highest measuremts fitted with an exponentialFunction.

ConclusionConclusion

The output signal from the straw The output signal from the straw tubes depends on the bias voltage.tubes depends on the bias voltage.

The dependence is exponential The dependence is exponential between 1400 and 1550 Voltbetween 1400 and 1550 Volt

Noise Noise measuremenmeasuremen

tt We measured the We measured the

number of fake number of fake trigger as a function trigger as a function of the trigger of the trigger treshold.treshold.

Without radioactive Without radioactive (upper figure).(upper figure).

With radioactove With radioactove source (bottom source (bottom figure). The source figure). The source was sentered abowe was sentered abowe straw 8 straw 8