Helsinki T2 status

• the 1st production GEM under tests (operational tests)

• the 2nd GEM not accepted due to persistent leakage current problems in two foils (all other parts finished) - wait for components for replacement (and for further GEMs)

• spare parts needed in future to avoid delays in the future

Risto Orava/ on behalf of Kari Kurvinen 8.11.2005

Characterisation of GEM foils:

A. leakage current measurementsB. visual inspectionC. optical scanning

Leakage current measurements of GEM foils• the four segments (A,B,C & D, see Fig.) of the GEM foils are measured separately by Picoamp /Voltage source device (Keithley 487).

• due to these observations, a graphical display (Labview) was added to the measurement system to detect & document instabilities as early as possible (the display was not yet available for the first production GEM).

• current limited by 100 M resistor (corresponding to the max current of 5 A at 500V).

• a foil is approved if the current stays at < 0.5 nA for 5+ min @500V

•leakage currents are measured three times during the assembly (the foil before and after framing, then after gluing into a stack).

36 measurements / detector

• so far 2 /12 foils found to be bad. These were observed to be temporarily short circuited during the second measurement! Both exhibited instabilities during the first measurement, still passed the criteria.

3 x 3 foils x 4

A bad GEM foil

TIFB-segment

C-segment

D-segment

A-segment is short circuited (60 – 150 k)

B,C & D segments OK

noise

HV ramp up

noise

noise

(Note: the time scale in the plots must be multiplied by two)

10 min0 min

6 min

6 min

0.5 nA

0.5 nA

0.5 nA

A ”good” GEM foil ?

(Note: the time scale in the plots must be multiplied by 2)

A-segment A-segment

in air

HV ramp up N2 flush started

N2 flush stopped

in N2

in N2

in N2

spark!

spark!

B-segment

C-segment

D-segment

> 5 min

> 10 min

noise

0.5 nA

0.5 nA

14 min 20 min

14 min

12 min

10 min

Visual inspection

• only the largest visible defects are observable• coordinates are recorded approximately• serious defects due to dust, stains or scratches are easy to see

number of recorded defects in the six latest foils:GEM 1 18, 12, 10 (top, middle, bottom)

GEM 2 10, 31, 40

General observation:the quality of GEM foils is good(i.e. is significantly improved from the past)

defect in the mask 0.5 mm

defect in the mask

2. Optical scanning of the GEM foils• scanning of the entire foil with a

resolution of 2400 (3200) dpi f easible• 0.5 (2) h scanning time per f oil• in a reflective or in a transparent mode

a) the most common defects recorded for the future reference (joint holes, stains, scratches)

b) blocked holes seen easily in the transparentmode (also partially blocked ones)

c) tracking of certain defects by sof tware f romthe picture fi le possible (e.g. by measuring the hole sizes)

Some improvements to the qualitychecking of the GEM manufacturing

1. Handling procedures of the separate detectorcomponents will be registered into a database

Optical scanning of GEM foils• scanning in mixed mode (transparent + reflective)•blue diffuser produces a colour contrast between the holes and copper surfaces1.8 million GEM holes

defects, dust, scratches,etc

scanned pictures can be analysed by using fitting algorithms to count anomalies and to register their coordinates

The worst foil so far: Blue curve shows all the seen objects; the red one only the ”roughly round ones” (e.g.scratches are filtered out). The number of defects (red ones > 80) was 240, while only 40 were found under visual inspection (see previous slide).

AIM: a quantitative measure of the quality of GEM foils