Update on TPC R&D

C. Woody BNL

DC Upgrades Meeting

October 9, 2003

C.Woody, Upgrades DC Meeting, 10/9/03 2

R&D Issues

• TPC drift cell now working

• Tests of new 3M GEM foils

• Electronics developments (see Chi’s talk)

• Plans for building prototype

C.Woody, Upgrades DC Meeting, 10/9/03 3

Test Drift Cell

Drift Stack

(presently 29 cm drift)

Used to study

• Drift velocities• Drift lengths• Diffusion parameters• Energy loss (dE/dx)• Study impurities• Readout structures• Field cage design

Lenses

Lower movable source

Laser

Triple GEM

Upper fixed source

Lens

Lab 2-86 in Physics

C.Woody, Upgrades DC Meeting, 10/9/03 4

Drift Cell MeasurementsAr/CO2 (80/20) Ar/CF4 (95/5)

Possible discrepency •Gas mixture uncertainty • 300 ppm O2 • 10-15 ppm H2O

Energy Resolution (Top 55Fe source)

Drift Velocities (laser)

22% FWHM/mean 28% FWHM/mean

* Datao Garfield

* Datao Garfield

C.Woody, Upgrades DC Meeting, 10/9/03 5

Charge Distribution from Drift Cell(top source, 2 mm pad readout)

Ar/CO2 (80/20) Ar/CF4 (95/5)

Measured

Simulation(N.Smirnov)

pad number

s=1.2 mm

pad number

pad number pad number

s=1.7 mm

s=1.1 mm s=1.4 mm

C.Woody, Upgrades DC Meeting, 10/9/03 6

GEM Foils from 3M

Received 2 batches (50 each) of 10x10 cm foils

Roll-to-roll process Limited to 12” width

3M Microinterconnect Systems Division, Austin, TXIn collaboration with Univ. Chicago (J.Collar)

C.Woody, Upgrades DC Meeting, 10/9/03 7

Testing Small 3M Foils

3 stage GEM with three 1” dia. 3M foils

80 mm (55 mm) holes spaced in a hexagonal pattern with 140 mm pitch

(approx. same as CERN foils)

Visually looks to be excellent quality

C.Woody, Upgrades DC Meeting, 10/9/03 8

Comparison of Small Triple GEMS

Small Triple GEMS in Ar/CO2

y = 1E-07e0.0709x

1000

10000

100000

1000000

300 320 340 360 380 400

deltaV(Foil) [V]

Gai

n

CERN

3M

Reproducibilty of 3M curve

Small Triple GEMS in CF4

100

1000

10000

100000

1000000

450 475 500 525 550 575 600 625

deltaV(Foil) [V]

Gai

n

CERN

3M

3M GEMs give higher gain and have somewhat different slopes

Ar/CO2 (80/20) CF4

C.Woody, Upgrades DC Meeting, 10/9/03 9

Electron Transfer Efficiency

Total Electron Transport Efficiency within Small Triple GEM Stack

0

0.2

0.4

0.6

0.8

1

1.2

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

Normalized Field Ratio: EGAP/EGEM [UTG/UGEM]

Eff

icie

ncy N

orm

ali

zed

to

~100%

CERN, Ar-CO2

CERN, CF4

3M, Ar-CO2

3M, CF4

C.Woody, Upgrades DC Meeting, 10/9/03 10

Gain Stability - Small 3M GEMs

Small 3M GEM Gain Stability in Ar/CO2 (80/20)

0

1

2

3

4

5

6

7

0 20 40 60 80 100 120 140 160

Elapsed Time after HV is applied [min.]

Gai

n N

orm

aliz

ed to

initi

al v

alue

Small 3M GEM Gain Stability n Ar-CO2 (80/20)

0

2

4

6

8

10

12

0 5 10 15 20 25 30 35 40 45 50 55

Elapsed Time After HV is Applied [hrs.]

Ga

in n

orm

ali

zed

to

in

itia

l va

lue

Small 3M GEM Gain Variation in CF4

0

0.5

1

1.5

2

2.5

3

3.5

0 25 50 75 100 125 150 175 200 225 250

Elapsed Time after GEM is charged [min.]

Ga

in N

orm

ali

zed

to

in

itia

l va

lue

Ar/CO2 (80/20) CF4

We observe a large gain variation with the small 3M GEMs with time

Time scales involved imply a possible charging effect in the foils

(Gas: 35 ppm H20, <1ppm O2)

C.Woody, Upgrades DC Meeting, 10/9/03 11

Gain Stability - Small CERN GEMs in Ar/CO2

Gain Stabilty of Small CERN GEM in AR-CO2 (80/20)

0

0.2

0.4

0.6

0.8

1

0 25 50 75 100 125 150 175 200 225 250 275

Elapsed Time After HV is Applied [min.]

Ga

in n

orm

ali

zed

to

in

itia

l va

lue

deltaV(Foil)=325 V

deltaV(Foil)=380 V

No large gain variations observed with small CERN GEMs

C.Woody, Upgrades DC Meeting, 10/9/03 12

Gain Stability - Large Foils

Gain Stability of Large (10x10cm) Triple GEM

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0:00 0:14 0:28 0:43 0:57 1:12 1:26 1:40 1:55 2:09 2:24

Elapsed Tim e [hr:m in]

Re

l. G

ain

Conical, 3M ; 320V [1]

Conical, 3M ; 320V [2]

Conical, 3M ; 320V [3]

Conical, 3M ; 320V {A fter P umping} [4]

Conical, 3M ; 320V {A fter P umping andCleaning} [5]Std. Conical, CERN; 340V

Std. Conical, CERN; 320V

Cylindrical, CERN; 340V

T

T

T

T

TT T

T Trip

T

T

T

3M

CERN

C.Woody, Upgrades DC Meeting, 10/9/03 13

TPC Prototype - To be built this year

• Full size module• Tests field cage design• Tests materials to be used in actual construction • Allows testing with cosmic rays• Provides structure on which to design and study readout plane• Test bench for new readout electronics