Evgeny Maev Aging Workshop at DESY 2001

Study of aging properties of the wire chamber, operating with

high-pressure hydrogen, designed for a precision measurement of the

µp-capture rate.

V. Andreev1, A. Fetisov1, V. Ganzha1, G. Gavrilov1, A. Krivchitch1,E. Kuznetsova1, V. Lebedev1, E. Maev1, O. Maev1, C. Petitjean2, G. Petrov1,

G. Schapkin1, G. Semenchuk1, L. Schipunov1, A. Vorobyov1

1Petersburg Nuclear Physics Institute (PNPI), Gatchina 188350, Russia2Paul Scherrer Institute, PSI, CH-5232 Villigen PSI, Switzerland

ABSTRACT

The project for high precision studies of the muon capture in hydrogen isbased on application of a multi-wire proportional chambers (MWPC) operatingin ultra pure deuterium-depleted hydrogen (protium) at high pressure. A spe-cial test setup was constructed at PNPI to investigate the MWPC performanceat the expected experimental conditions. The chambers were tested inside ofthe vessel filled with a clean hydrogen at 10 bar pressure. The aging studies ofthe MWPCs were performed under intense irradiation from the alpha-source(Am241) and beta-source (Sr90). For example, after 45 days of continuousirradiation by alpha-particles with four intermediate gas refillings we did notsee any changes in the currents,in the signal shapes, and in the counting rates.It was demonstrated that the MWPCs can operate without degradation atleast up to accumulated charges of 0.1 C/cm.wire. These irradiation conditionsare much more severe than in the real experiment. The electron microscopicand X-ray analysis of the anode and cathode wires revealed no serious signsof destruction of the wire surfaces. However, in several radiation tests anappearance of the dark currents was observed (up to 10mkA), the nature ofwhich is not yet clearly understood. During the study of the MWPC we haveobserved the appearance of short duration signals with the amplitudes anorder of magnitude larger than of normal signals from the alpha-particles. Thenumber of such signals (”streamers”) strongly depends on HV. We shall con-tinue these tests in the future with the goal to obtain more detail informationabout aging properties of the MWPCs, operating with high-pressure hydrogen.

Evgeny Maev Aging Workshop at DESY 2001

The test setup for studies of MWPCs and TPCs in hydrogen.

H2

PA2

PA1

PA3

PA4

PA5

PA6

PA7

PA8

PA9

PC2

PC1

cathode

filter

filter

filter HV2

HV1

HV3

PA1,3

PA2

PA4-9A.D.4-9

pump

A.D.2

A.D.1,3

Sr90

A.D.7

A.D.6

A.D.5

A.D.4

A.D.3

A.D.2

A.D.1

A.D.9

A.D.8

FADC1

FADC6

FADC5

FADC4

FADC3

FADC2

FADC6

FADC5

FADC4

FADC3

FADC2

FADC1

A.D.9

A.D.4

A.D.5

A.D.6

A.D.7

A.D.8

&

P.U.

1

C.U.

CAMAC

TRSTTINH

ORCLR

RQ

IN/OOUT

IN

CRATE

CONTR.PC

FCLR

Evgeny Maev Aging Workshop at DESY 2001

0

1000

2000

3000

4000

5000

6000

7000

8000

6.8 6.9 7 7.1 7.2

HV, kV

Gas

gai

n

electronsα-particles

Gas gain vs HV. Measurement with the MWPC operating in

10 bar hydrogen gas irradiated by α- and β-sources. The basic

parameters of MWPC are:

Anode wire plane: W(Au) wires, diameter 25 µm, 2mm wire spacing.

Cathode wire plane: Fe wires, diameter 50 µm, 0.5mm wire spacing.

Anode-cathode gaps: 2.5 mm

The MWPC’s showed stable operation up to HV=7.2 kV

(E=900 kV/cm on the surface of the anode wire) providing the

effective gas gain up to 2·103 and 8·103 while detecting α-particles

and relativistic electrons, respectively. The difference in gas gains

between α and β-particles is due to the space charge effect.

Evgeny Maev Aging Workshop at DESY 2001

0 1000 2000 3000 4000 5000 6000 7000

100

101

102

103

104

HV, V

Gai

n

ionization region

proportional region

Gas gain vs HV. Measurement with the MWPC operating in 10

bar hydrogen gas irradiated by α-source. The basic parameters

of MWPC are:

Anode wire plane: W(Au) wires, diameter 25 µm, 4mm wire spacing.

Cathode wire plane: Fe wires, diameter 50 µm, 1mm wire spacing.

Anode-cathode gaps: 3.5 mm

Evgeny Maev Aging Workshop at DESY 2001

t6

t5

t4

t3

t2

t1

6 anode

2 anode

3 anode

4 anode

5 anode

1 anode

12

8

4

16

8

32

16

32

16

16

16

8

8

140100 120 160 180 200

Time ( 1 ch = 10 ns )

Sequence of signals from FADC created by a β-particle from Sr90

crossing TPC nearly parallel to the anode plane.

Evgeny Maev Aging Workshop at DESY 2001

0

20

40

60

80

100

010

2030

4050

60700

10

20

30

40

50

60

70

80

90

100

events = 9781

Width, 1ch=10ns

Ageing test of the PC with α−source, anode=all, HV=5.9kV, events=10000 5.09.2000

Amplitude, channels

Nevents

The amplitude-width correlation of the signals from α-source (Am241)

at HV=5.9kV.

Evgeny Maev Aging Workshop at DESY 2001

0

20

40

60

80

100

010

2030

4050

60700

5

10

15

20

25

30

35

40

events = 9853

Width, 1ch=10ns

Ageing test of the PC with α−source, anode=all, HV=6.5kV(d), events=10000 6.09.2000

Amplitude, channels

Nevents

The amplitude-width correlation of the signals from α-source (Am241)

at HV=6.5kV.

During the studying of MWPC was observed the appearance of short

width signals ”streamers” (left region) with amplitude larger then nor-

mal signals of α-particles (right region). Their intensity strongly de-

pends on HV. Below 6 kV they are absent, and at 7 kV they contribute

∼ 50% of the total number.

Evgeny Maev Aging Workshop at DESY 2001

6 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 70

5

10

15

20

25

30

35

40

45

50

55 Ageing test of the PC with α−source

Yield of "streamers", %

V, kV

Intensity of the ”streamer” signals vs HV.

Evgeny Maev Aging Workshop at DESY 2001

Prototype of the detector for µCAP experiment.

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S1 S2 S3

Prototype of the µp-capture detector was designed and tested

in a muon beam at PSI. It consisted of two muon beam MWPCs

the TPC, and four planes of electron MWPCs located above the

TPC. The anode wires in the detection plane were oriented in

the X-direction (75 wires). The wires in the strip plane oriented

along the Z-direction were joint in 4 mm strips to detect the X-

coordinate of the stopped muon (38 strips). The 3 coordinates of

the muon stop were measured with the resolution of ± 1 mm (Y),

± 2 mm (X) and ± 2 mm (Z). This device is designed to select

clean muon stops in 3D space and also to measure the muon decay

electron trajectory.

Evgeny Maev Aging Workshop at DESY 2001

strips

anodes

cathode

grid

µ

This figure shows a schematic view of the time projection cham-

ber (TPC). The TPC contains four wire planes. The drift space

between the cathode and the grid planes is 12 cm. The ioniza-

tion electrons are driven through the grid plane to the anode wire

plane, and create avalanches around the anode wires. The sig-

nals are detected from the anode wires and also from the cathode

strips (groups of wires) in the strip plane.

Evgeny Maev Aging Workshop at DESY 2001

0 50 100 150 200 250 300 350 4000

50

100

150

200

250

300

Am

plit

ud

e, A

+20

× (N

a−1)

Time, channel=40ns

Nan

od

e

µ − e

12

11

10

9

8

7

6

5

4

3

2

1

The signals on TPC anode wires from µ-e decay event. The muon

can be seen stopping in the region of anode 4. The decay electron is

seen on anodes 4-12 going to the upper left.

Evgeny Maev Aging Workshop at DESY 2001

Stereoview of the final setup for µCAP experiment (scintillator array,

wire chambers and TPC vessel).

Evgeny Maev Aging Workshop at DESY 2001

Stereoview of TPC of the final setup for µCAP experiment.