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R&D on Hadron Blind detector, recent results 27.11.2002 - 15.01.2003 PowerPoint Presentation
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R&D on Hadron Blind detector, recent results 27.11.2002 - 15.01.2003. Issues addressed: - gain limits in CF 4 with heavily ionizing particles - operation with reflective CsI photo-cathode, gain and

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R&D on Hadron Blind detector, recent results 27.11.2002 - 15.01.2003


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slide1

R&D on Hadron Blind detector, recent results

27.11.2002 - 15.01.2003

Issues addressed:

- gain limits in CF4 with heavily ionizing particles

- operation with reflective CsI photo-cathode, gain and

ion back-flow, optimization of the powering scheme

- measurement of stability (first attempts)

slide2

Experimental set-up

Independent powering

of the mesh for the

measurement of signal

as a function of drift field

Hg lamp

Powering scheme

Absorber

Fe55

Am241

HV

40

Mesh

Mesh

R(0)

HV

3 (1.5)mm

3 (1.5)mm

CsI

R

GEM1

GEM1

R

1.5mm

1.5mm

GEM2

GEM2

R

1.5mm

1.5mm

R

GEM3

GEM3

R

2mm

2mm

2R

PCB

PCB

R = 10MW

Independent powering

of the G1 top for the measurement

of ion back-flow

pA

Set-up for the study of operation

with CsI photo-cathode

Set-up for the study of gain limits

slide8

Triple-GEM with reflective CsI photo-cathode, thickness 2000A.

Current to the PCB as a function of Vgem.

Amplification

Extraction

slide9

Current measured at the mesh ( Gain=1). HV is applied to

GEM1 with respect to the mesh.

Final procedure to determine current at gain=1: apply Vmesh = 1kV, wait 20 min, read current to the mesh.

slide10

Gain in Ar-CO2 and CF4 measured with UV illumination

Gain measured

with Fe55

Factor 2 discrepancy is not understood yet

slide12

Ion back-flow for different values of induction field. Optimization

of electrons collection efficiency.

WIS, 2.01.2003

slide14

History of the 2nd run with CsI photo-cathode. Each point is the measurement

of extraction to the mesh (current at gain=1). Medium-term stability

measurements were performed during day 3 (4 mC/cm2), day 4 (3 mC/cm2),

day 5 (2 mC/cm2).

Upper limit of the total charge in 10 years of PHENIX

operation estimeted to 1 mC/cm2

slide15

Stability measurements. UV intensity corresponds to ~108 photons/cm2/s.

In the 1st and 2nd runs UV and HV were applied simultaneously, in the 3d

run UV was applied 2h later than HV.

slide17

Summary.

- Triple-GEM provides stable operation in CF4 at gain 104

in short term (hours - days);

- Strong non-linearity is observed when total avalanche charge

exceeds ~3*106 electrons;

- Discharges in the presence of HIPs occur in CF4 at gain of ~106(small GEM,

no defects). In case of large GEM discharge threshold is determined by the

GEM quality rather than avalanche charge or voltage.

- Triple-GEM with CsI reflective photo-cathode shows stable performance

at gain of 104in short term (hours to days);

- Ion back-flow can be optimized down to the level of 0.7, it does not depend

on gas and electric fields inside GEMs package;

- No deterioration of CsI observed after delivering charge up to 9mC/cm2