Electron detectors

for HAPPEX2 and He

•Design•Tests with high E electrons•PMT tests•Installation in HRS

4

Focal plane Detector

= 65 Mhz Dose = 2 MRad

Geometry

Two segments geometry for HAPPEX2

Detector stack overlaps elastic line

100 x 600 mm

Mechanics

Brass-quartz stack

Light guide Filter box

5 inches PMT

Fused quartz

•Radiation hard (Babar, CMS, E158)

•Optical polished (15-20 Angstr)

• 92% transmission in the range [350,550] tested with optical bench and with cosmic rays

Magnetic materials

M(Fe) -> specified ~ 1%

P(Fe) -> a) Bext at focal plane b) r

<A> Mean Moeller asymmetry -> numerical calculations.

FA = M(Fe) x P(Fe) x <A>

False asymmetry

Bext

Polarized electronsN+ N-

Fe

Fe

-Bext <= 0.4 Gauss, r <=2

PFe < 10-5

-<AMoller> << 1 ppm

-Negligible contribution in the detector asymmetry.

Magnetic materials

Test with high energy electrons

h1 h2

Beam pipeMoeller dipole

Trigger scintillatorsHodoscope

Motorized rail

Selection of 2 e- of same energy

Resolution

•Ne/e- = 250

E/E = 18 %

Edge Effects

100 x600 mm

E/E=90%

E/E=20%

•Larger resolution balanced by extra statistics.•Need to correct for correlations between two segments for final result.

Real data to be analyzed

PMT tests

•PMT burle 8854

•Need wide range in gain (10E3-106) :

• 2 bases available: - Happex - Resistive, low gain

PMT test

Gain/IAnode correlations

Running conditions:

40 MHz, Filter 1/10 25 e/e I=1A with G=104

Preliminary results:

-Happex Base G/G =5% @ 1170V

-Resistive base: G/G= 2%@ 1420V

Installation in HRS

Horizontal rails

Installation in HRS

Installation in HRS

10 cm vertical gap between VDC and detector for scanners

Detector Change

•Remove 1 segment in each spectro. ~4h

•Start installation of previously prepared “L” detector.

•Assembly of the 2 removed segments for the 2nd “L” ~8h

•Installation of the 2nd “L” ~6h

Could be done within 1 day Man power : 5

WEB

Eveything at:

www-dapnia.cea.fr/Phys/Sphn/Parity/