slide 1

Diamonds in FlashSteve Schnetzer

Rd42 Collaboration Meeting

May 14

slide 2

The Flash Experiment

Measure to ~10% the fluorescence response of theatmosphere to the energy loss of particles in EM shower

Needed for calibrating energy response of cosmic ray fluorescence detectors

• SLAC 28 GeV beam into alumina target

• measure fluorescent yield after 2X0, 6X0, 10X0 and 14X0

• 14 day run in June plus shorter run in July

slide 3

Purpose of Diamonds

• Total particle yield

• Particle spectrum

• Lateral particle distribution

Use GEANT to get

downstream of target

Use diamond detectors to verify GEANT calculation

• lateral distribution of energy deposit

• absolute measurement of energy deposit

relatively easy

relatively hardcalibration

slide 4

10 Hz pulse duration 1 ps

• Measure shower at 2X0, 6X0, 10X0 and 14X0

• Beam: 28 GeV electrons

107 e /pulse

• Use four 1 cm x 1cm CD 100 series diamonds • Diamonds centered at x = 0cm, 5cm, 10cm, 15cm perpendicular to beam

Parameters

slide 5

Diamond Segmentation

pixel: 2.6 mm x 2.6 mm

3 x 3 pixel array

outer ring for definingfiducial region

segmented to help assurefull beam flux hits 3x3 region during calibration

active area 8 mm x 8 mm

slide 6

Ganging

at x = 5 cm ganged to 3 strips

at x = 10 cm & 15 cm ganged to 1 pad

slide 7

GEANT Simulations

2X06X0

energy depositedx= 0 cm

slide 8

GEANT Simulations

10X014X0

energy depositedx= 0 cm

slide 9

Charge Deposited

assumes: 13 eV per e-h pair

Depth Charge

2X0 2.0 x 107 C

6X0 1.5 x 107 C

10X0 2.6 x 108 C

14X0 3.2 x 109 C

charge deposited in central pixel

this charge deposited in 1 ps

charge for 1 mip = 2.0 x 1015 C

slide 10

Calibration

Calibrate linearity of response of diamond to

• large total charge deposition

• high ionization density

Use = 1 mm beam with target out 107 to 108 ppp to map out linearity of response

beam toroid provides precision intensity measurement

Decrease beam density by factor of 2 ( = 2 mm) to see how diamond response depends on ionization density

slide 11

Energy Deposit

charge on central pixel (C)

peak density (C/mm2)

107 on thick target1 mm beam (target out)2 mm beam (target out)CERN BCM test

in ~30 ns

14x0

10x0

6x0

2x0

Compared to CERN

~ 5 x higher peak density

~ 2 x more charge

~ 104 x faster deposit

108 107

108

109

slide 12

Readout Scheme

Vb

Rb

Cb

Cd

I 50 Cs Rs

diamond

ADC

one for each pixel

• VbCb >> 106 C

• Q/Cs << Vb

• RsCs = 100 ns

• RbCb << 0.1 s

Cs = 20 nF

Rs = 5 Cb = 400 nF

Rb = 2.5 k

100 ns shaping

slide 13

Inductive Voltage Drop

2 x 107 C charge deposited

charge in diamond is collected in about 10 ns

20 A over 10 ns

PC board has to be designed to minimize inductance

this current wants to turn on in ~ 1psthe bunch length of the beam

large inductive voltage drop voltage on diamond sags

slide 14

Inductance

Vb

Rb

Cb

Cd

I CsRs

diamond

inductance a problem here

• wire bond wire and PCB trace about 1 nH per mm

• use multiple wire bonds and traces

• should be able to keep inductance less than 5 nH

causes voltage across diamond to sag

slide 15

Spice Simulation

10 nH

5 nH

1 nH

voltage sags about400 V for 1 to 2 ns

input rise time 1 ps

voltage ondiamond

slide 16

PC Board

caps as close to diamond as possible

bias linecan have 1 cm hole here

signals routed by flat cable to ganging board

Vb

Rb

Cb

Cd

I CsRs

on ganging board

Cb on backside

on board

slide 17

X/Y Stage

~ 40 cm arm to keep stagesout from behind optical box backscattering

29.5 cm

slide 18

Readout

Diamond PC Board

biascoax

flat signal cable

Ganging Board

from control room

• • •coax signal lines

to control room

one for each diamond

• shaping resistors• ganging of signals

a few feet

slide 19

Issues

• absolute calibration of energy deposit calibrate with direct electron beam

• effect of ionization density vary density and intensity of electron beam

• low energy and stopping electrons need precise GEANT calculation

• neutron background

• current build up

• inductive effects minimize inductance 5 nH 400 V sag over 1 ns

• radiation damage on average 2 x 1013 e cm2 hr1 in central pixel we’ll measure it

slide 20

Challenges

• 2 times more charge per pulse than anything previous

• 5 times greater ionization density than anything previous

• First attempt at a few % measurement (10% is the standard)

• Very rapid 1 ps energy deposit