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SLAC Jan 2004

CCD Radiation Damage Studies
J. Brau, O. Igonkina, N. Sinev, C. Potter (University of Oregon)
January 9, 2004

Outline: · Introduction · Neutron and Electron irradiation · Study of SLD VXD3 · Measurement of the trap filling time · Conclusions

O. Igonkina for U.Oregon

CCD Radiation Damage Studies

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SLAC Jan 2004

CCD
The CCD at SLD has shown an outstanding performance, but it also saw the radiation damage when undamped beam run through the detector. signal loss

CCD gates

v v1 v2 3
~20 µ m

Pixel

p substrate

CCD readout

n channel

CCD is proposed as vertex detector for next linear collider. It has excellent space resolution ( 4µm) and is very thin (0.40.1%X0 ). But is it radiation tolerant?
O. Igonkina for U.Oregon

190K

220K

CCD Radiation Damage Studies

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SLAC Jan 2004

Study SLD VXD3 and spare CCDs

SLD VDX3 detector

CCD test stand

O. Igonkina for U.Oregon

CCD Radiation Damage Studies

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SLAC Jan 2004

Goals

· predict radiation damage of CCD in the environment of LC · to verify background conditions (source of radiation) at LC by studying SLD VXD3 CCD · to minimize impact of radiation damage on the operation Understand effects of radiation damage (quantitatively and qualitatively) by different type of particles (neutrons, electrons).
· 1998 : study of the CCD irradiated with 5 · 109 neutrons/cm2 . (J. Brau, N.Sinev, IEEE Trans. Nucl. Sci. NS-47 (2000) 1898) · 2003 step 1: study of the CCD irradiated with 1012 electrons (60 MeV)/cm2 . (J. Brau, et al., submitted to IEEE Trans. Nucl. Sci.) · 2003 step 2: combined study of these CCDs and SLD VXD3 (this talk)
O. Igonkina for U.Oregon CCD Radiation Damage Studies 4

SLAC Jan 2004

CCD Radiation Damage Test-stand
LEDs LFM

T=-73

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Data A/D board AUX Control board PC

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CCD
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Cryostat

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Fastbus crate N
2

Two types of LED were used : · "Narrow line" source which flashes only few pixels per column. The average signal intensity is about 1000 electrons/pixel · "Uniform" light source which flashes the complete CCD surface uniformly. The average signal intensity is about 25-30 electrons/pixel
O. Igonkina for U.Oregon CCD Radiation Damage Studies 5

SLAC Jan 2004

Timing Diagram of the test

Regular measurement scheme
Start of the cycle
LED BC I clk

Signal light pulse

Next cycle start

Signal readout 25 BC
Start of the cycle LED BC I clk

Data processing about 0.8 s

Measurement with sacrificial charge
Injection of traps filling charge Injection of test charge

Variable delay to allow traps emptying

Variable delay to allow traps filling

Data processing

O. Igonkina for U.Oregon

CCD Radiation Damage Studies

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SLAC Jan 2004

Measurements with narrow light
The method shows integrated number of traps in column

Blue - all traps are filled with sacrificial light Red - all traps are empty (results in signal loss)

Irradiation by neutrons as well as by electrons result in radiation damage (significant amount of traps are produced).
O. Igonkina for U.Oregon CCD Radiation Damage Studies 7

SLAC Jan 2004

Measurement with Uniform Light
Varying delay between sacrificial light and signal one could have all traps filled or empty

Each pixel is clearly identified

clusters of traps

traps are filled - no signal lost
sensitive to the clusters of traps

O. Igonkina for U.Oregon

CCD Radiation Damage Studies

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SLAC Jan 2004

Comparison of the electron and neutron damage

Using uniform light source the clusters of traps are identified Damage by neutrons is associated with clusters of traps, while electron irradiation results in few traps distributed uniformly over the surface

due

to neutrons

to due

electrons

deviation of Ntraps from average
O. Igonkina for U.Oregon CCD Radiation Damage Studies 9

SLAC Jan 2004

N

observ ed

/N

expected

where Nobserved is extracted with narrow light method, while Nexpected is signal loss estimated from the trap clusters.
After neutron irrad. After neutron+electron irrad. VXD3

1

5

20

No significant damage due to neutrons is seen in VXD3 data
O. Igonkina for U.Oregon CCD Radiation Damage Studies 10

SLAC Jan 2004

Observation of slow trap filling

N traps at given time/N traps at 33 ms

The observed number of traps depends on the delay time during which a charge packet remains within a pixel potential well and it is longer than predicted by theory.
assume small trap filling time assume large trap filling time

same plot, but for time < 3.5 ms

It may result from the extended distribution of the electrons beyond the confinement volume. Only few pixels show very small trap filling time average volume of the trap cluster is larger than traveling charge packet (J. Brau, et al., submitted to Comp.Phys.Comm.).
O. Igonkina for U.Oregon CCD Radiation Damage Studies 11

SLAC Jan 2004

Conclusions

· The combined study of the damage from neutrons and electrons is performed. Neutrons create clusters of traps while electrons create individual traps distributed uniformly over the surface. · The study of the SLD VXD3 detectors confirms that the the main damage is due to high energy particles like electrons or photons, while the contribution from neutrons is small. · Traps filling with signal charge takes noticeable time - much larger that the time signal spend in each pixel. We expect that the increased readout speed will lead to decrease of charge transfer inefficiency. · The study is to be continued
O. Igonkina for U.Oregon CCD Radiation Damage Studies 12