Background Issues: Real Time Radiation Measurement

S.M.YangEPC.IHEP

Mini-Workshop on BEPCII Background Study10-12 March 2008

Institute of High Energy Physics ,CAS

2

Outline

Detectors introduction Experiments introduction Some preliminary results Next to do

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Detectors PIN Diodes

Online dose rate measurement Installed on vacuum surface near IP For detector protection

RadFETs Online integrated dose measurement About 80 RadFETs mounted on EMC crystals Monitoring dose of CsI crystals

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PIN Diode

XRB100s-CB380 Hole-electron pairs generated

with income particles and bound electrons interaction 1 cm2, 380 μm Sensitivity: 0.25 nA/(mrad/s) Epoxy window depressing

light sensitivity Guard ring halving dark current Radiation damage: nAs/krad

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Dark Current Dark current increased with bias voltage

Terminal capacitance ↓ Response speed↑ Charge collection efficiency ↑

Dark current deeply depends on temperature 1.1 times/°C Temperature compensation needed Thermistors must be provided for each PIN Diode

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Current Measurement Capacitance integration Amplifier

7 internal + 1 external capacitance Ranges: 50pC /100pC…/350pC… 2 Integrator, no dead time 20 bits ADC Frequency up to 2KHz

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RadFET

RadFETs p-type MOSFETs Threshold voltage will increase after exposure

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RadFETs Readout & Calibration

Operation Modes: Exposure Mode Readout Mode Analog switch used 10min cycle Accuracy: 1mv

Calibration 60Co γ Source 8358000280 .D.ΔV

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First period of run Before Aug. 2007 SCQ was not installed Collimator was unavailable 6 PIN Diodes & 8 RadFETs was used

Background Measurement

10

75cm

1#

2#

3#

4#

5#

2. 22m

6#

3. 31m

1. 65m1. 65m

PI N Di odesRadFETs

30cm

10cm10cm10cm

0#1#2#

3#

4#

10cm10cm

40cm

e+ e-

5#6#7#

Z

X

Y

X

Y

X

Y Y

X

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Crotch PipeBoth Beams

e- Beam

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Radial Direction Distribution

• 75cm from the IP (e- upstream)• Horizontal ones suffered much more dose• Injections brought much higher background

Inner

Outer

Down Up

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Z Direction Distribution

• Crotch pipe position seemed to be the worst

• Mostly from electron beam

• Smaller vacuum chamber radius than design value (bottleneck)Crotch pipe (2.2m to IP)

3.3m to IP

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Int. Dose to the CsI Crystals

0

5

10

15

20

25

30

35

Int.D

ose

/ ra

d

RadFET 0#

RadFET 1#

RadFET 2#

RadFET 3#

Curr of e+

Curr of e－

Int Dose of RadFET at e- Up Stream

Time

00:00:002007-03-28

12:00:002007-03-28

00:00:002007-03-29

12:00:002007-03-29

0

10

20

30

40

50

60

70

Be

am

Cu

rre

nt /

mA

30cm

40cm

50cm

60cm

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Int. Dose to the CsI Crystals

40cm

50cm

60cm

0

5

10

15

RadFET 5#

RadFET 6#

RadFET 7#

Curr of e－

Curr of e+

Int Dose of RadFET at e+ Up Stream

0

10

20

30

40

50

60

70

Int.D

ose

/ ra

d

Be

am

Cu

rre

nt /

mA

00:00:002007-03-28

12:00:002007-03-28

00:00:002007-03-29

12:00:002007-03-29

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Int. Dose at the crotch pipe

0

1000

2000

3000

4000

5000

Int Dose

Curr of e－

Curr of e+

Time

Int.D

ose

/ ra

d

00:00:002007-03-28

12:00:002007-03-28

00:00:002007-03-29

12:00:002007-03-29

Int Dose of RadFET 4#

0

10

20

30

40

50

60

70

Be

am

Cu

rre

nt /

mA

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Preliminary Results

• The maximum Int. dose at the position of the inner most CsI crystals was about 10rads/day, which was about 10 times that of the design value.

• Injections brought much more doses.

• The total Int. dose from the electron beam was higher than that from the positron beam.

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Second period of run Oct, 2007 ～ Jan,2008 SCQ was installed Collimators were installed Detectors were rearranged

Background Measurement

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Detectors Arrangement (Oct.07)

ID Position (Z) Position

PD1 0.26m West from IP (58#BLM) (e+ upstream) Outside of Outer Ring

PD2 2.1m West from IP (57#BLM) Outside of Outer Ring

PD3 6m West from IP (56#BLM) Outside of Outer Ring

PD4 0.26m East from IP (61#BLM) (e- upstream) Outside of Outer Ring

PD5 2.1m East from IP (62#BLM) Outside of Outer Ring

PD6 6m East from IP (63#BLM) Outside of Outer Ring

RF0 1.75m East from IP (e- upstream) 50cm Down to Beam Pipe

RF1 1.75m East from IP 45cm Down to Beam Pipe

RF2 1.75m East from IP 40cm Down to Beam Pipe

RF3 1.75m East from IP 60cm Down to Beam Pipe

RF5 1.75m West from IP (e+ upstream) 40cm Down to Beam Pipe

RF6 1.75m West from IP 50cm Down to Beam Pipe

RF7 1.75m West from IP 60cm Down to Beam Pipe

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Detectors Arrangement (Oct,07)

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Status of Detectors (2007/12/28) Dark Currents of PIN Diodes

GT 470nA @ ±6m For a temperature precision of 0.02°C， the poor dose rate accuracy wo

uld be only 4mrad/s!!! GT 150nA @ ±0.26m Newly Installed:

5# @ 2.1m (e- upstream) about 100nA

2# @ -2.1m (e+ upstream) about 10nA

RadFETs Suffered Int. Dose from 1500 to 2700 Rad Accuracy was getting worse (±5rad)

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Early in the second period The position of inner most CsI Crystals upstream e- beamMore than 100rads for 10 days

The position of inner most CsI Crystals upstream e+ beamMore than 100rads for 10 days

Accelerator people were doing experiments

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Early in the second period

0.26m upstream e- beam

Background was still not acceptable

Mostly from injections and beam aborts

Usually, electron beam was much worseelectron beam injections

or aborts

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Experiments of Collimators

Storage ring collimators and transport line collimators.

Influences of collimators for stable beam run and injections were studied.

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10

100

1000

10000

100000

0

1

2

3

4

5

6

7

I nsi deOutsi deLi f et i me

Storage Ring Collimators

TimeCurrent

（ mA,10bucket ）

R4OCH02 Collimator position

outside inside

14:15 - 14:20 99.9 - 98.2 42(open) 42(open)

14:23 - 14:28 93 - 91.3 32(14) 32(14)

14:33 - 14:38 89.2 - 87.8 31 31

14:43 - 14:48 84.9 - 83.6 30 30

14:52 - 14:57 82 - 80.8 29 29

15:02 - 15:07 79 - 77.8 28 28

15:12 - 15:17 75.8 - 74.7 27 27

15:25 - 15:30 72.3 - 71.226(11.3)

26(11.3) Sharp signals typically 0.2~0.3mrad/s

caused by beam lifetime decrease were detected

No obvious effect was observed by tuning the collimator aperture!

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Time

Current（mA）

(electron beam Injection)

R4OCH02 Collimator position

outside inside

15:42:06- 15:42:35

0 - 89.242(whole

open)42(whole open)

15:43:26-15:43:35

88 - 106.8 32(14) 32(14)

15:43:39-15:43:56

107 - 155.426(11.3

)26(11.3

)

15:45:36-15:45:49

0-4026(11.3

)26(11.3

)

15:47:59-15:48:54

0 - 20626(11.3

)26(11.3

)

Storage Ring Collimators

• Injection background was much lower (0.2rad most).• Still no obvious effect for beam injection!!!• Beam aborts brought much higher doses!!

①

②

③

④ ⑤

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Beam Aborts Background

More than 9 rad

• For most serious PIN Diode (2.1m upstream e-),Beam abort could bring several rad of int dose.

• For detector safe, Dose of one injection and beam abort should be depressed to no more than 1 rad.

• Beam abort must be well treated.

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Transport Line collimator

Still high beam abort background

Much lower injection background

• The energy dispersion is ±0.3% in e- transport line . • The collimator aperture for setting emittance is ±3mm,namly ±1.7. • R4OCH02 is whole open .

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Positron Beam

Background was well controlled!

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Beam Abort Improved

Temporary beam abort system were used to let the beam lose in injection region by using injection kickers and a local bump in that region

Beam abort and injection were all well controlled!

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Electron-Positron Collision

0.26m upstream e-

2.1m upstream e-

Single beam background was good enough!But there was some trouble with e+e- collision.

e- always be worse!

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Beam Separated Injection

Everything seems OK now!

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SR Runing (From Feb.2008)

Background seemed to be acceptable even for difficult injections

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The inner most RadFET

SR Runing (From Feb.2008)

The value was getting smaller with time,It seemed to be annealing

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Conclusions Background was being effectively decreased. For single beam, background from injections an

d beam aborts is safe for CsI crystals. Synchrotron radiation is also safe enough. Injection with collision is not ideal, Beam must

be separated by tuning RF phase for injection.

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Next to do

Study of background source and proportion for radiation protection.

Improve the performance of radiation detectors for steady run measurement.

More experimental study of collimators. Background study after BESIII finally installed. Suggestions from you…

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Thank you!