Preliminary RP simulations concerning proton beam losses

in AWAKESilvia Cipiccia1,2, Eduard Feldbaumer2, Helmut Vincke2

1 University of Strathclyde2 CERN DGS/RP

Outline

• Implemented geometry• Accident scenario• Metal shielding effect– Prompt dose– Damage 2 Electronics

• Air Activation• Conclusions

Implemented Geometry

CNGS 2002:Simple clean geometry

80 cm thick concrete wall

50 cm Ø laser core

30 cm thick concrete wall

Preliminary AWAKE Geometry

Access gallery

p+ beam

e-gun room

CNGS target

Accident Scenario

• Beam Parameters:

• Copper target: Ø = 10 cm, l = 50 cm• Beam position: 10 cm before copper• 2 different scenarios (worst cases):– Full beam loss in front of big venting gallery– Full beam loss in front new electron gallery

• Dose conversion coefficient: EWT74 worst case scenario

p+ energy Energy spread Beam shape

400 GeV 0% Pencil beam

Dose limit for low-occupancy supervised radiation area: 15 Sv/h (to avoid future need for active dosimeter)

e- gallery big venting tunnel

Accident ScenarioEffective dose per incident proton (pSv/proton)

Accident scenario loosing 1 bunch of nominal beam (from Chiara):# Shots per Year

Bunch Intensity

Beam Lost per Shot

Total Loss

Steering 100 5E9 p+ 10% 5E10 p+

Accident 2 3E11 p+ 100% 6E11 p+

Target position dose/p+ @ access gallery

error Bunch intensity

Accident dose / bunch

e-BG 2.3e-4 pSv/p+ 9.9% 3e11 69 Sv

BVT 4.6e-4 pSv/p+ 4.9% 3e11 138 Sv

Safety Code F: Annual dose > 100 Sv Optimization required

Plasma cell

• P+ beam:– Beam size: s =250 mm

• Beam lost at the valve (valve fails opening)• Plasma Channel

• 5 m long• 4 cm Ø• Rb vapor (1015 cm-3 ->1.4x10-7 g/cm3)

• Fast Valve: 5 mm thick, 4 cm Ø, material steel AISI304• Metal shielding: cylinder

– inner diameter 30 mm, – thickness 2mm, – material steel AISI304 – length 6m

Fast valve close

Rbvapour

Metal shieldingFast valve open

vacuum

Proton beam evolution

From Alexey simulations:• Proton beam in plasma undergoes SMI->increasing in beam divergence

Initial distributions

sx,y 200 mm

0.024 mrad

0.36 mrad

sz 139 mm

Not-ionized

ionized

Proton beam evolution

Alexey-FLUKA Comparison

Proton distribution after plasma cell

Valve close accident scenario

Dose equivalent mSv/bunch (3e11 p+)

dose/p+ @ access gallery

error Bunch intensity

Accident dose / bunch

9.6e-6 pSv/p+ 10% 3e11 2.9 Sv

Preliminary: damage to electronics

From M. Brugger presentation for Cern Fluka user meeting 2008

commercial COTS hardened electronics

accelerators

!!! A Rough Overview Only !!!

Semiconductors

Polymers

Ceramics

Metals and alloys

• Cumulative damage

• Stochastic damage• From M. Brugger ‘Radiation Damage to electronics at the LHC’, IPAC2012:

– Commercial equipment: ~107 HEH/cm2/year

Closed valve accident scenario: D2E

1 MeV Neutron equivalent: safe limit 1013 n/cm2

HEH safe limit 107 cm-2 : exceeded in vicinity of plasma

0 10 20 30 40 50 60 70 80 90 1001.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

Det1Det2Det3Det4

cm

Gy

Energy Deposited safe limit 102 Gy

Shielding radius [mm]

Shielding length [m]

Dose equivalent[pSv/p+]

Dose equivalent[mSv/h]

error

3 6 4.1e-5 1.5e3 18%10 6 2.1e-7 7.56 70% 15 6 6.9e-10 2.45e-2 39%

10 mm steel 6 m long

15 mm steel 6 m long

3 mm steel 6 m long

Metal shielding effect: Dose equivalent [mSv/bunch]

10 mm steel 6 m long3 mm steel 6 m long

15 mm steel 6 m longFor 15 mm radius around plasma cell still 1-2 orders of magnitude higher than recommended value

Metal shielding effect: HEH fluence per year

safe limit 107cm-2

Metal shielding effect: 1 MeV n-eq per year

3 mm steel 6 m long 10 mm steel 6 m long

15 mm steel 6 m long

safe limit 1013 n/cm2

No metal shielding15 mm radius shielding

• Without metal shielding around plasma cell HEH fluence still higher than 107 cm-2

• Looking at beam profile: halo due to the interaction of proton beam with gas:

• Gas interaction length for 400 GeV p+: 109 cm -> in 10 m 3x105 p+ per beam interact with the gas and broaden the beam

Scattered particles

Metal shielding and gas effect:HEH fluence

0 10 20 30 40 50 60 70 80 90 1001.0E+0

1.0E+2

1.0E+4

1.0E+6

Worst position detector after 1 year

Det 2 3mm 6 m

Det 2 10mm 6 m

Det 3 15 mm 6 m

Distance from proton beam

ener

gy D

epos

ited

[Gy]

shielding radius [mm]

plasma cell radius [cm]

Shielding length [m]

cm-2/p+ cm-2/year

3 2 6 1.80E-03 8.71E+13

10 2 6 5.20E-07 2.52E+10

15 2 6 2.11E-09 1.02E+08Still 1 order of magnitude too high

HEH fluence summary:

Energy deposition comparison:

Metal shielding summary

From preliminary studies level below damage limit

1 MeV neutron equivalent

Air ActivationAir Activation studies in the CNGS target chamber during AWAKE operation

CNGS target chamber

He Tube1

Target Horn

He Tube2 Decay TubeBeam

Reflector

SIMULATION PARAMETERS:

• Proton beam starting point: Beginning of Plasma cell 33.01m upstream from CNGS target

• Irradiation time 1h• Air exchange rate: 16000 m3/h (CNGS flush mode)

Dose rate AWAKE-CNGS

Collimator

Target

No Target

CNGS targetCollimator

CNGS target

Three scenarios:Implemented geometry

Air ActivationDose rate evolution collimator

0 100 200 300 400 500 600 7000.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

0

10

20

30

40

50

60

70

dose ratedose rate - Air exchangecumulative dosecumulative - Air exchange

Time (min)

Dose

Equ

ival

ent R

ate

(mSv

/h)

Cum

ulati

ve d

ose

equi

vale

nt (µ

Sv)

6.5h

40 min

Ultimate beam 1h: 3.5E11 p/bunch, 0.14 Hz Air volume: 2492 m3

Air exchange rate: 16000 m3/h

Air Activation

0 100 200 300 400 500 600 7000.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

0

5

10

15

20

25

30

35

40

45

50

dose ratedose rate - Air exchangecumulative dosecumulative - Air exchange

Time (min)

Dose

Equ

ival

ent R

ate

(mSv

/h)

Cum

ulati

ve d

ose

equi

vale

nt (µ

Sv)

Ultimate beam 1h: 3.5E11 p/bunch, 0.14 HzAir volume: 2493 m3

Air exchange rate: 16000 m3/h

4.5h

30 min

Dose rate evolution target

Air Activation

Ultimate beam 1h: 3.5E11 p/bunch, 0.14 HzAir volume: 2493 m3

Air exchange rate: 16000 m3/h

0 100 200 300 400 500 600 7000.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

0

1

2

3

4

5

6

7

8

9

10

dose ratedose rate - Air exchangecumulative dosecumulative - Air exchange

Time (min)

Dose

Equ

ival

ent R

ate

(mSv

/h)

Cum

ulati

ve d

ose

equi

vale

nt (µ

Sv)

20 min

1.5h

Dose rate evolution no target

PROMT DOSE AND D2E SIMULATIONS• The presence of the metal shielding for the electron beam creates hard

environment for electronics. The level of radiation depends on the geometry of the shielding

• The minimum level of HEH fluence due to gas effect: 1-2 orders of magnitude higher than recommended -> shielding may be required

• Which material to use for the plasma cell wall? More details needed• Preliminary results only: waiting for technical design to implement final geometry

AIR ACTIVATION • Air inside CNGS target chamber considered radioactive after 1h of nominal AWAKE

beam operation• Airborne radioactivity level inside CNGS target chamber

• Limited stay area• Ok, no access required during AWAKE operation

• Radioactive Air release through access gallery: no access during proton operation• Ventilation and access requirements: still under discussion• Collimator should be removed, CNGS target removal not necessary

Conclusion

Thanks for your attention!