Radiation Levels in the CLIC Tunnel

Sophie Mallows

Thomas Otto

CERN SC/RP

Overview

Simulation of particle and radiation transport using FLUKA 2008

Simplified model of CLIC tunnel Scored

Absorbed doses in QP magnets 20 MeV hadron fluence, 1MeV neutron equivalent fluence,

Prompt doses in tunnel module

FLUKA Geometry

4.5m

Absorbed dose in QPs – Safe Limits

Magnetic Coils in QPs:Epoxy becomes brittleinsulation may break down

Damage is related to Absorbed Dose, SI unit: J/Kg, special unit: Gray (Gy)

From past experience, a dose of several MGy over the lifetime of a magnet is acceptable

Guideline for CLIC: D < 1 MGy/ year

Damage to Electronics - Effects

2 main effects:

Cumulative Effects (threshold) Total Ionizing Dose (Gray) Displacement Damage (1 MeV neutron

equivalent)

Single Event Effects (SEEs) (probability) Due to hadrons > 20 MeV

Damage to Electronics – Safe Limits

Dependent on Electronics For SEE’s can only calculate probability of risk

Levels used in for area classification in LHC study (R2E Study Group):

Calculation – Dose

Electronics:Low:  Dose <1Gy/yrMedium: 1Gy/yr < Dose < 1kGy/yrHigh: 1kGy/yr < Dose

QP Limit : D < 1 MGy/ year

1500 GeV electrons lost in main beam QPs Normalization : 180 continuous days running, fractional beam loss 2.5 10-7 per qp

Averaged over length of tunnel module Averaged over width of 20cm

Calculations -20 MeV Hadron Fluences

1500 GeV electrons lost in main beam QPs Normalization: 180 days continuous running, fractional beam loss 2.5 10-7 per qp

Low:  Fluence <1107 cm-2

Medium: 1108 cm-2 < Fluence < 1109 cm-2

High: 1109 cm-2 < Fluence

Averaged over depth of 20cmAveraged over length of tunnel module

Calculations - 1 MeV Neutron Equivalent Fluences on Silicon

1500 GeV electrons lost in main beam QPs Normalization : 180 days continuous running, fractional beam loss 2.5 10-7 per qp

Low:  Fluence <1108 cm-2

Medium: 1108 cm-2 < Fluence < 11010 cm-2

High: 11010 cm-2 < Fluence

Averaged over length of tunnel module Averaged over depth of 20cm

Additional Slides

Spatial distributionss of Dose

Normalization: 1 loss electron

Fractional Beam Losses for 1 MGy/yr

Electron losses in 1 QP Maximum dose per loss electron in scoring mesh (1cm3 bins) across QP Fractional beam loss requirements for 1 MGy/yr

Th. Otto, SC-RP, CERN CLIC Workshop 2008Radiation levels in the CLIC tunnel

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“Single event error” SEE, CNGS example

SEU: ionising radiation changes the content of a elementary memory cell of a digital processor, spuriously or permanently.

The critical quantity is fluence of hadrons with E > 20 MeV, 20 (cm-2)

Experience from CNGS: at 20 = 2 107 devices start to show errors

Guideline for CLIC: 20 < 106 … 107/year

T. Wijnands, TS-LEA