06.06.2005 DIPAC 2005, B.Dehning 1

Beam loss monitor system for machine protection

B. DehningCERN AB/BDI

06.06.2005 DIPAC 2005, B.Dehning 2

Beam loss measurement design approach

Damage(system integrity)

Quench(operationalEfficiency)

Scaling:

frequency of events

xconsequence

FailsafeRedundancy

SurveyCheck

Meantime

between failures

Methods:

Stop of next injection

Extraction of beam

Reduction of operational efficiency

Safety ProtectionRisk Availability

SILALARP

Systems:

Beam loss Monitors

Quenchprotection

system

Interlocksystem

¨Dump system

Design issues:

Reliable components

Redundancy, voting

Monitoring of drifts1 10-8 to

1 10-7 1/h

06.06.2005 DIPAC 2005, B.Dehning 3

Damage example and LHC consequences

Tevatron, December 5, 2003 Fast beam loss A Roman Pot moved into beam due to a controls error damaging of 2 collimators and 2 spool pieces

LHC extrapolation Energy in beam 7 times Tevatron Intensity of beam 30 times Tevatron Number of LHC of moving elements in the LHC about 200

How many Magnets and … are damaged?

06.06.2005 DIPAC 2005, B.Dehning 4

Stored beam energies

0.01

0.10

1.00

10.00

100.00

1000.00

1 10 100 1000 10000Momentum [GeV/c]

En

erg

y st

ore

d in

th

e b

eam

[M

J] LHC topenergy

LHC injection(12 SPS batches)

ISR

SNSLEP2

SPS fixed target

HERA

TEVATRON

SPSppbar

SPS batch to LHC

Factor~200

RHIC proton

Damage and Quench threshold to first order identical =>LHC will be exceptional

06.06.2005 DIPAC 2005, B.Dehning 5

LHC Bending Magnet Quench Levels

LHC quench values are lowest

steady state W/cm3Tevatron 7.47E-02RHIC 7.47E-02LHC 5.29E-03

1.E-3

1.E-2

1.E-1

1.E+0

1.E+1

1.E+2

1.E+3

1.E+4

0.01 0.1 1 10 100 1000 10000 100000

loss duration [ms]

W/c

m3

1.E-4

1.E-3

1.E-2

1.E-1

1.E+0

1.E+1

1.E+2

1.E+3

Gy/

s

Quench Power 7 Tev

Quench Power 450 GeV

(values proportional)

13 us J/cm3Tevatron 4.50E-03RHIC 1.80E-02LHC 8.70E-04

DESY 2.6 – 6.6 E-03

06.06.2005 DIPAC 2005, B.Dehning 6

Quench Levels and Energy Dependence

Fast decrease of quench levels between 0.45 to 2 TeV Similar behaviour expected for damage levels

06.06.2005 DIPAC 2005, B.Dehning 7

Failure rate and checks

Systems parallel + survey + check:

1. in case of system failure dump beam (failsafe)

2. verification of functionality: simulate measurement and

comparison with expected result

0.00000001

0.0000001

0.000001

0.00001

0.0001

0.001

0.01

0 50 100 150 200 250 300

time [a.u.]

failu

re r

ate

[a

. u.]

constant f. r.

systems parallel

systems parallel + surv.

systems parallel + surv. + check

06.06.2005 DIPAC 2005, B.Dehning 8

Role of the BLM System for the protection

SOURCES of beam losses

1. User/operator2. PC failures3. Magnet failures4. Collimators

failures5. RF failures6. Obstacles7. Vacuum8. …

HERA

Tevatron, LHC

Dumpsystem

Interlocksystem

Dumprequests

06.06.2005 DIPAC 2005, B.Dehning 9

Beam loss measurement system layouts

FNAL

LHC

Examples from:

SNS, LHC FNALLHC LHC

06.06.2005 DIPAC 2005, B.Dehning 10

Ionisation chamber SNS

Stainless steal Coaxial design, 3 cylinder

(outside for shielding) Low pass filter at the HV

input

Ar, N2 gas filling at 100

mbar over pressure Outer inner electrode

diameter 1.9 / 1.3 cm Length 40 cm Sensitive volume 0.1 l Voltage 2k V Ion collection time 72 us

06.06.2005 DIPAC 2005, B.Dehning 11

Ionisation chamber LHC

Stainless steal cylinder Parallel electrodes separated by

0.5 cm Al electrodes Low pass filter at the HV input

N2 gas filling at 100 mbar over

pressure Diameter 8.9 cm Length 60 cm Sensitive volume 1.5 l Voltage 1.5 kV Ion collection time 85 us

06.06.2005 DIPAC 2005, B.Dehning 12

Ionisation chamber measurements

Energy deposition (LHC)

Beam

scanned

Signal vs voltage (SNS)

06.06.2005 DIPAC 2005, B.Dehning 13

Ionisation chamber currents (1 litre, LHC)

450 GeV, quench levels (min)

100 s 12.5 nA

7 TeV, quench levels (min)

100 s 2 nA

Required 25 % rel. accuracy, error small against 25% => 5 %

100 pA

450 GeV, dynamic range min., used for tuning

10 s 10 pA

100 s 2.5 pA

7 TeV, dynamic range min.

10 s 160 pA

100s 80 pA

06.06.2005 DIPAC 2005, B.Dehning 14

Gain Variation of SPS Chambers

30 years of operation Measurements done with

installed electronic Relative accuracy

< 0.01 (for ring BLMs) < 0.05 (for Extr., inj.

BLMs) Gain variation only observed

in high radiation areas Consequences for LHC:

No gain variation expected in the straight section and ARC of LHC

Variation of gain in collimation possible for ionisation chambers

SPS BLMs

02468

101214161820

36 42 48 54 60 66M

ore

current [pA]

Fre

qu

en

cy

dis

trib

uti

on

0

20

40

60

80

100

120

140

160

Extr., inj. BLMs

Ring BLMs

Test with Cs137

Total received dose: ring 0.1 to 1 kGy/yearextr 0.1 to 10 MGy/year

06.06.2005 DIPAC 2005, B.Dehning 15

LHC acquisition board Current to Frequency

Converters (CFCs) Analogue to Digital

Converters (ADCs) Tunnel FPGAs:

Actel’s 54SX/A radiation tolerant.

Communication links:Gigabit Optical Links.

Surface FPGAs: Altera’s Stratix EP1S40 with 780 pin.

06.06.2005 DIPAC 2005, B.Dehning 16

LHC tunnel card Not very complicated design “simple” Large Dynamic Range (8 orders)

Current-to-Frequency Converter (CFC) Analogue-to-Digital Converter

Radiation tolerant (500 Gy, 1 107 p/s/cm2) Bipolar Customs ASICs Triple module redundancy

Reset time Integration time

V out

I +I -

ThresholdComparator

100 ns 100 ns to 100 s

06.06.2005 DIPAC 2005, B.Dehning 17

FNAL beam loss integrator and digitizer

Independent operation form crate CPU (FNAL, LHC)

Thresholds managed by control card over control bus (LHC combined)

VMEControl bus

Control bus

FNAL LHC

channels 4 16

Time resolution

21 s 40 s

# of running sums

3 11

windows 21 s to 1.4 s

80 s to 84 s

thresholds 4 12

Synchronized to machine timing

yes no

post mortem buffer

4k values

1k values

06.06.2005 DIPAC 2005, B.Dehning 18

FNAL abort concentrator

Measurements and threshold are compared every 21 s (fastest) (LHC 80 s)

Channels can be masked (LHC yes)

Aborts of particular type are counted and compared to the required multiplicity value for this type (LHC: single channel will trigger abort, channel can be masked depending on beam condition)

Ring wide concentration possible (LHC no)

06.06.2005 DIPAC 2005, B.Dehning 19

Beam loss measurement design approach

Damage(system integrity)

Quench(operationalEfficiency)

Scaling:

frequency of events

xconsequence

FailsafeRedundancy

SurveyCheck

Meantime

between failures

Methods:

Stop of next injection

Extraction of beam

Reduction of operational efficiency

Safety ProtectionRisk Availability

SILALARP

Systems:

Beam loss Monitors

Quenchprotection

system

Interlocksystem

¨Dump system

Design issues:

Reliable components

Redundancy, voting

Monitoring of drifts1 10-8 to

1 10-7 1/h

06.06.2005 DIPAC 2005, B.Dehning 20

Test Procedure of Analog Signal Chain

Basic concept: Automatic test measurements in between two fills

Measurement of dark current Modulation of high voltage supply of chambers

Check of components in Ionisation chamber (R, C) Check of capacity of chamber (insulation) Check of cabling Check of stable signal between few pA to some nA (quench level

region)

Not checked: gas gain of chamber (only once a year with source)

06.06.2005 DIPAC 2005, B.Dehning 21

CompareCRCs

Secondary B Signal(256 bits)

S/W & TTLoutput

Check CRCvalidity

DeMux

1 2 3 … 8

Truncateextra/redundant bits

(leave 160 bits)

Status10-bits

Primary A Signal (256 bits)

Only CRC

(4 byte)

Only CRC

(4 byte)

Signal Select(A or B)

ErrorError

Error

Error

Check CRCvalidity

Error

Reception______________ _ _

Tx Check&Signal Choice

______________ _ _

Tunnel Status Check______________ _ _

Format Data

______________ _ _

LHC transmission check

Signal Select Table

CRC32 check Comparison of 4Byte

CRCsOutput Remarks

A B

Error Error Error Dump Both signals have error

Error Error OK DumpS/W trigger (CRCgenerate or check

wrong)

Error OK Error Signal B S/W trigger (error at CRC detected)

Error OK OK Signal B S/W trigger (error at data part)

OK Error Error Signal A S/W trigger (error at CRC detected)

OK Error OK Signal A S/W trigger (error at data part)

OK OK Error DumpS/W trigger (one of the counters has

error)

OK OK OK Signal A By default (both signals are correct)

At the Surface FPGA:

Signal CRC-32 Error check / detection

algorithm for each of the signals received.

Comparison of the pair of signals.

Select block Logic that chooses signal to

be used Identifies problematic areas.

Tunnel’s Status Check block HT, Power supplies

FPGA errors Temperature

06.06.2005 DIPAC 2005, B.Dehning 22

Reliability Study (LHC)

False dumps per year

0%

10%

20%

30%

40%

jfet switch Power Supply monostable comparator integrator other

Lea

kag

e

General failure

Bre

akd

ow

n

Open

General

failure

Signal variation

Arc

Shorted input

Str

aig

ht

sect

ion

Open input

by G. Guaglio

Apportionment of yearly damage probability

0%

10%

20%

30%

40%

50%

Ion. Chamber Ion.C. cable Surface BLMTC Tunnel BLMCFC

Resistor shorted

Wrong energy signal?

Resistor increased

Capacitor decreased

Wire shorted changes

Solder joints

Mechanical divers

Insulation

Gas pressure

Dump switch

Memories

C open

Comparator

Integrator

Relative probability of a system component being responsible for a damage to an LHC magnet in the case of a loss.

Relative probability of a BLM component generating a false dump.

Most false dumps initiated by analog front end (98%) because:

1. Reduced check2. Quantity3. Harsh environment

Highest damage probability given by the Ionisation chamber (80%) because:

1. Reduced checks

2. Harsh environment

06.06.2005 DIPAC 2005, B.Dehning 23

Beam Loss Display

0

0.2

0.4

0.6

0.8

1

1.2

Mea

sure

d / T

hres

hold

Det

ecto

r 1

Det

ecto

r 2

Det

ecto

r 3

Det

ecto

r 4

Det

ecto

r 5

Det

ecto

r 6

. . .

Det

ecto

r40

00

R1

R2

R3

R4

R5

R6

War

ning

Dum

p

Inte

grat

ion

Tim

e In

terv

als

06.06.2005 DIPAC 2005, B.Dehning 24

Literature

SNS, Ion chamber, R.C. Witkover, BIW02 FNAL, BLM electronics, J.D. Lewis et al., IEEE 04 http://ab-div-bdi-bl-blm.web.cern.ch/ab-div-bdi-

bl-blm LHC

Reliability issues, G. Guaglio et al., BIW04, R. Filippini et al., PAC 05

Front end electronics, analog, thesis, W. Friesenbichler Digital signal transmission, thesis, R. Leitner Digital signal treatment, C. Zamantzas, this workshop

06.06.2005 DIPAC 2005, B.Dehning 25

Reserve slides

06.06.2005 DIPAC 2005, B.Dehning 26

Approximation of Quench Levels (LHC)

Dump level tables are loaded in a non volatile RAM Any curve approximation possible

Loss durations Energy dependence

Avarage approximation

1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

0.01 0.1 1 10 100 1000 10000 100000 1000000

loss duration [ms]

Arc

cha

mbe

r cu

rren

t (1

litr

e) [

A]

7 TeV high 450 GeV lowApproximation Approximation

1.E-05

1.E-04

1 10 100

Relative error kept < 20 %

06.06.2005 DIPAC 2005, B.Dehning 27

Drift times of electrons and ions (II)

06.06.2005 DIPAC 2005, B.Dehning 28

Drift times of electrons and ions (I)

06.06.2005 DIPAC 2005, B.Dehning 29

Response of ion chambers for different particle species

u+

u-

Gam

ma

e+

e-

pi+

pi-

neutr

on

pro

ton

Due to attenuation ofshower => increase of non linearity of chamber response

06.06.2005 DIPAC 2005, B.Dehning 30

Quench and Damage Levels

Detection of shower particles outside the cryostat or near the collimators to determine the coil temperature increase due to particle losses

1.E+04

1.E+05

1.E+06

1.E+07

1.E+08

1.E+09

1.E+10

1.E+11

1.E+12

1.E+13

1.E+14

1.E+15

1.E+16

1.E+17

1.E+18

1.E-02 1.E-01 1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06

duration of loss [ms]

qu

ench

leve

ls [

pro

ton

/s]

Quench level and observation range

450 GeV

7 TeV

DynamicArc: 108

Collimator: 1013

Damage levels

Arc

2.5 ms

Special & Collimator

1 turn

BLMS* & BLMC

06.06.2005 DIPAC 2005, B.Dehning 31

Energy spectrum of shower particles outside of cryostat

Energy [GeV]

1 bin = 5 MeV

• Energy spectrum:

Average energy deposition in the de-tector (air):

450 GeV: ~3.8 keV/cm 7 TeV: ~4.3 keV/cm

Shower particles in the detector per cm2 and lost proton for point losses

450 GeV: 5·10-4 - 3·10-3 part/p/cm2 7 TeV: 8·10-3 - 4·10-2 part/p/cm2

• Number of charged particles and energy deposition simulated:

06.06.2005 DIPAC 2005, B.Dehning 32

Ionisation Chamber Time Response Measurements (BOOSTER)

Chamber beam response Chamber current vs beam current

Intensity discrepancy by a factor two

Intensity density: - Booster 6 109 prot./cm2, two orders larger as in LHC

FWHMe-= 150 ns

length proton= 50 ns

80 % of signalin one turn

06.06.2005 DIPAC 2005, B.Dehning 33

Current to Frequency Converter and Radiation

Variation at the very low end of the dynamic range Insignificant variations at quench levels

CFC2-TOTAL-0Gy-1000Gy

1.0E-01

1.0E+00

1.0E+01

1.0E+02

1.0E+03

1.0E+04

1.0E+05

1.0E+06

1.0E+07

1.E-11 1.E-10 1.E-09 1.E-08 1.E-07 1.E-06 1.E-05 1.E-04 1.E-03

I in [A]

f o

ut

[Hz]

Ch2-CFC2-not-irr-1meas.Ch2-CFC2-not-irr-2meas.Ch2-CFC2-JFET-0GyCh2-CFC2-JFET-500GyCh2-CFC2-JFET-1000GyCh8-CFC2-not-irr-1meas.Ch8-CFC2-not-irr-2meas.Ch8-CFC2-JFETS-0GyCh8-CFC2-JFETS-300GyCh8-CFC2-JFETS-600GyCh4-CFC2-not-irr-1meas.Ch4-CFC2-not-irr-2meas.Ch4-CFC2-JFETS-0GyCh4-CFC2-JFETS-300GyCh4-CFC2-JFETS-600GyCh6-CFC2-not-irr-1meas.Ch6-CFC2-not-irr-2meas.Ch6-CFC2-JFETS-0GyCh6-CFC2-JFETS-300GyCh6-CFC2-JFETS-600GyCh8-CFC2-not-irr-1meas.Ch8-CFC2-not-irr-2meas.Ch8-CFC2-TOTAL-300GyCh8-not-irr-1meas.Ch8-not-irr-2meas.Ch7-not-irr-1meas.Ch7-not-irr-2meas.Ch5-not-irr-1meas.Ch5-not-irr-2meas.Ch3-not-irr-1meas.Ch3-not-irr-2meas.Ch1-not-irr-1meas.Ch1-not-irr-2meas.Ch1-CFC2-JFET-0Gy-not-irrCh1-CFC2-JFET-500Gy-not-irrCh1-CFC2-JFET-1000Gy-not-irrCh1-CFC2-JFETS-0Gy-not-irrCh1-CFC2-JFETS-300Gy-not-irrCh1-CFC2-JFETS-600Gy-not-irrCh1-CFC2-TOTA-300Gy-not-irr

Ch8-CFC2-TOTAL-0Gy-300Gy

1.0E-01

1.0E+00

1.0E+01

1.0E+02

1.0E+03

1.0E+04

1.E-11 1.E-10 1.E-09 1.E-08 1.E-07 1.E-06I in [A]

f o

ut

[Hz]

Ch8-CFC2-not-irr-1meas.Ch8-CFC2-not-irr-2meas.Ch8-CFC2-TOTAL-300Gy

Quench 7 TeV

Quench 7 TeV