beam loss monitoring system

E.B. HolzerCollimation Project External Review, CERN July 1, 2004

1

BEAM LOSS MONITORING SYSTEM

B. Dehning, E. Effinger, G. Ferioli, J.L. Gonzalez, G. Guaglio,

M. Hodgson, E.B. Holzer, L. Ponce, V. Prieto, C. Zamantzas

CERN AB/BDI

External Review of LHC Collimation Project

July 1, 2004


2

Outline

BLM System Hardware Dynamic Range Positioning of Monitors Signals from the BLM system

Simulations of Cleaning Insertions Momentum Cleaning (Igor A. Kurochkin, IHEP) Betatron Cleaning (M. Brugger, S. Roesler,

CERN SC/RP) Summary


3

THE BLM SYSTEM

Purpose: Machine protection against damage of equipment and magnet

quench

Setup of the collimators

Localization of beam losses and identification of loss mechanism

Machine setup and studies

Challenges: Reliable (tolerable failure rate 10-7 per hour per channel)

High dynamic range (108, 1013)

Fast (1 turn trigger generation for dump signal)


4

Families of BLM’s

BLMC & BLMS: In case of a non working monitor this monitor has to be repaired before the next injection

Type Area of use Time resolution Number of monitors

BLMC Collimation sections 1 turn ~ 100

BLMSBLMS*

Critical aperture limits or critical positions

1 turn(89 us)

~ 500

BLMA All along the rings (ARC, …)

2.5 ms ~ 3000

BLMB Primary collimators 1 turnbunch-by-bunch

~ 10


5

Loss Detectors: Ionization Chamber

New LHC chamber designDiameter = 8.9 cm,Length 60 cm, 1.5 litre,Filled with Ar or N2

SPS ChamberGas: N2, Volume: ~ 1 Liter,

30 Al disks of 0.5 mm,Typical bias voltage: 1500 V.


6

Secondary Emission Monitor

Diameter = 8.9 cmLength 15 cm


7

Dynamic Range (I)

Secondary Emission Monitor

P < 10-7 bar

Ionization Chamber

P > 1bar

Efficiency SE ~ 0.05 charges/particle

Efficiency ioniz. Chamber ~ 50 charges / (particle cm)

Efficiency Ionization Chamber / Efficiency SE ~ 3 104


8

Dynamic Range (II)

Beam Loss Current BLMC and BLMS*


9

System Layout

Threshold Comparator: Losses integrated in 12 time intervals to approximate quench level curve.


10

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

en

ch l

ev

els

[p

roto

n/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


11

Loss Levels and Required Accuracy

Relative loss levels

450 GeV 7 TeV

Damage to components

320/5short/long

1000/25 short/long

Quench level 1 1

Beam dump threshold for quench prevention

0.3 0.3/0.4 short/long

Warning 0.1 0.1/0.25short/long

Absolute precision (calibration)

< factor 2 initially: < factor 5

Relative precision for quench prevention

< 25%

Specification:


12

Monitor Positions in Arc

Installation of BLMAs on a SSS quadrupole


13

Monitor Positions in Collimation

Collimator interconnect with ion pump and BLM (possible positions)


14

Signals from the BLM system

• Dump signal to beam interlock controller (BIC), 2 types:– Not mask able: BLMC and BLMS, ~ 600 monitors.– Can be masked when “safe beam” flag is set: BLMA, ~ 3000

monitors• Post mortem:

– 2000 turns plus integral of 10 ms.• Logging:

– Once a second– Stored in database – Used for graphical representation in the control room:

Values measured for each detector and time interval are normalized by their corresponding threshold values.


15

“Artist View” of the Logging 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


16

Momentum Cleaning

IR3 (6.2) – length and positions of collimators have changed

TCP1

TCS3,2TCS 6,5,4

TCS1

• Activation will reduce the sensitivity of the monitors in the low signal range. Expected activation: 10-2 to 10-4 of mean loss rate (SPS 10-3)

• Monitors close to vacuum chamber to reduce cross talk and background.

• Monitors 30 cm downstream of collimator

BLM position

Igor A. Kurochkin


17

Relative contribution to BLM signal from primary inelastic interactions in the collimators

“Good” signal (from upstream collimator) BLM1 – 100% BLM2 – 4% BLM3 – 57.4% BLM4 – 9% BLM5 – 5% BLM6 – 4% BLM7 – 1%

TCP1 - major contributor to background BLM2 – 96% BLM7 – 20%

02

46

01

23

45

670.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Collimator

BLM

Igor A. Kurochkin

7 TeV

TCP

1TCS

1

BLM signal:• Good measure for heat load in the corresponding collimator• Does not represent the number of proton inelastic interactions of

the corresponding collimator

Igor A. Kurochkin


18

-200

20-40

-200

2040

0.050.1

0.150.2

0.250.3

0.35

x 10-5

x, cm

y, cm

0.05

0.1

0.15

0.2

0.25

0.3

0.35

x 10-5

-40 -20 02 04 0y, cm

Transversal Variation of Monitor Location

Best signal to background and signal to cross talk at position near to the beam

TCS1 Igor A. Kurochkin Total energy deposition. The contribution from beam 2 (crosstalk) is small (<1%) due to longitudinal distance.

Igor A. Kurochkin


19

Betatron Cleaning

Primary interactions

Inelastic interaction rate (star), threshold 20MeV

Comparison of energy deposition [GeV] to inelastic interaction rate in IP3:

• They scale for the downstream secondary collimators (2 – 3 GeV per inelastic interaction)

• Primary collimator: 0.4 GeV

• First secondary collimator: 3.3 GeV

M. Brugger, S. Roesler


20

Contribution to the number of inelastic interactions from beam particle losses in upstream collimators

• Values similar to momentum cleaning.

• Higher inter beam crosstalk can be expected due to reduced longitudinal distance between collimators of beam 1 and 2.

M. Brugger, S. Roesler


21

Summary

BLM system: machine protection– First priority (downtime)– Detectors next to possible loss locations protect local equipment

Monitors in collimation region– Measure energy deposition in the collimators– Can not measure primary inelastic interactions (response matrix)– High activation (reduce sensitivity)– Possible noise problems to be investigated (analogue signal

cables of BLMs are up to 300 m long and close to numerous stepping motor control cables)

beam loss monitoring system

Documents