Eva Barbara Holzer IEEE NSS, Puerto Rico October 26, 2005 1 Beam Loss Monitoring System of the LHC Eva Barbara Holzer, CERN for the LHC BLM team IEEE Nuclear

Eva Barbara HolzerIEEE NSS, Puerto Rico October 26, 2005 1

Beam Loss Monitoring System of the LHC

Eva Barbara Holzer, CERN

for the LHC BLM team

IEEE Nuclear Science Symposium

October 26, 2005

Fajardo, Puerto Rico



Specification and Requirements Architecture of the BLM System Threshold Calibration Summary


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

(Based on graph from R. Schmidt)

Quench Levels Units Tevatron RHIC HERA LHC

Instant loss (0.01 - 10 ms) [J/cm3] 4.5 10-03 1.8 10-02 2.1 10-03 - 6.6 10-03 8.7 10-04

Steady loss (> 100 s) [W/cm3] 7.5 10-02 7.5 10-02 5.3 10-03


Large Hadron Collider (LHC)

In LHC there are: 514 main quadrupoles 1232 main dipoles ~130 collimators and

absorbers

pp and PbPb Commissioning 2007


The BLM System: Purpose

Detection of dangerous beam losses generation of trigger for beam extraction

Setup of the collimators and continuously monitor their performance

Localization of beam losses and identification of loss mechanism

Machine setup and studies

Tevatron Collimator damage, 5.12.2003 (D. Still)

LHC Collimator prototype


The BLM System: Challenges

Reliable (tolerable failure rate 10-7 per hour per channel) Reliable components, radiation tolerant electronics Redundancy, voting Monitoring of availability and drift of channels

Less than 2 false dumps per month (operation efficiency) High dynamic range (108, 1013 – two monitor types at the same

location) Fast (1 turn, 89 s) trigger generation for dump signal Quench level determination with an uncertainty of a factor 2

(calibration)


Locations

6 detectors around each quadrupole (~3000) Maskable: Beam abort signal can be ignored, when the stored energy in

the beam is below the damage limit

Critical aperture limits or critical loss positions (~400) Non-maskable

Collimators and absorbers (~150) Non-maskable

Plus a set of movable BLMs

All non-maskable monitors have to be available before injection


Quench and Damage Levels

Arc Dipole Magnet

Dynamic RangeArc: 108

Collimator: 1013


Signals from the BLM system

Dump signal to the LHC beam interlock system (LBIS), 2 types (maskable and non-maskable)

Post mortem Up to 1000 turns plus averages of 10 minutes

Data for the control room and logging (1Hz)

“Artist’s View” of the Beam Loss Display (C. Zamantzas)

0

0.2

0.4

0.6

0.8

1

1.2

Measu

red

/ T

hresh

old

Dete

cto

r 1

Dete

cto

r 2

Dete

cto

r 3

Dete

cto

r 4

Dete

cto

r 5

Dete

cto

r 6

. . .

Dete

cto

r

4000

R1

R2

R3

R4

R5

R6

Warn

ing

Du

mp

Inte

grati

on

Tim

e In

terva

ls





Monitor Types

Design criteria: Signal speed and robustness Dynamic range (> 109) limited by leakage current

through insulator ceramics (lower) and saturation due to space charge (upper limit).

Ionization chamber: N2 gas filling at 100 mbar over-

pressure Length 50 cm Sensitive volume 1.5 l Ion collection time 85 s

Both monitors: Parallel electrodes (Al, SEM: Ti)

separated by 0.5 cm Low pass filter at the HV input Voltage 1.5 kV

Secondary Emission Monitor (SEM): Length 10 cm P < 10-7 bar ~ 30000 times smaller

gain


System Layout

Threshold Comparator: Losses integrated and compared to threshold table (12 time intervals and 32 energy ranges).

LBIS





Threshold Determination

Beam dump threshold set to 30% of the magnet quench level Specification:

Calibration of Thresholds: Based on simulations Cross-checked by measurements when possible Beam tests might be necessary to reach the required precision

Aim of calibration relate the BLM signal to the: Number of locally lost beam particles Deposited energy in the machine component Quench and damage levels

Absolute precision (calibration)

factor 2 (final)factor 5 (initial)

Relative precision for quench prevention

< 25%


Warm MagnetCold MagnetCollimator


Proton loss locations (MAD-X, SIXTRACK, BeamLossPattern, measurements: LHC beam)

Hadronic showers through magnets (GEANT, measurements: HERA/DESY, LHC beam)

Magnet quench levels as function of proton energy and loss duration (SPQR, measurements: Laboratory, LHC beam)

Chamber response to the mixed radiation field in the tail of the hadronic shower (GEANT, GARFIELD, measurements: booster, SPS, H6, HERA/DESY)

(S. Redaelli, L. Ponce)

Injection Optics, 450 GeV, Horizontal Halo



(E. Gschwendtner)











3Vacuum tube

First layer Second layer

Spacers

Conductors

Cryogenic System

metalheliuminsulation-channels

Inner layerOuter layer

Helium Helium

heat source

(D. Bocian)











Summary – Features of the BLM System

Large dynamic range High reliability and low false beam abort rate (radiation tolerant

electronics, fail safe design) Extensive simulations for threshold calibration Dynamically changing threshold values


The LHC BLM Team

LHC Machine Protection Working Group (http://cern.ch/lhc-mpwg) LHC Collimation Working Group (http://cern.ch/lhc-collimation)

Bernd Dehning, Ewald Effinger, Jonathan Emery, Gianfranco Ferioli, Jose Luis Gonzalez, Edda Gschwendtner, Gianluca Guaglio, Michael Hodgson, Eva Barbara Holzer, Daniel Kramer, Roman Leitner, Laurette Ponce, Virginia Prieto, Markus Stockner, Christos Zamantzas

Contributions from members of the:

Documents

Eva Barbara Holzer IEEE NSS, Puerto Rico October 26, 2005 1 Beam Loss Monitoring System of the LHC Eva Barbara Holzer, CERN for the LHC BLM team IEEE Nuclear