LHC Instrumentation Status and Challenges

LHC InstrumentationStatus and Challenges

12th Beam Instrumentation Workshop

Fermilab

1st - 4th May 2006

Rhodri Jones(CERN Beam Instrumentation Group)

12th Beam Instrumentation Workshop, May 2006 - Rhodri Jones (CERN - AB/BI)

Overview

• General LHC construction status

Instrumentation• What’s required & when

• Status of Distributed Systems Beam position measurement Beam loss measurement

• Status of Systems with US-LARP involvement Tune, chromaticity & coupling measurement Luminosity Monitors Schottky Monitors


LHC Construction Status

TI8 successfully commissioned in 2004

Nearly 3/8ths of the LHC Installedwith over 500 cryomagnets in place



Final Magnet Preparation



Magnet Lowering& transportation






Instrumentation - what’s required & when• Sector test & first turn (end 2006 or early 2007)

Screens, BPMs, fast BCT, BLMs

• Circulating beams at 450 GeV (end 2007) DC BCT & lifetime Tune Coupling & Chromaticity Emittance: wire scanners.

• Snapback and Ramp Continuous Orbit, Tune, Coupling & Chromaticity (+ feedback) Continuous emittance monitoring: synchrotron light, IPM

• First Collisions Luminosity Schottky

?25ns ops I

Install Phase II and MKB

25ns ops II

75ns ops

43 bunch operation

Beam commissioning

Machine checkout

Hardware commissioning

?25ns ops I

Install Phase II and MKB

25ns ops II

75ns ops

43 bunch operation

Beam commissioning

Machine checkout

Hardware commissioning

Stage I II III

No beam Beam

IV

Beam


Beam Position System Challenges• Choice of button electrode pick-up

Requires feedthroughs that can operate at ~4K Maximise aperture & signal strength Minimise transverse impedance

• Dynamic Range From 1 bunch of 1×109 charges to 2808 bunches of 1.7×1011 charges

• 114dB dynamic range

• Linearity Better than 1% of half radius, ~130μm for arc BPMs

• Over whole intensity range

• Over large fraction of the aperture

• Resolution In the micron range for accurate global orbit control

• Driven by collimation requirements

• Over 120 collimator jaws in the LHC


BPM Acquisition Electronics

• Fast normalisation (< 25ns) bunch to bunch measurement

• Reduced number of channels (x2) normalisation at the front-end

• Signal dynamic independent of the number of bunches Input dynamic range ~45 dB

• Full LHC dynamic range ~114dB

No need for gain selection

• ~10 dB compression of the position dynamic due to the recombination of signals

• Independent of external timing

• Currently reserved for beams

with empty RF buckets between

bunches

LHC 400MHz RF

1 bunch every 10 buckets

• Tight time adjustment

• No Intensity information

• Propagation delay stability and

switching time uncertainty are

the limiting performance factors

LimitationsAdvantages

Amplitude to Time Normaliser


-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

Time [ns]

Am

plitu

de A

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Am

plitu

de B

A

B

1.5nsB + 1.5ns

A + (B + 1.5ns)A B

Beam

The Wide Band Time Normaliser


-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

Time [ns]

Am

plitu

de A

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Am

plitu

de B

A

B

1.5nsA + 1.5ns

A + (B + 1.5ns)A B


t depends on position

B + (A + 1.5ns)


-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

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Time [ns]

Am

plitu

de A

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Am

plitu

de B

A B

A+(B+1.5ns)

B+(A+1.5ns)+10ns

System output


Interval = 10 1.5ns


LHC Beam Position System Layout

CAL. and TESTGENERATOR ADC

LOWPASS

FILTER

CALIBRATOR

PICK-UP

50 CABLE

Intensity

Measurement

Trigger

AutoTrigger

50 CABLE

LOWPASS

FILTERCALIBRATOR

NORMALISER INTEGRATOROPTICAL

LINK

TUNNEL SURFACE

DAB


What one can do with such a SystemUsed extensively in CERN-SPS for electron cloud & instability studies.


ramp

injection at 26 GeV

450 GeV

Time(ms)

~ measurement noise !!

BPMReading

(m)

feedback off

feedback on

Position distribution@ 100 Hz = 8.5 m

Orbit feedback results from the CERN-SPS


The LHC Beam Loss SystemCoping with a Huge Stored Beam Energy

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

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


The LHC Beam Loss SystemRole of the BLM system:

1. Protect the LHC from damage

2. Dump the beam to avoid magnet quenches

3. Diagnostic tool to improve the performance of the LHC

Name Type Number Area of use MaskableTime resolution

BLMAI Ionisation Chamber ~3000 Arcs yes 1 turn

BLMCIBLMCS

Ionisation ChamberSEM

~150~150

Collimation regions

no 1 turn

BLMSIBLMSS

Ionisation ChamberSEM

~400~150

Critical aperture limits or positions

no 1 turn

BLMB ACEM ~10Primary collimators

yesbunch-by-bunch


BLM Detection Range

• Pilot bunch of 5×109 close to damage level at 7TeV• Loss of 0.003% of nominal beam over 1s can create a quench at 7TeV

Dynamic RangeArc: 108

Collimator: 1013

1 pilot bunch

Full LHC fill


Beam Loss Detectors• Design criteria: Signal speed and reliability

• Dynamic range (> 109) limited by leakage current through insulator ceramics (lower) and saturation due to space charge (upper)

Secondary Emission Monitor(SEM):

Length 10 cm P < 10-7 bar ~ 30000 times smaller gain

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


BLM Threshold Level Estimation


BLM Acquisition Electronics

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

Implemented on BDI DAB64x


Tune, Chromaticity & Coupling• Clear three step approach:

1) Day 1 with kicked beams and classical motion analysis• Q kicker for both planes & both beams (limited to 2Hz rep rate)

– Base Band Tune (BBQ) system for tune & coupling– Head-tail system for chromaticity

• Chirp excitation using the transverse damper– allows faster repetition rate if required

2) Day N with PLL tune tracking (US-LARP)• p/p modulation via RF will allow chromaticity measurement

3) Day N++ with PLL measurement & Feedback (US-LARP)• Tune, chromaticity & coupling

• For operational beams the additional problems will be: lowering the excitation level to an insignificant level coping with coupling achieving compatibility with resistive transverse damping

Collaboration with BNL via US-LARP


Measuring with Little or No Excitation – The Base Band Q Measurement (BBQ) System

Direct Diode Detection (3D)


Record from the RHIC BBQ system

Horizontal plane – no added excitation!


The BBQ System for the LHC• Will be installed in the LHC as:

Standard Q-meter The acquisition system for the PLL system

• Advantages Sensitivity (noise floor of RHIC system in the 10 nm range) Virtually impossible to saturate Simplicity and low cost Base band operation

• Excellent 24 bit audio ADCs available• Signal conditioning / processing is easy

Independent of the machine filling pattern

• Disadvantages It is sensitive to the "bunch majority”

• Gating needed to measure separate bunches (successful in Tevatron for pbars)– This is NOT foreseen for LHC start-up

Sensitive to rapid intensity changes (RHIC experience with beam loss)

Test systems now installed in the SPS, PS, LEIR, RHIC & Tevatron


PLL Tune Measurement SystemCollaboration with BNL as part of the US-LARP programme

• Advantages Provides a continuous tune measurement & can be used for feedback Precision a function of bandwidth (~10-5 for 1-10Hz) Necessary for continuous coupling and chromaticity measurements Can be used in a feedback loop

• Problems Requires constant excitation

• For proton & heavy ion machines this implies small amplitudes.

PLL functioning strongly linked to Coupling• Large coupling can

– cause PLL to jump from H to V tune peaks

– break any tune feedback loop

Coexistence with transverse damping


Measurement of Coupling using a PLL Tune Tracker

Frequency

Am

plitu

de

FFT of Horizontal Acquisition Plane

Start with decoupled machine

Fully coupled machine: = |C-|

Only horizontal tune shows up in horizontal FFTGradually increase coupling Vertical mode shows up & frequencies shift

Hor

Ver

Set TunesHV


Measurement of Coupling using a PLL Tune Tracker

x

y

Q1

Q2

A1,xA2,x

A1,y

A2,y

x

y

Q1

Q2

A1,xA2,x

A1,y

A2,y

x

y

Q1

Q2

1,x

1,y

2,x

2,y

Tracking the vertical mode in the horizontal plane &vice-versa allows the coupling parameters to be calculated


Measurement of Coupling using a PLL Tune Tracker (RHIC Example)

Eigenmode 2

Qx,0

Qy,0

|C-|

Eigenmode 1

Eig

en

mo

deo

r u

np

ert

urb

ed

tu

ne

va

lue

Co

up

ling

Am

plit

ud

e o

r u

np

ert

urb

ed

tu

ne

sp

lit

Eigenmode 2

Qx,0

Qy,0

|C-|

Eigenmode 1

Eig

en

mo

deo

r u

np

ert

urb

ed

tu

ne

va

lue

Co

up

ling

Am

plit

ud

e o

r u

np

ert

urb

ed

tu

ne

sp

lit

Fully coupled Tunes entirely definedby coupling


Tune & Coupling Feedback at RHIC (2006)


Luminosity Monitoring• Requires a region where signal is proportional to collision rate

Can be found in the neutral absorber (TAN) at ~150m from the IP Ionisation chambers supplied by LBNL (Berkeley) as part of US-LARP

• The Challenges Has to withstand harsh radiation environment Has to provide 40MHz bunch by bunch data with 1% relative accuracy

TAN


Macor Shell

CopperElectrodes

GroundPlane

TAN Luminosity Monitor


TAN Luminosity Monitor

PreAmp Shaper S&H ADC

1FF

100ns 25ns 40MHz

CuDipole


LHC Schottky Monitors• What does Schottky measurement offer

Non-invasive tune, chromaticity, momentum & emittance measurement• The Challenges

Obtaining Schottky data above coherent spectrum (GHz regime) Allowing bunch to bunch measurements Increasing signal to noise ratio to allow pilot bunch measurement Keeping the impedance seen by the beam low in the coherent spectrum

2211

21

21

21

rev

12

2

)(

2

1

WAWA

WW

WWC

WWp

dp

f

ffq

A1 A2

W1 W2

f1 f2

Tevatron Example


The LHC Schottky System

4.8 GHz 60 x 60 mm aperture x 1.5 meters long

Slotted Waveguide Pickup


LHC Schottky Monitors• LHC System Specifications

Based on FNAL travelling wave pick-up

• 4.8 GHz center frequency• 200 MHz bandwidth

minimum to allow bunch by bunch gating

One Horizontal and Vertical tank for each LHC ring

Gating on single or multiple bunches

Double down conversion• RF synchronous LO from

4.8GHz to 40MHz• Fixed LO from 40MHz to

<100kHz Digitisation using 24bit audio

ADC


Summary

• The LHC beam instrumentation has moved from the R&D stage to the construction stage Installation of most monitors is foreseen for the Autumn of 2006

• Significant progress made to address the remaining challenges Much of this has been made possible through the US-LARP collaboration

and the testing of new techniques on existing machines such as RHIC and Tevatron.

• LHC to turn on with a comprehensive set of beam instrumentation

AcknowledgementsMany thanks to all the members of the Beam Instrumentation Group at CERN & our US-LARP collaborators for their input for this presentation.

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LHC Instrumentation Status and Challenges

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