beam instrumentation overview status for initial commissioning & recent results with bbq &...

Beam Instrumentation Overview

Status for initial commissioning & recent results with BBQ & PLL

LHC Machine Advisory Committee

7th December 2006

Rhodri Jones (CERN – AB/BI)

LHC Machine Advisory Committee December 2006 - Rhodri Jones (CERN - AB/BI)

Overview

• What’s required & when

• Status of BI Systems Orbit & trajectory measurement Beam loss measurement Synchrotron light monitor Other Systems

• Recent Results with the BBQ & PLL system US-LARP Collaboration with BNL & FNAL Tune, chromaticity & coupling measurements

• RHIC and SPS results


Instrumentation – the essentials• First turn

Screens, BPMs, fast BCT, BLMs

• Circulating beams at 450 GeV BPMs, DC BCT & lifetime, BLMs Tune & chromaticity Emittance: wire scanners.

• Snapback and Ramp Continuous Tune, Coupling & Chromaticity Orbit (+ feedback) BLMs to beam interlock controller etc. Continuous emittance monitoring: synchrotron light


100 Warm, Button Electrode BPMsButtons Recuperated from LEP

LHC BPM System - General Layout

24 Directional Couplers52 Enlarged Button& 8 Trigger BPMsInteraction Regions912 Button Electrode BPMs (24mm)

for theMain Arcs & Dispersion Suppressors

Total of 1186 BPMs for the LHCand its Transfer Lines

36 Warm BPMs -34mm Button Electrodes

54 Special BPMs for Tune & Chromaticity,Transverse Damper & RF, Beam Dump


Delivery Status of BPM Hardware

• BPM components all delivered 3750 standard and 500 enlarged buttons 3724 pre-formed arc cables and 592 special configurations 430 coupler feedthroughs 1000 cryostat feedthroughs

• Warm BPM & stripline electrode production Manufactured by BINP

• initial delivery non conform• delivery schedule was a worry in 2005 MAC presentation

Extensive follow-up during 2006 by both AB/BI & AT/VAC• Delivery of all components now complete (few non-conformities pending)

• Special BPMs for Tune Measurement & Dump Design only completed early 2006 Production by TS/MME and CECOM (Italy) Delivery was “just in time” for LSS4 installation Awaiting final delivery of dump line BPMs


Installed BPMs• Total of ~660 cold BPMs installed (~330 SSS)• Warm BPMs in LSS 8, LSS 1L and LSS 4 all installed

Enlarged button BPMsinstalled in Point 4

Warm directional couplerinstalled in Point 8


Status of BPM Acquisition System• Series Production of all components underway

Wide Band Time Normaliser(40MHz position measurement)

• 480 of 2400 front-end cards received• 200 of 2400 digitiser cards received• all delivery to be completed by March 2007

Digital Acquisition Board(DAB64x - TRIUMF)

• Standard for BPM, BLM, Fast BCT, Wire Scanners,Luminosity & Q measurement

• 220 of 1200 BPM type modules received• 185 of 500 BLM type modules received• all delivery to be completed by March 2007

• Reception Testing 2 automated test benches constructed and manned by external personnel Used for adjustment and calibration of all Wide Band Time Normaliser Cards Beam simulator allows position & intensity linearity measurement for all cards All data stored in MTF & linked to serial number chip located on each card


Status of BPM Acquisition System

• Installation Tunnel installation and hardware

commissioning has started in 8L• 23 of 34 positions in place

(92 channels)

• Infrastructure Nearly all fibre-optic, coaxial cable and WorldFIP control links in place

• LSS7 and LSS3 will be equipped with radiation hard fibres

• Produced by Fujikura (Japan) – first batch in production

• Tests by Fraunhofer Institute and mixed field test in the SPS has shown them to be an order of magnitude less susceptible than the standard CERN mono-mode fibre

BPM/BLM limit of 6dB


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

BLMQI Ionisation Chamber ~3100 Arcs yes 1 turn

BLMCIBLMCS

Ionisation ChamberSEM

~150~150

Collimation regions

no 1 turn

BLMEIBLMES

Ionisation ChamberSEM

~400~150

Critical aperture limits or positions

no 1 turn

BLM__ ACEM (phase II) ~10Primary collimators

yesbunch-by-bunch


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 production at IHEP

• After readjustment of the production schedule in March a constant rate has now been achieved

• SEM production to start after ionisation chamber production is complete

Ionisation chamber production

0

500

1000

1500

2000

2500

3000

3500

4000

4500

24/03/06 02/07/06 10/10/06 18/01/07 28/04/07 06/08/07

time

# o

f io

nis

ati

on

ch

am

be

rs

schedule

at CERN

needed for installation

Sector 7 – 8fully equipped with ionisation chambers


BLM integration and installations• Integration of monitors in layout of ARC, IR 1 and IR 8 finished• Integration will continue for the remaining points following installation schedule• IHEP installation team (1 team leader and 4 technician):

test of monitors with radiation source, shrinking of insulation tube, mounting of monitors, cable tray/cable fixation and electrical test of system

in case of accelerated interconnection closure an increase in the team is possible

ARC quadrupole with 3monitors on either site

Beam I

Beam II

Triplet quadrupole magnets IR 8


First use of LHC chamber design at CERN

270cm

comparison measurement-simulation, vertical pit1

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

-157.5 -146.3 -135 -123.8 -112.5 -101.3 -90 -78.75 -67.5 -56.25 -45 -33.75 -22.5 -11.25 0 11.25 22.5 33.75 45 56.25 67.5 78.75 90 101.25

112.5 123.75

135 146.25

157.5

cm

char

ges/

pot

meas: nominal

sim: nominal

Fluka simulation; P. Sala et al

3.20 m

• CNGS Secondary beam width measurements• Interleaved CERN produced and IHEP

produced LHC type Ionisation Chambers Give very similar response


BLM Acquisition Electronics

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

Implemented on BDI DAB64x


BLM test measurements at the SPS dump

Remaining beam dumped at end of slow extraction

FULL beam intensity ondump

Remnant decay after full intensity dump

Injection & acceleration losses

• Validation of complete BLM readout electronics chain 200MHz fixed target beam Use of SPS ionisation chamber located near the internal SPS dump


Measuring Beam Size

• Beam Profile Measurements in the LHC Workhorses

• Synchrotron light monitor

• Wire scanners for cross calibration

For injection & matching• OTR screens

For ions• Rest Gas Ionisation Monitor (BGI)

– Also used as back-up for SR monitor


Synchrotron Light Monitors (BSRx)

BSRT light source: 5T Superconducting undulators• Latest news: both SC undulators in place, see next CERN bulletin!

Congratulations to the AT/MAS team


Synchrotron Light Monitors

• 36 Tons of shielding and support structure in place

• Dielectric coated silicon extraction mirror first of its type - replaces traditional beryllium mirror over 98% reflectivity in visible/IR achieved by a small Scottish company

(Helia) using similar techniques to coating silicon diodes


• LHC BSRT fast camera tested in the SPS, Nov 2006 Image is single turn beam intensity seen by OTR screen Scale in pixels optical magnification gives 20x20mm frame.

• Able to capture and store raw images at the SPS revolution frequency Will have to optimise the trade off between transfer rate, data treatment &

dead time between measurements

Synchrotron Light Monitor (BSRT)


Abort Gap Monitor (BSRA)• System based on gated photomultiplier

• Tested in the SPS with synchrotron light source on fixed target beam Observation of injection kicker gap while beam is debunched before extraction.

• Worked extremely well

• Gain of photomultiplier is not as high as advertised Requires 15x more light

• For LHC a longer integration time is possible (every ms for SPS)

• BUT BSRA will require more light than anticipated at expense of BSRT


Wire scanner tanks and mechanisms

in place

DCCT and FBCTawaiting final

installation

Rest gas ionisation chambers and compensation

magnets in place

Dump line BTV tanks

awaiting final installation

Other Systems• Nearly all specialised BI equipment located in LSS4

After LSS8 this was the second full LSS to be installed A big effort made by BI technicians and engineers during 2006 together

with TS/MME and AT/VAC to get everything ready in time• We just about made it !!


Tune, Chromaticity & Coupling• Clear three step approach:

1) Day 1 with kicked beams and classical motion analysis• Q kicker for both planes & both beams located in Pt 4• Chirp excitation using the transverse damper

2) Day N with PLL tune tracking (US-LARP)• Recent experience gives us the hope that N is small!

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

• Requirements for stable PLL operational: lowering the excitation level to an insignificant level coping with coupling coping with chromaticity achieving compatibility with resistive transverse damping

Collaboration with BNL & FNAL via US-LARP


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

Direct Diode Detection (3D)


Continuous FFT and PLL Implemented in FPGA

3DFront-End

PID

PID

DAC

ADC

KICKERBBQ pickup

BEAM

Frequencygenerator

FixedAmplitude

Correction

Correction

Sin/CosExcitation

Ampl FB Off

Sweep/Lock

PhPh

A

A

A cos(wt)

PLL

PLL

PLL

A sin(wt)PLL

+-

+-A

I

I

BEAM

Amp. reference

Phase referenceDelay compens. f

40Mhz

A

Uses Standard DAB64x Module

PhPh

A

A

A cos(wt)

PLL

PLL

PLL

A sin(wt)PLL

A

I

I

BEAM

cordic

x

ya

a x

y

cordic

x

ya

a x

y

cordic

x

ya

x

y

aLPIIR

LPIIR

CORDIC: polar rectangular avoids large LUTs uses simple operations saves FPGA space !


Setting-up the 25ns Beam in the SPS

Low intensity beam

Residual oscillationwithout additionalexcitation clearlyvisible


PLL tracking in the SPS

• Nominal Beam - PLL OFF tune hardly visible

• Nominal Beam – PLL ON tracking achieved throughout cycle

Resonantly Extracted 25ns Beam in the SPSReal-time Tune Display


PLL Measurement on SPS Fixed Target Cycle

Tracks tune change of ~0.1 units per second


PLL Measurement during Collimator MD

Resolution of 10-6 achieved with 1s integration


Beam Transfer Functions in the SPS

• When things go wrong – thought to be due to a coupled bunch instability! Stable phase shifts – PLL can no longer lock Multiple peaks appear in Beam Transfer Function

• Standard Beam Transfer Function


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

By looking at contribution of vertical PLL in horizontal plane &vice-versa the degree of coupling can be calculated


Tune & Coupling Feedback at RHIC (2006)


Continuous Chromaticity Measurements• The focus of the development for 2007

RHIC to attempt chromaticity feedback SPS used to qualify new techniques for the LHC

• RF modulation with PLL Tune Tracking Standard technique used at RHIC & Tevatron may not be compatible with nominal collimator settings in LHC

• Other techniques under test Fast RF phase modulation – tests at FNAL & SPS (RF power an issue for LHC) Additional side exciters within PLL to measure tune width (phase slope) Continuous head-tail measurement with PLL excitation

• Constant phase shift proportional to chromaticity• Requires sensitive measurement of head & tail oscillations diode detection!!


Summary• Both large distributed systems (BPM/BLM) currently on schedule

Production of ionisation chambers at Protvino is progressing smoothly• One of the major worries last year

• Support for AB/BI from TS Significant support for Design and from the main CERN workshops Regular meetings have allowed problems to be solved quickly and priorities to be

juggled to fit with installation requirements

• Most Vacuum Hardware now in place in Point 4 Attention can turn to completing and testing the final electronics

• Tune, Coupling and Chromaticity Measurement Combination of BBQ and PLL is proving very powerful RHIC demonstration of combined tune and coupling feedback is very encouraging All efforts in 2007 will be focused on adding chromaticity feedback to the list

• Outlook for LHC commissioning All necessary instrumentation for the start-up foreseen to be in place Functionality will evolve through the commissioning phases

beam instrumentation overview status for initial commissioning & recent results with bbq &...

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