A Short History of Nearly Everything Michele Viti

A Short History of Nearly Everything

Michele Viti

07 August 2009 Michele Viti 2

Outline

• Myself

• About my work in Zeuthen– ILC overview– Beam energy measurement – An brief overview of my work and results

• Magnetic measurements• Relative beam energy resolution• Laser Compton energy spectrometer


Myself

• I was born 31 years ago somewhere in Italy

• I studied physics at the Perugia university


Myself

• Master degree in 2004.• Title of the thesis : “Evaluation of a Tracking

Algorithm for the Trigger of KOPIO Experiment on the Decay

”.

• I continued working on this topic until the project was canceled by the DOE.

00 LK


Myself

• I moved then to Germany and started in February 2006 my PhD.

• I joined the Linear Collider working under the supervision of H.J. Schreiber.

• Title of the thesis “Precise and Fast Beam Energy Measurements at ILC”.


ILC

•30 Km electrons/positrons linear accellerator

•Total energy in the cms 500 Gev (upgradeable 1 Tev)

•High luminosity (2*10^34 /cm^2*s)

•A machine for precise measurements


ILC: Precise Top Mass Measurements

• Many Standard Model depends strongly on the value of the Top Mass.

• Well understood background, clean experimental environment

• Best direct measurement of the top mass will be at ttbar threshold

– Vary the beam energy (Precise Beam Energy Measurements)

– Count number top-antitop events.

4103175

50

GeV

MeV

M

M

t

t


Basic Requirements for Beam Energy Measurements

• In order to make a precise measurement of the top quark mass we need to know some “input” parameters very well such as the mean energy of the bunch

• We need to have a fast (bunch-by-bunch), precise and non-destructive monitor for beam energy

• Direct measurement of energy at the IP is very difficult. We want to measure the beam energy upstream, downstream the IP plus a slow monitoring at the IP

• Relative Energy precision required for upstream measurements

410

t

t

b

b

m

m

E

E


Magnetic Chicane Energy Spectrometer

Bdld

LEb

•Electrons are deflected in this chicane and the offset in the mid-chicane is anti-proportional to the energy.

•Measuring this position with some special devices (Beam Position Monitor, BPM) together with B-field integral we have access to the beam energy

•Method well tested used at LEP with a precision of 4107.1

offset d

magnets

L

BPM BPM

BPM


Experiment T474/491

• At the End Station A (ESA) a 4-magnet chicane energy spectrometer was commissioned in 2006/2007 (experiment T474/491).

• The goal is to demonstrate the feasibility of the system.


End Station A

• Characteristic:– Parasitic with PEP II

operation– 10 Hz and 28.5 GeV– Bunch charge, bunch

length energy spread similar to ILC

• Prototype components of the Beam delivery System and interaction Region.


End Station A

Parameter SLAC ESA ILC-500

Repetition Rate 10 Hz 5 Hz

Energy 28.5 GeV 250 GeV

Bunch Charge 2.0 x 1010 2.0 x 1010

Bunch Length 300-500 m 300 m

Energy Spread 0.2% 0.1%

Bunches per train 1 (2*) 2820

Microbunch spacing (20-400 ns*) 337 ns

Beam Parameters at SLAC ESA and ILCBeam Parameters at SLAC ESA and ILC


Experiment T474/491• Institutes involved: SLAC, U.C. Berkeley, Notre Dame, Dubna, DESY, RHUL, UCL,

Cambridge • 2006:

– January (4 days): commissioning steering BPMs– April(2 weeks): commissioning cavity BPMS, optimization digitization and

processing– July(2 weeks): commissioning interferometer and stabilty data taken with

frequent calibrations• 2007:

– March(3 weeks): Commissioning and installation magnets: first chicane data!!!– July(2 weeks): Additional new BPM in the centre of the chicane.

Magnetic measurements



• B-field Integral, essential parameter for beam energy measurement.

• Need to be measured with an accuracy of 50 ppm.

Bdl



• Between November 2006 – February 2007 measurements on these magnets were performed in the SLAC laboratories (DESY, Dubna, SLAC).

• Purpose of the measurements:– General understanding and characterization of the magnets

• Stability of the B-field and B-field integral with fixed current and switching the polarity.

• Monitoring of the residual B-field.• B-field map.• Measurement of the temperature coefficient for B-field and B-field

integral .

– Development and test a procedure to monitor the B-field integral.



• Monitor of the B-field integral: in ESA no device was available to measure directly this quantity.

• Solution: measure the B-field in one point and from that determine the integral.– Basic assumption BdlB

When the field is changing in one point, changes everywhere by the same amount. The field shape stay constant



• To measure the B-field in one point an NMR probe was used.

• Flip coil technique to measure for B-field integral.

• Calibration of the NMR: determination of the slope and intercept for the relation.

• Comparison of the prediction with the measurement.

01 pBpBdl



• The total error on the estimation of the B-field integral using the one-point B-field measurement was

• Main contributions are alignment errors of the devices.

• Several suggestions were given to improve the results.

ppmBdl

Bdl184

Relative beam energy resolution


Relative Beam Energy Resolution

• At the End Station A several problems occurred for 4-magnet chicane prototype

• A complementary method to cross-check the absolute energy measurement was not implemented

• Only relative energy measurement possible at ESA



• The offset d in the mid-chicane point is determined by two points, namely Xb and X0

• Xb is measured by the BPMs the mid-chicane and X0 is extrapolated using BPMs upstream and downstream of the chicane.

Beam direction



• BPMs, Beam Position Monitors. They measure the transverse position (X and Y) and angle (tilt) in the X-Z and Y-Z plane (X’ and Y’).

• Accuracy on position measurement < 500 nm.



• X0 can be written as

• For zero current magnet Xb=X0, the BPM measures directly X0.

• The coefficients in Eq. above can be determined with a minimization.

NNNNNNNN ycycxcxc

ycycxcxccX

''

''0

)4()3()2()1(

1)4(

11)3(

11)2(

11)1(

10



• One fundamental condition: the magnetic chicane must work symmetrically

• The upstream path must be restored downstream

Beam direction



• Unfortunately this was not the case of the 4-magnet chicane in ESA

• For a given current the magnet fields were different up to ~3%

• BPMs downstream could not be used to determine X0. This resulted in a worse resolution for d.



• A resolution of 24 MeV was found (Resolution -- the smallest amount of energy change that the instrument can detect reliably)

• For a beam energy of 28.5 GeV this corresponds to a relative resolution of ~

• The largest contribution to this number comes from the resolution on d (>2 microns).

4105.8

Laser Compton Energy Spectrometer



• At LEP it was possible to have redundant beam energy measurement devices cross check!!!

• At ILC so far, complementary methods for upstream beam energy measurements not implemented.

• Studying the feasibility of an upstream energy spectrometer based on Compton backscattering (CBS) events.



• Compton process with initial electron not at rest.• Energy spectrum for electrons (photons) present a sharp

cut-off (Compton edge).

• Scattered particles collimated in forward region.

2

min, 41

m

EEE

Eb

be




Energy measurement

• , is the center of gravity of the scattered photons, or, equivalently, the end point of the SR fan.

• , position of beam, possible to measure with BPMs

• , position of the electrons with minimum energy.

edgeX

beamX

0X

0

2

4 XX

XX

E

mE

beam

beamedgeb



• Beam parameters– Beam energies 50-500 GeV– Beam size in x (y) 20-50 (2-5) microns

• Geometrical parameters– Drift distance 25-50 m– B field 0.28 T, magnet length 3 m

• Laser parameters– Smaller wavelength preferable (e.g. green laser)– Pulsed laser with 3 MHz frequency– Laser spot size 50-100 microns– Laser pulse energy must ensure 10^6 scatters (e.g. 30 mJ per pulse)– Crossing angle ~8 mrad

• Accuracy required to achieved – < 1-2 microns– < 1-2 microns– < 20 microns

0XbeamXedgeX

410/ bb EE



• Beam position can measured with a normal BPM (very well know and precise technique).

• Edge position: Diamond strip detector or quartz fiber detector. Basic simulation shows that this feasible.

• Photon detection: Basically 2 possibilities, using the backscattered photons or the synchrotron radiation photons.



• Number of backscattered photons (BP) 4 order of magnitude less than SR photons

• <Energy> BP ~100 GeV, <energy> SR photons ~3 MeV.• 2 possibilities

– Place a thick absorber in front of detector and measure the profile of shower (signal from BP dominant), quartz fiber detector suitable.

– No absorber, detector in front of the photon beam (signal from SR photons dominant). Novel detector under development in DUBNA (Xenon gas detector).

• Main problem for both configurations: very high radiation dose (10-100 GGy per year).


Conclusions

• A prototype of 4-magnet chicane was built in ESA. • The absolute value of the B-field integral can be

monitored with an accuracy 184 ppm (ESASLAC note and PAC poster)

• The resolution of the chicane was found to be ~24 MeV, where the main contribution is the resolution on the beam offset in the mid-chicane (to be published…)

• A novel method based on Laser Compton events was studied(NIM publication). An experiment is under study to proof the feasibility (proposal in preparation).

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A Short History of Nearly Everything Michele Viti