NEW COMMENTS TO ILC BEAM ENERGY MEASUREMENTS BASED ON

SYNCHROTRON RADIATION FROM MAGNETIC SPECTROMETER

E.Syresin, B. Zalikhanov-DLNP, JINR

R. Makarov-MSU

K.Hiller, H.J. Schriber-DESY, Zeuthen

SCHEME OF MAGNET SPECTROMETER

Scheme of magnetic spectrometer applied for ILC beam energy measurement.

GEANT SIMULATION

R. Makarov

E=250 GeV+50 MeV- blue histogram

E=250 GeV-wight histogram

Left SR fan spot edge

SR fan left edge displacement xleft7-8 μmSR fan right displacement xright5-6 μmSimulated energy resolutionRequired resolution

12 μm/50 MeV2.5 μm/50 MeV

SIZE OF SR DETECTOR Electron energy spread in bunch

310/ EE

EELx edgeE 2/1

Soft photon angle spread

3/1/5.0 Rsr 12 rad at photon energy 20 keV and electron energy of 250 GeV.

sredgeSR Lx 1 750 m

Fringe field in the magnetic rigidity at magnetic field variation of

%1/ BB

(Bl)/Bl ≈ 4∙10-2

)2()(2/1 lBlBLx edgeR 600 m

Interaction of hard SR photons with a vacuum pipe material became to additional SR at low energy and an increase of the SR fan horizontal size.

2/1222

edgeSR

edgeR

edgeE

edge xxxx

The horizontal width of active detector area has been comparable with 1 mm at registration of soft SR.

1mm.

25 m.

ELECTRON ENERGY SPREAD

Comparison of SR spot edges for monochromatic electrons at E=250 GeV (red color) and electron energy spread of ±125 MeV at E=250 GeV (white color)

R. Makarov

GEANT SIMULATION

K.H. Hiller

Multiplicity of photons radiated by an electron whihin spectrometer magnet,GEANT simulation

5N

Average number of photons radiated by one electronMeVE 8.3

Average photon energy

SR calculations<N>=(5/2·31/2)··eB/m·Lmag/c=4.8

<E>=(8·31/2/45)·Ecr=3.6 MeVEcr=0.66 Ee

2(GeV)·B(T)=11.6 MeV- critical photon energy

=1/137.

PHOTON ENERGY SPECTRUM

K.H. Hiller

Energy of photons radiated within the spectrometer magnet

SR calculation Power density

SP

d

Nd

cr

0

crcrS 3/1/33.1 crcrcr

S

exp

316

227

Photon Distribution

SP

d

Nd

cr

0

REFLECTION MIRRORSFOR SOFT SR

The application of mirrors permits to avoid the problems related to SR radiation protection however the installation of mirrors reduces the energy resolution at fixed coordinate resolution and detector position.

Lam=40 m

mirror-spectrometer magnet distance

Lm-d=10 m

mirror-detector distance

REFLECTION OF SOFT SR RADIATION BY MIRROR

φmax (rad) ≈ 0.08/Eγ (keV)=4 mrad

mirror critical angle at large atomic number Zand electron energy of 20 keV

0

0,2

0,4

0,6

0,8

1

0 10 20 30

photon energy, keV

Re

fle

cti

vit

y

Dependence of Rh mirror reflectivity on photon energy.

The mirror reflected surface is placed at angle of

φ=3 mrad

to beam axis.

DETECTOR SHIELDING AT MIRROR SCHEMEThe coordinate of left SR spot edge is equal to

2/22/)2/( dmmaL LLLAMLLAx =8.3 cm.

The coordinate of left hard SR spod edge corresponds to

xSR=3.1 cm.

The distance about

Δx= 5 cmbetween soft SR channel and ILC beam pipe can be used for detector shielding and reduction of hard SR intensity.

In this case we assume that before mirror the horizontal size of vacuum chamber pipe can be increased from 4 cm up 7 cm on a length of 40 m from middle of analyzed magnet.

After mirror two special channels of length 10 m will be constructed to transportation of soft SR radiation to detector.

ENERGY RESOLUTION IN MIRROR SCHEME

2/11

dm

L

LL

x

E

E

=1 ·10-4

at detector coordinate resolution of δx=2 µm.

MIRROR PARAMETERS

dmir25- 50 μm

mirror thickness

srLy 1 0.6 mm

vertical size of SR spot on mirror

lmir=(LAM+La-m) 0.1/2φ=65 cm

length of left mirror

The mirror reflect soft SR generated inside analyzing magnet on length of 0.1 LMM 30 cm at deflection angle of 0.1 /20.05 mrad.

MIRROR HEATING

Mirror adsorption

>50-100 keV

μμ0·0 /

050-100 keV, μ05-10 cm2/g

Photon energy losses in both mirrors at photon energy

Q ≈ N (ε /εcr)1/3 ·d ∙(2lmir/Lam) μ0·dmir·0 /

Total energy losses in mirror per bunch

Q ≈ 3N ∙(2lmir/Lam) μ0·dmir·0 ≈3·1014 eV≈45 J

N = 1011 is the number of hard SR -quants in the bunch,

єcr = 11.4 MeV is the critical photon energy.

Rh mirror ( =12.4 g/cm3, dmir=25 m)

Energy losses in mirror per train

Nbunch=4800

Q=NbunchQ ≈200 mJ

PHOTON ENERGY LOSS IN MIRROR

CREMNIUM DETECTOR

Semiconductor SR detector scheme at sub μm resolution.

Si

=2.3·105 Ohm·cm

=12

rel=0 250 μs

Ge

=47 ·cm 

=16

rel=07 ns

rel -charge relaxation time

B.Zalikhanov

Si DETECTOR SIGNAL

In Si detector pulse duration is defined by

RCstr50 ns

Cstr=0S/d1 nF-capacity of detector strip

(S=2.5·10-5 m2, d=3 m)

R=50 -resistance of amplifier

Amplification conversion 50 V/1 nCV1.5 V

at number of electrons of 1.5·108

DETECTOR NOISE

B. Zalikhanov

C

kTV 2

Voltage fluctuation caused by heating noise

C

kT

C

Ne

ΔN – number of charge particles in detector strip

Minimal -quanta energy required for production of signal larger than heating noiseW=ΔNE = Ji·(kTC)1/2/e 50 keV

Ji=3.6 eV energy required for e-hall pair production

Resolution related to current noiseW2Ji Nc

1/2 ·(rel/c)1/260 keVNc106 - number of free charges in Si (nsi=1.1·1010 cm-3),

cd/-E2·10-10 s - time of free charge collection on strip electrodes at -=1.3 cm2/(V·s), E=1 kV/cm

Ratio of heating and current noisesto photon energy per strip

(W2+W2

2)1/2/NE10-5

N=106 - number of photon with energy of E10 keV per strip

GAS AMPLIFICATION DETECTOR B. Zalikhanov

Amplification coefficient N/N010-100N=N0exp (dc-a)

P=50-100 Atm, dc-a2 mm cathode anode distance10-20 cm-1 Taunsend coefficient

P

EB

P

P in Torr, B=30·10-3 V-1, E=V/d0.5 kV/cmEan/E10 electric field near anode (10-15 m)

Number of soft photons at E10 keV per strip

Number of secondary electrons per strip

After amplification at K=10

The signal at amplifier conversion of 5 V/1 nC

N 106

Ne108

Ne109

V1.5 V

The position measurements of both horizontal edges for SR fan permits to determine the beam energy with a resolution of E/E 5∙10-5.

The energy resolution obtained in GEANT simulations corresponds to 12μm/50 MeV at electron energy of 250 GeV. The scaling sensitivity 12μm/50 MeV at electron energy of 250 GeV permits to reach the energy resolution of ΔE/E ≈5∙10-5 at spatial resolution of 2-3 μm.

A high position resolution detectors (2-3 μm) for a low energy gamma registration within large radiation background are proposed. Detector production may be carried out by methods used in the microelectronic industry.

Conclusion