Denis Anielski 02.04.2009 1

Detector systems to find HFS of 209Bi80+ @ ESR

Emission characteristics Counting rates at existing mirror section Straight on detector option Parabolic mirror system Outlook

Denis Anielski, Volker Hannen, Raphael Jöhren, Christian Weinheimer

Westfälische Wilhelms-Universität Münster02.04.2009

Denis Anielski 02.04.2009 2

• Relativistic Doppler Effect

λ = λ´γ(1- βcos(θ)) θ= 0° → 640nmλ´ = 1555nm θ= 40° → 1000nm

• Observed angle

• Boost

Relativistic Doppler Effect and Boost (β = 0.71)

Denis Anielski 02.04.2009 3

Simulation of Boost

Polar angles in the comoving system Polar angles in the lab system(Isotropic light source)

A(0°,10°) = 4%A(10°;30°) = 25%A(10°;50°) = 52%

→ Most photons not in straight forward direction, because of sin(θ) in solid angle!

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Ideas For Detector Systems

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General Assumptions

Number of excited ions: 2 e5 Lifetime in lab system: 82 ms [1]

Lifetime in comoving system: 116 ms QE = 10% Circumference of ESR: 108 m β = 0.71

[1] V. M. Shabaev, PHYSICAL REVIEW A, JAN 1998

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Mirror System

• 10 elliptical mirrors on a 65cm section• Original simulation software not

available• First order estimate: geometric count

rate estimate• Realistic simulations using GEANT4

under progress

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Estimated counting rate

Counting rate is proportional to

Emitted photons per second NPh = N/tau = 1,72 e6

Ratio of totally emitted photons A = 0.38 (646 nm – 950 nm; 5°-37° )

Loss by reflexion and transmission R*T = 1/3 (R=0.35!!!)

Quantum efficency QE = 0,1

Relevant beam section b = 0.065m/ 108m

Geometry of mirror system g = 2/3

Number of windows (dia: 7cm) # = 3

→ f = NPh · A · g · RT · QE · b · # = 26 Hz

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Straight on option

• Diameter of window: 60mm• Straight beam section: 17 m• Distance – beam – detector: 3,5 m• All Photons are focused on detector by a lense• Transmission of lense: 0.9

→ 0,36 Hz (simulation c++)

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Parabolic mirror

Detects forward emission

→ short wavelengths

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Parabolic mirror

Assumptions

• Reflectivity coefficient: 0.8

• Hole in mirror with diameter of 2cm for the beam

www.edmundoptics.comGEANT4 model

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2-flange option

• Diameter of flange for mirror: 10 cm

• Diameter of flange for detector: 3.8 cm

• Distance: Beam - Detektor: 30 cm

• Straight section before mirror: 5 m

• Radius of mirror: 5 cm

• Lightguide as interface from window to detector

• GEANT4 simulation (Volker Hannen)

→ 15 Hz

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2-flange option

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1-flange option – C++ Simulation

• Diameter of flange: 20 cm

• Distance: Beam - Detektor: 25 cm

• Straight section before mirror: 5 m / 10 m

• Radius of mirror: 7.5 cm

• Radius of detector/ focussing system: 3 cm

• Counting rate is multiplied by 0.9 because of slit

→ 45 Hz / 60 Hz

(Flange is just in front of mirror system!)

Possible improvement with recessed exit window (distance beam – exit window = 15cm): 154 Hz

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CPM beam tests

• Two setups have been installed at ESR yesterday

• Investigations of background photons and behaviour of CPM next to dipole magnet

• Positions:– 2-flange option– Straight on option

• Detectors: Channel-Photomultiplier– Easy to handle – Low dark count rate– Only 2% QE around 650nm – Suitable for 244nm transition at SPECTRAP

(QE= 18%)

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Conclusions

Mirror system:

26 Hz, but dark counts of three detectors, broad wavelength range Reflexion of mirror? Not all three windows present ???

Straight on

very low rate ( < 1Hz) ???

Parabolic mirror

System with highest counting rate on a SINGLE detector Small wavelengths (640 – 680nm) !!!

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Outlook

• Test of Hamamatsu R943-02 PMT(suitable detector for parabolic mirror system)

• Detailed GEANT4 simulation of existing mirror system and search for best parameters of parabolic mirror system