1. CR Time-of-Flight detector Present status
Marcel Diwisch
II. Physikalisches Institut, Justus-Liebig-Universität Gießen, Germany
Outline
Isochronous Mass Spectrometry
Dual ToF detector system at CR
New dimensions of ToF detector
Technical issues

2. Overview FAIR
ESR

3. Isochronous Mass Spectrometry (IMS) at FRS-ESR
Time-of-Flight detector
Resolving power:
FWHM = 2 x 105
Accuracy: 10-6
Half-life: ~10 s
B ~ 10 mT
E ~ 1 kV/cm
Developed in Gießen (J. Trötscher NIM B70:455–458, 1992)

4. Overview FAIR CR

5. Velocity measurement = improve isochronicity
Collector Ring
Injection
(*) S. Litvinov, PhD thesis (2008)
L = 221,45 m
Bρ = 13 Tm
γt = 1,43-1,84
Δp/p = (0,22 – 0,62)%
εx = 100 mm mrad (*)
isochronous
mode
magnet
stoch. cooling pick-up/kicker
inj./extr. kicker
RF cavity
detectors / beam diagnostics
valves
TOF-1
Figure: A. Dolinskii
Dual detector system:
Velocity measurement = improve isochronicity
TOF-2

6. CR Simulations
Monte Carlo simulations (MOCADI) for ions circulating in
the CR with γt=1,67
Present 40 mm diameter of foil is too small for needed acceptance
⇒ 80 mm diameter of foil

7. Design of new detector Main challenge: Possible solution:
larger carbon foil diameter needed
increase carbon foil diameter to 80 mm
larger total detector geometry
higher electrical field strength
longer flight path from foil to MCPs
better homogeneity of (electrical) fields
larger absolute time of flight
by changing electrode shape
time uncertainty increases
and electrode positions
limited space in CR

8. CR Simulations SIMION grid creation
and calculation of electrical fields
CAD-drawing y x z
ESR-ToF Detector
CR-ToF Detector
x-dimension
300 mm
565 mm
y-direction
90 mm
180 mm
z(beam)-direction
154 mm
236 mm
Simulation of secondary electrons

9. Design of new detector (Electrodes)
Efficiency forward (%)
77,4
Efficiency backward (%)
76,8
Efficiency coincidences (%)
66,9
Timing accuracy (ps) 37
Efficiency forward (%)
97,0
Efficiency backward (%)
97,2
Efficiency coincidences (%)
96,6
Timing accuracy (ps) 25
Electron Transport Only

10. Design of new detector (Magnet)
COMSOL simulations for necessary magnet homogeneity
needed relative homogeneity: <10-3
in a 180 mm radius
with 240 mm gap
198 mm
poleshoe diameter minimum 800 mm

11. CR Simulations ESR CR L = 108 m L = 221,45 m Bρ = 6,4 Tm Bρ = 13 Tm
Δp/p = 0,2 %
εx = 7 mm mrad
L = 221,45 m
Bρ = 13 Tm
γt = 1,67
Δp/p = 0,5 %
εx = 100 mm mrad
TOF detector (1x)
TOF detector (2x)
B-field
homogeneity radius
100 mm
B-field
homogeneity radius
200 mm
Foil diameter 40 mm
Efficiency ≈ 78%
Timing accuracy ≈ 45 ps
Foil diameter 80 mm
Efficiency ≈ 98%
Timing accuracy ≈ 35 ps

12. Technical Issues Construction of TOF detectors in ESR
same technique will be used for CR
But magnets and detector will be larger!!!

13. Technical Issues

14. Tests for new detector Questions:
80 mm foils produceable? Yes! TU Munich produces them
Can one handle 80 mm foils? Will be tested
Impact of larger foils to timing? Will be tested
First measurements with 40 mm foils have been performed

15. Acknowledgements ILIMA TOF Detector Working Group
U. Czok, T. Dickel, M. Diwisch, H. Geissel, C. Hornung, R. Knöbel,
N. Kuzminchuk-Feuerstein, W.R. Plaß, C. Scheidenberger, H. Weick
Dr. T. Faestermann and Dr. R. Gernhäuser for providing us with carbon foils
Funding: BMBF (06GI9115I), HGF (NAVI), GSI (strategic university cooperation GSI-JLU-FAIR)
HIC for FAIR

16. Velocity determination
Second term of equation not vanishing for non isochronous ions
Correction by measuring velocity in 22 m distance: