Results from the FRS Ion Catcher with projectile and fission fragments Timo Dickel GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt II. Physikalisches Institut, Justus-Liebig-Universität Gießen, Germany Overview • The FRS Ion Catcher a test facility for the LEB • Prototype of the Stopping Cell for the Super-FRS at FAIR • Multiple-Reflection Time-of-Flight Mass Spectrometer • Measurements at the FRS Ion Catcher in 2014 • Conclusions and Outlook NUSTAR Annual Meeting, Darmstadt/GSI, March 2 – 6, 2015
Low Energy Branch of the Super-FRS at FAIR LEB of the Super-FRS: universal and fast production - high selectivity - cooled exotic nuclei 100...1500 MeV/u ~ eV ~ keV ~ MeV/u Experiments Fragment Buncher / Stopping MR-TOF Target Separator Degrader (Trap, Laser,..) Cell MS Primary Beam In-flight In-flight Stopping / Isobar Momentum Separation Production Thermalization Separation Compression SuperFRS LEB MATS / LaSpec MATS (Precision Measurements of very short-lived nuclei using an Advanced Trapping System for highly charged ions) LaSpec (Laser Spectroscopy) Eur. Phys. J. Special Topics 183 (2010) 1 T. Dickel, Results from the FRS Ion Catcher with projectile and fission fragments, NUSTAR Annual Meeting, Darmstadt/GSI, March 2 – 6, 2015
Stopping Cell Principle Range Bunching p’ p+ p Monoenergetic p’ p Ion Beam p’ p- p Ion Beam with Different Monoenergetic Momenta H. Geissel et al., NIM A 282 (1989) 247 Degrader Dispersive p+ p, p, p- p H. Weick et al., NIM B 164 (2000) 168 Stage C. Scheidenberger et al., NIM B 204 (2003) 119 Decreases range straggling by more than an order of magnitude Enables stopping of ion produced at relativistic energies in gas-filled stopping cells Stopping Cell DC (+RF) DC+RF High- Low-energy energy ion ion beam beam RF structure: M. Wada et al., NIM B 204 (2003) 570 funnel or carpet G. Savard et al., NIM B 2004 (2003) 582 Converts high energy, large emittance beam in low energy, low emittance beam T. Dickel, Results from the FRS Ion Catcher with projectile and fission fragments, NUSTAR Annual Meeting, Darmstadt/GSI, March 2 – 6, 2015
Stopping Cell Design Cryogenic Operation Operate He-filled stopping cell at cryogenic temperature (~70 K) • Ultra-pure helium (freezing-out of contaminants) - Ideal for ion survival, 2+ charge state possible - No formation of molecules/adducts • Reduced radial ion diffusion • Reduced requirements for cleanliness easier, more flexible construction P. Dendooven et al., NIM A 558 (2006) 580 S. Purushothaman et al., NIM B 266 (2008) 4488 High-density Operation Use RF structure with small spacing to achieve high RF repelling field (PCB-based RF carpet instead of RF funnel) • High stopping gas densities • Less complex construction than RF funnels Diameter: 250 mm M. Wada et al., NIM B 204 (2003) 570 M. Ranjan et al., Europhys. Lett. 96 (2011) 52001 Electrode spacing: 0.25 mm T. Dickel, Results from the FRS Ion Catcher with projectile and fission fragments, NUSTAR Annual Meeting, Darmstadt/GSI, March 2 – 6, 2015
Prototype of the Stopping Cell for the LEB 100 cm Extraction RFQ Exit hole RF carpet DC cage electrodes Insulation vacuum 223 Ra source Inner chamber Developed in Collaboration (cooling by cryo- Outer chamber cooler ~ 70 K) (room temperature) M. Ranjan et al., Europhys. Lett. 96 (2011) 52001. W.R. Plaß et al., Nucl. Instrum. Methods B 317 (2013) 457. M. Ranjan et al., Nucl. Instrum. Methods A 770 (2015) 87. T. Dickel, Results from the FRS Ion Catcher with projectile and fission fragments, NUSTAR Annual Meeting, Darmstadt/GSI, March 2 – 6, 2015
Motivation: TOF Mass Spectrometry in Nuclear Physics Enables high performance • Fast access to very short-lived ions (T 1/2 ~ ms) • Sensitive, broadband, non-scanning efficient, access to rare ions Conventional TOF-MS achieve medium mass resolving power only Solution to achieve high mass resolving power and accuracy: Multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS) Detector Ion source / injection trap H. Wollnik et al., Int. J. Mass Spectrom. Analyzer Ion Processes 96 (1990) 267 Applications in nuclear physics • Direct mass measurements of exotic nuclei C. Scheidenberger et al., Hyperfine Interact. 132 (2001) 531 • High-resolution isobar separator W.R. Plaß et al., NIM B 266 (2008) 4560 • Diagnostics measurements: Monitor production, separation and low-energy beam preparation of exotic nuclei W.R. Plaß et al., Int. J. Mass Spectrom. 394 (2013) 134 T. Dickel, Results from the FRS Ion Catcher with projectile and fission fragments, NUSTAR Annual Meeting, Darmstadt/GSI, March 2 – 6, 2015
Multiple-Reflection Time-of-Flight Mass Spectrometer Separated Ions Ions Kinetic Energy 1.3 keV 2 m Mass Measurement W.R. Plaß et al., Int. J. Mass Spectrom. 394 (2013) 134 m/Δm ~ 10 5 -10 6 , Full Mass Range, m/Δm > 10 5 T. Dickel et al., NIM A 777 (2015) 172 - 188 m/Δm ~ 10 3 -10 4 Mass Accuracy ~ 10 -6 -10 -7 M. I. Yavor et al., IJMS (2015) in press T. Dickel, Results from the FRS Ion Catcher with projectile and fission fragments, NUSTAR Annual Meeting, Darmstadt/GSI, March 2 – 6, 2015
MR-TOF-MS: Mass Resolving Power Time-of-Flight / ms Mass Measurement 0 2 4 6 8 10 12 14 16 18 Accuracy 5 5x10 m/ m = 450,000 Mass Resolving Power (FWHM) ~10 -7 5 (m/ m)(N turn ) 4x10 Transmission efficiency 5 3x10 up to 70% 54 turns Sensitivity 5 2x10 2 ms ~10 ions m/ m = 100,000 5 1x10 N T T turn 0 m / m ( N ) Isobar separator with turn 2 2 2 T ( N T ) high ion capacity 0 turn 0 0 100 200 300 400 500 >10 6 ions/s Number of Turns World-wide unique combination of performance characteristics! 133 Cs + , Ion kinetic energy 1.3 keV T. Dickel, Results from the FRS Ion Catcher with projectile and fission fragments, NUSTAR Annual Meeting, Darmstadt/GSI, March 2 – 6, 2015
FRS Ion Catcher a Test Facility for the LEB 100...1500 MeV/u ~ keV ~ eV ~ MeV/u Experiments Fragment Buncher / Stopping MR-TOF Target Separator Degrader Cell MS (Trap, Laser,..) Primary Beam In-flight In-flight Momentum Stopping / Isobar Separation Production Compression Thermalization Separation SuperFRS LEB MATS / LaSpec W.R. Plaß et al., NIM B 317 (2013) 457 T. Dickel, Results from the FRS Ion Catcher with projectile and fission fragments, NUSTAR Annual Meeting, Darmstadt/GSI, March 2 – 6, 2015
Setup at the FRS Ion Catcher at GSI Cryogenic Diagnostics Stopping Cell Unit Time-of-Flight Mass Spectrometer Cooling System T. Dickel, Results from the FRS Ion Catcher with projectile and fission fragments, NUSTAR Annual Meeting, Darmstadt/GSI, March 2 – 6, 2015
Systematic Investigations calculated for max DC field using mobility theory 40 measurments using pulsed 223Ra source mean extraction time (ms) Extraction time: 30 • Extraction time independent of areal density 20 • given by mechanical desgin of stopping cell 10 0 0 2 4 6 8 10 area density (mg/cm^2) 1.5 Normalized Counts 1.0 Stability of operation: from production to mass measurement 0.5 Stable over one week beam time 213 Fr measured with MR-TOF-MS in High Resolution mode 0.0 0 2 4 6 8 Time / d T. Dickel, Results from the FRS Ion Catcher with projectile and fission fragments, NUSTAR Annual Meeting, Darmstadt/GSI, March 2 – 6, 2015
Improved Total Efficiency • Carpet with improved electrical desgin: • Higher RF-amplitude possible and lower temperatures Year Max. RF-amplitude Temperature of RF coil 2012 80 Vpp 270 °K 2014 140 Vpp 150 °K Ion survival and extraction • Improved bake-out + New carpet 100 efficiency / % better cleanliness Higher ion survial and extraction efficiency (eg. 223 Th) 50 0 2011 2012 2013 2014 • Higher differential pumping Year of experiment Higher areal density Higher stopping efficiency 2012: 3.1 mg / cm² 2014: 6.3 mg / cm² Improved total efficiency up to 30% Factor 2 higher than 2012 T. Dickel, Results from the FRS Ion Catcher with projectile and fission fragments, NUSTAR Annual Meeting, Darmstadt/GSI, March 2 – 6, 2015
Mass Measurement: Uranium Projectile Fragments 6 • Mass window of ~ 30 u Data 220 Ra 2+ Gaussian Fit • Mass resolving power ~ 120,000 Half-life: 17.9 ms 11 ions • Doubly charged 4 Counts • Shortest half-life • Highest sensitivity 2 0 110,002 110,004 110,006 110,008 mass-to-charge / (u/e) + + 129 Xe 132 Xe + 5 SF + 136 Xe + + + 128 Xe 131 Xe 100 + 5 SF + 134 Xe Counts + 124 Xe + + 2+ 124 Xe 124 Xe + 5 SF 220 Ra + 4 SF + 4 10 SF 1 30 32 34 36 38 40 42 44 46 48 50 TOF-4,528.83 µs (µs) T. Dickel, Results from the FRS Ion Catcher with projectile and fission fragments, NUSTAR Annual Meeting, Darmstadt/GSI, March 2 – 6, 2015
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