RFQ Beam Coolers
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RFQ stands for Radio-Frequency Quadrupole (also known as a Quadrupole mass analyzer when used as a mass filter), an instrument that is used in mass spectrometry. The RFQ was invented by Prof. Wolfgang Paul in the late 50's / early 60's at the University of Bonn (Germany). Paul shared the 1989 Nobel prize in Physics for his work.
By aligning four rods and applying an RF voltage between opposite pairs, a quadrupole field is created that alternated focuses in each transverse direction. Sample for mass analysis are ionized, for example by laser (MALDI) or discharge (electrospray or Inductively Coupled Plasma, ICR) and the resulting beam is sent through the RFQ and "filtered" by scanning the operating parameters (chiefly the RF amplitude). The gives a mass spectrum, or fingerprint, of the sample. Residual gas analysers use this principle.
A "cooler" is a device that lowers the temperature of an ion beam by reducing its energy dispersion , beam spot size, and divergence - effectively increasing the beam brightness (or brilliance). Several ion beam cooling methods exist. In the case of an RFQ, the most prevalent one is buffer-gas cooling, whereby an ion beam loses energy from collisions with a light, neutral and inert gas (typically helium). Cooling must take place within a confining field in order to counteract the thermal diffusion that results from the ion-atom collisions.
Applications of ion cooling to Nuclear Physics (notably, mass measurements):
Despite its long history, high-sensitivity high-accuracy mass measurements of atomic nuclei continue to be very important areas of research for many branches of physics. Not only do these measurements provide us with a better understanding of nuclear structures and nuclear forces but they also offer insight into how matter behaves in some of Nature’s harshest environments. At facilities such as ISOLDE at CERN and TRIUMF in Vancouver, for instance, measurement techniques are now being extended to short-lived radionuclei that only occur naturally in the interior of exploding stars. Their short half-lives and very low production rates at even the most powerful facilities require the very highest in sensitivity of such measurements.
Penning traps, the central element in modern high-accuracy high-sensitivity mass measurement installations, enable measurements of accuracies approaching 1 part in 10^11 on single ions. However, to achieve this Penning traps must have the ion to be measured delivered to it very precisely and with certainty that it is indeed the desired ion. This imposes severe requirements on the apparatus that must take the atomic nucleus out of the target in which it has been created, sort it from the myriad of other ions that are emitted from the target and then direct it so that it can be captured in the measurement trap.
Cooling these ion beams, particularly radioactive ion beams, has been shown to drastically improve the accuracy and sensitivity of mass measurements by reducing the phase space of the ion collections in question. Using a light neutral background gas, typically helium, charged particles originating from on-line mass separators undergo a number of soft collisions with the background gas molecules resulting in fractional losses of the ions’ kinetic energy and a reduction of the ion ensemble’s overall energy. In order for this to be effective however, the ions need to be contained using transverse radiofrequency quadrupole (RFQ) electric fields during the collisional cooling process (also known as buffer gas cooling). These RFQ coolers operate on the same principles as quadrupole ion traps and have been shown to be particularly well suited for buffer gas cooling given their capacity for total confinement of ions having a large dispersion of velocities, corresponding to kinetic energies up to tens of electron volts. A number of the RFQ coolers have already been installed at research facilities around the world and a list of their characteristics can be found below.
| Name | Input Beam | Input Emittance | Cooler Length | R0 | RF Voltage, Freq, DC | Mass Range | Axial Voltage | Pressure | Output Beam Qualities | Images |
|---|---|---|---|---|---|---|---|---|---|---|
| Colette[1] | 60 keV ISOLDE beam decelerated to ≤ 10 eV | ~ 30 π-mm-mrad | 504 mm (15 segments, electrically isolated) | 7 mm | Freq : 450 – 700 kHz | -- | 0.25 V/cm | 0.01 mbar He | Reaccelerated to up to 59.99 keV with long. energy spread ~10 eV | COLETTE1
COLETTE2 |
| LPC Cooler[3] | SPIRAL type beams | Up to ~ 100 π-mm-mrad | 468 mm (26 segments, electrically isolated) | 15 mm | RF : up to 250 Vp, Freq : 500 kHz – 2.2 MHz | -- | -- | up to 0.1 mbar | -- | LPC1
LPC2 |
| SHIPTRAP Cooler[4] | SHIP type beams 20-500 keV/A | -- | 1140 mm (29 segments, electrically isolated) | 3.9 mm | RF: 30-200 Vpp, Freq: 800 kHz – 1.2 MHz | up to 260 u | Variable: 0.25 – 1 V/cm | ~ 5×10-3 mbar He | -- | SHIPTRAP1 |
| JYFL Cooler[7] | IGISOL type beam at 40 keV | Up to 17 π-mm-mrad | 400 mm (16 segmentes) | 10 mm | RF: 200 Vp, Freq: 300 kHz – 800 kHz | -- | ~1 V/cm | ~0.1 mbar He | ~3 π-mm-mrad, Energy spread < 4 eV | JYFL1 |
| MAFF Cooler[9] | 30 keV beam decelerated to ~100 eV | -- | 450mm | 30mm | RF: 100 –150 Vpp, Freq: 5 MHz | -- | ~0.5 V/cm | ~0.1 mbar He | energy spread = 5 eV, Emittance @ 30keV: from = 36 π-mm-mrad to eT = 6 π-mm-mrad | -- |
| ORNL Cooler[10] | 20-60 keV negative RIBs decelerated to <100 eV | ~50 π-mm-mrad (@ 20 keV) | 400 mm | 3.5 mm | RF: ~400 Vp, Freq: up to 2.7 MHz | -- | up to ±5 kV on tapered rods | ~0.01 mbar | Energy spread ~2 eV | ORNL1 |
| LEBIT Cooler[11] | 5 keV DC beams | -- | -- | -- | -- | -- | -- | ~1×x10−1 mbar He (high-pressure section) | -- | LEBIT1 |
| ISCOOL[12] | 60 keV ISOLDE beam | up to 20 π-mm-mrad | 800 mm (using segmented DC wedge electrodes) | 20 mm | RF: up to 380 V, Freq: 300 kHz - 3MHz | 10-300 u | ~0.1V/cm | 0,01 - 0,1 mbar He | -- | ISCOOL1 |
| ISOLTRAP Cooler[14] | 60 keV ISOLDE beam | -- | 860 mm (segmented) | 6 mm | RF: ~125 Vp, Freq: ~1 MHz. | -- | -- | ~2×10-2 mbar He | elong ≈ 10 eV us, etrans ≈ 10p mm mrad. | ISOLTRAP1 |
| TITAN RFCT[15] | continuous 30–60 keV ISAC beam | -- | -- | -- | RF: 1000 Vpp, Freq: 300 kHz - 3 MHz | -- | -- | -- | 6 π-mm-mrad at 5 keV extraction energy | TITAN1 |
| TRIMP Cooler[16] | TRIMP beams | -- | 660 mm (segmented) | 5 mm | RF= 100 Vp, Freq.: up to 1.5 MHz | 6 < A < 250 | -- | up to 0.1 mbar | -- | TRIMP1 |
| SPIG Leuven cooler[17] | IGISOL Beams | -- | 124 mm (sextupole rod structure) | 1.5 mm | RF= 0-150 Vpp, Freq.: 4.7 MHz | -- | -- | ~50 kPa He | Mass Resolving Power (MRP)= 1450 | SPIG1
SPIG2 SPIG3 |
| Argonne CPT cooler | -- | -- | -- | -- | -- | -- | -- | -- | -- | CPT Cooler1
CPT Cooler2 |
| SLOWRI cooler | -- | -- | 600 mm (segmented sextuple rod structure) | 8 mm | RF= 400 Vpp, Freq.: 3.6 MHz | -- | -- | ~10 mbar He | -- | -- |
| -- | -- | -- | -- | -- | -- | -- | -- | -- | -- | -- |
Contents |
[edit] See also
[edit] References
- ^ M. Sewtz, C. Bachelet, N. Chauvin, C. Guénaut, E. Leccia, D. Le Du and D. Lunney (2005). "Deceleration and cooling of heavy ion beams: The COLETTE project". Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 240 (p. 55-60).
- ^ Cyril Bachelet (2004). "Mesure de Masse de Noyaux à Halo et Refroidissement de Faisceaux avec l'Expérience Mistral". PhD Thesis. . Université Paris XI, France
- ^ Guillaume Darius (2004). "Etude et Mise en oeuvre d'un Dispositif pour la Mesure de Paramètre de Correlation Angulaire dans la Désintégration du Noyau Hélium 6". PhD Thesis. . Université de Caen / Basse-Normandie, France
- ^ S. Rahaman, M. Block, D. Ackermann, D. Beck, A. Chaudhuri, S. Eliseev, H. Geissel, D. Habs, F. Herfurth, F.P. Heßberger et al. (2006). "On-line commissioning of SHIPTRAP". International Journal of Mass Spectrometry 251 (p. 146-151).
- ^ Jens Dilling (2001). "Direct Mass Measurments on Exotic Nuclei with SHIPTRAP and ISOLTRAP". PhD Thesis. . University of Heidelberg, Germany
- ^ Daniel Rodriguez Rubiales (2001). "An RFQ Buncher for Accumulation and Cooling of Heavy Radionuclides at SHIPTRAP and High Precision Mass Measurements on Unstable Kr Isotopes at ISOLTRAP". PhD Thesis. . University of Valencia, Spain
- ^ A. Jokinen, J. Huikari, A. Nieminen and J. Äystö (2002). "The first cooled beams from JYFL ion cooler and trap project". Nuclear Physics A 701 (p. 557-560).
- ^ Arto Nieminen (2002). "Manipulation of Low-Energy Radioactive Ion Beams With an RFQ Cooler; Applications to Collinear Laser Spectroscopy". PhD Thesis. . University of Jyväskylä, Jyväskylä, Finland
- ^ J. Szerypo, D. Habs, S. Heinz, J. Neumayr, P. Thirolf, A. Wilfart and F. Voit (2003). "MAFFTRAP: ion trap system for MAFF". Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 204 (p. 512-516).
- ^ Y. Liu, J.F. Liang G.D. Alton, J.R. Beene, Z. Zhou, H. Wollnik (2002). "Collisional Cooling of Negative-Ion Beams". Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 187 (p. 117-131).
- ^ G. Bollen, S. Schwarz, D. Davies, P. Lofy, D. Morrissey, R. Ringle, P. Schury,T. Sun, L. Weissman (2004). "Beam cooling at the low-energy-beam and ion-trap facility at NSCL/MSU". Nuclear Instruments and Methods in Physics Research A 532 (p. 203–209).
- ^ I. Podadera Aliseda, T. Fritioff, T. Giles, A. Jokinen, M. Lindroos and F. Wenander (2004). "Design of a second generation RFQ Ion Cooler and Buncher (RFQCB) for ISOLDE". Nuclear Physics A 746 (p. 647-650).
- ^ Ivan Podadera Aliseda (2006). "New Developments on Preparation of Cooled and Bunched Radioactive Ion Beams at ISOL-Facilities: The ISCOOL Project and Rotating-Wall Cooling". PhD Thesis. . CERN, Geneva, Switzerland
- ^ T. J. Giles, R. Catherall, V. Fedosseev, U. Georg, E. Kugler, J. Lettry and M. Lindroos (2003). "The high resolution spectrometer at ISOLDE". Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 204 (p. 497-501).
- ^ J. Dilling, P. Bricault, M. Smith, H. -J. Kluge and TITAN collaboration (2003). "The proposed TITAN facility at ISAC for very precise mass measurements on highly charged short-lived isotopes". Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 204 (Pages 492-496).
- ^ Emil Traykov (2006). "Production of Radioactive Beams for Atomic Trapping". PhD Thesis. . University of Groningen, The Netherlands
- ^ P. Van den Bergh, S. Franchoo, J. Gentens, M. Huyse, Yu.A. Kudryavtsev, A. Piechaczek, R. Raabe, I. Reusen, P. Van Duppen, L. Vermeeren, A. Wiihr (1997). "The SPIG, improvement of the efficiency and beam quality of an ion-guide based on-line isotope separator". Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 126 (Pages 194- 197).
[edit] Bibliography
- SHIPTRAP collaboration, J. Schönfelder, D. Ackermann, H. Backe, G. Bollen, J. Dilling, A. Dretzke, O. Engels, J. Estermann, D. Habs, S. Hofmann, F. P. Hessberger, H. -J. Kluge, W. Lauth, W. Ludolphs, M. Maier, G. Marx, R. B. Moore, W. Quint, D. Rodriguez, M. Sewtz, G. Sikler, C. Toader and Chr. Weber (2002). "SHIPTRAP—a capture and storage facility for heavy radionuclides at GSI". Nuclear Physics A 701 (p. 579-582).
- G. Sikler, D. Ackermann, F. Attallah, D. Beck, J. Dilling, S. A. Elisseev, H. Geissel, D. Habs, S. Heinz, F. Herfurth et al. (2003). "First on-line test of SHIPTRAP". Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 204 (p. 482-486): 482. doi:.
- J.B. Neumayr, L. Beck, D. Habs, S. Heinz, J. Szerypo, P.G. Thirolf, V. Varentsov, F. Voit, D. Ackermann, D. Beck et al. (2006). "The ion-catcher device for SHIPTRAP". Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 244 (p. 489-500): 489. doi:.
- J. Szerypo, A. Jokinen, V. S. Kolhinen, A. Nieminen, S. Rinta-Antila and J. Äystö (2002). "Penning trap at IGISOL". Nuclear Physics A 701 (p. 588-591): 588. doi:.
- T. Faestermann, W. Assmann, L. Beck, H. Bongers, W. Carli, M. Groß, R. Großmann, D. Habs, P. Hartung, S. Heinz et al. (2004). "The Munich Accelerator for Fission Fragments - MAFF". Nuclear Physics A 746 (p. 22-26): 22. doi:.
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- S. Schwarz, G. Bollen, D. Lawton, A. Neudert, R. Ringle, P. Schury and T. Sun (2003). "A second-generation ion beam buncher and cooler". Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 204 (p. 474-477): 474. doi:.
- J. Clark, R. C. Barber, C. Boudreau, F. Buchinger, J. E. Crawford, S. Gulick, J. C. Hardy, A. Heinz, J. K. P. Lee, R. B. Moore et al. (2003). "Improvements in the injection system of the Canadian Penning trap mass spectrometer". Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 204 (p. 487-491): 487. doi:.
