RFQ Beam Coolers
Encyclopedia
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 alternates focuses in each transverse direction. Samples 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). This gives a mass spectrum, or fingerprint, of the sample. Residual gas analyzers use this principle as well.
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 trap
s, 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 trap
s 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.
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Quadrupole mass analyzer
The quadrupole mass analyzer is one type of mass analyzer used in mass spectrometry. As the name implies, it consists of 4 circular rods, set parallel to each other. In a quadrupole mass spectrometer the quadrupole is the component of the instrument responsible for filtering sample ions, based on...
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 alternates focuses in each transverse direction. Samples 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). This gives a mass spectrum, or fingerprint, of the sample. Residual gas analyzers use this principle as well.
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
CERN
The European Organization for Nuclear Research , known as CERN , is an international organization whose purpose is to operate the world's largest particle physics laboratory, which is situated in the northwest suburbs of Geneva on the Franco–Swiss border...
and TRIUMF
TRIUMF
TRIUMF is Canada’s national laboratory for particle and nuclear physics. Its headquarters are located on the south campus of the University of British Columbia in Vancouver, British Columbia. TRIUMF houses the world's largest cyclotron, source of 500 MeV protons, which was named an IEEE Milestone...
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 trap
Penning trap
Penning traps are devices for the storage of charged particles using a homogeneous static magnetic field and a spatially inhomogeneous static electric field. This kind of trap is particularly well suited to precision measurements of properties of ions and stable subatomic particles which have...
s, 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
Phase space
In mathematics and physics, a phase space, introduced by Willard Gibbs in 1901, is a space in which all possible states of a system are represented, with each possible state of the system corresponding to one unique point in 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
Buffer gas
A buffer gas is an inert or nonflammable gas. In the Earth's atmosphere, nitrogen acts as a buffer gas. A buffer gas adds pressure to a system and controls the speed of combustion with any oxygen present...
cooling). These RFQ coolers operate on the same principles as quadrupole ion trap
Quadrupole ion trap
A quadrupole ion trap exists in both linear and 3D varieties and refers to an ion trap that uses constant DC and radio frequency oscillating AC electric fields to trap ions. It is commonly used as a component of a mass spectrometer...
s 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.
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| Name | Input Beam | Input Emittance | Cooler Length | R0 | RF Voltage, Freq, DC | Mass Range | Axial Voltage | Pressure | Output Beam Qualities | Images |
|---|---|---|---|---|---|---|---|---|---|---|
| Colette | 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 | 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 | 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 Atomic mass unit The unified atomic mass unit or dalton is a unit that is used for indicating mass on an atomic or molecular scale. It is defined as one twelfth of the rest mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state, and has a value of... |
Variable: 0.25 – 1 V/cm | ~ 5×10-3 mbar He | -- | SHIPTRAP1 SHIPTRAP2 |
| JYFL Cooler | 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 JYFL2 JYFL3 |
| MAFF Cooler | 30 keV beam decelerated to ~100 eV | -- | 450 mm | 30 mm | 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 | 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 ORNL2 ORNL3 |
| LEBIT Cooler | 5 keV DC beams | -- | -- | -- | -- | -- | -- | ~1×x10−1 mbar He (high-pressure section) | -- | LEBIT1 LEBIT2 LEBIT3 |
| ISCOOL | 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 - 3 MHz | 10-300 u | ~0.1V/cm | 0,01 - 0,1 mbar He | -- | ISCOOL1 ISCOOL2 ISCOOL3 ISCOOL4 |
| ISOLTRAP Cooler | 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 ISOLTRAP2 |
| TITAN RFCT | continuous 30–60 keV ISAC beam | -- | -- | -- | RF: 1000 Vpp, Freq: 300 kHz - 3 MHz | -- | -- | -- | 6 π-mm-mrad at 5 keV extraction energy | TITAN1 TITAN2 TITAN3 |
| TRIMP Cooler | 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 TRIMP2 TRIMP3 |
| SPIG Leuven cooler | 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 | -- | -- |
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