The present invention relates to an apparatus for generating
and selecting ions used in a heavy ion cancer therapy facility according to the
preamble of independent claim 1.
From US Patent 4,870,287 a proton beam therapy system is
known for selectively generating and transporting proton beams from a single proton
source. The disadvantage of such a system is, that the flexibility to treat patients
is quite limited to relatively low effective proton beams.
From document PETERS A et al, BEAM INSTRUMENTATION WORKSHOP
2000, NINTH WORKSHOP,CAMBRIDGE MA USA 8-11 MAWY 2000, no. 546, pages 519-526, AIP
Conference Proceedings, 2000, ISSN: 0094-243X beam diagnostics for heavy ion cancer
therapy facility are known. This document is the bases of the preamble of independent
From the paper of MURAMATSU M et al, 7TH INTERNATIONAL
CONFERENCE ON ION SOURCES; TAORMINA; ITALY; 7-13. SEPT. 1997, vol. 69, no. 2, pages
1076-1078, Review of Scientific Instruments, Feb. 1998, ISSN: 003-6748, an electron
cyclotron resonance ion source with permanent magnets is known.
It is an object of the present invention to provide an
improved apparatus for generating and selecting different ions useful in an ion
beam cancer therapy facility.
This object is achieved by the subject matter of independent
claim 1. Features of preferred embodiments are defined with dependent claims.
The invention concerns an apparatus provided for generating,
extracting and selecting ions used in an ion cancer therapy facility. The apparatus
comprises an independent first and an independent second electron cyclotron resonance
ion source for generating heavy and light ions, respectively. Further is enclosed
a spectrometer magnet for selecting heavy ion species of one isotopic configuration
positioned downstream of each ion source; a magnetic quadrupole triplet lens positioned
downstream of each spectrometer magnet; a switching magnet for switching between
high-LET ion species and low-LET ion species of said two independent first and second
ion sources. An analyzing slit is located at the image focus of each spectrometer
magnet and a beam transformer is positioned in between the analyzing slit and the
magnetic quadrupole triplet.
Such an apparatus has the advantage, that the possibility
to help patients is largely improved by providing two independent ion sources and
a switching magnet to select the proper ion species for an optimal treatment. Further
the apparatus has the additional advantage that two independent spectrometer lines
(one for each ion source) increase the selectivity of the apparatus and improve
the purity of the ion species by separating with high accuracy the ion species selected
for acceleration in the linac from all the other ion species extracted simultaneously
from the ion sources.
For the intensity controlled rasterscannner ion beam application
system different beam intensities within an intensity range of 1/1000 are provided
in a preferred embodiment of the invention for each individual synchrotron cycle.
The apparatus has the advantage to control the beam intensity at a low energy level
in that the beam is destroyed along a low energy beam transport (LEBT) line in between
the magnetic quadrupol triplet and an radio frequency quadrupole accelerator (RFQ).
In particular, irises with fixed apertures are provided after a switching magnet
as well as before and after a macropulse chopper and at an RFQ entrance flange.
An intensity measurement of the relative intensity reduction versus the magnet current
of the center quadrupole of the magnet quadrupole triplet lens downstream of the
image slit of the spectrometer is carried out for the apparatus of the present invention
and shows that the beam intensity is reduced by about a factor of 430 starting from
the default setting of the quadrupole magnet down to zero current. A further reduction
of the beam intensity leading to a degradation factor of 1000 can be achieved by
an additional reduction of the field of the third quadrupole of the magnetic quadrupole
triplet. A very smooth curve is obtained, providing a good reproducibility of the
different intensity levels.
Therefore, unnecessary radioactive contamination of the
machine is avoided since beam intensity is controlled at the lowest possible beam
energy, i.e. in said low energy beam transport line. Because the synchrotron injection
scheme is not changed for the different beam intensity levels, i.e. the number of
turns injected into the synchrotron are the same in all cases, the full dynamic
range of 1000 is provided by the intensity control scheme in the LEBT. In the apparatus
the beam loss occurs mainly in the LEBT, i.e. the relative intensity reduction is
almost the same measured directly behind the LEBT at a low energy level and measured
in the Therapy beam line at an high energy level. Furthermore, beam profiles are
measured at different locations along the accelerator chain and at the final beam
delivery system of the therapy beam line. No differences could be observed in the
beam profiles as well as in the beam positions for the different beam intensities.
This is a very important advantage in order to provide reliable and constant and
not intensity dependent beam parameters at the treatment locations particularly
when the apparatus is applied for a heavy ion cancer therapy facility.
The beam transformer positioned in between the analyzing
slit and the magnetic quadrupole triplet has the advantage to measure and monitor
one-line the ion beam current of the ion species selected for acceleration without
destroying the ion beam. Because this transformer is positioned upstream of the
magnetic quadrupole triplet used for the intensity reduction the beam transformer
monitors continuously the non-degraded ion beam current while intensity of the linear
accelerator beam can be changed from pulse to pulse using triplet magnets. This
is very important for an on-line monitoring of the performance of the selected ion
In a first preferred embodiment a solenoid magnet is located
at the exit of each ion source. This embodiment has the advantage that the ion beams
extracted of each ion source are focused by a solenoid magnet into the object point
of the spectrometer.
In an other preferred embodiment a magnetic quadrupole
singlet is positioned downstream of each ion source. This quadrupole singlet has
the advantage to increase the resolution power of each spectrometer system and to
provide a flexible matching between the ion sources and the spectrometer systems.
The ion sources comprise exclusively permanent magnets.
These permanent magnets provide a magnetic field for the ion sources and have the
advantage that no magnet coils are required, which would have a large power consumption
for each ion source. Additionally to the large power consumption these magnet coils
have the disadvantage, that they need a high pressure water cooling cycle, which
is avoided in the case of permanent magnets within the ion sources of the present
invention. This has the advantage to reduce the operating costs and increase the
reliability of the apparatus of the present invention.
Beam diagnostic means are located upstream each spectrometer
magnet. Such beam diagnostic means can measure the cross-sectional profile of the
beam and/or the totally extracted ion current. Said beam diagnostic means preferably
comprises profile grids and/or Faraday cups.
A further embodiment provides a beam diagnostic means located
at each image slit. This embodiment has the advantage to measure the beam size and
beam intensity for different extracted ion species and to record a spectrum.
In a preferred embodiment of the invention, said focusing
solenoid magnet is positioned downstream of said macropulse chopper and upstream
of said radiofrequency quadrupole accelerator. This has the advantage that the beam
is focused by the solenoid magnet directly to the entrance electrodes of the radio
frequency quadrupole within a very short distance between the solenoid lens and
the beginning of the RFQ electrodes of about 10 cm.
A further preferred embodiment of the present invention
provides diagnostic means comprising a Faraday cup and/or profile grids within the
low energy beam transport system (LEBT) downstream of a switching magnet. These
diagnostic means are not permanently within the range of the ion beam, but are positioned
into the range of the ion beam for measurement purposes. The Faraday cup captures
all ions passing the switching magnet and the profile grids measure the local distribution
of ions within the beam cross section. During an operation cycle these diagnostic
means are driven out of the range of the ion beam.
In a further embodiment the alternating stems within said
radio frequency quadrupole are mounted on a common water cooled base plate. This
has the advantage that the energy loss of the RFQ is conducted toward to outside
of the chamber and do not damage the stems or the electrodes of the RFQ.
The base plate is made of an electrical insulating material.
This has the advantage that the stems are not short circuit, though they are acting
as inductivity whilst said mini-vane pairs forming electrodes are acting as capacitance
for a &lgr;/2 resonance/structure.
The invention is now explained with respect to embodiments
according to the subsequent drawings.
Fig. 1 shows a schematic drawing of a complete injector
linear accelerator for an ion beam application system comprising an apparatus for
generating and selecting ions used in a heavy ion cancer therapy facility.
Fig. 2 shows a schematic drawing of a detail of figure
Fig. 3 shows examples for beam envelopes of an apparatus
for generating and selecting ions and along a low energy beam transport line.
The reference signs within Fig. 1, 2 and 3 are defined
- First electron cyclotron resonance ion sources for heavy ions like
- Second electron cyclotron resonance ion sources for light ions like H2
+, or 3He+
- Solenoid magnet at the exit of ECRIS1 and ECRIS2
- Beam diagnostic block comprising profile width and/or Faradays cups
- Collimator slit
- Collimator image slit .
- beam transformer
- Magnetic quadrupole singlets of first and
- second branch
- Quadrupole doublet
- Magnetic quadrupole triplet
- Spectrometer magnet of first and
- second branch
- Switching magnet
- Macropulse chopper
- Radio-frequency quadrupole accelerator
- IH-type drift-tube linac
- Stripper foil
- a) (Fig. 3) Beam envelopes according to a beam emittance of 120 &pgr; mm mrad
- b) (Fig. 3) Beam envelopes according to a beam emittance of 290 &pgr; mm mrad
The tasks of the different sections of Fig. 1 and Fig.
2 of an apparatus for generating and selecting ions to supply an injector system
and the corresponding components can be summarized in the following-items:
1. The production of ions, pre-acceleration of the ions to a kinetic energy of 8
keV/u and formation of ion beams with sufficient beam qualities are performed in
two independent ion sources and the ion source extraction systems. For routine operation,
one of the ion sources can deliver a high-LET ion species (12C4+
and 16O6+, respectively), whereas the other ion source may
produce low-LET ion beams (H2
+ or 3He1+).
2. The charge states to be used for acceleration in the injector linac are separated
in two independent spectrometer lines. Switching between the selected ion species
from the two ion source branches, beam intensity control (required for the intensity
controlled raster-scan method), matching of the beam parameters to the requirements
of the subsequent linear accelerator and the definition of the length of the beam
pulse accelerated in the linac are done in the low-energy beam transport (LEBT)
3. The linear accelerator consists of a short radio-frequency quadrupole accelerator
(RFQ) of about 1.4 m in length, which accelerates the ions from 8 keV/u to 400 keV/u,
a compact beam matching section of 0.25 m in length and a 3.8 m long IH-type drift-tube
linac (IH-DTL) for effective acceleration to the linac end energy of 7 MeV/u.
4. Remaining electrons are stripped off in a thin stripper foil located about 1
m behind of the IH-DTL to produce the highest possible charge states before injection
into the synchrotron in order to optimize the acceleration efficiency of the synchrotron
Table 1 shows charge states of all proposed ion species for acceleration
in the injector linac (left column) and behind of the stripper foil (right column).
Ions from source
Ions to synchrotron
+ or 1H3
The design of the apparatus for generating and selecting
ions and the injector system of the present invention has the advantage to solve
the special problems on a medical machine installed in a hospital environment, which
are high reliability as well as stable and reproducible beam parameters. Additional
advantages are compactness, reduced operating and maintenance requirements. Further
advantages are low investment and running costs of the apparatus.
Both the RFQ and the IH-DTL are designed for ion mass-to-charge
ratios A/q ≤ 3 (design ion 12C4+) and an operating
frequency of 216.816 MHz. This comparatively high frequency allows to use a quite
compact LINAC design and, hence, to reduce the number of independent cavities and
RF power transmitters. The total length of the injector, including the ion sources
and the stripper foil, is around 13 m. Because the beam pulses required from the
synchrotron are rather short at low repetition rate, a very small rf duty cycle
of about 0.5 % is sufficient and has the advantage to reduce the cooling requirements
very much. Hence, both the electrodes of the 4-rod-like RFQ structure as well as
the drift tubes within the IH-DTL need no direct cooling (only the ground plate
of the RFQ structure and the girders of the IH structure are water cooled), reducing
the construction costs significantly-and improving the reliability of the system.
To provide very stable beam currents without any pronounced
time structures as well as high beam quality an Electron Cyclotron Resonance Ion
Source (ECRIS) is used for the production of 12C4+ and
16O6+ ions (ECRIS 1 in Fig. 1 and Fig. 2). For the production
of proton and helium beams two different ion source types can be used. Either an
ECR ion source of the same type as used for the production of the high-LET ion beams
will be applied here as well (ECRIS 2 in Fig. 1 and Fig. 2) or a special low-cost,
compact, high brilliance filament ion source may be used.
In case of an ECR ion source, molecular H2
+ ions will be produced in the ion source and used for acceleration in
the linac. In case of the filament source, H3
+ ions are proposed, providing the same mass-to-charge ratio of
A/q = 3 as of the 12C4+ ions. For production
of the helium beam, 3He1+ ions will be extracted from the
source in both cases. To avoid contaminations of the beam with other light ions
produced simultaneously in the ion source, 3He is proposed instead of
The maximum beam intensities discussed for the synchrotron
are about 109 C6+ ions per spill at the patient. Assuming
a multi-turn injection scheme using 15 turns at 7 MeV/u, a bunch train of about
25 µm length delivered by the LINAC is injected into the synchrotron. Taking
into account beam losses in the synchrotron injection line, the synchrotron and
the high energy beam line, this corresponds to a LINAC output current of about 100
eµA C6+. Considering further beam losses in the LEBT, the LINAC
and the stripper foil, a minimum C4+ current of about 130 eµA extracted
out of the ion source is required. The minimum ion currents required for all ion
species discussed here are listed in Table 2 (called I
However, the ion sources taken into consideration should be tested with an ion current
including a safety margin of at least 50 %. These values are called I
safe in Table 2 and range between 150 eµA for 16O6+
and 1 emA for H2+. For the sake of stability, DC operation is proposed
for the ECR ion sources.
Table 2 shows parameters for extraction voltages and ion currents extracted
out of the ion sources of the present invention for different ion species.
For the extraction system, a diode extraction system consisting
of a fixed plasma electrode and a single moveable extraction electrode is proposed
for the ECR ion sources. The extraction voltages Uext necessary for a
beam energy of 8 keV/u are also listed in Table 2. In case of 12C4+
and 3He1+ extraction voltages of 24 kV are required. In case
of a proton beam delivered directly from the ion source, the required extraction
voltage of 8 kV would be rather small to achieve a proton current of 2 mA. Furthermore,
significant space-charge problems have to be handled within the low-energy beam
transport line and the RFQ accelerator in such a case. Hence, the production and
acceleration of molecular H2
+ and H3
+ ions, respectively, is proposed.
The independent first and second electron cyclotron resonance
ion sources (ECRIS1 and ECRIS2) provide a very well suited solution for an injector
linac installed at a hospital, the magnetic fields are provided exclusively by permanent
magnets. This has the large advantage that no electric coils are required, which
would have a very large power consumption of up to about 120 kW per ion source.
In addition to the large power consumption, the coils have the disadvantage to need
an additional high-pressure (15 bar) water cooling cycle, which is not as safe as
the permanent magnet ion sources of the present inventrion. Both aspects have the
advantage to reduce the operating costs and increase the reliability of the present
The main parameters of a suitable high-performance permanent
magnet ECRIS of a 14,5 GHz SUPERNANOGAN are listed in Table 3, and are compared
to the data of two ECR ion sources using electric coils, which are the ECR4-M (HYPERNANOGAN)
and the 10 GHz NIRS-ECR used for routine production of 12C4+
beams for patient irradiation at HIMAC and at Hyogo Ion Beam Medical Center.
For SUPERNANOGAN, the plasma confinement is ensured by
a minimum-B magnetic structure with magnetic parameters quite close to the ECR4-M
ones, but with a reduced length of the magnetic mirror (about 145 mm instead of
190 mm) and a smaller diameter of the plasma chamber (44 mm instead of 66 mm). The
maximum axial mirror-fields are 1.2 T at injection and 0.9 T at extraction. The
weight of the FeNdB permanent magnets amount to roughly 120 kg, the diameter of
the magnet body is 380 mm and its length is 324 mm.
For our purpose, SUPERNANOGAN has been tested at an ECR
ion source test bench. For all ion species proposed here, the required ion currents
could be achieved in a stable DC operating mode using extraction voltages close
to the values required for the injector linac and at moderate rf power levels between
about 100 W and 420 W. For O6+ as well as for He1+ even about
twice the required currents I
safe could be achieved easily. For the production of 12C4+
CO2 has been used as main gas as also applied at GSI for the production
of 12C2+. Experimental investigations at HIMAC have shown
that the yield of 12C4+ ions can be enhanced significantly
using CH4 as main gas. Further improvements of the C4+ production
performance can be expected for SUPERNANOGAN as well if CH4 would be
used as main gas. The measured geometrical emittances of around 90 % of the beams
range between 110 mm mrad for 16O6+ and up to 180 mm mrad
for He1+ and 12C4+, corresponding to normalized
beam emittances of 0.4 to 0.7 mm mrad.
Table 3 shows a comparison of some ECR ion sources. ECR4-M ≡ HYPERNANOGAN,
values in brackets for ECR4-M are for 18 GHz operation, the other values are for
14.5 GHz operation. For NIRS-ECR, the values in brackets are obtained using an improved
14 - 18
Plasma chamber inner ∅
Magnets for axial field
Coil power consumption
Yoke outer length
Yoke outer ∅
Length of magnetic mirror
ext, max (achieved)
Measured ion currents:
Two results obtained with ECR4-M for C4+ and
O6+ are also listed in Table 3, demonstrating that the required ion currents
can be exceeded by a certain amount. Some ion currents obtained with NIRS-ECR are
also listed in Table 3. The values in brackets are obtained with the upgraded version
which consists of an improved sextupole magnet. Again, all values exceed the currents
required here by a certain amount. The measured normalized beam emittances range
from about 0.5 mm mrad for C4+ to roughly 1 mm mrad for a 2.1 emA H2+
beam. The NIRS-ECR has a number of advantages: For the comparatively light ions
proposed for patient irradiation like carbon, helium and oxygen, a 10 GHz ECR source
seems to be powerful enough to produce sufficiently high ion currents if the diameter
of the plasma chamber is large enough. On the other hand, the confining magnetic
field can be smaller at 10 GHz as compared to 14.5 GHz (used for ECR4-M), reducing
the power consumption of the electric coils by about 40 %. Furthermore, the NIRS-ECR
is in operation at HIMAC especially for the production of 12C4+
beams. Like at the project proposed here, the injection energy at the HIMAC injector
is also 8 keV/u and the extraction voltage applied for the production of
12C4+ beams is 24 kV.
These parameters are the same in the present case. Additionally,
a number of improvements have been applied to NIRS-ECR mainly in order to increase
the reliability of the source as well as the lifetime of critical source components
and the maintenance intervals.
The electron cyclotron resonance ion sources of the present
- 1. a DC bias system:
In order to increase the source efficiency for high charge state ions, both SUPERNANOGAN
as well as HYPERNANOGAN are equipped with a DC bias system. The inner tube of the
coaxial chamber is DC biased at a voltage of about 200 - 300 V,
- 2. a gas supply system:
To ensure a sufficient long-term stability of the extracted ion current, the thermo-valves
for the main and the support gas are regulated by suitable thermo-valve controllers.
Furthermore, temperature regulated heating jackets are applied to the thermo-valves
to stabilize their temperature. Pressure reducers are used between the main gas
reservoirs and the thermo-valves.
- 3. an RF system:
High power klystron amplifiers with an rf output power of about 2 kW are used (14.5
GHz or 10 GHz depending on the ion source model). To guarantee a high availability,
one additional generator is available for substitution in case of a failure of the
amplifier in operation. Therefore three generators are provided in case of the present
invention for the two ECR ion sources (ECRIS1 and ECRIS2). Fast switching between
the individual generators is possible. Remote control of the output power levels
of the generators between 0 and maximum power is provided. The output power levels
are controlled by active control units to a high stability of &Dgr;P/P
≤ 1%. The total rf power transmitted from the generators can be reflected
by the ion source plasmas in some cases. Hence, the generators of the present invention
can be equipped with circulators and dummy loads which are able to absorb the complete
power transmitted from the generators without causing a breakdown of the generators.
The measurement of the reflected power is possible for routine operation.
Such an ECR ion source is a preferred solution for the
production of the highly charged C4+ and O6+ ion beams for
a therapy accelerator. In principle, the same source model can also be used for
the production of H2
+ and He+ beams, providing some additional redundancy. Alternatively,
a gas discharge ion source especially developed for the production of high-brilliant
beams of singly charged ions can be provided for the production of H3
+ and 3H1+ beams.
The plasma generator of the source is housed in a water-cooled
cylindrical copper chamber of 60 mm in diameter and about 100 mm in length. For
plasma confinement, the chamber is surrounded by a small solenoid magnet with a
comparatively low power consumption of less than 1 kW. On the back of the chamber,
the gas inlet system is mounted, and, close to the axis, a tungsten filament is
installed. The front end of the chamber is closed by the plasma electrode, which
can be negatively biased with respect to the anode (chamber walls). For ion extraction,
a triode system in accel/decel configuration is used. The geometry of the extraction
system of the present invention has been carefully optimized (supported by computer
simulations) for different extraction voltages around 22 kV and 55 kV.
If the source is operated with hydrogen at small arc currents
of ≤ 10 A, the H3
+ fraction of the beam is as high as about 90 % with a minor amount of
H+ ions (≤ 10 %) and only a very small fraction of H2
+ ions. The H+ portion increases with increasing arc current.
However, for the production of an H3
current of a few mA only, an arc power of less than 1 kW at small arc currents
of a few amperes is sufficient, providing an ideal solution for the therapy injector.
For these parameters, a lifetime of the tungsten filament of roughly 1000 h is expected
for DC operation. To further increase the lifetime, a pulsed operation mode of the
source is proposed. The stability of the extracted ion current in pulsed mode with
a measured beam noise level of only about 1 % is even better than for DC operation.
The use of this ion source has a number of economical and
technical advantages as compared to an ECR ion source of the state of the art:
- 1. The investment costs for the gas discharge ion source of the present invention
are at least about five times lower than for an ECR ion source (including the RF
generator). In addition, the costs for operational maintenance are lower, in particular,
compared to an ECR ion source with electrical coils. For example, the klystron of
the RF generator for an ECR ion source of the state of the art must be replaced
- 2. The use of H3
+ for acceleration in the linac has several advantages: Because it has
the same mass-to-charge ratio of A/Q = 3 as of the 12C4+
ions, the linac cavities are operated at the same rf power level in both cases.
This ensures a very stable operation of the linac, increasing the reliability of
the system. Furthermore, a very fast switching between 12C4+
+ beams would be possible. In addition, space-charge problems along the
LEBT and the RFQ accelerator are minimized for H3
+ beams as compared to H2
+ or H+ beams.
- 3. Much higher beam currents are available.
- 4. High-brilliant ion beams with normalized beam emittances of &egr;n
< 0.1 &pgr; mm mrad, i.e. about one order of magnitude smaller as compared
to the H2
+ beams from the ECR ion sources. E.g. a normalized 80 % beam emittance
of 0.003 &pgr; mm mrad was measured for a 9 mA He+ beam at an extraction
voltage of 17 kV.
Fig. 3 shows examples for beam envelops of an apparatus
for generating and selecting ions and along a low energy beam transport line. In
Fig. 3 beam envelopes in horizontal direction (upper part) and vertical direction
(lower part) are plotted for two transverse beam emittances of a) 120 &pgr; mm
mrad (&egr;n = 0.50 &pgr; mm mrad) and b) 240 &pgr; mm mrad (&egr;n
= 1.0 &pgr; mm mrad). The beam emittances are identical in x and y direction and
are based on the values measured for the ECR ion sources used in the present invention,
which range between about &egr;n ≈ 0.5 - 0.7 &pgr; mm mrad
for carbon, oxygen and helium ion beams and up to about &egr;n ≈
1.0 &pgr; mm mrad for H2
+ beams. The boxes in Fig. 3 mark the different magnets and their aperture
radii. The simulations start at an object focus located in the extraction system
of the ion source and end at the beginning of the RFQ electrodes.
The beam parameters at the starting point of the simulations
are determined by the geometry of the ion source extraction system including the
aperture of the plasma electrode as well as by the operating parameters of the ion
source, which influence the shape of the plasma surface in the extraction aperture
of the plasma electrode. To provide a flexible matching of beam parameters at the
starting point of the spectrometer system, i.e. different beam radii, different
divergence angles as well as a displacement of the object focus in axial direction,
two focusing magnets are used in front of the spectrometer magnets SP1, SP2 as shown
in Fig. 1 and Fig. 2.
First of all, the ion beams extracted from each ion source
are focused by a solenoid magnet SOL as shown in Fig. 1 and Fig. 2 into the object
point of the subsequent spectrometer. The beam size and location in the bending
plane of the spectrometer at this point can be defined by a variable horizontal
slit (SL). To increase the resolving power of the spectrometer, which is proportional
to the maximum horizontal beam size within the bending magnet, and to reduce the
vertical beam width along the spectrometer magnets SP1, SP2 a single horizontally
defocusing quadrupole magnet QS is located in between the object focus of the spectrometer
and the spectrometer magnets SP1, SP2. The subsequent double focusing 90° spectrometer
magnets SP1, SP2 have a radius of curvature of 400 mm and edge angles of 26.6°.
For ion beams with a mass-to-charge ratio of A/Q = 3 and an energy
of 8 keV/u, it is excited to 0.1 T only. The theoretical mass resolving power of
the system at the following image slit (ISL) of
is sufficient to separate the desired 12C4+ ions from other
charge states and from several other light ions.
Following the image slits ILS as shown in Fig.1 and Fig.
2, a magnetic quadrupole triplet QT1, QT2 focuses the beams to an almost circular
symmetry along the common part of the LEBT between the switching magnet SM and the
Finally, a solenoid magnet is focusing the ion beam into
a small matched waist at the beginning of the radio frequency quadrupole (RFQ) accelerator.
A pair of chopper plates for macro-pulse formation is placed in between the switching
magnet And the RFQ.
Beam diagnostic means BD comprise profile grids and Faraday
cups which are located behind the extraction systems of the ion sources ECRIS1 and
ECRIS2 at the object foci of the spectrometers SP1, SP2 and at the image slits ISL.
Further beam diagnostic boxes are positioned behind of the switching magnet and
upstream of the solenoid magnet in front of the RFQ. For on-line beam current measurements,
a beam transformer is provided in each of the ion source branches in front of the
magnetic quadrupole triplets QT1 and QT2.