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MISHA ( Multicharged Ion Source for HAdronterapy ). State of the art.
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MISHA (MultichargedIon Source forHAdronterapy)
State of the art • Two ECR ion sources of the SUPERNANOGAN type, built by the Pantechnik according to the up-grading and the specifications set by INFN-LNS, are in operation and fulfillthe actual requirements of a hadron therapy facility, but in the near future higher performances and other beams will be required. • A further increase of accelerator reliability involves the improvement of the beam brightness and new ion species, which can be achieved with the design and construction of a new ECR ion source, able to provide more than 600 eµA of C4+ within emittance figure of 0.75π mm. mrad. • Nowadays commercial ECRIS are not able to produce 600 eµA of C4+ at 8keV/A with a normalized emittance of 0.75 π mm mrad. • A third generation ECR ion source is able to produce very high current intensity of MCI and HCI, but it is too expensive and it is not compatible with a hospital environment.
State of the art • A draft of the MISHA design, i.e. an ECR ion source which includes innovative characteristics already tested in other developments of the Ion Source R&D Team of INFN-LNS, was available in 2009. • Some minor issues remained to be tested, with particular regards to beam noise and reproducibility. • It has been proposed to make systematic tests with a fully superconducting ECR ion source, in order to have a complete variability of the magnetic field, permitting to comply with the needs above cited. • Unfortunately it was not possible to perform the tests neither at the SERSE source of INFN-LNS (different priorities), nor at VENUS source at LBL (under refurbishment after a failure), so that only SECRAL source at IMP-Lanzhou and SUSI at MSU-NSCL could help us in this job. A test was agreed with SECRAL, but early in Oct. ‘09 the Director of IMP decided to anticipate an upgrading and to cancel this test. • We agreed to make the tests with the SUSI source in December ’09 (snow&ice at MSU).
Experimentswerecarried out with pure gas and lowerpower density toevaluateonly the effectof the magneticfieldprofile.
A clearsignature: dampingof the EEDF hot electron component The damping of high energy electrons with an appropriate gradient of the magnetic field in the ECRIS plasma trapwasconfirmed at MSU better emittance and smaller beam noise!
Ion Dynamics and Beam Formation The plasma dynamics heavily affects the beam emittance The influence of the ion dynamics on the plasma star shape at the extraction side is confirmed also experimentally. Lateral ion losses are confirmed also by observation of depositions in case of gold plasmas.
Modeling of electron and ion dynamics Hollow beams are probably a consequence of plasma depletion in the near axis region The density distribution explains why for some frequencies the beams appear hollow Plasma density distribution The depletion of plasma in near axis region is due to the structure of electromagnetic field. Electric field pattern
Useof the FTE (FrequencyTuningEffect) Evident improvements of the transmission in LINAC and in CYCLOTRONS by means of FTE have been observed at CNAO, INFN-LNS, INFN-LNL, JYFL, MSU, HIT, etc.
Main characteristics • MISHA is a hybrid ECRIS: the radial confining field is obtained by means of a permanent magnet hexapole, while the axial field is obtained with a set of four superconducting coils. • The superconducting system will be Helium-free at 4.2 °K, by using two cryocoolers. • The magnetic field values are following the scaling laws (R. Geller) and the High-B-mode concept (G.Ciavola & S.Gammino), experimentally validated in ’90s at INFN-LNS and at MSU-NSCL. • The operating frequency of 18 GHz has been chosen to maximize the plasma density taking into account the availability of commercial microwave generators and the specificity of the installation in a hospital environments. • The electric insulation is chosen in order to operate at 40 kV, that is higher than needed for the CNAO, but it may be useful for future Hadronterapy facilities with Synchrotron or Cyclotron accelerators.
Three electrodes extraction system C4+ (600µA) geometrical emittance: 170 π mm mrad
New LEBT • The main elements: • a solenoid downstream the source • three steerers - a quadrupole and a triplet • a 60° dipole • a new switching magnet with two entrances (30° and 90°) • this new dipole will replace the present spectrometer • two tanks with beam diagnostic instrumentations • (wire scanners, slits and Faraday cups) • a Pepper Pot Emittance measurement system.
New LEBT Horizontal and vertical beam dimensions along the LEBT extension Optical functions from MAD8 The 60° dipole resolution is 73 while the minimum resolution necessary to select 16O5+ from 12C4+ ions is 30 (for calculation a geometrical emittance of 300 π mm rad has been considered)
Perspectives • Existing ion sources are working according to the specifications • Minor upgrading of the existing sources is possible to improve the reliability, but the access to larger brightness is not expected. • An innovative source named MISHA, with a new LEBT, has been designed to provide larger brightness and ion beam variety. • The MISHA source may provide the beam required byany type ofHadrontherapy facility. • According to the experience of our team, the construction of the source and the LEBT should take about 24 months in total. • The assembly and commissioning will be performed at INFN-Pavia lab, available for CNAO (12 months duration). • The installation in CNAO accelerator room will take about three months in two or three slots. • The application for different programmes is envisaged (PO FESR Sicily).
