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Register a new userProgress of the Development of the ELI-NP GBS High Level Applications
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Giovanna Campogiani
Publication date
2017
fields
Physics
and research's language is
English
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The Gamma Beam System (GBS) is a high brightness LINAC to be installed in Magurele (Bucharest) at the new ELI-NP (Extreme Light Infrastructure - Nuclear Physics) laboratory. The accelerated electrons, with energies ranging from 280 to 720 MeV, will collide with a high power laser to produce tunable high energy photons (0.2-20MeV ) with high intensity (10e13 photons/s), high brilliance and spectral purity (0.1% BW), through the Compton backscattering process. This light source will be open to users for nuclear photonics and nuclear physics advanced experiments. Tested high level applications will play an important role in commissioning and operation. In this paper we report the progress and status of the development of dedicated high level applications. We also present the results of the test on the FERMI LINAC of the electron trajectory control method based on Dispersion Free Steering.
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The machine described in this document is an advanced Source of up to 20 MeV Gamma Rays based on Compton back-scattering, i.e. collision of an intense high power laser beam and a high brightness electron beam with maximum kinetic energy of about 720 MeV. Fully equipped with collimation and characterization systems, in order to generate, form and fully measure the physical characteristics of the produced Gamma Ray beam. The quality, i.e. phase space density, of the two colliding beams will be such that the emitted Gamma ray beam is characterized by energy tunability, spectral density, bandwidth, polarization, divergence and brilliance compatible with the requested performances of the ELI-NP user facility, to be built in Romania as the Nuclear Physics oriented Pillar of the European Extreme Light Infrastructure. This document illustrates the Technical Design finally produced by the EuroGammaS Collaboration, after a thorough investigation of the machine expected performances within the constraints imposed by the ELI-NP tender for the Gamma Beam System (ELI-NP-GBS), in terms of available budget, deadlines for machine completion and performance achievement, compatibility with lay-out and characteristics of the planned civil engineering.
We study the production of radioisotopes for nuclear medicine in (gamma,gamma) photoexcitation reactions or (gamma,xn + yp) photonuclear reactions for the examples of ^195mPt, ^117mSn and ^44Ti with high flux [(10^13 - 10^15) gamma/s], small beam diameter and small energy band width (Delta E/E ~ 10^-3 -10^-4) gamma beams. In order to realize an optimum gamma-focal spot, a refractive gamma-lens consisting of a stack of many concave micro-lenses will be used. It allows for the production of a high specific activity and the use of enriched isotopes. For photonuclear reactions with a narrow gamma beam, the energy deposition in the target can be reduced by using a stack of thin target wires, hence avoiding direct stopping of the Compton electrons and e^+e^- pairs. The well-defined initial excitation energy of the compound nucleus leads to a small number of reaction channels and enables new combinations of target isotope and final radioisotope. The narrow-bandwidth gamma excitation may make use of collective resonances in gamma-width, leading to increased cross sections. (gamma,gamma) isomer production via specially selected gamma cascades allows to produce high specific activity in multiple excitations, where no back-pumping of the isomer to the ground state occurs. The produced isotopes will open the way for completely new clinical applications of radioisotopes. For example ^195mPt could be used to verify the patients response to chemotherapy with platinum compounds before a complete treatment is performed. In targeted radionuclide therapy the short-range Auger and conversion electrons of ^195mPt and ^117mSn enable a very local treatment. The generator ^44Ti allows for a PET with an additional gamma-quantum (gamma-PET), resulting in a reduced dose or better spatial resolution.
The international Muon Ionization Cooling Experiment (MICE) will perform a systematic investigation of ionization cooling of a muon beam. The demonstration is based on a simplified version of a neutrino factory cooling channel. As the emittance measurement will be done on a particle-by-particle basis, sophisticated beam instrumentation has been developed to measure particle coordinates and timing vs RF. The muon beamline has been characterized and a preliminary measure of the beam emittance, using a particle-by-particle method with only the TOF detector system, has been performed (MICE STEP I). Data taking for the study of the properties that determine the cooling performance (MICE Step IV) has just started in 2015, while the demonstration of ionization cooling with re-acceleration is foreseen for 2017.
Future colliders such as NLC and JLC will require a highly-polarized macropulse with charge that is more than an order of magnitude beyond that which could be produced for the SLC. The maximum charge from the SLC uniformly-doped GaAs photocathode was limited by the surface charge limit (SCL). The SCL effect can be overcome by using an extremely high (>1019 cm-3) surface dopant concentration. When combined with a medium dopant concentration in the majority of the active layer (to avoid depolarization), the surface concentration has been found to degrade during normal heat cleaning (1 hour at 600 C). The Be dopant as typically used in an MBE-grown superlattice cathode is especially susceptible to this effect compared to Zn or C dopant. Some relief can be found by lowering the cleaning temperature, but the long-term general solution appears to be atomic hydrogen cleaning.
We study and discuss electron acceleration in vacuum interacting with fundamental Gaussian pulses using specific parameters relevant for the multi-PW femtosecond lasers at ELI-NP. Taking into account the characteristic properties of both linearly and circularly polarized Gaussian beams near focus we have calculated the optimal values of beam waist leading to the most energetic electrons for given laser power. The optimal beam waist at full width at half maximum correspond to few tens of wavelengths, $Delta w_0=left{13,23,41right}lambda_0$, for increasing laser power $P_0 = left{0.1,1,10right}$ PW. Using these optimal values we found an average energy gain of a few MeV and highest-energy electrons of about $160$ MeV in full-pulse interactions and in the GeV range in case of half-pulse interaction.
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