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Méot, François

Publications and source records attributed to Méot, François.

8 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Large radial shift experiments in RHIC and their implications for EIC design

The Hadron Storage Ring (HSR) in the future Electron-Ion Collider (EIC) must operate over a broad range of design circumferences. In 2018 preliminary beam studies on the circumference adjustment capabilities of the Relativistic Heavy Ion Collider (RHIC) were performed by applying a small momentum offset to the circulating bunches without adjusting any bending magnets. The off-momentum linear optics were corrected back to on-momentum conditions. Applying a similarly small deviation to the dipole fields of a select set of bending magnets provides a large radial shift over much of the RHIC (or HSR) circumference while leaving the design trajectory unchanged in the insertion regions. Here, this paper presents the design of the different lattice configurations foreseen as the most viable options for the required HSR circumference changes, and highlights the modifications necessary for regular operations and to allow for testing these new settings in RHIC. Experimental results from 2021 and 2022 are reviewed and compared to model predictions obtained from both MAD-X and Bmad. The implications of these results for HSR design are discussed.

43 PARTICLE ACCELERATORS↗
DOE OSTI2024

A possible origin of the 10~15% polarization loss observed in RHIC beyond 100 GeV

This Tech. Note summarizes the outcomes of numerical simulation of strong resonance crossing using RHIC lattice, collision optics. The regular RHIC snake configuration is used, i.e. 2 snakes at their 3 o’clock and 9 o’clock locations. The working point used is Qx/Qy=28.685/29.673. These numerical experiments are performed with, in mind, the 15% polarization loss observed (measured?) during the ramp between 100 GeV and 255 GeV, and the possibility for the present simulations to point to possible cause(s). As a matter of fact, it has been stressed in many occasions that it should be checked with simulations how much the vertical orbit would need to be in order to affect polarization. The question has been addressed with SPINK in the past, yet it has to be addressed again, following in particular changes on the signs of vertical BPM mechanical offsets which happened in January 2010. A summary of RHIC polarization data over the years is given below, for the record.

43 PARTICLE ACCELERATORS↗
DOE OSTI2023

Commissioning results of the BNL Alternating Gradient Synchrotron booster AC dipole

Here, an AC dipole has been installed in the AGS booster as part of polarized beam developments for the future Electron Ion Collider (EIC). This will allow preserving helion beam polarization through two intrinsic resonances during acceleration to an energy corresponding to |$Gγ$| = 10.5. AC dipoles can preserve polarization by forcing the beam to undergo large amplitude vertical betatron oscillations. These coherent oscillations cause all particles to sample the strong horizontal fields of quadrupoles, and result in a full spin flip. In preparation for the AC dipole being used for polarized helions, it was first commissioned with polarized protons. The proton extraction energy was raised to allow protons to cross $Gγ$ = 0 + $v_y$ = 4.8087. As an artifact of the experiment using polarized protons, the booster settings for bunch extraction interfered with the coherent oscillations and limited the maximum coherent amplitude. This interference will be well separated in the case of polarized helions. Polarized protons crossed the $Gγ$ = 0 + $v_y$ intrinsic resonance with a full spin flip through use of the AC dipole. Simulations of the resonance crossing using Zgoubi accurately predict the polarization relative to the coherent amplitude.

43 PARTICLE ACCELERATORS↗
DOE OSTI2023

Helions below |Gγ| = 10.5 in AGS

Polarized helion collisions are part of the Electron Ion Collider physics program. The required intensity at collision is 1.2×10 11 at 70% polarization. The EBIS source is expected to provide 2×10 11 helions/bunch at 80% polarization. To reach the EIC requirements, the AGS at extraction will need 1.5×10 11 helions/bunch and negligible polarization loss. A critical point for polarization loss in the injectors is the AGS injection energy, which can occur at either |Gγ| = 7.5 or |Gγ| = 10.5. Injection at |Gγ| = 7.5 will result in 80% beam loss and 2.5% polarization up to |Gγ| = 10.5.

43 PARTICLE ACCELERATORS↗
DOE OSTI2023

On polarization and snake arrangements in RHIC: Case of RHIC and EIC HSR tunes p and 3He

This Tech. Note summarizes the outcomes of numerical simulations of strong resonance crossing using RHIC lattice, as a tentative assessment of HSR expectations, with variants including: regular RHIC tunes, HSR fractional tune values, collision or injection optics, and various 2, 4 or 6 snake configurations. This is a first part of simulation studies regarding RHIC and the EIC HSR lattices, a second part concerns the latter specifically and will be released in a separate Tech Note.

43 PARTICLE ACCELERATORS↗
DOE OSTI2023

Transformative Technology for FLASH Radiation Therapy

The general concept of radiation therapy used in conventional cancer treatment is to increase the therapeutic index by creating a physical dose differential between tumors and normal tissues through precision dose targeting, image guidance, and radiation beams that deliver a radiation dose with high conformality, e.g., protons and ions. However, the treatment and cure are still limited by normal tissue radiation toxicity, with the corresponding side effects. A fundamentally different paradigm for increasing the therapeutic index of radiation therapy has emerged recently, supported by preclinical research, and based on the FLASH radiation effect. FLASH radiation therapy (FLASH-RT) is an ultra-high-dose-rate delivery of a therapeutic radiation dose within a fraction of a second. Experimental studies have shown that normal tissues seem to be universally spared at these high dose rates, whereas tumors are not. While dose delivery conditions to achieve a FLASH effect are not yet fully characterized, it is currently estimated that doses delivered in less than 200 ms produce normal-tissue-sparing effects, yet effectively kill tumor cells. Despite a great opportunity, there are many technical challenges for the accelerator community to create the required dose rates with novel compact accelerators to ensure the safe delivery of FLASH radiation beams.

43 PARTICLE ACCELERATORS↗
DOE OSTI2022

Modeling and implementation of vertical excursion FFA in the Zgoubi ray-tracing code

Vertical Fixed Field Accelerators (vFFAs) feature complex and highly non-linear magnetic fields, which require simulation codes allowing step-wise particle tracking. Methods to model the 3D magnetic field of scaling vFFAs have been developed in the ray-tracing code Zgoubi. The field modeling and particle tracking methods include the field non-linearities, the fringe fields, and the field superposition of neighboring magnets. The procedure implements the vFFA analytical field expressions, allowing design studies and parameter optimizations using the Zgoubi built-in fit method. The vFFA procedure has been applied to a ten-fold symmetry ring with a triplet focusing structure designed to accelerate protons from 3 MeV to 12 MeV and studied under the ISIS-II proton driver prototype project. Results from particle tracking in externally generated 3D semi-analytical field maps and the developed vFFA analytical model are shown to be in excellent agreement.

43 PARTICLE ACCELERATORS↗