Proposed injection of polarized He3+ ions into EBIS trap with slanted electrostatic mirror* A.Pikin, A. Zelenski, A. Kponou, J. Alessi, E. Beebe, K. Prelec, D. Raparia Brookhaven National Laboratory *Work supported under the auspices of the U.S. Department of Energy

The goal: injection of polarized He3 + into the EBIS trap The problems: Depolarization in magnetic field during injection Injection into EBIS (low charge state multiplication) 1.Depolarization: using He3 + with atomic polarization parallel to nuclear (Murnick, Mei 1985) Method: 3S 1 3P 1 (F=3/2, 1/2) (circularly polarized narrowband laser) 3S 1 – as a result of charge exchange of He3+ on alkali atoms Ionization – preferably by resonant ionization using UV laser, or charge exchange in a vapor μ 680 MHz

Optical pumping of 3 He 1 metastable atoms in collinear beams technique nm

Direct optical pumping of the “fast” 3 He(2S) beam (proposal). After Na-neutralizer cell almost 100% of He-atoms are in (2 3 S 1 ) state. Energy defect-0.38 ev. Direct optical pumping can produce near 100% nuclear polarization in He(2S) states. P( He ++ ) ~80-90%. He + source Na-vapor cell He(2S) EBIS ionizer EBIS ionizer 4 He-gas Ionizer cell He + He mA of a 0.75 keV energy He + ion beam Optical pumping at 1083 nm ~3 kG field He(2S)

Layout of EBIS with external ion beam line

2. Injection into EBIS “Fast” potential trapping of traversing ions. Requires pulsed primary ion beam to fill the trap “on a fly” with limited maximum trapping time (traversing time). For 50 eV He3+ to fill an ion trap of a 10 A electron beam I He3+ ~1.5 mA with emittance ε RMS norm ≈0.02 mm*mrad “Slow” trapping of ions traversing through the trap. Only ions, which reduced their axial energy per charge between two axial barriers get trapped. The known mechanisms – ionization and energy exchange with ions and molecules during traversing through the trap. The injection time can be longer than the ionization time.

The idea of continuous ion injection – to transfer part of longitudinal ion energy into transverse when the ion is reflected by an electric field which is not parallel to the axis of ion motion (without changing the total energy) so that longitudinal energy reduces and the ion got trapped. The existing radial potential well allows us to do this without losing ions within certain longitudinal energy spread of ions.

The process of ion trapping with such mirror has been simulated with 2- dimensional program TRAK and 3-dimensional program KOBRA3-INP on simplified models of EBIS/EBIT. Parameters of these models are: Electron beam current – 5.0 A, zero current of ion beam, Electron energy – 25 kV Electron beam diameter – 6.0 mm Inner diameter of drift tubes – 20.0 mm Magnetic field – 3 kGs 2-D simulations has been done with cylindrical symmetry, so that the plane mirror was substituted with conical mirror with gap of 1.7 mm. Mesh size: mm, number of electrons – 100, number of ions - 100

2-D model and field distributions:

Electron beam transmission:

Ion beam transmission with no mirror engaged:

Axial potential distribution in the trap with mirror engaged:

Ion trajectories with mirror engaged:

Simulated trajectory of a single trapped ion (out of 100 other ions):

For mirror angle 45 0 the trapping statistics:

Similar calculations has been done for mirror angle 20 0, 45 0 and 60 0 and for different voltages on a mirror drift tube on a trap side (drift tube No.3)

3D model: Mesh: Z: 1mm, X and Y: 0.5 mm Number of electrons: 500 Number of ions: 1000 Hovi Kponou

Electric field in 3D model (a – without el. beam, b- with el. beam): a b

Axial electric field distribution with ion trap:

Electron trajectories: Ion trajectories (60 0 ):

Results of 3D simulations:

Angular dependence of the trapping efficiency:

Possible solutions for the mirror angle adjustment: 1. Modifying the mirror voltage by adjusting the potential on a part of the mirror, which is opposite to the injection side while keeping the potential on a mirror tube on a trap side fixed. Presumably this can change the position and angle of the reflecting equipotential with respect to the axis. 2. Using extra wedge-shaped tube(s) with controllable voltage.

Plan for mirror test on BNL Test EBIS:

Simulation of electron beam transmission in Test EBIS with slanted mirror:

Resume: 1.Injection of polarized He3 into EBIS trap in a form of He3+ ions from outside polarizer/ion source should be greatly simplified with a slanted electrostatic mirror on a side of EBIS ion trap opposite the injection end. Such mirror transfers part of longitudinal energy of ions traversing the trap into transverse component. Reduction of longitudinal component of ion energy in a space between two axial potential barriers prevents the traversing ions from escaping the trap on a way out and therefore this is a mechanism of continuous ion accumulation. Without limitation for a minimum ion current (which for a pulsed ion injection can be a problem) this method has all other advantages of pulsed ion injection and can be more feasible than the “fast” injection method. 2. With all quantitative differences in simulations with 2D and 3D programs it was demonstrated that at certain conditions the continuous trapping of ions traversing the EBIS trap by transferring part of longitudinal energy into transverse is possible and the optimum efficiency exceeds 40%.