Charge Exchange Cell
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The charge exchange cell is designed to provide a collision vapor thickness
of ~1015 atoms/cm2 to allow multiple collisions and
the following reactions to occur:
X+ (fast)+V 
X0 (fast) + V+
X0 (fast)+ V
X- (fast)+ V+where X+ is a positive atomic RIB and V is the collision vapor. For atomic RIBs equilibrium fractions of negative ions can usually be attained with cell thickness of 1015 atoms/cm2 and result in efficiencies ~10-50%. Molecular RIBs, on the other hand, generally require greater cell thickness (e.g. 1016 atoms/cm2 ) to attain maximum efficiencies since dissociation unlike the above reactions is not an equilibrium process and is favored by more collisions.
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In order to be useful operationally the cell must employ re-circulating
features and/or conductance limitations which allow the cell to operate
at elevated pressures of ~10-2 Torr while maintaining beam line
pressures of 10-6-10-7 Torr without excessive loss
of vapor. See this schematic diagram for details
of the cells construction.
- Once a positive beam enters the charge exchange cell the emerging beam will contain fast neutral particles, positive and negative ions. The negative component of the beam emerging from the cell is measured by the application of transverse electric field to the beam to deflect the negative ions into an off-axis cup. Recently this configuration has been converted into an on-line energy spectrometer by addition of a thin analyzing slit to the cup. The resolution of this device is sufficient distinguish atomic and molecular ionic fragments produced during the break up of simple low-Z molecules such as AlF. Direct on-line energy analysis of the post charge exchanged beam is now possible. An example of this type of energy spectra is found here.
RIB Injector |
Target |
Ion Source |
HV Platform |
Charge Exchange Cell |
Isobar Separator |
Beam Development
For questions about this page please contact the HRIBF User Liaison.
This file last modified Friday August 12, 2005