Emittance studies with an Allison scanner

Abstract

The Spallation Neutron Source H − source on the ion source test stand is being used to study the emittance of the H − -ion beam injected into the SNS radiofrequency quadrupole ͑RFQ͒. The emittance measurements are performed with a LBNL Allison scanner that underwent several modifications. The slit width was optimized to improve the signal-to-noise ratio. In addition, the electric deflector plates were replaced with plates featuring a staircased surface. This modification is shown to suppress over 99% of ghost signals generated by the beam hitting the deflector plates. Both modifications, combined with noise suppression measures and a self-consistent analysis, yield highly accurate results. Measured emittances are presented as a function of the ion-beam current.

Emittance and proton fraction measurement in High current electron cyclotron resonance proton ion source

“…slit-slit, slit and collector, electric sweep, quadrupole scan, pepper pot etc. [4][5][6][7][8][9][10][11][12][13][14]. In our study we have used a slit-slit emittance measurement method.…”

High resolution phase space measurements with Allison-type emittance scanners

“…Analytic and simulation results above reveal two significant corrections on the data analysis of Allison scanners relative to the conventional treatment that assumes symmetric dipole placement and thin slits [1,2]. One correction arises from asymmetry in dipole placement and alters the proportionality constant in the linear relation between dipole voltage (V 0 ) and selected angle (x 0 ref ).…”

“…3 for ballistic simulations. The red rectangle represents the position resolution Δx ideal and angle resolution Δx 0 ideal predicted by the conventional treatment ( [1,2], also reproduced under Case I in Table II), where…”

“…The noise removal scheme employed here has no capability to correct for ghost signals caused by particles that scatter after impacting the E-dipole plates; such ghost signals have been mitigated by using E-dipole plates whose surfaces have a staircase profile to reduce grazing incidences [2,23]. Figure 17 shows an ellipse that surrounds the entire beam distribution, thereby defining a region that contains the beam.…”

“…[1] and summarized in Ref. [2]. They constitute the conventional analysis model which assumes the scanner has an idealized geometry with uniform hard-edge dipole fields, thin slit-plates, and longitudinally symmetric placement of the E-dipole.…”