Ion Beam Extraction and Optics
Paper Title Page
TUZO01
 Beam Extraction Results with KAERI 14.5 GHz ECR Ion Source  
 
  • B.H. Oh, D.S. Chang, C.K. Hwang, S.R. In, S.H. Jeong, J.-T. Jin, T.S. Kim, C.H. Lee, K.W. Lee
    KAERI, Daejon, Republic of Korea
  • E.-S. Kim, C.S. Seo
    IBS, Daejeon, Republic of Korea
  
  A 14.5 GHz electron cyclotron resonance ion source has been designed and fabricated at KAERI (Korea Atomic Energy Research Institute) to produce multi-charged ion beams (particularly C6+ ion beams) for medical applications. During the first beam extraction experiments with the developed ion source, it was found that C4+ beam of 15 eμA and Ar15+ beam of 1 eμA were the optimized beam current. A big current loss was made along the beam transport path from the ion source to the entrance port of an analyzing magnet because of long beam line and small acceptance of the magnet. A new Einzel lens is added in the beam line to minimize the beam loss, and the second beam extraction experiments have been made. In this paper the beam experimental results with the KAERI ion source, including the hard X-ray spectrum from the ECR plasma and the emittance measurement results of carbon beam, will be discussed.  
slides icon Slides TUZO01 [6.584 MB]  
 
TUZO02 Detailed Investigation of the 4D Phase-Space of an Ion Beam 30
 
  • H.R. Kremers, J.P.M. Beijers, S. Brandenburg, V. Mironov, S. Saminathan
    KVI, Groningen, The Netherlands
  
  A second order transfer matrix is calculated, which is used in the calculation of a 4D phase-space distribution of a 24.6 keV He1+ beam. The calculated distribution matches a 4D phase-space distribution measured with the KVI pepper pot emittance meter. The pepper pot emittance meter is installed in the image plane of a dipole magnet acting as a charge-state analyser directly downstream the KVI AECR ion source. From the second order transfer matrix simple analytical equations are derived by retaining the terms for angular coefficients. These simple equations describe the main features of the phase-space correlations in the image plane. The equations show also that the subset of the 4D phase-space distribution, selected by one pepper pot aperture, results in multiple beam-lets. Due to this successful matrix modelling we conclude that the 4D phase-space distribution measured is fully determined by the ionoptical properties of the magnet.  
slides icon Slides TUZO02 [6.348 MB]  
 
TUZO03 New Extraction Design for the JYFL 14 GHz ECRIS 34
 
  • V. Toivanen, T. Kalvas, H. A. Koivisto, J.P.O. Komppula, O.A. Tarvainen
    JYFL, Jyväskylä, Finland
  
  Funding: VT acknowledges the financial support of the Ehrnrooth foundation.
A new extraction system has been designed and constructed for the JYFL 14 GHz ECRIS at the Department of Physics, University of Jyväskylä (JYFL). The goal of the new design is to improve the performance of the ion source and increase the transmission efficiency of the low energy beam transport and the accelerator. The new extraction system is designed to be able to handle higher beam currents, yield better beam quality and offer more tuning flexibility. The design was made with the aid of simulations performed with the IBSimu code. The suitability of the code for this task was verified by simulating the old extraction system and good agreement between simulations and measurements was achieved. The new extraction system has been constructed, installed and tested. The new design, simulations and the first measurement results will be presented. 		 
slides icon Slides TUZO03 [4.470 MB]  
 
TUZO04 Space Charge Compensation Measurements of Multicharged Ion Beams Extracted from an ECR Ion Source 38
 
  • D. Winklehner
    LBNL, Berkeley, California, USA
  • D.G. Cole, D. Leitner, G. Machicoane, F. Marti, L. Tobos
    NSCL, East Lansing, Michigan, USA
  
  Space charge compensation* due to the interaction of the beam with residual gas molecules is a well-known phenomenon for high current injector beam lines. For beam lines using mostly magnetic focusing elements and for pressure above 10-6 mbar, full neutralization has been observed. However, due to the low pressure required for the efficient transport of high charge state ions, beams in ECR injector lines are typically only partly neutralized. With the performance increase of the next generation ECR ion sources it is possible to extract tens of mA of beam current. In this high current regime, non-linear focusing effects due to the space-charge potential of the beam become more and more important. In order to develop a realistic simulation model for low energy beam transport lines, it is important to estimate the degree of space charge compensation. In this contribution we report on measurements of the beam potential (and neutralization), performed after the extraction region of the ECR ion source, in dependence of the base pressure in the beam line and other source parameters using a Retarding Field Analyzer (RFA). Results are discussed and compared to simulations.
* When the beam interacts with the residual gas, electrons are separated from gas molecules and accumulate inside the beam envelope, thereby compensating the space-charge (aka neutralization) 		 
slides icon Slides TUZO04 [4.192 MB]  
 
WEYO01 The Einzel Lens Longitudinal Chopper 95
 
  • K. Takayama, T. Adachi
    KEK, Ibaraki, Japan
  • T. Adachi, K.W. Leo
    Sokendai, Ibaraki, Japan
  
  The Einzel lens longitudinal chopper [1] placed just after the ECRIS has been developed for the KEK digital accelerator [2] and is being operated without trouble over more than 1 year. Propagation of a msec-long ion pulse extracted with the ECRIS extraction voltage V1, is fully controlled by superimposing a rectangular-shape pulse voltage V2 (<0) on the fixed Einzel lens voltage V3 (V3 > V1). For most of time region (~msec), beam propagation is blocked, meanwhile for a time region (~5 μs), where V2 is on and V2 + V3 < V1, the beam can propagate downstream under the optimized transverse matching condition. Namely, the superimposed voltage V2 + V3 works as a gate voltage. This negative pulse voltage is produced by the solid-state switch driven Marx Generator, promising a fast rising/falling feature in the pulse profile. This chopper enjoys a lot of figure of merits originated from the fact that the beam can be handled at its minimum energy region:
  1. low electron emission,
  2. low voltage,
  3. low energy X-ray, and
  4. low cost.
This type chopper should be expected in a wide variety of ion beam applications. Comparison with other type choppers will be discussed.
[1] T. Adachi, K.W. Leo et al., "A Solid-state Marx Generator driven Einzel Lens Chopper", Rev. Sci. Inst. 82, 083305 (2011).
[2] T.Iwashita et al., "KEK Digital Accelerator", Phys. Rev. ST-AB 14, 071301 (2011). 		 
slides icon Slides WEYO01 [5.566 MB]  
 
WEYO02 Experimental Results: Charge-state and Current-density Distribution at the Plasma Electrode of an ECR Ion Source 101
 
  • L. Panitzsch, T. Peleikis, M. Stalder, R.F. Wimmer-Schweingruber
    IEAP, Kiel, Germany
  
  We have measured the current-density in very close vicinity (15 mm downstream) of the plasma electrode of our hexapole-geometry electron-cyclotron-resonance ion source (ECRIS). For this, we equipped our 3D-movable puller electrode with a customized Faraday Cup (FC) inside. To achieve high spatial resolution we reduced the aperture of the puller electrode to only 0.5 mm. Thus, the source-region of the extracted ion beam is limited to a very small area of the plasma electrode's hole (d = 4 mm). The information about the charge-state distribution and the current density in the plane of the plasma electrode is conserved in the ion beam and was scanned by remotely moving the small-aperture puller electrode (incl. FC) across the aperture of the plasma electrode. From additional m/q- measurements for the different positions we can deduce that different ion charge-states are grouped into bloated triangles of different sizes but with the same orientation in the plane of the plasma electrode with the current density peaking at the centre. This confirms simulations by various groups as well as some emittance measurements, but adds spatial resolution for the different charge-states.  
slides icon Slides WEYO02 [2.298 MB]  
 
WEYO03 Ion Beam Extraction from Magnetized Plasma 106
 
  • P. Spädtke, R. Lang, J. Mäder, F. Maimone, J. Roßbach, K. Tinschert
    GSI, Darmstadt, Germany
  
  With increasing the total extracted current for any ion source, the optimisation of the extraction system becomes more important, because of the space charge effect. Several attempts have been made in the past to simulate the extraction from an Electron Cyclotron Resonance Ion Source (ECRIS) in a correct way. Most of these attempts failed, because they were not able to reproduce the experimental results. The best model up to now is given by the following procedure: tracing the magnetic field lines through the extraction aperture, looking where these field lines are coming from; using these coordinates of the magnetic field line as starting points for ions to be extracted; the initial current of each trajectory is determined by theoretical assumptions about the plasma or by a plasma simulation; Child's law is applicable locally only in direction of the magnetic field, if no emission limited flow is present.  
slides icon Slides WEYO03 [16.955 MB]  
 
WEPP08 Emittance Measurements for U Ion Beams Produced from RIKEN 28 GHz SC-ECRIS 130
 
  • K. Ozeki, Y. Higurashi, T. Nakagawa, J. Ohnishi
    RIKEN Nishina Center, Wako, Japan
  
  In order to investigate the ion optical parameters of the beam line of RIKEN 28 GHz SC-ECR ion source into the new heavy ion linac (RILAC II), we measured the emittance of the heavy ion beams form RIKEN 28 GHz SC-ECR ion source. In the test experiments, we observed that the emittance of the U35+ beam was ~100 π·mm·mrad (4 rms emittance), which is smaller than the acceptance of the accelerator (~160 π·mm·mrad). The emittance with 28 GHz was almost same as that with 18 GHz and independent on the injected RF power (1~2 kW). The size of emittance increased with decreasing the charge state. We also measured the emittance of U and oxygen ions under the same condition. In this experiment we observed that the emittance of oxygen ions was always larger than the U ion beam for same M/q. In this contribution, we report the experimental results for emittance measurement of highly charged U, Xe and O ions from RIKEN 28 GHz SC-ECR ion source in detail.