The Debrecen ECR Project S.Biri and J.Vámosi Institute of Nuclear Research (ATOMKI) of the Hungarian Academy of Sciences

H-4001 Debrecen, P.O.Box 51, Hungary

ABSTRACT To facilitate heavy ion collision research in atomic and nuclear physics a decision has been made in our institute to establish a heavy ion physics facility. The facility will consist of an ECR high charge state heavy ion source, of a 500 KV electrostatic or quadrupole accelerator and of the cyclotron of the institute. After gaining the financial support to design and build the ECR source (i.e. for the first part of the project) the program has been started in the fall of 1992. To visualize the complex magnetic field inside the ECR chamber a special computer code was written which can handle e.g. the POISSON/PANDIRA output files as input data files. The field lines and resonance surfaces are calculated and stored in a DXF format file which is the drawing interchange file format of the well-known professinal AutoCAD design software. Using the wide-range set of tools provided by AutoCAD one can visualize the structure of the magnetic bottle in 3D. The first results of such visualisations are shown. The design of the room-temperature 14 GHz ECR ion source has been started very recently.

1. Introduction Experimental atomic and nuclear physics research in ATOMKI have been based on the particle accelerators of the institute. During the almost 40-years history of the institute the beam power of the accelerators was increased continuously: 1962 : Cockroft-Walton generator 1969 : Van de Graaff generator 1971 : Van de Graaff generator 1985 : variable energy cyclotron

→ → → →

U=0.8 MV U=1 MV U=5 MV K=20.

The latest trend of accelerator based atomic and nuclear physics research is undoubtedly heavy ion collision physics. Our participation in front line research programmes requires the extension of our atomic and nuclear physics studies into this direction. To facilitate heavy ion collision research in atomic and nuclear physics a decision has been made in the ATOMKI to establish a heavy ion physics facility. The facility will consist of an ECR ion source, of a 500 KV electrostatic (or quadrupole) accelerator and of the MGC (K=20) cyclotron of the institute [1].

Beside the ECR ion source, which - can be used alone (low energies up to 20 keV/amu), - will be coupled to an electrostatic accelerator (medium energies up to 200 keV/amu) and - installed at the cyclotron (high energies up to 4 MeV/amu), one gets a special heavy ion facility not available in Central- and Eastern-European countries and it makes a variety of research programs possible. The scheme of the planned facility can be seen in Fig.1.

Fig.1. Schematic view of the planned heavy ion physics accelerator facility.

The realization of the facility has been suggested in three steps. First the ion source will be built in the rooms used formerly by the Cockroft-Walton generator and it will be applied for atomic physics investigations at low energies. In the second step the ECR source will be mounted on a 300-500 KV platform to get an electrostatic accelerator for medium energies. Finally in the third step the source will be coupled to the cyclotron and further on will be used alternately in the low/medium and high energy ranges. During the operation of the ECR source at the cyclotron, a hollow-cathode type ion source will be used at the static accelerator to produce single charged ions for the users [2].

2. The heavy ion physics facility - planned research The research activity at the proposed heavy ion facility will include investigations with a variety of ion beams at low and medium energies in atomic physics, solid state and plasma physics, while in the high energy range atomic physics, nuclear spectroscopy and applications will be the main topics.

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Atomic physics. There are two important research fields in which the atomic physics group of the institute had experience in the past several years and which are planned to be the starting points of an atomic physics research activity at the ECR source. These are (1) the emission of Auger-electrons following collisional excitations of atoms (ions); (2) the emission of the primarily ejected electrons from the collision (with a special emphasis on the forward electron ejection). Both processes are investigated using specially constructed highresolution electrostatic electron spectrometers developed in our institute during the last two decades. Atomic physics investigations with multiple charged heavy ions are performed with beams of high-power ion sources or with high-energy heavy ion accelerators; the range between them has not been covered. If after the ECR source an electrostatic or quadrupole accelerator will be applied, a new experimental area would be opened, covering partly the gap between the energy of the ECR's (500 keV/amu). The most interesting fields to study are: charge exchange processes, molecular mechanism, direct ionization, ion-solid state interaction, quantum electrodynamical effects. Nuclear physics, nuclear spectroscopy. One of the most important direction of progress in nuclear physics is heavy ion physics. In large nuclear physics research centres heavy ion physics is the main field of research, and smaller laboratories in the neighbouring countries do significant efforts to establish heavy ion accelerators. Some proposed experiments with heavy ions are: determine new level parameters by (heavy ion, xn) reactions, study of the structure of high-spin levels (rotational bands, back-bending, yrast-levels), proton-neutron multiple high-spin states of the odd-odd nucleus, Coulomb excitation. Applications. Among the many industrial, medical etc. applications we plan to deal with production of nuclear filters, investigation of the radiation damage in various materials, materials sciences.

3. The ECR ion source A detailed proposal [3] of the planned facility has been sent to some competitions. In the middle of 1992 the first part of our application (i.e. the ECR source) was selected for funding. Because of the limited financial support we decided to build it ourselves in our institute, using at the same time experiences from other laboratories. In fact the program has became the top job in ATOMKI and started in the fall of 1992. To start such a project in a small laboratory it is very important to collect information on the subject in question. So first an intensive data collecting on the parameters and performances of existing (and also dismantled and planned) ECR sources has been carried out. Because of the large amount of information data were saved in a database file using our special computer code (ECRIS.EXE) written in Clipper. The code makes the data searching, ordering and filtering possible in a quick and interactive way. In fig.2. an example of the code output is shown.

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Fig. 2. A PrintScreen copy of the PC display when running the database code. AR11 and KR22 are the reached Ar11+ and Kr22+ beam currents in µA. These high charge states are required for the ATOMKI cyclotron.

The difficulties in design of an ECR source can be summarized in two main reasons. The first is that the number of the free, changeable parameters after completing a source (i.e. during operation) radically less than it was during design. Second, the exact effect of these parameters on the plasma and beam C.S.D. have not cleared yet enough. In fig.3. we attempted to summarize (using among others the establishements in [4]) and to order into groups the external and internal parameters of ECR sources. Examining the parameters and performances of different ECR sources, knowing the strict A/Q≤4 condition for our cyclotron and estimating the cost and the cost/power ratio of various ways, a room-temperature 14 GHz ECR source seems the optimum choice for us. In the near future we begin the design of the exact structure of the NdFeB hexapole. As a starting point the arrangement written in [5] and [6] is considered. The coil-system and the whole mechanics are planned to be the most flexible for alterations. The ECR source is considered to be not only a tool for executing physical experiments but as the object of examinations at the same time. This fact will also be taken into account during design.

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Fig. 3. A rough summary of the connections between parameters. Te , ne , τi and n0 are the electron temperature, density, the ion confinement time and the density of neutrals, respectively. I tot is the total extracted beam current, q and qmax are the average and maximal charge, and I q+ is the beam current with required charge. Arrows show the main directions of the effects of the external parameters.

4. 3D visualisation of the magnetic field Because of the difficult magnetic structure of the ECR ion source we consider important to find a quick and simple way to visualize the magnetic field in 3D already during design and later, during operation as well. This way can also help in understanding the physics of ECR sources. The AutoCAD designing software supports 3D objects visualization. Our purpose was to transform the output data of popular magnetic field calculating codes into field line datafile that the AutoCAD can import. For this purpose the POACAD PC-code was written. POACAD can handle the POISSON and PANDIRA output files (after some manual preprocessing ) as input data files. It does not mean a limitation for use: it is easy to modify the code that it handles other output files of different magnetic field calculation codes. The drawing of a field line can be initiated by mouse or from keyboard on the graphics screen from any point within the hexapole tube. A schematic front and side view of the hexapole are displayed and the user can move using the mouse and/or the keyboard v in X-Y plane and in Z direction . The actual cylindrical coordinates and the value of the B = ( Br , Bφ , Bz ) are also displayed. To determine the points of a field line the following simple differential equation has to be solved:

v v v dr ( s ) B (r ) = v v , ds B (r )

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v v where r ( s ) is the parametric form of the curve of the field line, s is the length of arc and B is the magnetic induction vector. We used the Runge-Kutta method to solve this equation. A field line is constructed as a 3D polyline. The coordinates of the breakpoints of this polyline are saved in a DXF format file. This is the drawing interchange file format of AutoCAD. The DXF file of the resonant surface is also generated pressing the appropriate key.

The code was written in C++ language. All the graphics cards are supported when working on graphics screen. In fig. 4. the logical scheme of the calculation-visualisation can be seen.

Field line DXF file

POISSON OUTPUT POACAD

AutoCAD

Res. zone DXF file

PANDIRA OUTPUT

Fig. 4. The way from POISSON to AutoCAD through POACAD.

Besides, POACAD has a built-in permanent and coil magnetic field calculation functionality for simple PM-geometry and air-cored coils only. Using the wide-range set of tools provided by AutoCAD one can visualize the structure of the magnetic bottle in 3D. In fig. 5,6 and 7 the first results are shown. We are going to develop POACAD further into a more interactive and quick, easy-to-learn tool perhaps running under Windows. According to our expectations the code and the method shown in fig. 4. will be well applicable soon directly to design the magnetic system. In the future we plan to study the frequency modes inside the cavity and the plasma itself (here it must be mentioned an also interesting attempt described in [8]).

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Fig. 5. Typical field lines starting from the north poles of the hexapole at the chamber middle plane (on the left, bottom circle). Right is the projected view from the chamber end.

Fig. 6. The resonant surface and a closed flux tube (left). As it was shown in [7] there exist opposite conditions for them. Right: projected view from the end of the chamber. Only 3 curves of the resonance surface are drawn.

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Fig. 7. Field lines starting from one pole. The right side represents the view a charged particle can 'see' during energy gaining (crossing the resonant zone). The arrow on the left shows the place of this imagined particle in the chamber.

5. Conclusion The program of building a room temperature 14 GHz high charge state ECR ion source has been started very recently. The klystron has been ordered. The design of the magnetic systeme will start in the near future using the POISSON-POACAD-AutoCAD codes.

Acknowledgements The authors would like to thank J.Arje, K.E.Stiebing and M.Loiselet for the useful discussions.

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References [1]

S. Biri, J. Pálinkás, A. Valek, "Heavy ion facility in ATOMKI", presented in XIII. Int. Conf. Cycl. Appl., Vancouver, Canada, July 1992.

[2]

S.Biri, J.Pálinkás, "Extraction and focusing electrode arrangement for a hollow-cathod ion source", submitted to the Review of Scientific Instruments.

[3]

"The heavy ion physics program of the ATOMKI". Institue of Nuclear Research, Debrecen, 1991. Internal material in Hungarian and - in shortened form - in English. Compiled and edited by S.Biri.

[4]

C.Lyneis, "ECR Ion Sources for Accelerators", presented in XIII. Int. Conf. Cycl. Appl., Vancouver, Canada, July 1992.

[5]

P.Schiemenz, A.Ross and G.Graw, "High field permanent sextupole magnets for SternGerlach separation in atomic beam sources", Nucl. Instr. Methods A305 (1991) 15.

[6]

H.Streitz, O.Frohlich, K.E.Stiebing, K.A.Muller, K.Bethge, H.Schmidt-Bocking, E.Salzborn, M.Schlapp, R.Trassl, "Optimierung des Hexapolsystems fur die EZRQuelle mit ANSYS", Annual Report of IKF, 1991.

[7]

G.Melin, C.Barue, F.Bourg, P.Briand, J.Debernardi, M.Delaunay, R.Geller, A.Girard, K.S.Golovanivsky, D.Hitz, B.Jacquot, P.Ludwig, J.M.Mathonnet, T.K.Nguyen, L.Pin, M.Pontonnier, J.C.Rocco, F.Zadworny, "Recent developments and future projects on ECR ion sources at Grenoble", Proc. 10th Int. Workshop on ECRIS, Knoxville, Nov. 12, 1990.

[8]

Y.Jongen, "Confinement and charge state distribution in ECR sources", 3rd ECR Workshop, Darmstadt, 1980.

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