HAL Id: jpa-00223702
https://hal.archives-ouvertes.fr/jpa-00223702
Submitted on 1 Jan 1984
HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.
L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
FIELD PROPERTIES OF A THREE ORBIT
PROTOTYPE SECTOR MAGNET FOR THE 4 GeV CW ELECTRON MICROTRON
K. Thompson, R. Lari, R. Wehrle
To cite this version:
K. Thompson, R. Lari, R. Wehrle. FIELD PROPERTIES OF A THREE ORBIT PROTOTYPE
SECTOR MAGNET FOR THE 4 GeV CW ELECTRON MICROTRON. Journal de Physique Collo-
ques, 1984, 45 (C1), pp.C1-229-C1-232. �10.1051/jphyscol:1984146�. �jpa-00223702�
J O U R N A L D E PHYSIQUE
Colloque C I , supplement a u no I, Tome 45, janvier 1984 page C1-229
F I E L D P R O P E R T I E S O F A T H R E E O R B I T PROTOTYPE SECTOR MAGNET FOR T H E 4 G e V CW E L E C T R O N MICROTRON~
K.M. Thompson, R.J. Lari and R.B. Wehrle
Argonne NationaZ Laboratory, Argonne, IZZinois 60439, U.S.A.
Rdsumd - Un aimant secteur prototype d'un MICROTRON ii 4 GeV a 6td construit en grandeur nature. La gEom6trie du secteur est re~roduite exactement en ce qui concerne les trois orbites d16nergie la plus basse. On pr6sente les r6sul- tats des mesures du champ magn6tique faites avec et sans anneau de garde ainsi qu'avec et sans cales de r6glage aux psles.
Abstract
-
A full scale prototype magnet has been built for the sector magnets in the 4 GeV Electron Ucrotron. It exactly duplicates the geometry of the sector magnet for the three lowest energy orbits. It has been measured with and without end guards and pole tip shims and the results are presented.Introduction
The six 609 metric ton sector magnets dexigned far the proposed CW 4 GeV Electron Microtron (GEM) at Argonne have a complex geometry. Each magnet is 13.4 m long with a maximum pole width af 1.84 m. The geometry consists of : a stepped edge at the low energy end of the pole, a Purcell field homogenizing gap between each pole tip and yoke, an end guard which sucrounds the main coils, beam shielding steel plates extending from the upper to the lower end guards, auxiliary coils used to control the amount of flux in the end guards and shield plates, steel pole tip shims, and pole face correction coils. Reference 1 contains more details of this design.
The magnetic field properties of these magnets have been studied using both computational as well as measurement techniques. Central field uniformity studies were reported1 in March 1983 at the Particle elerator Co f rence. This gave results for some early calculations2 using T R 3 and TOSCA's9 and measurements near the magnet edges. This early work, however, has not completely quenched the doubts about the field properties at the low energy, dispersive edge of these magnets.
In order to develop more supporting evidence for the feasibility of the proposed design of the sector magnet, a 3-orbit prototype magnet was built to full scale.
Measurements were made on this magnet and 3D magnetostatic field calculations were made using 1010 steel elements arranged in exactly the same geometry as the built magnet.
The measurements made so far are by no m a n s romplate hut are a beginning of those required to fully develop this magnet. The measurements have been made with and without end guards and with one set of steel skims at the edges of the poles. The three objectives of this endeavor are to show that: 1) the field p ofile along the beam path falls off at least as sharply as the Enge short-tail
t; ,
2) the field contours can be oriented to about f5O of the intended directions (perpendicular to the beam paths for the present cases), aad 3) the ieegrals of the first order derivatives of the vertical field with respect to the direction perpendicular to the exterior beam path are small camparsd ts tka first quadrupole in the dispersive straight section beam line.+
Work supported by the U.S. Department of EnergyArticle published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984146
C1-230 JOURNAL DE PHYSIQUE
The recent calculation on this magnet used the proprietary 3D magnetostatic program called T0SCAts5 which was developed at the Rutherford Appleton Laboratory. The resulting vertical field calculations were analyzed in the same manner as the measured data. Both sets of results are presented here and the differences are discussed.
Three-Orbit Prototype
This prototype exactly duplicates the proposed geometry of the three lowest energy orbits in the sector magnets for the 4 GeV electron microtron. The three dispersed, exit edges as well as the cQmmon entrance edge a e all accessible in this magnet. Details of the design were reported elsewhere.? Figure 1 shows an expanded view with the major components rmned. The shield plates are abgut 1 cm thick and the top and bottom corners next to the main coils have a 3.2 cm bevel.
The thickness af the end guard steel is 3.2 cm at all points around the main coil. The Purcell filter gap is 0.3 cm, or 10% of the main gap. The auxiliary coils have about 15% of the ampere-turns of the main coils, aiding the central field and reducing the flux through the end guards and shield plates.
UPPORT BARS
YOKE SPACER
u METER
Fig. 1. Expanded View of 3-Orbit Fig. 2. Plots of Calculated and Prototype Magnet Measured Edge Field Profiles Measurement System
A high precision measuring system8 was used to obtain the field data for this magnet. A Hall probe having a 0.005%/OC temperature coefficient was moved by a computer controlled manipulator which is capable of positioning the probe to within R t B errors of less than 39.05 ma (0.002 inch) over a 100 cm by 50 cm area. An NMR magnetometer was used to set the central field to 1.054 T for all measurement runs.
Magnetic Field Measurements
Measurements have heen made only across the exit (stepped) edge of the number three orbit so far. With this limited set of data, however, the three field profile properties of interest could be studied.
The measurements were made for three separate conditions: 1) with no end guards or pole tip shims, 2) with end guards and shield places but no shims, and 3) with
end guards and 6.4 mm square steel shims at the edges of the top and bottom poles. No results will be presented here for the no end guard case. The field profiles for the other two cases are shown in Fig. 2 for a path along the exterior beam .path. A plot of an Enge short-tail is also shown for comparison.
The locations of the field contours at 0.3, 0'5, and 0.7 Bo were found for several paths perpendicular to the edge and on either side of the beam location at the edge of the pale and are shown i n Table 11 The field gradients, B', with respect to the direction parallel to the pole edge were found for points along a line coincident with the external beam path. Intiegrab of these values are shown in Table I.
TABLE Z. Contour Orientations and Gradient Inteerals "
Contour 'Orientations JB'd9.
0.3 Bn 0 . 5 Rn 0.7 Bo T/M*
No Shims +5.g0 +6.4" +6.g0 0.18 With Shims +5.8' +6.0° +5.1° 0.20 TOSCA:
No Shims +7.4" +8.1° +8.0° 0.18 Calculations using TOSCA
The three-orbit prototype magnet was calculated by TOSCA using the mid-plane as the base plane and extending upwards in six block layers. Only linear elements (i.e., 8 noded blocks) were used to build up the geometry. The reduced scalar potential was used in the coil regions and under the pole tip. Total scalar potential was used in the 1010 steel blocks and other air regions. A total of 12857 nodes, 11160 elements, and 906 subdivided blocks were used in this finite element geometry. The base plane geometry is shown in Fig. 3. Each finite element shown was further subdivided by the number indicated on the boundary. The subdivisian in the vertical direction was 3, 2, 2, 1, 1, and 3 for the 6 block layers respectively. Planes 1 and 2 had the geometry shown in Fig. 3 but planes 3 through 7 had slightly different geometries in khe end guard region. The volume of interest (shown dashed) contained a greater density of nodes. About 3.4 hours of IBM 3033 time vas required to do 27 iterations and reduce the RMS change of the non-linear matrix terms to 0.00006.
4 2 2 4 2
1 1-
2 2
2
2 4
4
4 4
4
4 2
2
2 2
2
2 2
3 3
2 2
2 1 2 2 4 2 12141 4
. . .
3 2 2
Fig. 3. Base Plane TOSCA Geometry
Results of these calculations are shown in Fig. 4 as a plot of B vs X,Z. Notice how the waatusated steel shield located at x
>
25, z>
13 reduces the field to less than 30 gauss for x>
27. The effect of saturation of the corner of the pole at (20,3) i s obsarvable but can he corrected with pole tip shims. Figure 5 shows a plot of the differences between the calculated fields and the measured fields.C1-232 JOURNAL DE PHYSIQUE
The largest differences of f3.5% occur i n the region of largest gradient.
Gradients of 1640 g/cm and absolute positional tolerances of M.02 cm account for only 0.3% of the differences. To reduee this difference further would require wing moxe linear elements or changing to quadratic elements (i.e., 20 noded blocks) in the region of interest.
Fig. 4. TOSCA Calculations of B (x.2) Fig. 5. TOSCA Calculations Minus
Y Measured Values
Conclusions
The plots in Fig. 2 clearly show that all calculations and measurements on this magnet fall off considerably more sharply than the Enge short-tail. The angles of the field contour lines are also shown in Table I to be almost within the target range of f5O. These results can undoubtedly be improved with further adjustments in the shape of the pole tip shims. Q£ course, the edge of the pole could be machined at an angle of about 6- which would reduce the gradient integrals by a factor of 6 and produce contours within f1° of being perpendicular. The fact, however, remains that the integrated gradients shown in Table I are small compared to the first quadrupole in the adjacent beam Lines (5 to 10 T/M-M) implying that the quadrupole can easily correct for even the errors found in these early results.
Figure 5 shows good agreement between the TOSCA calculations and the field measurements in the high gradient fields and excellent agreement in the more uniform field regions.
References
K. M. Thompson, M. H. Foss, and E. J. Lari, "Field Properties for a 4 GeV Microtron Sector Magnet," IEEE Trans. on Nut. Sci. NS-30, 3611 (1983).
M. H. Foss, "A Three-Dimensional Field Pragzam," IEEE Trans. on Nuc. Sci.
NS-30, 2856 (1983).
A. M. Winslow, Journal of Computational Physics,
,
149 (1967).J. Simpkin and C. W. Trowbridge, "Three Dimensional Non-Linear Electromagnetic Pield Computation uaing Scalar P~tentials," IEE Proceedings, 127, Part B, 16 (1980).
-
J. Simpkin, TOSCA User Guide 3D Static Electramagnntic/Electrostatic Analysis Package. Version 3.1, May 1982, RL-81-070.H. A. Enge, Review of Scientific Instruments,
35,
278 (1964).R. B. Wehrle et al., "Prototype Sector Magnets for the GeV Electron Microtron (GEM), IEEE Trans. on Nuc. Sci. NS-30, 2859 (1983).
K. M. Thompson, "Precision Magnet Measuring System," Argonne National Laboratory Report ANL-GEM-14-81 (1981).
