HAL Id: jpa-00223715
https://hal.archives-ouvertes.fr/jpa-00223715
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.
HIGH-FREQUENCY MAGNET FOR SEPARATING BEAMS IN COLLIDERS
Y. Baconnier, J. Dupin, R. Guinand, K. Kissler, W. Middelkoop, G. Paillard, A. Warman, J.-P. Zanasco
To cite this version:
Y. Baconnier, J. Dupin, R. Guinand, K. Kissler, W. Middelkoop, et al.. HIGH-FREQUENCY MAG- NET FOR SEPARATING BEAMS IN COLLIDERS. Journal de Physique Colloques, 1984, 45 (C1), pp.C1-297-C1-300. �10.1051/jphyscol:1984159�. �jpa-00223715�
JOURNAL DE PHYSIQUE
Colloque C1, suppl6ment au no 1, Tome 45, janvier 1984 page C1-297
HIGH-FREQUENCY MAGNET FOR SEPARATING BEAMS IN COLLIDERS
Y. Baconnier, 3. Dupin, R. Guinand, K.H. Kissler, W.C. Middelkoop, G. Paillard, A. Warman and J.-P. Zanasco
C. E. R. N . , 121 1 Geneva 23, Switzer Land
RESUHB
Un prototype d-aimant 130 kHz H culasse en ferrite conGu pour sCparer des faisceaux de paquets de protons et d'antiprotons dans un collisionneur de haute 4nergie a 6tC construit et test4 sour vide jusqu'l 620 gauss. Les problemes principaux sont 1'6vacuation de la puissance dissipee dans la ferrite et la tenue en tension de 18 bobine par rapport i la culasse.
A prototype 130 kHz ferrite-cored magnet designed for separating bunched beams of protons and antiprotons in a high-energy collider has been built and tested in vacuum up to 620 gauss. The main problems are the removal of the power dissipated in the ferrite and the withstand voltage of the coil in relation to the yoke.
INTRODUCTION
The beam-beam tune shift in s colliding-beam machine may be minimised by separating the beams at the interaction points not used for physics experiments. The beams can be separated either with electrostatic separators or by using magnetic separators (1) with an alternating positive and negative field synchronised with the passage of bunches of particles and antiparticles. Kagnetic separators have the advantage of being shorter and less subject to breakdown. The frequency of the exciting a.c. of the magnets depends upon the number of bunches of particles and the circumference of the machine. In the SPS. the fundamental frequency for these magnets is 130.12 kHz for three bunches each of protons and sntiprotons. Horizontal rather than vertical separation is preferred in view of the aperture of the vacuum chamber of the collider.
REOUIREHENTS FOR A HORIZONTAL MAGNETIC SEPARATOR These magnets must be fitted in the short straight sections of the SPS which limits their maximum length and defines their required aperture 2 The frequency and deflection power are discussed in reference (2). A figure of 6 times the mean besm size (+ 3 0 ) Was selected as the minimum separation between the two beams. The magnet must be fitted in a vacuum chamber in order to minimise the gap height and to provide the best possible withstand voltage. It must also be radiation resistant and properly cooled.
Table 1 shows the main psrameters for the windov frame magnet.
Frequency (kHz) 130
Deflection at 270 GeV (mrad) 67.8X10-P Integrated magnetic strength
for a 6 o separation (Tm) 610x10-4 Max. field strength (gauss) 950 Max. overall length (coil) (mm) 710 Max.length of ferrite yoke.
blocks copper . . cool in^ plates - . (mm) 640
Gap height (mm) 28
Gap width (m) 148
Good field width at .+ lo-* (mm) 120
Max.temperature rise of
cooling water ( " C ) 15
Possible radiation dose on magnet (grey) 10' Max.distance between transmitter
and magnet (m) 800
ELECTRICAL CIRCUIT
The circuit diagram in fig.1 comprises:
1) a 130 M z / 3 S k W transmitter with a water-cooled power tetrode;
2 ) A 50-ohm coaxial line 800 metres long
corresponding to the distance between the auxiliary building and the magnet's location in the machine;
3) a resonant circuit consisting of:
a) the 130 kHz magnet;
b) a low-loss capacitor bank C, + C,.
4) three loops For adjusting the phase, amplitude and tuning;
The matching of the 50-ohm line to the resonant circuit and the tuning of the latter are obtained using two motor-driven variable capacitors C, and C,.
The transmitter must provide enough power to compensate:
1) the losses along the 50-ohm line;
2) the losses in the capacitor bank and C,;
3 ) the losses in the magnet:
a) through the Joule effect in the "skin" of the copper conductor of the coil;
b) by hysteresis and eddy currents in the yoke;
4) the losses in the connections and contacts.
Fig. 1 Circuit diagram MGNEr
The prototype HRFP magnet is of window frame type with a single turn coil. Its essential dimensions are given in Table 1 and fig.2. One of the main problems in designing this magnet was the cooling of the yoke which is heated by hysteresis and eddy current losses. Therefore. we had to use a law-loss ferrite and to design sn efficient cooling system of the core: the yoke was made of cells which each consist of 6 blocks, 25 mm thick. of a ferrite type 3 Fl made by Philips (3). Each block is cooled by two
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984159
Cl-298 JOURNAL DE PHYSIQUE
Coil: 6 t u b e s 5 x 4 mrn b r a z e d Y T G Z i G e T ( 3 o x 4 )
Kaflon foils 50 -
/I
Copp.?! cooling..p!ater r h m t h i c k e a c h )
U p p e r water- cooled plate --
L o w e r - w a t e r - . .
I
side w a t e r - c o o l e d plate \Cell of 6 ferrite blocks 25 mm. thick~ i 2. uain dimensions ~ . OF the magnet and arrangement of the ferrite cells of the core
intermediate copper plates 2 mm thick, one on either The yoke assembly is firmly compressed along the three side except for the 'end ferrites. The end cooling exes in a thick-walled stainless steel box fitted with plates had to be removed because of the eddy currents 226 small screw-jacks (fig.3 h 4). This arrangement which appeared in the capper owing to the end flux and provides a pressure of some 4 d a N . ~ m - ~ along the the 25 mm end cell was replaced by two &ells 8.5 and three axes, thus ensuring good heat transmission 12.5 mm thick with two 2 mm thick copper plates in through the various contacting surfaces.
between (fig.? d 3). On the outside of the yoke the copper plates are bent back over half the thickness of each ferrite and capped by five water-cooled copper cooling elements. The cells are electrically insulated by a 50-micron Kapton foil fitted between the copper end the ferrite. The longitudinal composition of the yoke is summarized in the following table :
Thickness of the 20 cells of 6 ferrite blocks of the body Thickness of the 4 cells of 6 ferrite blocks at the ends Thickness of 46 sets of
6 intermediate copper cooling plates Thickness of the i n s ~ l a t i n ~ Kapton foil between copper and ferrite
- Length of yoke 636.3 mm Fig. 4. Arrangement of the stainless steel box and its 226 screw-jacks around the yoke
The ferrite 3F1 has low hysteresis losses and average resistivity. The hysteresis losses may be empirically expressed by
Ph (kW/ma) = h. B~
where B is the induction in the ferrite in tesla and h and k are parmeters inherent of the material considered and dependent upon temperature; they are deduced from the values of uQ = uiltgd (pi, being the initial relative permeability) measured by the manufacturer as a function of B according to the relation
The hysteresis losses dissipated in the ferrite by small transverse sections of the volume were assessed with the aid of the HAGNET-INDUCT-LGO program ( 4 ) by calculating B and Ph = h.Bk at every point in the two-dimensional network. This gave a map of the hysteresis 1 0 ~ 6 8 ~ (fig. 5 and 6) and the total inductance per unit length.
The eddy current losses are expressed by
PERTES D I N S LA FERRITE P; . ~ Z ~ P ~ ~ ~ ~ E ~ O ~ K I L O W A T T S / M E T R E FORHULE : .50000000E-04 .B*+ 3-17 Pig. 5 . Hysteresis losses map (partial) from IULGNET-INDUCI-LGO with ferrite 3Fl at Bgap= 0.095T and 70 "C.
where
e, in metre,
B, in tesla
is the thickness of the cells constituting the yoke;
is the resistivity of the ferrite, measured at frequency f, at a given temperature:
is the induction in the ferrite.
The eddy current losses were evaluated assuming a uniform distribution of the induction in the ferrite.
A few figures for yoke losses as a function of temperature and of induction are given for ferrite 3F1 in Table 3 and fig. 6 for the prototype magnet.
4 CORE LOSSES
drawn-Out l i n e r : evaluated from an aversge B
dashed l i n e r : results of magnet P T O I ~ M I .
/
Pig. 6. Hysteresis + eddy current losses versus gap induction at 20 and 70'C (calculated) for Prototype magnet
The calculation of the losses in the ferrite blocks made it possible to estimate the maximum temperature rise of the material in the most critical areas, i.e. around the coil and on the ferrites nearest the water outlets. The law of heat conduction was applied to trapezoidal heat "tubes" of the cooling copper plates, assuming a parabolic law of distribution of the power dissipated along the height of the trapezia. This led to the temperature rises shown in the Following table :
Temperature rises at 0.095T. in ' C IMax.around1 I
I the coil IAverarelMinimm
I I I
bt max. in ferrite i 31 i 3.5 i 1
At through Kapton 11 I 1
At copper plate
I
14 1 1.5I
i.5At contact with coolant 1 2 1 0.5 1 0.5
At cooling water 8 1 4 1 0.5
t water inlet
f
18 1 1 8 1 I8I I I
t ferrite i 84 i 28.5 i 21.5 The coil has a single turn (fig.7 and Table 5 ) in order to limit the terminal voltage to 8.2 kV at 130 kHz and 0.095 tesla. It is made of 6 hollow copper tubes brazed together.
The alternative magnetic Field induces eddy currents in the coil and reduces the conduction layer to the internal "skin.' of the conductor on the side of the magnet pole-pieces and gap. The result of this phenomena is to increase the R.P. resistance of the coil expressed by
p W H c = 6.7 mohm at 30°C where
Losses in Ferrite 3F1
c is the skin thickness = (pln~f)~.' ITemp'Cl Final tori 1980 1 equalling 0.187 mm for copper at 130 kHz.
I Hysteresis losses at i 2 0 i 1 . 2 ~ 1 0 ~ ~ ~ 2 . 7 ~ kw/m3j
1 130 kHz ( 0 tesla) 1 70 11.47~10'xB~-~~kW/maI
I I I I
I Hysteresis losses at 1 20 ( 199 kwlma i I 0.095T 1 70 1 84.5 kW/m3 1
I - -
I DC resistivity I I
1 20 1 45 0hm.m I
I j 70 1 16 0hm.m I
I I I I
1 A.C. resistivity 1 20 1 7 0hm.m I
I at 130 kHz 1 70 1 5 0hm.m I
I I I I I
I Eddy current losses 1 20 1 22.4 k w / m ~ I 1 a t 0 . 0 9 5 ~ 1 7 0 1 31.4 " I I I Total losses
I at 0.095 T
9. is the average length of the conductor=2.08 m, H is the height of the coil copper in the
notch = 30 mm,
p is the resistivity of the copper.
In order to maintain insulation up to 16 kV.
Isolawerke (Breitenbach), in accordance with our specifications (3) developed a sandwich type strip consisting of polyimide (50 microns Kapton H) and Samica pre-impregnated with Novalac resin, of a total thickness of 0.1 mn. 15 mm wide. The first samples with 1 mm of insulation withstood a voltage of 70 kV d.c.
The 1 mm insulation around the coil obtained by winding 6 turns of this strip around it with B half overlap and baking the assembly in the oven under pressure in a specially designed mould for 6 hours at 165 'C has a low Outgassing rate of ZXlO-*
torr.L.5-'cm-' after baking in vacuum at 150°C . The manufacturer insulated three coils which had been made at CERN; they were tested at the works st 25 kV/SO Hz after immersion in water for 24 hours
JOURNAL DE PHYSIQUE
and wrapping in aluminium, and subsequently at 30 kV d.c. at CERN.
Fig. 7. View of the single turn coil Table 5
Mechanical characteristics of the coil (mm) Overall length of coil 710
Average length of copper 2080
Dimensions of 6 tubes 4.95 X 4 . hole 0 2.8 brazed together
Cross-section of coil copper 30 X 4
HIGH-VOLTAGE FEED-THROUGH
This coaxial feed-through (fig. 8 and ref. 3) is designed to pass an average current of 1500 A at a peak voltage of + 16 kV max. The contacts of the h.v. plug.
both inside and outside the vacuum tank. were made using reinforced "multi-contact" rings. The internal (h.v.) and outside (earth) conductors are of gold plated copper. Their respective diameters are 40 and 85 m. The internal conductor is cooled by conduction and by compressed air, the external one by s small water circuit. The insulation between the two is provided by a special component of pure brazed alumina.
Fig. 8. Cross section of the coaxial high-voltage feedthrough foe I m ~ = 1500 A and 130 kHz (m.c. :multicontacts).
CAPACITOR BANK C,/CJ
The water-cooled-capacitors C3 have been mounted on copper plates in order to minimize the resistance of this part of the circuit. The complete capacitor bank, rectangular in shape, consists of four pairs of copper Rlates each capable of taking sixteen 5.5 nF capacitors of the "ceramic disc" type Draloric for 11 kV and tg6 L3 x
Two motor-driven, each ZnF, variable capacitors are fitted in the space made between the two pairs of plate's arranged in parallel. The connections between the capacitor bank and the h.v. feedthrough consist of sheet-copper plates with a circumference, of 300 mm. In view of the measured magnet inductance of 4.7 uH, 57 fixed capacitors C (3) and 2 variable capacitors of 2 nF were arran;ed in parallel to provide a total average capacitance of 319 nF for 130 kHz. The spiral cooling circuits on the earth side of capacitors C are connected in parallel and. the water flow rate of each of the four plates is monitored.
S U m R Y OF THE MAIN CHARACTERISTICS OF THE MAGNET AND ITS ELECTRICAL CIRCUIT
Magnetic and electrical characteristics
Maximum induction 0.095 T
Average relative permeability 2000 of the ferrite 3F1
Packing factor 0.85
Maximum current. peak 2116 A
Maximum current. RnS 1550 A
Magnet resistance calculated at 130 k ~ z 6.7 mR Calculated induction of magnet. D.C. 4.4 VH Peak voltage, connections included 8.22 kV
Reactive power 8.7 W A R
Losses at-130 kHz in the copper 15.0 kW in ferrite 3F1 1 25'C 12 kW in ferrite 3F1 1 70PC 7 kW in capacitors C3 2.6 kU in the connections
and contacts 7.5 kW
in the 800 m
of 50 ohms line 2.6 kW Total losses at 130 kHz
(with 9.5 kW in the ferrite)
Hvdraulic characteristics Flow rate Temp.rise
ce.s-l) c-c)
- Coil 0.37 9.7
- Yoke cooling plates for an
average loss of 9.5 kW 0.25 9.1 - Bank of 57 capacitors 0.13 4.8
FIRST TESTS
A maximum induction of + 0.062 T at 130 kHz with a peak current in the magnet of 1385 A at 5.5 kv has been obtained in an initial set of measurements in air and thereafter in vacuum. A corona effect was visible in air over a good half of the coil on the h.v. side.
Measurements in air were interrupted by the breakdown oE the first coil at the h.v. input bush in the yoke, and the measurements in vacuum were interrupted at about the same power stage by a failure in the power amplifier. S o far, the temperatures of the ferrites have been checked only using 37 - 110 'C self-adhesive temperature indicators arranged on the pole-faces of the magnet. During the last measurements at 0.062 T , no probe exceeded 37 'C either on their end ferrite blocks. with their reduced thickness of 8.5 m , or on the internal blocks.
AKMOWLEDGEMENTS
The authors are very much indebted to MM. A. Bonier, R. Bonvin, P. Cr@tin, M. Faure, 0. Gelard, M. Laffin, Miss M. Laurent, M. A. Rizzo, Mrs. Thomashausen for their help in designing, construction, mounting and reporting the prototype magnet.
References
1. A proposal for magnetic separators for pj; operation of the SPS.
Y.Baconnier 61 A.Warman - CERN-SPSIAOP178-19, Dec.78 2. Some remarks on a system of pE magnetic separators J. Dupin. K.H. Kissler, W.C. Midde1koop.A. Wsrman SPS-ABT-EX/KHK/111t.Note179-1. 23 July 1979 3. Technical Specifications:
- Ferrite blocks - CERN-SPSIABTIWCMIDS-156, 8/3/79
- RF Power Amplifier - SPS-ABT/AW/jf/D5-158, 20/3/79
- Capacitor Bank - SPS-ABTIAWID5-164. 14/6/79
- Isolation des bobines-SPS-ABT-EX/JD/D5-186.18/4/80 - Traversee 6tanche HT - SPS-ABT-EXIJD. 1/10/80
4 . - Progrm "WE'. .R.Perin and S.Van der Meer.CERN 67-7
- Program "KAGNET".Ch. Iselin, T600 - CERN Comp. Lib.
- Program "MAGNET-INDUC-LGO.' A. Hilaire, private communication.
