This paper describes a high-voltage, high-current power supply for the injector synchrotron dipole magnets at APS. In order to reset the dipole magnets in each cycle two different current waveforms are suggested. The first current waveform consists of three sections, namely: dc-reset, linear ramp, and recovery sections where injection is done ``on the fly``. The second current waveform consists of six different sections, dc-reset, transition to injection level, injection flat level, parabolic, linear ramp and recovery sections. The effect of such waveforms on the beam is discussed and the power supply limitations to follow such waveforms are given. The power supply limitations are due to the power components and control loops. The reference for the current loop is generated by a DAC which is discussed

Despe, O. D.

Fathizadeh, M.

McGhee, D. G.

Mills, F. E.

Turner, L. R.

UNT Digital Library

A High-Current, High-Voltage Power Supply with Special Output CurrentWavefonn for APS Injector Synchrotron Dipole Magnets4The submitted manus_:riDt has been authored ' • 'b_a contr_to,o,theu.s. Go..... en, ANL/CP--73788u.de,cootractNo.W_,-,O_ENO-38.M. Fathizadeh,O.D. Despe, D.G. McGhee, F.E.Mills,L. R. TurnerAccordingly, the U. S. Government retains anonexc,us_ve,roya, y,_,ceriseto_b,sh Argonne National Laboratory, APS DE92 004132or reproduce the published form of thiscontribution, or allow others to do so. for 9700 S. Cass Avenue, Argonne, IL 60439U. S. Government purposes.Abstract II. WAVEFORM REQUIREMENT• .This paper describes a high-voltage, high-current power The field in the injector synchrotron magnet must rise 2supply for the injector synchrotron dipole magnets at APS. from 0.045 T (450 MeV) to 0.7 T (at 7 GeV) within 250 ms.In order to reset the dipole magnets in each cycle two If the rate of change of the field remains constant, then afterdifferent current waveforms are suggested. The first current a short initial time, the induced eddy current in the 1-mmwaveform consists of three sections, namely: dc-reset, linear thick stainless steel vacuum chamber will be constant.ramp, and recovery sections where injection is done "on the However, because of the shape of the of the vacuumfly". The second current waveform consists of six different chamber, the field produced due to the eddy currents, hassections, dc-reset, transition to injection level, injection flat sextupole and 10-pole components as well as thelevel, parabolic, linear ramp and recovery sections. The predominant dipole component. At the full field, (7.0GEV,effect of such waveforms on the beam is discussed and the 0.7 T), the sextupole component from the eddy currentpower supply limitations to follow such waveforms are constitutes a negligible fraction of the total dipole field, butgiven. The power supply limitations are due to the power at the injection level (450 MeV, 0.045 T) it can lead to ancomponents and control loops. The reference for the current unacceptable tune shift in the synchrotron. Theloop is generated by a DAC which is discussed, inhomogeneous eddy-current field is predicted to be:I. INTRODUCTION B = - 0.09 r 2 + 20 r 4 (1)The injector synchrotron of the Advanced Photon Source where, r is the radius in meters and B is in teslas. At aconsists (APS) of 68 dipole magnets connected in series, reference radius of 0.025 m, the sextupole componentTwo identical 12-phase power supplies are used to energize predominates. At the full field (0.7 T) the sextupole to thethe chain of 68 magnets from two feed points 180° apart. To dipole components ratio is acceptable, but at the injectionmonitor the current in the magnets only one transductor is level (0.045 T) this ratio is relatively large. If the field risesused. Two control loops are utilized to regulate the current quadratically with time from 0.045 T at time zero to a levelin the magnets. Fast correction for the line transients is with slope equal to the slope of the linear _amp of 4 Mms,provided by a fast-response voltage loop controlled by a then the field will be 0.09 T at time 33.5 ms. This will behigh-gain, slow-response current loop. The regulator card followed immediately by a linear ramp to 0.7 T at time 250controls the fitting pulses for two sets of identical 12-phase ms. The ratio of the sextupole to dipole components wouldwye group power supplies. These pulses are transmitted to start at zero, gradually increase to a maximum at 33.5 ms,the second power supply via optical links, and then decrease during the linear ramp. If the field risesThe injector synchrotron boosts the positron beam energy quadratically all the way to 0.7 T, then the maximum ratio offrom 450 MeV to 7.0 GeV. It has a circumference of 368 m the sextupole to dipole will be twice that seen in the case of(one third of the storage ring) and operates at a repetition rate the linear ramp.of 2 Hz. The magnetic field must change from a certain low Two different waveforms are considered and are shownvalue to a certain high value. Several waveforms can be in Figures 1 and 2 respectively. In the Figure 1 the currentused to accommodate this change of magnetic field, waveform consists of a dc-reset value of 30 A, a rampCommon waveforms used are ramp, sinusoidal, parabolic or section and a recovery section. The injection is done "on thea combinatior, of these. However, quick changes of the fly". In Figure 2, the current changes from a 30 A dc-resetmagnetic field can cause large eddy currents resulting in the value to a 60 A injection level via a ramp section. Atdisruption ot the beam and consequent loss of control, injection, a parabolic section starts until its slope equals 4Therefore, the magnetic field must change gradually from Mms where the current continues on a linear ramp to the450 MeV to 7.0 GeV within 250 ms. extraction level of 1044 A, followed by the recovery section.The total resistance of the magnets is R = 594 ml2, the total1 Work supported by U.S. Department of Energy, Office of Basic Energy inductance of the magnets L = 261 mH and the power supplySciences under Contract No. W-31-109-ENG-38. rating is calculated by the following equation with 10% cabledrop allowance:_ ';J.' .... ,. ,=,,,-rL_UNLIMITED_':........ ' _"_ _ DISTRIBUTION OF THIS DUL, U,V,,--.... L-1di Based on a recent calculation [2], the horizontalV = I.._[ + Ri (2) chromaticity due to the eddy currents is +8 units with thenatural chromaticity of-15 units. The vertical chromaticityThus the power supply is rated 1100 A and 1900 V. The due to the eddy currents is -8 units with the naturalmaximum deliverable current per millisecond of the power chromaticity of-12 units. Both in the horizontal and verticalsupply at the extraction level is only 4 A/ms. Thus, almost 8 motions, the higher momentums of the eddy currents willms is needed to change from 30 A to 60 A level. As shown, contribute to a tune shift of 10E-3 at 1% of the momentum,in Figure 2 the current starts out quadratically (section 1), which is considerably larger than the expected momentum.followed by a linear ramp (section 2) up to the extraction Therefore, a simple current waveform with the "injection onlevel 250 ms later. Section 3 starts the recovery phase where the fly" as shown in Figure 3 can be used.the current ramps down to the reset level at about 8 A/ms.This increased rate will leave enough time for the reset _,j_ion Exu-,_tJon t_jcaionperiod and the transition time to the injection level before thestart of the next cycle without exceeding the dynamic ZSOms_ 2_m,_capability of the magnet current regulator. About 115 ms areavailable to share between sections 4 and 6 in any desiredratio.injection Extn_on Injection250n-n_ "-""----- 250ms ,3---..... i___el .... TLME,,2....._ _j___o_-_vl--___ _._ 1R* tt_vol__ l?_2 _ _ , Figure 3 Selected Current Reference for InjectorSynchrotroniii.DIGITAL TO ANALOG CONVERTERREFERENCETLMEThe basic analog reference block (ARE) used by almostFigure 1 Power Supply Current Output "Injection on the fly"ali the power supplies in the APS project is shown in Figure4.Injection Extraction /njtx:tJon250 m__------_ _ 250 ms_, Up Count Analog CounReset CIR _ DACFigure 4 Analog Reference Block, / I1 17Z'-2 " I : It is seen that the analog output is generated by a digital/. ____ __te,,__- _1- to analog converter (DAC) fed from the output of an UP/DNR,._tt_,,__[_ counter. Therefore, the analog output can only be changedby counting up or down input pulses. This configuration wasrtME chosen to provide a reference block with the following highlydesirable features: 1) soft/smooth changes of referenceFigure 2 Power Supply Current Output with 60 A Injection voltage, since counter output can only change by countingLevel. pulse inputs, 2) high noise rejection due to the integrationeffect of the counting process, and 3) a small number ofUse of quadratic wave,_orm can produce a smaller but cables between the counter and the remote power supplyvariable sextupole component which may require a which simplifies the use of optical coupling, furthercomplicated correction if its effect still is not negligible. A reducing interference during signal transmission.linear ramp will produce a higher but constant value of thesextupole component which is simpler to compensate.A. Reference DAC Specifications vacuum chamber eddy currents induced when accelerationoccurs. The advantage of the first method is the simplerThe DAC used in the reference supply is an Analog Device waveform required to generate the accelerating field. ExceptADl 145A with the following specifications: for the field states at injection (resting dc field for the firstmethod versus dynamic ramping field for injection on theResolution 16 bits fly) and the short time for transilion from reset level to dcDifferential & Integral Nonlinearity 1 LSB resting level of the second method, the waveform for the restStability (Long Term, ppm FSR/1000 hrs) 0.2 of the synchrotron cycle is the same for both methods.(total drift, 0-50 deg C) 1 LSB Results of later calculations [2] have shown that theSettling time (1/2 LSB, 10 V step) 6 Its effects of the eddy currents in beam injection are not as badas earlier feared. Therefore, the simpler method ofB. Waveform Generation for Injector Synchrotron "injection on the fly" is the strategy that will be used.C. SEGMENTS OF WAVEFORMThe generation of the voltage reference waveform usedby the synchrotron dipole magnet current regulator is basedon the arbitrary function generator (AFG) design used for the Segment 1 - Linear Ramp: This segment starts about 40injector synchrotron correction magnets [3]. As described ms before the injection pulse from the .nominal reset level ofearlier, the synchrotron cycle is divided into two main phases 30 A, rising at an average rate of 4 A/ms until extractionof injection/acceleration and extraction/recovery. These time, 250 ms after injection. Injection is about 60 A.phases are further divided into sub-segments as illustrated in Segment 2 - Main Recovery: After beam extraction, theFigure 3. field is taken down to the value referred to as the reset levelThe AFG uses 2K x 9 first-in-first-out (FIFO) memory to (about 30 A). The average rate of field decrease is aboutstore parameters of the desired function. The function is twice the acceleration rate in order to leave time for the otherrepresented by a series of points P (time, pulse ENable) at segments in the recovery phase.each pulse of the scan clock. The other parameter associated Segment 3 - Return Reset: The UP/DN counter of thewith each clock tick is the direction information DIP,. Hence ARB is quickly reset to zero to provide a known absoluteonly 2 bits are required to encode the value of the function at value of reference for the DAC and the counter. Error ineach clock time regardless of the DAC resolution. These two pulse count from any source is therefore removed everypieces of information are initially calculated in the power cycle. "l'he counter is then quickly pulsed to the reset levelsupply control unit (PSCU) that services the injector count. Since these pulses are high frequency and the count issynchrotron dipole power supply, and then loaded into FIFO. small, the magnet current regulator essentially does not haveThe Pulse ENable (PEN) status and DIR stored in the sufficient time to react to the momentary change before theFIFO are scanned out in synchronism with the iitjection reference voltage is back at the reset level.pulse. These data control the gating and routing of each Segment 4 - Reset Dwell This is a time interval wherepulse to the UP/I3N counter. In this manner the particular the field is held at a steady value, the reset level. This levelwaveform for the acceleration of the beam and recovery of is adjustable to enable the operator to optimize the field.the injector synchrotron dipole magnet is generated. This process helps to produce stable and repeatable fieldThe ARB and AFG utilize programmable logic devices patterns.(PLD) to reduce count and wiring complexity in thehardware. This is expected to improve the reliability of the IV. CONCLUSIONsubsystems. Flexibility in updating :he waveform for theacceleration phase is built into AFG. The update process The effect of the vacuum chamber eddy currents on theitself is transparent to but in sync with the synchrotron cycle, dipole field was discussed and it was noticed that theAs mentioned earlier, two injection strategies are being sextupole field is the dominant undesirable component.considered for use: 1) injection "on the fly" at the initial Several alternatives to correct the sextupole effect werelinear ramp following a parabolic field rise starting at a dc examined, lt was concluded that using a quadraticreset level of about 30 A; 2) injection from a resting dc-level waveform can produce a smaller but varying sextupoleinto a quadratically rising field for the initial portion of the components which may require a complicated correction ifacceleration phase followed by a linear ramp to full energy at its effect still is not negligible. However, a linear ramp willextraction. Extraction occurs at the same energy level in produce a higher but constant value of the sextupoleboth cases. In the second method the sum of the dwell times component which can be corrected in simpler fashion. Thus,at the reset level, and the injection level plus the transition the "injection on the fly" method using a linear ramp thattime between them, approximately equals the reset level starts from an adjustable reset level and ramps to thedwell time in the first method. The advantage of the second extraction level was selected.method is its essentially zero value of the undesirable fieldcomponents at injection time. This field is due to theV. REFERENCES[1] M. Fathizadeh, "Design and Simulation of HighAccuracy Power Supolies for Injector SynchrotronDipole Magnets," Presented in Particle AcceleratorConference, San Francisco, CA 1991.[2] F.E. Mills, Private Discussion.[3] O.D. Despe, "Arbitrary Function Generator for APSInjector Synchrotron Correction Magnets," Presented inParticle Accelerator Conference, San Francisco, CA1991DISCLAIMERThis report was prepared as an account of work sponsored by an agency of the United StatesGovernment. Neither the United States Government nor any agency thereof, nor any of theiremployees, makes any warranty, express or implied, or assumes any legal liability or responsi-bility for the accuracy, completeness, or usefulness of any information, apparatus, product, orprocess disclosed, or represents that its use would not infringe privately owned rights. Refer-ence herein to any specific commercial product, process, or service by trade name, trademark,manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recom-mendation, or favoring by the United States Government or any agency thereof. The viewsand opinions of authors expressed herein do not necessarily state or reflect those of theUnited States Government or any agency thereof.

A high-current, high-voltage power supply with special output current waveform for APS injector synchrotron dipole magnets

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A high-current, high-voltage power supply with special output current waveform for APS injector synchrotron dipole magnets

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