http://accelconf.web.cern.ch/AccelConf/c81/papers/ep-10.pdfInternational audienc

Ducoudret, B.

Joubert, A.

Labussiere, F.

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GANIL RF SYSTEMS FEEDBACK CONTROL SYSTEMS AND ELECTRONICS B. DUCOUDRET, A. JOUBERT, F. LABUSSIERE. GANIL (G~and Accele~ateu~ National d'Ions Lou~ds) BP 5027 14021 CAEN Cedex Tel(31) 94 81 11 Telex : 170533 F. Abstract.- The philosophy, technology and results concerning the tuning, the amplitude, the phase regula-tion and control including beam phase correction for all resonators are described. A CAMAC microprocessor unit is used to automatically start and survey the RF voltage of each independant RF resonator. All this devices are finally controlled by the main computer. Experimental results on the injector cyclotron are given. 1. Servo tuning system.-1.1. Trimmer The fine tuning adjustment is obtained by a ± 20° rota-ting loop working in the short circuit region of the resonator l . This loop moved by a fast DC motor is water cooled for RF power losses up to 1 kW in the worst con-ditions. As shown on fig. 1 the phase error signal is the phase difference between grid and plate RF voltage of the po-wer amplifier final stage through two balanced coaxial cables and two broadband quadrature hybrids. GRID Rf VOLTAGE o· PfllSnr IF DC LOOP PHASE NETWORK POWER OTOR ~ SO· COMP I AMlt AMPl. R£SDHPTOR Fig. 1 Main servo tuning system. Working Frequency MHz 6 14 Relative frequency deviation for ± 20° - ± 310- 4 ± 510- 4 loop rotation Corresponding fre-quency deviation kHz ± 2 ± 7 Frequency Hz 2 resolution RF degree 0,1 Settling time for 40Hz disturbance ms 32 40 Open loop gain at 1 Hz - 50 Small signal unity gain bandwidth Hz 20 Movable panel : me-chanical resolution m 10-6 Electrical resolution RF degree 3,5 0,6 Table 1 .2. g~~~~~~_~~~i~~_~f_~~~~~l~_E~~~l The movable panel actuator is driven by a stepping mo-tor and a hydraulic piston. Since the trimmer frequen-cy deviation is small, the movable panel action can be triggered if necessary by an extreme angle position of the rotating loop. (Fig.2) Table 1 gives the main cha-racteristics. DC ~'T/III JI: COMPARATOR ::rr- WITH HTSTfRf51S CLOCK L-----<--' '-'-----'DRIVER o CLOCK ADJUST. 5T£PP/116 MOTOR Fig. 2 : Complementary servo loop. fCHAHICAl ACTUATOR MOVABlE PRNEL 2. Amplitude regulation system.- This is a classical analog device L using high quality components 3 in order to have a relative dee voltage stability better than 10- 4 • An automatic gain control system keeps the open loop gain constant over more than 20 dB dee voltage variation. Another additionnal servo loop working via a microprocessor keeps the RF amplier gain nearly cons-tant whatever is the RF frequency and the RF power. (Fig.3) See table 2 for main characteristics. Amplitude regulation system. ID Rf PMR AMPl.lF1fR Proceedings of the 9th International Conference on Cyclotrons and their ApplicationsSeptember 1981, Caen, France407Open loop gain at 300 Hz 600 Hz Small signal unity gain bandwidth Amplitude range (after detection) Spectral purity: (amplitude noise only) : Residual AM for 50Hz and harmonics Regulation accuracy Absolute thermal drift (including dee voltage probe,diode detector and offset voltage drift) Reference voltage generator stability Table 2 dB dB kHz V dB -VrC V/day 57 51 12 I to 9 < 90 dB below the carrier <±5 10-s IO- s 2,510- S Performances have been tested with spectrum analysis technique. Fig.4 g ives the amplitude regulation accu-racy and the open loop gain. This analysis was done on injector cyclotron dee voltage after detection. :r: l-e. ) a z « '" " :r: ~ '" -0-- --_._-~------10-·p"ipple level ~ -- - ~ '1 "0 .10 20 10 kH. r. /270ti1distu,.b. ~ ..-OP[N lOOP 1 I U 1\/1",1 1\ V \ IV V W\ "" A VrI\ ClO:;f.D '-.I'0vAJ\ 10n 200 300 "DO Hz Fig. 4 : Amplitude noise spectrum analysis. 2 • b 8 1 00 3. Computer control.- Each RF resonator including RF power amplifier and electronics is directly controlled by a local CAMAC microprocessor 4 working with a program mabie controller for interlocking problems (Fig.5)This system has been designed to have three working mode possibilities : a) ~~£~~~£_~£~~_~~ig_~£~E~~~E_~g~_!£~~!_~~~f_~i~E£EE£-cessor A RF specialist is required to start and survey manual-ly the resonator. The programmable controller must be operational in any case to respect several safety and interlocking conditions. b) ~i~~£~~_~~~_~~ig_~£~E~~~E A non RF specialist operator can switch on in local mo-de the concerned resonator. All the starting steps and surveying are automatic. SRFETr } (OKOITIOKS Philosophy of the computer control. c) !~~_~~~!~_~~~ig_i~_f~!!Y_£E~E~~i£g~! This is the normal mode of operation from the main control room . 4. Phase regulation system 4.1. ~~~~_E~g~!~~i£g_~y~~~~ (one per resonator) Even with a good amplitude regulation the RF resonator voltage has much phase noise (Fig.6). A fast servosys-ternS has been designed to reduce the phase noise level to less than .05 0 phase deviation. This device needs a very pure phase reference signal. Our pilot synthe-sizer has a signal to noise ratio greater than 100dB at 200 Hz of the carrier. The long term phase stabili-ty and the absolute value of the RF phase cannot be obtained with this phase lock system only. This last role lS devoted to the slow system. 0 0 3 .6 0 1. ClOSED LOOP OPrH lOOP O. 0 0 I1('Lu. O. 0 V 1f!r.J., ,.I O . 1.11 ", , ~ 'VI.I II . = 6 ..&~l' .~LJ.._,,~ 'l~ ?Ill . 11''''' ..,.' """1' I"'" -1000 HI 600 600 400 200 ZOO 4(10 600 &CIO + lOOOHI Fig. 6 : phase noise spectrum analysis. (The amplitude regulation is on) As shows Fig. 7 the fast loop is made with two impor-tant components designed at GANIL : a) the phase comparator is made of an analog multiplier Saturated mode provides constant transmittance over a range greater than 20 dB RF amplitude variation. b) the phase modulator using vector addition technique ................... combined with output regulation level gives an ampli-tude rejection better than 55 dB. The main loop characteristics are summarized on table3. Fig. 7 : Principle of fast phase loop system. TO RF PWR RMP!. The setting of the phase closed loop in case of fre-quency change is entirely done with a single CAMAC microprocessor. The phase reference can be added to the back beam pha-se signa1 6 (by mean of a special input) to lock the RF phase to the beam phase itself. The bandwidth of this complementary servo system is around 1 kHz.(Fig.8) Proceedings of the 9th International Conference on Cyclotrons and their ApplicationsSeptember 1981, Caen, France408Open loop gain at 300 Hz dB 40 600 Hz dB 34 Small signal unity gain bandwidth kHz 12 Spectral purity : (phase noise only) dB < 80 dB Residual PM for 50 Hz below the and harmonics carrier Table 3 Fig. 8 : Beam correction system. 4.2. ~~~~~_~~i~~~~~~~_~r~~~~_~~~~~~~_~r~~~~E~~~ -Slow stabilisation. The principle of operation is shown on Fig. 9. The phase setting system operates with two kinds of phase shifters : a) stepping phase shifter. This type of phase shifter is made of stepping delay lines which are CAMAC controlled and programmed. The elementary delay is 0.66 ns and the total delay is 160 ns per unit corresponding to more than 360 0 phase rotation at 6.4 MHz. b) continuously variable phase shifter. This second type made of a length variable line (micro-strip) actuated by a slow AC motor has a maximum de-lay of 1 ns and provides the phase interpolation wi-thin only one step delay of the previous delayline. 6 WAYS SPLITTER PILOT I-----==:t: ... YNTHESllfR IWN CO/t1PUTER [ONTROL CAHAC MICROPROCESSOR SAMPLING [OAXIAL RfLAYS REF HAS[ H£Tj!~:-;:-::-I TO FAST PHnSE LOOP (rig. 7) j RF PROBE FROM THE 6 RESONATORS () BAiJJifii COAXIAL LINES Fig. 9 General phase adjustment system. The injector cyclotron dee voltage is the phase refe-rence for all others RF systems. The phase difference is directly read from the concerned resonator by a sampling phase meter (Hewlett Packard Vector - Volt-meter). Its analog phase information is sent to a CA-MAC microprocessor. After on-line calculations the chosen phase value is indexed to the corresponding stepping phase shifter through the CAMAC SUS. Then the phase value is periodically corrected as a function of the slow phase drift. Of course the phase values are adjustable from the main control room. This system can moreover receive slow corrections co-ming from the beam phase measuring system. References. 1. B. DUCOUDRET, A. JOUBERT; Etude du systeme d'ac-cord rap ide asservi pour l'injecteur II ; GANIL 79N/ 004/HF /01. B. DUCOUDRET ; Systemes d'accord rapides asservis des CSS et de II : Optimisation sur base d'essais ; GANIL 79N/149/HF/28. 2. B. DUCOUDRET, A. JOUBERT, G. SCHMIECHEN ; Stabili-sation de l'amplitude HF des resonateurs CSS GANIL 80R/068/HF /10. 3. A. JOUBERT, M. TRIPON; Diviseurs capacitifs pour l'amplificateur 100 kW et pour les resonateurs ; GANIL 79N/111 /HF /21. 4. B. PI~UET, Programme JCAM de demarrage et de ges-tion des cavites HF. GANIL 81/023/CC/02. 5. A. JOUBERT, J.C. LABICHE, Stabilisation de la phase HF des resonateurs CSS. GANIL 79R/34/HF/09. 6. F. LOYER, Diagnostic de phase centrale a sonde ca-pacitive. GANIL 79R/168/CC22. Proceedings of the 9th International Conference on Cyclotrons and their ApplicationsSeptember 1981, Caen, France409

GANIL RF systems : feedback control system and electronics

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