49 . . * I - . . s. .- * . 2N .: a 5. 1 * - 14 .. .. . ; 1:. .. ... IL .. . ! . . . =*: : ! . . . .., . .1 US1. PT. ". ... . VAL Selle : .. .. .. .1. - . 1 , 7 . . . . ir ... ..4 * : . * . . . 11 , . . 2. 3 ... ,' "! . ' A. it' . HELS . - 12 S . " ..tis. WE . . . . - . - ...! . . . ' t' ..' UNCLASSIFIED ORNL L . . 1.. . . . . . . * . '. 5.-1 .. . RE - . : . F. . . V ! EU- W . ' ! .. . . .. . . . . . 1 :.. ... . . . Yr ' P ut *** NA " Fr.'.. DAY IG ,': . . . ; . * ... i . 1137 ul . TAN . . : : . . T . . ! . ORNUP 1137 CONF-650306-55 A27 1985 LEGAL NOTICE Tudoru m Gement pour vorte Meteor the buttons Omotor, merret nga what the dominated : men har het onthou dat door in our the end IMPROVEMENTS IN here, who hriad * non haberle r , onde omsten dutened to the report may not hantering THE ORIC RF SYSTEM matwnty mund 1:Arnemu. Dobitna w roo m or hoe om rondly to the warm , er en god del ponte S. W. Mosko and N. F. Ziegler in in the waves permet a won a contento natoto wangu where of contentor who c o m a replege outrowe, with well that Oak Ridge National Laboratory weil er det en het ontstorheter har tendens to mom momen Moration par Mapleguen mirnet Oak Ridge, Tennessee w me out , or we complement met entretir. Summary . 4,. ' 1 The Oak Ridge Isochronous Cyclotron has been operating since January 1963, Initial expe- rience with the rf system was enlivened by destructive sparking and general instability at the upper end of the rf tuning range. A network of protective devices developed during the past two years almost eliminates spark damage and improves the stability of the system. A multi- stage rf voltage regulator was also developed and installed. i September of 1963. Initially, there was heavy sparking on the drive line; the feedthrough bushing !vacuum seal) was broken on several occasions. The bushing is approximately half- way between the PA plate and the drive capacitor. The sparking probably resulted from high rf voltage developed in the PA plate circuit whenever transient conditions in the resonator caused sufficient detuning to unload the PA. An early version of the transient con- trol network caused a momentary interruption of rf excitation whenever a lr 18 of dee voltage was detected. The addition of several other fault detectors has improved the network con- siderably and allows the use of the rf regulator. Introduction The Oak Ridge Isochronous Cyclotron is a fixed-frequency AVF niachine with variable particle and enurgy capability. The MOPA rf system is continuously tunable from 7.3 to 22, 1 Mc/8 and has a power output in excess of 300 kW. Incentive for installation of the rf level regulator came from expected improvement in accelerated beam quality and improvement of rf system stability. The latter was expected since the regulator would prevent sudden increases in dee voltage hat could lead to sparking. Transient Protection Circuitry .. The block diagram in Fig. 1 shows the amplifier chain with some of the automatic tuning devices, the rf level regulator, and the transient control network. The master signal generator uses a phase-locked oscillator and supplies a 3-V, 120-mW signal with frequency stability of 1 pp 106 to the amplifier chain. The first three amplifier stages are combined in a single unit known as the intermediate amplifier. The IA has automatic tuning and its output is regulated at 300 V rf peak, The transient protection systom is a group of fault detectors and limiters which, when triggered, reduce the rf excitation level through a reduction of bias voltage on the tran- sient control tube (V6401). A set of clamping circuits, triggered whenever V6401 grid bias is less negative than either V6402 or V6104 grid biae, locks the automatic tuning servos and holds the dee rf voltage regulators in an unsatu- rated condition. The 4CX 5000A driver amplifier (DA) sup- plies the 2 to 4 kW drive sigral required by the RCA 6949 power amplifier (PA). Both stag8are grid driven amplifiers with automatic tuning. The PA is coupled to the resonator through a "drive capacitor" and a short transmission line (less than 14) called the "drive line." There are seven limiters in the system; each is similar except in regard to the transient detector with which it is used. Each limiter is diode-coupled to the transient control tube grid circuit, (the transient control bus). Each of the coupling diodes is reverse-biased, except when the respective limiter drives the transient control bus more positive than its normal - 18 V bias level. The limiter circuit demanding the greatest reduction of rf excitation at any given instant controls the excitation level, ... The dee volta ge and thus the power output is controlled by modulating the grid bias of the DA. The bias voltage developed across the DA grid resistor is controlled by any one of three 6CA7 tubes in series with the bias supply. V6:04 (see Fig. 1) is the output stage of the rf regulator, V6401 is the transient control tube, and V6402 controls the bias when the rf regulator is off (manual operation). Normally, two of the control tubes are cut off. - .- - ..- History of Operation The PA plate rf limiter prevents the plate rf voltage from exceeding the dc voltage whenever, typically, a 1088 of PA load results from detuning of the resonator. Without the limiter, the voltage on the unloaded PA plate circuit swings high enough to initiate drive-line sparking. The PA plate rf level limiter circuit is shown in Fig. 2. The rf and dc voltage levels The rf system was put in operation in January 1963, but the rf level regulator and the transient control circuitry were not added until m. ptut tipini .. in 1 . !. "Research sponsored by the U. S. Atomic Energy Commission under contract with the Union Carbide Corporation. PATENT CLEARANCE OBTAINED: RELEASE TO IS APPROVED. PROCEDURES ARYAN EIBNI AGARVING SECTION. The limiter prevents the DA from drawing grid current and thereby developing self bias. This limitation is essential for stable operation of the rf regulator, are compared in differential amplifier Q31 and Q32. Normally Q32 is cut off. As long as the collector of Q is +12 V, Q34 is cut off and the output voltage of the limiter is -28 V. If the PA rf voltage becomes equal to or greater than the dc level, Q34 saturates and the transient control bus is grounded through the collector of Q34. The trigger circuit comprising Q35 and Q36 turns on indicator light I-31 whenever the collector of Q34 swings more positive than -8 V. The Regulator A voltage-tuned audio oscillator and loud speaker is connected to the transient control bus. The speaker, located in the control room, emits a rather unpleasant screech when a fault occurs. The cyclotron operator is thus "encouraged" to correct the fault, The rt regulator consists of a three-loop feedback system as shown in Fig. 1. The feed- back signals are proportional to DA plate rf voltage, the PA plate rf voltage, and the aee rf voltage. Errors are amplified and applied to the grid of the DA through the regulator contro? tube V6104, Design of the regulator was complicated by the fact that part of the loop is a carrier The 'air drive line spark detector" is a trigger circuit which completely cuts off the rf excitation when drive line sparking occurs, A pair of strategically placed photoelectric detec- tors are used to sense visible light resulting from rf sparking on the air side of the drive line feed-through bushing. The spark detector mini- mizes drive line damage when sparking does occur. tuned circuits, and by large non-linearities such as sparking in the dee system. The design is thus compromised by the requirement that the system remain stable over a wide range of operating conditions. The "vacuum drive line spark detector," also a trigger circuit, sense8 sparking conditions on the vacuum side of the drive line bushing. The detector is a high voltage electrode located in the vacuum system near the feedthrough bushing. Leakage current to ground through the ionized residual gas, resulting from sparking, triggers the limiter. The vacuum drive line spark detector also serves as a means to prevent operation of the rf system under poor vacuum conditions. The response of a tuned circuit operating at resonance, to a modulating signal of fre- quency v is 1/(1 + jvluc), where Vc = fc/2ac, and fc is the carrier or resonant frequency. Since the operating frequency of the cyclotron is variable over the range of 7. 3 to 22. 1 Mc/s, the transfer functions of the rf amplifiers for modulating signals also vary over wide ranges, As an example, it is estimated that V. for the resonator varies over a ten-to-ong range. The transfer functions of the regulator amplifiers have been restricted to provide stability over the complete frequency range, Circuit diagrams of the regulator ampli- fiers are shown in Fig. 3. The approximate transfer functions with the modulating frequency v in kc/s are: The PA high voltage interlock is a trigger circuit which prevents operation of the rf system in the absence of PA plate dc voltage. The cir- cuit is used mainly for protection of the PA tube. The trigger cuto the ri drive off whenever the crowbar fires, and it helps prevent excessive PA grid dissipation, which might occur if the PA plate voltage was accidentally lost. (1 + jv/0.06)(1 + ju/0.75) G,975 (1 + ju/0.01)411 + jv/500) (1 + iv/6): 1 Gz ~ 75 71 + ju70.08)ť + 30/500) The PA plate current limiter holds back the rf excitation sufficiently to keep the PA plate current below the maximum allowable level. This prevents unnecessary firing of the crowbar and operation of the HV circuit breakers. G3 ~ (T + jV/0.2121°+ 307300) The PÅ grid current limiter holds the grid current below the maximum rated value for the tube. Both the PA plate and the PA grid current limiters help protect the PA tube from damage which could occur if the PA plate circuit were inadvertently detuned. These limiters are also particularly useful in their ability to prevent the rf regulator from overdriving the PA, A circuit diagram of a typical rf detector, or de-modulator, is shown in Fig. 4. The de. tectors are located in the cyclotron yault while the regulator amplifiers are remotoly located some 100 feet away. This particular detector circuit has a fairly low output Impedance so that the regulator responso is not seriously affected by the long signal cables, The detec- tors normally operate with a dc grid bias such that the tube conducts only on the positive rf peake. : The DA grid bias limiter coinpares the DA grid bias level to the peak rf drive voltage, Each regulator is equipped with a clamp triode on its input circuit. These clampa, as previously mentioned, hold the regulator ampli- fiers in a condition corresponding to minimum dee rf voltage. The clamp signals decay slowly so that the regulator regains control without pro- ducing serious overshoot in rf excitation. Another function of the clamp circuits is to hold the regulator amplifiers in a condition corre- sponding to maximum dee volta ge when the rf excitation is manually controlled (unregulated). This protects the detectors from being over- driven and keeps the regulator loop unsaturated so that it is possible to switch from regulated to unregulated operation, or vice versa, without interrupting the rf excitation. The regulator reduces rapid variacions in dee voltage to about 0.3% and hoids the average value to about 0, 1% over short periods (several minutes). Control of slow variations is limited primarily by drift in the dee-tip voltage divider aid deiector, When the rf excitation is operated unrogulated, the dee rf voltage is modulated some 20% to 30% by mechanical vibration in the resonator and by the ripple in the PA plate do power supply. Conclusion Following the installation of the regulator and the transient protection network, the ORIC rf system has proved to be quite reliable. Damage to equipment by rf sparking is now quite rare. The regulator, originally considered a useful accessory, is now considered essential to cyclotron operation. In fact, it is very difficult to produce an external ion beam without the help of the rf regulator, An example of the effect of the regulator on beam quality is shown in Fig. 5. The curves show beam attenuation in the last few orbits before deflection and after the beam is deflectec. The lower curve was made without the regulator while the upper curve was made with the regu- lator, Orbit bunching due to radial oscillation of the beam is observable only when the rf regulator is in operation. References 1. R. J. Jones, et al, Nucl. Instr, and Meth. 18, 19 (1962). . S. W. Mosko, et al, International Confer. ence on Sector-Focused Cyclotrons, CERN 63-19 (1963). ORNL-DWG 68-1777 CROWBAR ** CROWBAR AUTO TUNING SERVO AUTO TVAINO SERVO QRIVE UNE AUTO TUNING SERVO DA 4CX5000A MASTER SIGNAL GENERATOR AUTO FEED- THROUGH BUSHINO INTERMEDIATE 300v RF AMPLIFIER TUNINO SINO DETECTOR 800 OC POWER SUPPLY 6CAT V6401) 6CATI V6104 OCATI DETECTOR SH RF LEHSL REGULATOR LOOP DETECTOR CLAMP CLAMP CLAMP CLAMP CONTROL PA HV INTERLOCK REFERENCE ☆ DA GRID BIAS LIMITER TRANSIENT CONTROL LOOP AUDIO ALARM PA PLATE CURRENT LIMITER * ☆ PA GRID CURRENT LIMITER * PA PLATE RF LIMITER - 20v * AIR DRIVE LINE SPARK DETECTOR MANUAL LEVEL CONTROL REFERENCE VAC DRIVE LINE SPARK DETECTOR Fig. 1. Block diagram of ORIC rf system. ORNL-DWG 65-1776 r +12 v . T . :: 4.5k $ $1.5K 9.1 k : :.. 62 k . TRANSIENT CONTROL BUS ..' , 0.015 '' CR32 IN457 '.- * 5. k .. -- FEN P.A. PLATE D.C. LEVEL 5.1k Av D.C./5 kvm D.C. . GROUND .: :.-'. 3100 § . LCR34 16.5 . . 34 10kB 3.9 kB ... . .. .4 NE $2.4k 36.2 | 0.001 - - P.A. PLATE RF LEVEL Av O.C./5 kv RF PEAK 36.8 K $ 150 K 5.4 ks - 12 v CR34 4N295 910 .8.2 - 28 v Fig. 2. PA Plate rf lovel limitor. ORNL-DWG 65-4773 + 150 v -12 v 0.1 42 K$ $10k $12K 30 k, 4w V2 6BQ71 * NE-2 NE-2 820 26807 Q3 Q41 Qgod 221 5.9 kg -0.0015 54 K 100 K R2 +12v C2 25 * C 3 M, 100 k, $ 100 k, ca 12 12k 12W 2 wş ş i n the home theater 750 K -300 v 100 K PHIL BRICK :P2 1 Lam -12v OK Fig. 3(A). Amplifier G, al. I ûz. ORNL-DWG 65-1779 . . + 300V +75 v DA GRID BIAS 3 15K . 800 v POWER 820 pf 4.7MB 330 pf SUPPLY 0.2 MB 30.2M 47 pt 315* 86485 +0.01 NE-2 64855 15965 SNE-2 SIOM 45965 6CAT 16 3M 3063 5k 300K -300v IN457 PHILBRICK K2-P IN457 Sik BIOK : : 12 V. Fig. 3/8). Amplifier Gz. ORNL-DWG 65-1772 + 75 v 0.04 22 RF att -- 5703 INPUT 0.004 $10K 0.004 REGULATOR INPUT 3 40K DC REFERENCE VOLTAGE - 12 v Fig. 4. Typical of detector. ORNL-DWG 65-1774 J C INTERNAL DEFLECTED BEAM BEAM TREGULATOR ON RELATIVE BEAM INTENSITY REGULATOR OFF . .. . . . 29 33 . 31 ORBIT RADIUS (in) Fig. 5. Effect of regulator on beam quality. .. ri .: . 7 . . .. . .. . - . : > TE : ". 22 3. - " - : : Tk . 1 . 7 ! M ' " 1 T YA ca 1 DATE FILMED 16 / 21 /65 12. 9 A i . * .. fet . ' 1. 11 LEGAL NOTICE - This report was prepared as an account of Government sponsored work. Neither the United States, nor the Commission, nor any person acting on behalf of the Commission: A. Makes any warranty or representation, expressed or implied, with respect to the accu- racy, completeness, or 18efulness of the information containod in this report, or that the use of any information, apparatus, method, or process disclosed in this report may not Infringe privately owned rights; or B. Assumos any liabilities with respect to the use of, or for damages resulting from the use of any information, apparatus, method, or process disclosed in this report. As used in the above, "person acting on behalf of the Commission" includes any em- ployee or contractor of the Commission, or a niployee of such contractor, to the extent that such employee or contractor of the Commission, or employee of such contractor prepares, disseminates, or provides accost to, any information pursuant to his employment or contract with the Commission, or his employment with such contractor. ma INS . -- Ti . . " L PA . . IYOT Nissa - END w ord ." . . * A UR .. 9.12 A 2 S . I .11 SP 3 CI E 127 * ! . 3 . . P . : . 1.