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• W801787270 abstract "SLAC- PUB-4906 LB1--26809 March 1989 (A) TIMING AND RF SYNCHRONIZATION FOR FILLING PEP/SPEAR WITH THE SLC DAMPING RINGS' M . T. RONAN, D. J. LAMBERT AND K. L. LEE Lawrence Berkeley Laboratory, BerkeJey, California 94720 and D. R. BERNSTEIN, P. CORREDOURA, R. K. JOBE, M . C. Ross, B. RoSTER, J. VANCRAEYNEST AND G. Stanford Linear Accelerator Center, Stanford University, Stanford, California 94309 ZAPALAC ABSTRACT An innovative timing and RF synchronization system has been built and commissioned which allows the direct injection of 1 nun U z e+ or e- bunches from the SLC Damping Rings (VRF = 714 MHz) into the storage rings PEP (VRF = 353 MHz) and SPEAR (VRF = 358 MHz). The required relalive stabil- ity of these oscillators is 10- 9 since the beams may be stored in each damping ring (DR) for up to 0.2 sec during which no timing correction is made, and must be delivered within a. 0.5 osee window. This stability has been obtained by phase- locking the storage ring RF to the LINAC- DR master oscilla- tor. In order to obtain bunched beams for acceleration in the LINAC 10.5 em RF structure while maintaining the storage ring timing requirements, the Subharmonic Buncher and Damping Ring RF are phase-shifted using GaAs digital circuitry. This paper describes (I) the phase-locked loops, (2) tbe RF distri- bution system, (3) the S-band resettable dividers and (4) the interpulse timing system components used in this project. 1. INTRODUCTION Recently, the PEP and SPEAR e+ e- storage rings at the Stanford Linear Accelerator Center have been operated again for High-Energy Physics. With the upgrade of the linac for operation of the SLC having been completed, the new acceler- ator systems including an Electron Gun with a Subharmonic Buncher, an olf-axis high-yield Positron Source as well as elec- tron and positron Damping Rlngs, are now being used to fill the storage rings. Using the high intensity beams from the Elec- tron Gun and Positron Source and the low emittances obtained using the Damping Rings in conjuction with the Subharmonic Buncher which compresses the electron pulse from the gun to fill only one linac RF hucket, the storage rings were being filled efficiently in minutes. Several improvements to the linac timing and control systems, which were needed in order to allow the new accelerator systems to be controlled hy the storage rings and to synchronize the storaqe ring filling operation with the SLC damping rings, are descnbed in this paper. 2. SLAC TIMING SYSTEM Programmable Delay Units 2 (PDU's) use the 119 MHz signal to generate precisio~ trigger signals in delay increments of 8.4 nsee for up to several Interlaced beams. The PEP and SPEAR storage rings operate at RF frequen- cies of 353.210 MHz and 358.540 MHz, respectively. Unfor- tunately, these frequencies are not harmonics of the linac RF frequency, 476 MHz, so that the storage rings are not simply locked to the linac Master Oscillator. During storage ring fill- ing in the past, the linac fiducial pulse was derived from the timing of the particular storage ring RF bucket to be filled. The PEP and SPEAR timing systems provide a 1.7-msec-long burst of pulses, synchronized to the revolution of the particular bucket being filled, at frequenc ies corresponding to the revolu- tion frequencies of 136 KHz and 1.28 MHz, respectively. These . . . . 10 MHz bandwidth signals are transmitted upstream on the MDL to the Iinac injector where the first pulse within a power line zero-crossing gate generates a fiducial pulse which triggers the linac timing system and selects the preferred storage ring turn . Just prior to beam time, a pattern reference pulse is sent by the storage ring timing system to the injector where it is used to determine the actual timing of the gun trigger. Electrons and positrons from an in-line positron source were simply timed. to the storage ring pattern reference pulse and delivered within the selected 2.8 nsee RF bucket window; how- ever, each 1-2 nsec thermionic gun pulse would fill severallinac 2.856 GHz RF buckets, thus dominating the timing error in fill- ing a storage RF bucket. In addition, the relatively low yield of positrons with large beam emittance from the in-line target made positron filling quite a cha.llen~e. The new timing system eliminates the need for the old positron source and takes ad- vantage of the high intensity, low emittance SLC beams from the damping rings. 3. TIMING SYSTEM UPGRADE The LINAC Timing System l , as modified for the Stanford Linear Collider (SLC) project, provides a multitude of pro- granunable trigger signals with a jitter of less than 100 psec with respect to the beam and the Klystron 2.856 GHz RF over the three kilometer length of the linear accelerator. Using sub- harmonics of 476 MHz for the linac Master Oscillator to drive the RF reference lines via a temperature stabilized Main Drive Line (MOL) and 8.5 MHz for the Damping Ring revolution fre- quency, the timing system was designed to provide triggers at a fixed time with respect to beams in the damping rings and at a fixed phase of the 360 Hz line frequency to reduce power line AC effects in accelerator operation. Basically, a trigger signal generated on the first edge of the 8.5 MHz falling within a gate derived from the 360 Hz zero-crossing in the Master Trigger Generator (MTG) pro- duces a fiducial which is superimposed on the 476 MHz sig- nal in the Fiducial Generator and is then transmitted on the MDL. At each of 30 sectors, the composite signal is picked- off and amplified for multiplication to 2.856 GHz by the Klystron subboosters. A fiducial detector unit (FIDO) scales down the reference RF to generate a resynchronized 119 MHz clock with a missing-pulse marker for resettahle delay counters. ·Work supported hy Department of Energy contracts DE-AC03-76SF00098 and DE-AC03- 76SF00515. We have designed , built and operated the electronic timing system required to fiU PEP and SPEAR using beams from the SLC Damping Rings . The timing constraints were that aU linac pulses occur at a fixed phase of the 360 Hz power line cycle (as is done for other modes of linac operation), that the CW de- vices in the linac (Subharmonic Buncher and Damping Rings) be phase-shifted to the S-Band bucket chosen by the storage ring burst, that the storage ring master oscillators remain phase stable with respect to the linac RF system and, finally, that the beam be delivered to the storage ring within 0.3 nsec of the re- quested time at pulse rates of 10-60 Hz. Within our scheme, for initial operation with a minimal impact on fill times, the linac is operated with only one bunch at a time since fully in- terlaced multi bunch operation would require phase shifting the beam in the damping rings in order to maintain synchroniza- tion with the storage rings and the 360 Hz line frequency. The damping times are maintained to be a fixed number of damp- ing ring revolutions so that the damping rings can be treated as delay lines allowing the damping times to be adjusted to match 360 Hz zero-crossing time intervals. For PEP/SPEAR filling, we operate the front two-thirds of the linac as closely as possible to SLC operation. Follow- ing Fig. I, a timing reference signal is sent from the storage rings to the Injector where the CW RF system controlling the Subharmonic Buncher (SHB) and Damping Rings is phase- shifted and a linac fiducial is generated. About 1 msec later, the gun is fired at a fixed pbase of the SHB by a Trigger Gate and Synchronizer (TGAS) module to produce electrons and store them in the electron damping ring. At a subsequent power line cycle, the electrons are extracted, accelerated, and delivered for electron filling or targeted at Sector 20 to produce positrons which are then returned to the positron damping rings for Presented at the IEEE Particle Accelerator Conference, Chicano, IL, March 20-29, 1989" @default.
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• W801787270 title "Timing and RF Synchrotronization for Filling PEP/SPEAR with the SLC Damping Rings" @default.
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