Definitions and Descriptions

ALPHA:: A large, powerful, and extremely stable, Alpha brand computer processor. MCC is the name of the Alpha that serves as the central host for the control system, referred to in this document as "the Alpha". MCC is also often called "the VAX", the brand formerly used. MCC runs the SLC control program (SCP), houses the central database, runs a process called PARANOIA that logs error and informational messages, and communicates with the microprocessors throughout the site via SLCNET. A second Alpha called MCCDEV is used to support software development efforts, and may be used as a backup host in case of MCC hardware failure. Both are located in the computer and networks room in Building 5.
CV: Crate Verifier: A CAMAC module that occupies the first slot of every crate. Monitors crate power, crate supply voltages, and local temperature. Used by the control system to verify crate power and proper crate operation. Also contains read and write registers and a command line spy register that can be utilized for problem diagnosis. Its signals travel on the backplane of the crate to and from the micro via the SCC.
DAC: Digital-to-Analog Converter: A CAMAC module that converts 16 channels of digital input signals (typically from the control system) to analog output signals that are used by analog devices such as magnet power supplies. Generally used in conjunction with a SAM, which performs the opposite function: analog-to-digital conversion, necessary for reading back measurements from analog devices. A DAC is used to change subbooster phase by converting a digital signal from the control system to an analog output voltage used to control the phase shifter in the RF Drive Unit.
EMHP: EMHP power supply: EMHP is the brand name of this large power supply. The EMHPs referred to in this system are free-standing cabinets located at the end of each odd sector, that serve as a bulk supply for all klystron focusing magnets in that sector and the subsequent sector. Their output is 200 Volt, 250 Amp DC power, connected in parallel to the 16 sector klystrons to provide ~15 Amps to each focusing magnet. The EMHPs are connected to an IDIM and IDOM that allow ON, OFF, and RESET functions, as well as some status readbacks, to be accessed through the SCP; and a SAM module that monitors its output voltage and current. EMHPs are also used elsewhere in the accelerator system as power supplies for strings of beamline magnets and some other large, DC devices.
FIDO: Fiducial Output: A chassis that extracts the T-zero fiducial pulse from the 476 MHz MDL, and outputs the fourth subharmonic 119 MHz timing signal with fiducial to PDUs. The fiducial carried by the MDL is marked by a double-amplitude pulse; the fiducial signal output by FIDO is marked by a missing cycle (i.e. a cycle having zero or low, unchanging amplitude), to tailor its output for the PDU. The FIDO chassis is located in rack A of klystron station 1 in every sector, and feeds the PDUs that control the timing of the sector's subbooster, klystrons 1-6 of that sector, and klystrons 7 and 8 of the previous sector.
FIDO AMP: FIDO Amplifier: A chassis located just above the FIDO chassis in rack A of klystron station 1 in every sector, that amplifies the MDL signal for use by the FIDO. FIDO amps can also be used for distribution to multiple FIDOs, but in the linac there is always one of each per sector.
GLASSMAN: Glassman power supply: A high-voltage DC power supply for the subbooster modulator. The subbooster modulator performs the same function for the subbooster's internal klystron as a regular modulator (see modulator) does for a 5045 klystron, but its set-up is different; for example, the subbooster modulator is triggered by a high-current switching tube instead of a thyratron, and receives its bias voltage from a dedicated Glassman supply instead of a bulk-supply VVS.
IDIM: Isolated Digital Input Module: A general-purpose digital input module, where 'input' is with respect to the central control system. An IDIM is necessary anywhere a digital status is monitored (e.g. flow switches, motor controls, modulator status). Each module can monitor up to 32 signals on channels numbered 0-31, and there may be multiple IDIMs in a crate. IDIM is non-latching and has no write function, so it monitors digital statuses in real time only (compare to its latching counterpart LDIM). IDIM and IDOM are also used to remotely control EMHP klystron focus magnet bulk power supplies (ON, OFF, and RESET) and VVS's (ON, OFF, and voltage ramping) via the SCP.
IDOM: Isolated Digital Output Module: A general-purpose digital output module, where 'output' is with respect to the central control system. An IDOM is necessary anywhere a device is controlled digitally. Each module manages up to 32 signals on channels numbered 0-31. See IDIM.
I-Phi-A: Isolator, Phase Shifter, and Attenuator: A chassis that functions as a controller for the fine-tuning of phase and amplitude for the RF drive signal transmitted from a subbooster to a klystron. Consists of a FOX phase shifter (a rotary field, continuous phase shifter that utilizes a stepper motor) driven by the MKSU; a solid state PIN diode attenuator that utilizes a programmed current source from the MKSU; and an RF voltage detector that supplies both a front panel diagnostic monitor and a video signal to the MKSU that allows for remote monitoring of the drive pulse.
KLYS: Klystron: A device that acts as a microwave power amplifier, used to generate high-power, radio-frequency (RF) electromagnetic waves that are output to the accelerator's disk-loaded waveguide and used to accelerate the beam. There are eight klystrons per linac sector, spaced 40 feet apart in the klystron gallery. Linac klystrons are model 5045, with average power 42 kW, gain 53 dB, and operating frequency 2856 MHz. Each klystron has its own modulator, housed near it in the klystron gallery. The modulator supplies the proper voltage pulse to a cathode inside a sealed vacuum tube in the klystron, which creates and accelerates a beam of electrons from the cathode toward an anode at the far end of the tube. A powerful solenoid electromagnet concentrates these electrons into a narrow beam, which then travels toward the anode through a series of tuned resonant cavities and drift tubes. The first resonant cavity is a "buncher" cavity, driven by a 2856 MHz drive signal from the sector's subbooster. Just before the cavity, the subbooster's signal is synchronized with the modulator's bunch pulse by an I?A chassis, that acts as a fine-tuning phase shifter for that klystron. The drive signal imposes a velocity modulation on the passing electron beam, which clusters the electrons into discrete bunches spaced apart by one wavelength of the RF. In the final cavity of the tube, these concentrated bunches induce and then amplify a resonant EM field, which is extracted through a waveguide into the SLED cavity. SLED stores up the energy using a loading effect, and then discharges it rapidly into waveguides that carry the high-power RF to the linac. The output is then divided into two equal parts, and carried down to the accelerator tunnel through two waveguides. In the tunnel, the signals are halved again, creating four equal signals in separate waveguides that are input to the accelerator at 10-foot increments. For more information on how a klystron, modulator, and subbooster work, see the Basics page [coming soon].
MDL: Main Drive Line: A gas-filled coaxial waveguide that runs the length of the klystron gallery, and carries the 476 MHz RF signal with fiducial that is ultimately used for all klystron and timing instrumentation. The MDL signal is generated by the master oscillator, a solid-state oscillator and amplifier, along with a fiducial generator, located in the Sector 0 alcove. The MDL is a rigid 3-1/8" cable mounted to the ceiling of the klystron gallery on rollers, anchored to the gallery floor by rigid mounts at the beginning of each sector, and equipped with periodic expansion joints designed to absorb changes in length due to thermal expansion. Its signal is picked off at the beginning of each sector and sent to both the sector's subbooster RF drive unit (SBDU, a.k.a. RFDU), and the sector's FIDO chassis. The SBDU uses the MDL signal to generate both the phase reference line (PRL), and the subbooster's 2856 MHz RF output to klystrons. The FIDO extracts and converts its fiducial pulse to provide the T-zero timing signal to the sector's PDUs, which control the timing of pulsed devices (such as the subbooster, klystrons, BPMs, and pulsed magnets). Because the MDL signal affects the timing and phases of all other RF devices in the accelerator, phase stability is extremely important. An interferometry system housed in the Sector 0 alcove monitors changes in phase of the round-trip signal, which occur primarily due to diurnal temperature fluctuations, and can apply compensatory phase shifts to the subbooster drive line (SDL) of each sector. Alternatively, a temperature and pressure model can be used to measure and maintain MDL phase.
MICRO: Microprocessor: A microcomputer that sends and receives signals to/from the Alpha, and controls all devices in a local area via CAMAC. In the linac, there is one micro per typical sector, located in the I&C alcove. The micros use a multibus architecture that provides support for an arbitrary number of single-board cards that plug into its backplane. Every micro contains a CPU card that houses the micro's memory and processor; an FSK modem card that interfaces with SLCNET, the broadband communication system between micros and the Alpha; an MBCD card that interfaces between the micro and its associated CAMAC crates; a PNET modem that receives the timing information broadcast on SLCNET; and possibly others. Numerous (~10) subjobs run on a micro at once, that handle various tasks. For the linac RF system, a klystron subjob handles downloading and updating PIOP programs and databases, and has the ability to perform operations either in parallel on all PIOPs controlled by that micro, or on a single PIOP associated with a particular klystron or subbooster.
MKSU: Modulator Klystron Support Unit: A head unit (chassis) that interfaces between an individual klystron and the control system, via a PIOP module. The MKSU contains all digital and analog circuitry to monitor, control, and trigger a single klystron station. Its hardware consists of an open-frame chassis with a power supply and relay protection logic for hard interlocks; a buss interface board that receives modulator trigger signals from the PIOP and generates modulator triggers; a front panel board for local control or to attach an oscilloscope; a PAD interface board connected to the local PAD; a digital board containing a DAC that receives and transmits control signals to and from associated devices (e.g. the FOX phase shifter stepper motor); an analog board containing an analog-to-digital converter (ADC) for all analog and video signal monitoring; and a monitor board containing additional analog and digital inputs and outputs. MKSU also drives the FOX phase shifter and contains buffer circuitry for the attenuator in the I?A. "Maintenance" mode for the MKSU prohibits the associated klystron from accelerating beam and permits front panel control of the MKSU (useful for commissioning of new klystrons); "Online" mode disables the MKSU front panel, and allows the associated klystron to accelerate beam and be controlled by the SCP.
MOD: Modulator: A high-voltage pulse transformer that provides well-formed and timed voltage pulses to the cathode of a klystron tube. The resulting voltage difference between the cathode and anode causes electrons to flow through the tube, ultimately generating the klystron's high-power RF output. There is one modulator for every klystron, housed in a large cabinet in the klystron gallery near its associated klystron. The timing for the modulator's transfer of energy to the klystron is regulated by a trigger that fires the modulator's thyratron, which acts as a "switch". The thyratron can be made to fire at various repetition rates from 10 to 180 pps, in increments of 10 pps, depending on the accelerator program (60 Hz up to sector 3, 30 Hz thereafter for the current PEP-II program). The modulator's pulse shape and width are determined by tuning the inductors in its pulse-forming network. A delay network in the MKSU is used to synchronize the voltage pulse with linac beam time. For more information on how a modulator, klystron, and subbooster work, see the Basics page [coming soon].
PAD: Phase and Amplitude Detector: A head unit (chassis) used to monitor phase and amplitude of RF signals. PADs perform numerous monitoring and readback functions, including: measurements of magnitude and phase of RF pulses; video signals of pulse measurements; ability to take triggered measurement samples at sampling times specified by the control system; and instrument control and calibration functions. All klystron and subbooster PAD signals are digitized and then transmitted to the control system via a PIOP (sometimes by way of an MKSU). There is a dedicated PAD for every subbooster as well as one for every individual klystron. RF phases are measured with respect to the Phase Reference Line (PRL) in that sector, which is input directly to every klystron and subbooster PAD..
PDU (PDU-II): Programmable Delay Unit: A CAMAC module that provides up to 16 channels of trigger timing signals, that are independently delayed by some number of ticks with respect to the fiducial signal received from the FIDO. Ticks in the linac RF system are time increments of about 8.4 ns (1/119 MHz). Every triggered device (klystrons, BPMs, pulsed magnets, et al.) receives its timing information from a PDU, so there is a PDU in almost every CAMAC crate. The timing delays for each device for every beamcode are stored in the database Pattern Timing Table in terms of number of ticks, and are sent to the PDUs from the micro. The PDU then sends appropriate triggers to device controls (such as PAUs, BPMPs, and PIOPs) on the upper backplane of the CAMAC crate..
PIOP: Parallel Input/Output Processor: A CAMAC module that contains an internal microprocessor, which interfaces between the control system and an MKSU for linac klystrons, or is used for readback to the control system for linac subboosters. There is one PIOP for every klystron and every subbooster in the linac. For the klystron system, the MKSU interfaces the PIOP with all other control and measurement devices. The PIOP manages triggering of klystron modulators, by receiving timing signals from the PDU on the CAMAC backplane and sending trigger signals to the MKSU over a data cable; transmits PAD and other readback measurements to the control system; monitors klystron protection interlocks and inhibits modulator triggering when a signal exceed its database limit; and contains fast time plot (FTP) diagnostics, which have the ability to sample a quantity (such as phase or amplitude) on each of 64 successive beam pulses, with each sample time-delayed by a specified increment from that of the previous pulse. FTPs are used for analysis of pulse shape (phase or amplitude of pulse vs. time), pulse to pulse jitter (relative sample time-delay equal to zero), amplitude vs. drive (saturation plot), and klystron voltage or current (either vs. time or pulse-to-pulse). The PIOP data display, accessible from the individual linac klystron panels on the SCP, provides a useful summary of statuses monitored by the PIOP. PIOP receives FTP requests and sends data through the SCC, via the CAMAC backplane, to and from the micro..
PRL: Phase Reference Line: A coaxial cable carrying a highly-stabilized RF signal that functions as a phase reference for one entire sector, against which other RF phases in that sector are measured. Additionally, the PRL phase of each sector is compared to that of the previous sector to maintain accurate phasing across the length of the linac. The subbooster drive unit in each sector receives the 476 MHz main drive line signal, multiplies it by six, and drives it through a stable amplifier and into the PRL. The PRL runs the length of the sector and terminates at a reference line phase monitor in the beginning of the next sector, which is used to compare phasing between the two sectors. All klystron and subbooster RF phases are measured by comparison with this stable reference, via a PAD. PRLs are insulated coaxial cable, with foam dielectric and a temperature-stabilized water jacket, hung from the ceiling in the klystron gallery. (**Note that the acronym PRL is also commonly used in reference to the positron return line, but in this document it always refers to the phase reference line.).
REF PHS MON: Reference Line Phase Monitor: A phase monitor that sits on top of the sector subbooster cabinet, and compares the phases of that sector's phase reference line (PRL) with that of the previous sector. Also known as a head-to-tail phase monitor..
RFDU: (RF) Subbooster Drive Unit: Another name for the Subbooster Drive Unit (see SBDU)..
SAM: Smart Analog Monitor: A CAMAC module that performs analog-to-digital conversion. SAMs are typically used to convert readout signals from analog devices (such as small magnet power supplies, thermocouples, etc.) and convert them to floating-point digital outputs in Volts, that can be read by the control system. It contains an internal microproccessor that handles up to 32 signal channels with fully automatic ranging, polarity, and calibration..
SBDU: Subbooster Drive Unit: A chassis located near the top right-hand side of the subbooster racks in each sector, that receives the 476 MHz main drive line signal and multiplies it by six to generate the sector's 2856 MHz phase reference line (PRL), and the drive signal for the sector subbooster. The PRL signal is a continuous output that is generated and amplified by the SBDU, and output to a coaxial cable that runs the length of the sector, to provide a stable phase reference against which all other phases in the sector (such as those of the subboster and klystron RF outputs) are measured. The drive signal for the sector subbooster is generated by a separate channel in the SBDU. The SBDU multiplies the MDL signal by six, phase-shifts and attenuates it, and then outputs a pulsed 2856 MHz signal at a user-defined (variable) repetition rate, which has remained set at 120 pps since SLC running and for all of PEP-II. This signal essentially does for the subbooster what the subbooster in turn does for the klystrons: it accelerates some electrons and decelerates others in the subbooster's internal klystron tube, causing them to compact into discrete bunches spaced exactly one 2856 MHz wavelength (c / 2856 MHz) apart. These bunches ultimately generated the subbooster's RF output to the klystrons..
SBDU PS: SBDU Power Supply: A power supply chassis for the subbooster drive unit. The SBDU power supply chassis is located directly above the SBDU at the top right-hand side of the subbooster's hardware racks..
SBI: Subbooster Interface: A double-width CAMAC module that provides triggers to the subbooster modulator. These triggers enable the subbooster modulator to send a voltage pulse to the subbooster klystron, generating RF output on the sub-drive line (SDL). SBI triggers have the form of pulse-pairs, and are sent out continuously at 360, 180, or 120 pps, depending on the accelerator program (120 for the current PEP-II program). For a given pulse, the timing for the triggers may be shifted by the SBI to either ACCELERATE, to accelerate beam in the linac; or STANDBY, to fire the subbooster when no beam is present in the disk-loaded waveguide. Like all CAMAC modules that control pulsed devices, the SBI receives timing information from the PDU on the backplane of the CAMAC crate; but whether the SBI triggers the subbooster at ACCELERATE or STANDBY time is determined by a front-panel input on the module, that comes from the BCS control chassis in MCC. More information on subbooster output and timing will be available at some point on the Basics page of this website..
SBST: Subbooster: An RF device containing a small, internal klystron and modulator system, that produces the 2856 MHz RF that functions as a drive signal for klystrons. This drive signal is responsible for the bunching of electrons in the klystron tube that ultimately generates the klystron's RF output. There is one subbooster located near the beginning of each sector in the klystron gallery, that provides the drive line for the eight klystrons in that sector. High-voltage power for the subbooster's modulator is supplied by a Glassman power supply. Each subbooster has an associated Subbooster Drive Unit chassis (SBDU), which receives the 476 MHz main drive line (MDL) signal, multiplies by six to 2856 MHz, and then splits it to drive the sector's phase reference line (PRL) and sub-drive line (SDL). The PRL is a continous 2856 MHz signal that is used to maintain the phases of the sector's subbooster and klystrons, and the phase difference between adjacent sectors. The SBDU phase-shifts and attenuates the SDL signal, which is pulsed at a variable repetition rate, depending on the accelerator program, that has remained set at 120 pps since SLC running and for all of PEP-II. The SDL signal is first picked off and sent to the subbooster's PAD, which measures SDL phase with respect to the PRL, then travels down the length of the sector and is picked off for each klystron. Each klystron pick-off passes through an I?A module, which phase-shifts and attenuates the drive signal in order to synchronize that individual klystron's RF output with the phase of the linac beam. The subbooster receives its triggers from the control system via a subbooster interface (SBI) CAMAC module, located in Crate 2 in the gallery. Status readbacks for the subbooster, including (this and that), are sent to the control system via the PIOP. Technically, the subbooster drive pulse is actually a pulse-pair, consisting of one standby pulse that always fires at standby (non-beam) time, and one accelerate (ACC) pulse that fires at one of two possible times: either at beam time (the moment when a beam pulse is passing), if any klystrons in that sector are set to accelerate on that beam code; or at a database-specified non-beam time, if none of the sector's klystrons are active on a passing beam pulse at that time. For more information on how a subbooster works, see the Basics page [coming soon]. .
SCC: Serial Crate Controller: A CAMAC module that acts as a controller for the crate by interfacing with the associated micro. SCC is a double-wide module located in the last two slots (24 and 25) of every crate.
SDL: Subbooster Drive Line (or Sub-Drive Line): A 1.75", rigid coaxial waveguide that carries the 2856 MHz drive signal from a subbooster to klystrons. The typical linac sector contains one subbooster that drives that sector's eight klystrons. Where the SDL is picked off for each klystron, it passes through an I?A module, which attenuates the signal to the necessary amplitude for the klystron, and phase-shifts it to synchronize the klystron's RF output with linac beam time.
SLCNET:: A broadband CATV (cable) local area network used for communication between the Alpha and micros. Each micro is directly connected to the Alpha by a SLCNET line, through which it receives all digital control signals and transmits all digital readbacks. Timing information is transmitted through a dedicated subchannel of SLCNET called PNET. SLCNET connects to the Alpha via external gateway modems located in the MCC computer and networks room. For more information on SLCNET and other site cable networks, see Cable Networks.
SLED: SLAC Energy Doubler Cavity: A specially-designed resonance cavity attached to the 5045 model SLAC klystron that receives and stores up the klystron's RF output energy until it reaches saturation, and then rapidly discharges the energy into the linac via a clever "switching" method. The end result is an RF output with shorter duration and nearly doubled amplitude as compared to that of the same klystron without SLED. All linac klystrons subsequent to the DRIP are equipped with SLED. For a good introduction to how SLED works, see SLED for Dummies.
STB (STB-II): Simple Timing Buffer: A CAMAC module that works in conjunction with the PDU, and performs the following functions: measures time of occurrence of a pulse from the PDU (i.e. a trigger pulse) with respect to the fiducial; converts backplane signals from the PDU, including both trigger pulses and the 119 MHz plus fiducial sent from FIDO, to front panel NIM pulses; and serves as a voltage monitor for the crate power supply, via LEDs on its front panel. The front of the module contains a LEMO connection for every PDU channel, as well as one for the fiducial signal, that can be used to attach oscilloscopes or voltage detectors for analysis of the converted NIM pulses. STB always sits next to the PDU in a crate.
TRIM: klystron focus magnet trim supply: A 60 Volt, 20 Amp dedicated power supply that is wired in series with an individual klystron's focusing magnet power supply line from the EMHP bulk supply. The trim supply is a housed in a blue-colored chassis that is rack-mounted at the bottom of rack A for the typical klystron station. Although it is called a "trim", it actually serves as a boost to bring the solenoid current up to the necessary value; it does not have a shunt capacity. The basic idea is that an underpowered solenoid would result in an underfocused electron beam inside the klystron tube, causing losses. For more information about how a klystron works, see the Basics page [coming soon].
VAX:: A brand of computer formerly used as host computers for the control system. Some VAXes are still in use, but the central host computers MCC and MCCDEV are now Alpha brand (see ALPHA).
VVS: Variable Voltage Substation: A variable-voltage transformer that receives 12KV power from the SLAC site master substation (located just south of linac sector 30) via underground transmission lines, and steps it down to a variable output voltage of 450-600 Volts. VVSs are located in the klystron gallery in even-numbered sectors, and each provides power to the klystron modulators in that sector and the sector before it. From sectors 4-30, the VVSs are numbered sequentially, corresponding to half the sector number (for example, the VVS in sector 10 is called VVS 5). Two more VVSs numbered 1A and 1B serve the front end of the linac. Output is controlled by a DC reference voltage ranging from 90-120V. When turning on a VVS, the reference voltage is typically ramped up to 90 and then 120V in order to reduce shock on both the VVS's internal electronics, and the klystron tubes, which receive their voltage pulses from the VVS-powered modulators. VVSs are equipped with breakers that are linked to the Personnel Protection System (PPS), so that a trip in the PPS can cause VVS breakers to open, eliminating power to associated modulators and therefore preventing klystrons from accelerating beam, and eliminating the RF radiation hazard.