Accelerator-related glossary and facts for the use of the FY2004 Scheduling Physicist and beyond ...
Please do send an email to me at email@example.com if you think something here is not accurate enough or wrong !!!
AC dipole in the AGS is used to flip the spin of the entire ensemble of protons (for example) upside-down at a resonance energy (during ramping) and therefore maintain the polarization. Without it, each proton may change its spin orientation depending on the amplitude of the betatron oscillation and as a result the overall polarization of the ensemble of protons is reduced. This AC dipole provides a big betatron oscillation and forces a maximum spin orientation change (180o) at the resonance energy --- by all the action of all quadrupoles in the ring --- for each proton and therefore avoids the overall polarization from being reduced due to random spin orientation.
ACG stands for the "Access Control Group", which is responsible for the safety system in our collider/accelerator complex.
AGS is divided into 12 sectors or superperiods (A, B, ... L) and each sector has 20 sets of dipole magnets plus 2 (=1 vertical @#3 + 1 horizontal @#17) quadrupole and 2 (=1 vertical @#7 + 1 horizontal @#13) sextuple magnets. The circumference of the AGS is 4 times that of the Booster and this is why the AGS can have 4 times as many bunches as the Booster at the same RF frequency.
The circumference the AGS is 807.12 m.
By 2005, there are 2 "snakes" in AGS, the cold (super-conducting) snake (20%) and the warm snake (5%). 100% means that the spin is flipped from up to down completely. 20% (5%) means that there is only a partial flip of 20% (5%) and the complete flipping needs 5 (20) AGS turns.
AMMPS stands for the AGS Main Magnet Power Supply.
AtR stands for the "AGS-to-RHIC" (line).
* is theβ (amplitude-function in the phase oscillation) at the collision/interaction point.
"Bdot" effect: The change of magnetic field strength (dB/dt) during ramping etc. creates eddy current loops in the beampipe which reduce the magnetic field strength of the magnet. To compensate for this ( and since one cannot possibly laminate the beampipe :-), special current windings with the current in the opposite direction are placed near the beampipe to minimize the Bdot effect.
"blw" stands for "back-leg winding" which is located in D6 to correct the magnetic field in the beam pipe where a normal Booster beam circulates.
BLAM stands for the Beam Loss Analysis Monitor which uses current transformers to monitor the beam loss distribution in the RHIC tunnel and the XY lines of the AtR. It knows how much beam loss (or really how many ions/particles) is acceptable in various places of the RHIC (due to various shieldings) and sends alarms to the Main Control Room when the beam loss levels reach 50% and 90% of the limits (with respect to the controlled area limit of 5 mrem/hour). The acceptable levels at various places were calculated by A. Stevens.
BLIP stands for the Brookhaven Linac Isotope Producer.
BMMPS stands for the Booster Main Magnet Power Supply.
Booster is divided into 6 sectors (A, B, ... F). Each sector has 6 dipole magnets and 8 quadrupole magnets.
The Booster is connected to the "alternate" power line whereas the rest of BNL is linked with the "preferred" power line. It does not have a M-G as in the AGS.
The circumference of the Booster is 201.78 m.
BPM stands for the Beam Position Monitor. Sometimes, people also call it "PUE".
BtA stands for the "Booster-to-AGS" (line). The Booster vacuum system is separated from the BtA line by a vacuum valve.
Bunch merging is mainly to increase the intensity per bunch in the AGS and thus RHIC. Without bunch merging, 24 bunches of the AGS are filled 4 times by 6 bunches of the Booster (ie., 24 = 4 x 6). With bunch merging, 6 bunches in the Booster are merged to 3 bunches and the AGS are filled 8 times (ie., 24 = 8 x 3). After the AGS bunches are filled, the AGS will be debunched and then rebunched (by increasing the RF voltage slowly) to 4 equally spaced bunches. To narrow the individual bunches (in phase/space), 8 or 12 RF harmonics of potential will be applied to have 4 bunches in the 8 or 12 buckets in the AGS.
C3 in the Booster is an electrostatic inflector used to bend heavy ions. We can run protons without the C3 inflector. C3 is in front of the location where the Tandem-to-Booster (TTB) beamline joins Booster.
C5 in the Booster is one of the regular "lattice" dipole magnets of the Booster. Its main job is keeping the circulating beam happy. It has the additional task of accepting the incoming H- from the LINAC (when we run protons), and so has a special beam pipe and special "eddy current" windings to compensate for the Bdot effects in the special vacuum chamber. H- ions are stripped on a carbon foil located just after C5 to become protons.
Chromaticity e (say) is defined and related to the tune v and the momentum dispersion dp/p as:
dv = e * dp/p
The chromaticity changes sign before and after the transition.
In RHIC, the cogging procedure includes the following:
Make the frequencies of the yellow and blue rings the same, typically keeping the frequency in the yellow ring and move that of the blue ring to the frequency of the yellow ring, then 'lock' them in place;
once they have the same frequencies, we have to move one 'chain' with respect to the other such that their respective first bunches arrive at the same time in a given IR (typically IR4 and IR10 = opposite site of 4). This is done by changing the phase between them.
cogging", it means that we have to line up the Booster RF and the AGS RF in
order to allow the bunches to get passed on from the Booster
to the AGS.
Contactor and Crowbar (which are quite common in many accelerator-related
systems, power supply, RF devices etc.):
A contactor may be used in AC or DC circuits whereas a crowbar seems to be only used in DC.
A contactor is an electrically controlled switch that will open the circuit to protect devices, magnets etc. Eg. when a quench happened, in order to protect the superconducting magnet, the system tries to shut down the power supply and at the same time also open up the contactor in case the power supply were not shut down successfully.
A crowbar is an electrical circuit used to protect the power supply or the circuit attached to the power supply. When a voltage over a threshold ("overvoltage") is detected, a short circuit path would be created to dissipate the energy. Eg. for a power supply with capacitors that can sustain only (say) 100 V, if there are voltage > 100 V, the capacitors would be damaged if there is no crowbar.
D6 septum in the Booster is used to extract beam to NSRL. D3 is also a septum but it has a thinner coil (compared to the coil in D6) to help kick the beam into the appropriate position at D6. See also the so-called "blw".
DCCT stands for the DC Current Transformer which measures the total beam current (vs WCM measuring the beam current in a bunch).
DEC stands for the Department Emergency Coordinator which is one significant safety function of the MCR Operation Coordinator (OC). Often when the MCR is not staffed, the CAS (CA support) Watch will act as the DEC.
Gap cleaning makes use of some special kickers at 2 o'clock to clean those unused buckets (5 in 55 bunch running mode or 10 in 110 bunch running mode). The kickers "kick" the particles in those buckets transversely so that they would eventually hit with the collimators.
HARP is a multi-wire instrument like the SWIC but unlike the SWIC, it doesn't have gas in it. It depends on secondary emissions of particles which hit the multi-wires to create electrical signals. Compared to the SWIC, the HARP is more useful for higher intensity beams and the HARP may not detect anything when the intensity is too low.
Hi-pot test in the superconducting RHIC ring can only be done when the helium pressure is ~5 times of the atmospheric pressure. Otherwise, the corona (discharge) effect would ruin the hi-pot test which relies on the existence of only very small current.
IPM stands for the "Ionization Profile Monitor" which measures transverse beam profiles by collecting electrons from residual gas ionization. More details can be found here.
Lambertson magnets in RHIC (injection area ~5 and 6 o'clocks) are special warm magnets with two apertures (holes), one for injected beams and the other for circulating beams, so that they can co-exist.
Landau cavities are used to help reduce the longitudinal emittance of the heavy ion beam.
Lifetimes of gold-gold stores >> lifetimes of proton-proton stores is mainly because the IBS (inter-beam scattering) effect is much smaller in proton beams than gold beams.
Luminosity = f nbunch Nblue Nyellow / ( 4 π σx σy ) where σx & σy are the transverse beam sizes
Nblue Nyellow / ( 4 π
ε rms * rms
*) assuming σx= σy= σ & ε
Nblue Nyellow (1.5 βγ
) / (
ε N *
normalized emittance at
95%, εN = 6 (βγ ) rms , )
have the relativistic meanings, not to be confused with * and the revolution frequency f
in RHIC is about 78.1 kHz for 100 GeV gold ion beams.
) have the relativistic meanings, not to be confused withβ
and the revolution frequency f in RHIC is about 78.1 kHz for 100 GeV gold ion beams.
MCC stands for the Motor Control Center. In the LINAC building, there are 4 of them, L1 ... L4 in which L3 is linked with the Control Group equipment for the Booster .
MLI stands for the "Multi-Layer Insulation" used for the superconducting magnets in the RHIC ring. See this picture with captions added. ( This picture was originally obtained from G. McIntyre. ) When the magnets are cold, we should not open up/break the magnet vessels because the water condensation absorbed by the MLI may never come out and this affects the insulation effectiveness. Therefore, the magnets need to be warmed up (to about room temperature) before they should be opened.
Motor-Generator (M-G) is used to keep the AGS power usage fluctuation minimal so that LIPA would be happy.
NEG (as in NEG-coating) stands for the Non-Evaporated Getter.
NSRL stands for the "NASA Space Radiation Laboratory" which was originally called the "Booster Applications Facility" (BAF).
PASS stands for the "Particle Accelerator Security System".
permit link connects with different equipment (such as the abort kicker, roman pots etc.) and constantly poll their status. If any equipment that it polls do not respond properly, it will not allow the machine to have beam. Sometimes, it is the connectors in the link which cause problems. At least, part of its existence is for our safety.
PLC stands for the "Programmable Logic Controller" which is like a micro-computer in a crate responsible for relay logics.
PPM stands for "Pulse-to-Pulse Modulation". It is a mode used to run NSRL and RHIC concurrently. In this mode, a 6 second cycle is used. As shown in this figure, the first part (2.88 s) is used for filling the AGS whereas the second part is used for NSRL. More can be learnt from this document.
PUE stands for the Pick-Up Electrode. See BPM.
quench link's main function is to prevent magnets from quenching by monitoring the voltages due to induction during ramping (L dI/dt), across some resistance (eg. the lead) etc. If the voltage is above certain threshold, a QLI (quench link interrupt) will be issued to drop the current in the superconducting magnet (and this in turn would result in a beam loss). QLI occurs sometimes due to problem not necessarily related to the magnet quenches, such as spikes in the power supply or even connection failure.
RF: People often say it's a high level or low level problem. "High level" really means "high power" ~ kW whereas "low level" means "low power".
RF window is really a ceramic window which is transparent to the RF waves (but not to the light waves that our eyes depend on). It separates the vacuum in the beampipe from the air in the waveguide and power amplifier.
transition energy for Au(79+) is ~23 GeV
circumference is ~3.8 km
360 buckets in the ring and each bucket is ~36 ns => revolution period ~ 13 micro-seconds
In 55 bunch running mode, every other 6 bucket is filled (=>bunches) except at the beginning/end where there is a gap of 30 (+5) buckets vacated for the purpose of leaving enough time (~1 micro-second ) for the abort kicker to rise to its full voltage
RF only at 4 o'clock
looking down from sky, +ve charges in the blue ring move clockwise and counter-clockwise in the yellow ring
both primary and secondary collimators are at 7 o'clock and 8 o'clock, both located downstream of beams going through PHENIX
abort kicker at 10 o'clock
RHIC does not need M-G because the RF/magnetic field and thus power goes up slowly due to the fact that those magnets in RHIC are super-conducting and their magnetic field can't be increased too quickly
SCR stands for the "Silicon Controlled Rectifier" which functions as a relay switch to turn on certain amount of power. Websites such as this have more explanation. We have 3 phases of power cycles and this gives us a close to constant power supply. The trigger to the SCR is connected by optical links. If one of the optical links is broken, we would see sharp trough in the power/current distribution.
Sources for the Tandem and LINAC: In the Tandem, all sources are originally in solid forms. To produce Fe or oxygen ions, we use iron oxide; to produce Ti or protons, we use Titanium hydride (TiH2). Cs hitting on the hot filament are attracted to the electrode at ~-300 kV containing iron oxide (for example). Cs is used to reduce the work function of the metal surface. The negative ions are thus produced and repelled away by the -300 kV. Magnets at the end would extract the desirable ions among all negative ions into the Tandem beamline.
Fe2O3 or other iron oxides are ionized to FeO- before we get Fen+ and On-
TiH2 is ionized to TiH- before we get Tin+ and protons.
For our LINAC (the Linear Accelerator) which has been used to produce only protons, hydrogen gas is used.
Stripping foils: for the case of gold (Au) beam in the RHIC, the following details are involved:
in the Tandem, gold atoms are stripped to Au(32+) ions;
in the BtA line, Au(32+) ions are further stripped to Au(77+) ions, the so-called helium-like gold; silica foils are considered because they offer better momentum uniformity but otherwise carbon foils are better;
in the AtR line, Au(77+) ions are finally stripped to Au(79+) ions. But here, the usual Al2O3 flag (which is typically used for measuring position) is used for stripping since almost anything would do at this high energy.
SWIC stands for the "Segmented Wire Ionization Chamber" (with 2 sets of gold-plated tungsten wires, horizontal and vertical, between 2 high voltage Al foils) which is used for beam profile measurement in 2 dimensions. Compared to the HARP, the SWIC is more useful for lower intensity beams. When the intensity is too high, the multiplicities may be too much for the SWIC to deal with.
SWM stands for the "Switching Magnet" which sits in front of the W beam dump and bends ions/particles either through the X line into the blue line or throuhg the Y line into the yellow line.
The kinetic energy coming out of the Tandem is ~V*(1+Q) where V is the terminal voltage and Q the charge (state). "1" in the above formula is due to the transition from Au- to Au0. At the nominal mode, V = 14 MV and Q = 12e. Another possible mode is V = 13 MV and Q = 13e. Both stages gives a kinetic energy of 182 MeV. The mode with Q = 13e does not as well because it is less abundant than Q = 12e.
Some more notes after a tour in Tandem mainly by Peter Thieberger and also a bit by Chuck:
Tandems MP6/MP7 began operation in 1970/71 (about the time that I was born !).
The gas mixture inside is SF6/Nitrogen (~50%/50%) at 10 atmospheric pressure.
The voltage for Fe/Ti ions is ~13 MV, ~10 MV for Si ions and ~11-12 MV for C ions.
Some parts of the "Getter" vacuum system in the Tandem have not been touched for ~15 years !
At least, in this run FY2004, MP7 is mainly for the RHIC operation and MP6 is for NSRL and outside users.
Transition energy is a relativistic border that may be reached in every synchrotron if one keeps on increasing the beam energy. f = v/(2*pi*R) => df/f = dv/v - dR/R. Below the transition energy, df/f > 0, high-energy particles take less time (higher frequency) to navigate the accelerator than low-energy particles. But above the transition energy, when the particle speed is very close to the speed of light, it is the increase of R that becomes the dominant effect, df/f < 0, and thus high-energy particles take longer (lower frequency) to move around the accelerator than do low-energy particles.
Due to significantly smaller emittance and the phase instability in the synchrotron oscillation, the beam with large enough intensity tends to be very unstable when the transition energy is reached. Near the transition energy, the accelerating voltage is jumped in phase (of the synchrotron oscillation) so that the accelerating particles from the rising slope of the synchrotron oscillation would find themselves on the descending slope. This way, the particles can be further accelerated to energies beyond the transition energy. One may also design the synchrotron (such as increasing the circumference) to make the transition energy occur above the operating beam energy.
TSP stands for the "Titanium Sublimation Pump". When heated, the Titanium is sublimated from the filament (in the middle of the pump) and the vapor coats the nearby walls of the chamber. The resultant clean Titanium film/surface effectively removes the active gases.
TTB stands for the Tandem-to-Booster line.
Tune is the number of betatron (transverse) oscillations per turn in a cyclic accelerator. Qx and Qy are used to represent horizontal and vertical tunes respectively. When Qx = 28.72, typically the integer part (28 in this case) is not mentioned and people say Qx = 0.72.
Vacuum systems in various parts of the accelerator/collider complex (at BNL) are generally powered on all the time, even when the entire complex is shut down for many months.
VJR stands for the "Vacuum Jacketed Return" which is an evacuated conduit that the helium process lines and the (RHIC) rings' electrical lines travel through as they pass over an area without magnetic elements. Two examples are the warm bore areas between Q3 and Q4 and the path the conductors take to and from the valve boxes.
WCM stands for the "Wall Current Monitor" which measures the beam current in a bunch and in turns gives the bunch intensity.
WFD stands for the "wave form digitizer", something used by the Polarimetry/Jet Target group people. This was kind of home-made. Since both groups share the same WFD (at least before and during 2005), one group has to stop to let the other group take measurements.