2.1.1 General
with the assistance of the
APS Ring Managers
1.0 Introduction
2.0 Injection System
The Advanced Photon Source (APS) is a third-generation synchrotron radiation source that stores positrons in a storage ring. The choice of positrons as accelerating particles was motivated by the usual reason: to eliminate the degradation of the beam caused by trapping of positively charged dust particles or ions. The third-generation synchrotron radiation sources are designed to have low beam emittance and many straight sections for insertion devices.
The parameter list is comprised of three basic systems: the injection system, the storage ring system, and the experimental facilities system. The components of the injection system are listed according to the causal flow of positrons. Below we briefly list the individual components of the injection system, with the names of people responsible for managing these machines in parentheses:
The parameters listed here are the result of dedicated work by APS personnel over the years. The numbers, collected from all ring managers, are the most recent ones available. If in doubt about a specific parameter, please consult the individual managers of the appropriate machines as listed above. If there are any further approved changes, I would appreciate being told, so the parameters may be updated. It is in everyone's best interest to keep the parameter list current.
Hana M. Bizek, ASD
2.0 Injection System
The Injection System supplies a 7-GeV positron beam for injection into the storage ring and is composed of the following component systems.
2.1 Linear Accelerator (Linac)
The Advanced Photon Source linac system consists of a 200-MeV, 2856-MHz, S-band electron linac and a 2-radiation-length-thick tungsten target followed by a 450-MeV positron linac. It achieves the design goal for positron current of 8 mA and produces electron energies up to 650 MeV without the target in place.
The linac is designed to accelerate 30 ns-long pulses containing 50 nC of electrons to an energy of 200 MeV at 48 pulses per second. The 480-W beam is focused to a 3-mm-diameter spot on a 7-mm-thick tungsten target that serves as a positron converter. Bremsstrahlung-pair-produced (BPP) positrons and electrons are refocused by a 1.5-T pulsed coil and are directed into the positron linac. Both electrons and positrons are captured and can be accelerated to about 450 MeV.
Parameters of the linacs are given below.
2.1.5 Beam Diagnostics (number of each type)
2.2 LTP (Linac to PAR) Transport Line
The first section of the 450-MeV positron beam transport line from the positron linac to the PAR contains 10 quadrupoles and one bending dipole.
Parameters of the low energy transport line between linac and PAR are given below.
2.3 Positron Accumulator Ring (PAR)
The PAR is a DC storage ring with a circumference of 30.667 m (1/12 of the injector synchrotron). The 450-MeV positrons from the positron linac are injected and accumulated in the horizontal phase space of the PAR at a 60-Hz rate. As many as 24 linac macropulses can be accumulated as a single bunch in the PAR during each 0.5-s cycle of the injector synchrotron. This leaves 0.1 s for final compression of the PAR bunch length before extraction and injection into one of the 352-MHz rf buckets of the injector synchrotron.
The 30-ns positron pulses are accumulated in a first harmonic 9.8-MHz rf system operating at 40 kV. A 30-kV, 12th harmonic cavity is turned on for the final compression of the accumulated bunch length. The total number of positrons injected into the PAR can be as large as 3.6 × 1010 (24 pulses × 1.6 × 109/pulse).
Parameters of the PAR are given below.
2.3.1 PAR Technical Components
2.3.1.1 Magnets
2.3.1.4 Beam Diagnostics (number of each type)
2.3.2 Lattice and Orbit Parameters
2.3.3 Lattice Components for 1/4 Machine (B
= 1.5010 T·m at 0.45 GeV)
The second section of the 450-MeV positron beam transport line from the PAR to the injector synchrotron (also known as booster) contains 11 quadrupoles and two horizontal bends. The two bends in opposite polarities form an achromatic horizontal parallel translation together with four quadrupoles.
Parameters of the low energy transport line from PAR to injector synchrotron (or booster) are given below.
2.5 Injector Synchrotron (Booster)
The injector synchrotron has a circumference of 368 m (one-third that of the storage ring) and operates at a repetition rate of 2 Hz. Once each cycle the positron bunch accumulated in the PAR is transferred to the injector synchrotron for acceleration to 7 GeV. At 7 GeV the beam bunch is extracted and transported to the storage ring for injection.
The parameters of the injector synchrotron are given below.
2.5.1 Injector Synchrotron Technical Components
2.5.1.1 Magnets and Power Supplies
2.5.1.2 Injection Equipment
2.5.1.5 RF System
2.5.1.6 Beam Diagnostics (number of each type)
2.5.2 Lattice and Orbit Parameters
=23.3495 T· m)
2.6 BTS (Booster to Storage Ring) Transport Line
The 7-GeV positron beam bunch accelerated in the injector synchrotron is transported to the storage ring for injection into a predesigned rf bucket every one-half second. The transport line consists of 12 quadrupoles and four horizontal bends. Two equal and opposite sets of septum magnets are used for extraction from the synchrotron and injection into the storage ring. The bends make up for the difference in orientation between the synchrotron orbit at extraction and the storage ring orbit at injection. The quadrupoles are arranged and powered to match the machine parameters of the booster to those of a stored beam in the storage ring.
Parameters of the high energy transport line are given below.
2.6.2 Beam Diagnostics (number of each type)
The function of the storage ring is to confine a 7-GeV positron beam to circulate stably around the ring. The very narrow and high intensity beam radiates synchrotron radiation of high brilliance over a wide range of wavelengths. The general design performance parameters of the storage ring are given below.
3.1 Storage Ring Technical Components
The storage ring consists of the following technical components.
3.2 Lattice and Orbit Parameters
The magnets are arranged in a regular lattice around the 1104-m-circumference ring in 40 cells forming 40 zero-dispersion, 5.2-m-long straight sections to accommodate insertion devices. The straight sections are joined by two-bend achromatic sections. This so-called Chasman-Green lattice produces a low emittance and hence a narrow beam.
The ring lattice and the resultant orbit parameters are given below.
3.2.1 Cell Parameters (7 GeV, B = 23.3495 T · m)
3.3 Storage Ring Tolerance Tables
3.3.1 Orbit Positioning and Stability
The positron beam must not jitter or drift by more than 10% of its phase space area. This translates into 5% along any phase-space direction, either position or angle. Using the beta functions at the center of the APS insertion devices, this translates into
3.3.2 Magnet rms Alignment Tolerances - Short Range (component to component across 1 to 2 sectors)
3.3.3 Maximum Allowable Misalignment Tolerances - Short Range
3.3.7.1 Performance Requirements
(source: Technical Specifications for Undulator A, Doc. No. 41010101-00002)
3.3.7.3 Alignment
(source: Installation and Alignment of the ID Vacuum Chamber, Procedure No. XF-IP3)
3.3.9 Injection Power Supplies
3.4 Storage Ring Injection System
The 7-GeV beam bunches from many pulses of the injector synchrotron are injected into pre-designed rf buckets around the storage ring orbit. At 3.6 x 1010 positrons/bunch 60 bunches will give the nominal design current of 100 mA. Injection is accomplished by using septum and bumper magnets.
Parameters of the storage ring injection septa and magnets are given below.
Parameters of the vacuum system are given below.
The energy lost by the positron beam into synchrotron radiation is replenished by a 352-MHz radiofrequency system consisting of 16 cavities and associated power suppies installed around the ring circumference.
Parameters of the rf system are given below.
A large number of beam monitors which measure beam intensity, position, and profile are installed around the circumference of the ring. Signals from these monitors are processed and transmitted to the controls system.
Types, characteristics, and numbers of beam monitors are given below.
3.6 Storage Ring Radiofrequency System
4.0 Experimental Facilities System
The experimental facilities will include construction of a set of insertion devices, front ends of beamlines, first optics, and complete beamlines including experimental stations.4.1 Insertion Devices
4.1.1 Undulator A Parameters and Specifications
4.1.2 Wiggler A Parameters and Specifications
