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ALICE (accelerator)
Encyclopedia
Accelerators and Lasers In Combined Experiments (ALICE), or Energy Recovery Linac
Prototype (ERLP) is a project to build a 35MeV energy recovery linac at Daresbury Laboratory
in Cheshire, England. The project was originally conceived as a test bed for 4GLS
, and consists of:
The ALICE accelerator is an Energy Recovery Linac (ERL) that incorporates all the features of the 4th generation light source albeit at smaller scale. An ERL is not restricted by the dynamic properties of storage rings and, therefore, can attain an unprecedented electron beam brightness limited only by the electron gun. Energy recovery allows also a significant increase in an average power of the light sources (without building a dedicated power station nearby!).
The ability to produce ultra-short electron bunches well below 1ps and an availability of several light sources of different “colour” open up numerous possibilities for conducting investigations of fast processes on a femtosecond scale in molecular and solid state physics to name but a few.
There are plans to extend the ALICE project by adding a 19-cavity
accelerating Non-Scaling FFAG ring, known as the EMMA
project. Planning for the EMMA machine is underway and construction began in September 2009. Commissioning of the EMMA machine is due to begin in March 2010.
The electron beam is then injected into the superconductive linac (booster), accelerated to the energy of 8.35MeV and transported to the main linac that increases the beam energy to 35MeV. Both superconductive linacs are cooled down to approximately 20 K with liquid helium. The accelerating phase of the main linac is chosen such that a specific energy chirp is introduced along the bunch so that it can be later compressed longitudinally in a magnetic chicane (bunch compressor). The beam reaches the chicane after being turned by 180° in the first triple bend achromat ARC1.
After compression, the beam, consisting now of sub-picosecond bunches, enters the magnetic undulator that constitutes a major part of the mid-IR Free Electron Laser (FEL). This laser generates IR light with the wavelength of ~5mm.
The spent electron beam is returned back to the entrance of the main linac via the second ARC2 at a precise time when the RF phase is exactly opposite to the initial accelerating phase. This condition requires an accurate adjustment of the electron beam path length that is accomplished by moving the ARC1 as a whole. The beam is now decelerated thus giving its energy back to the electromagnetic field inside the linac RF cavities (energy recovery) and emerges from the linac having the original energy of 8.35MeV. This energy recovered beam is diverted to the beam dump ending its short but useful life
Linear particle accelerator
A linear particle accelerator is a type of particle accelerator that greatly increases the velocity of charged subatomic particles or ions by subjecting the charged particles to a series of oscillating electric potentials along a linear beamline; this method of particle acceleration was invented...
Prototype (ERLP) is a project to build a 35MeV energy recovery linac at Daresbury Laboratory
Daresbury Laboratory
Daresbury Laboratory is a scientific research laboratory near Daresbury in Cheshire, England, which began operations in 1962 and was officially opened on 16 June 1967 as the Daresbury Nuclear Physics Laboratory by the then Prime Minister of United Kingdom, Harold Wilson...
in Cheshire, England. The project was originally conceived as a test bed for 4GLS
4GLS
The 4GLS was a proposed 4th Generation Light Source, based at the Daresbury Laboratory in Cheshire, England, intended to combine energy recovery linac and free electron laser technologies to provide synchronised sources of synchrotron radiation and free electron laser radiation covering the...
, and consists of:
- A 350keV photoinjector laserLaserA laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
. - An 8.35MeV superconducting RFRadio frequencyRadio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
booster linac. - A 35MeV superconducting RF main linac in which energy is recovered from used electron bunches and given to new bunches.
- An infraredInfraredInfrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
free electron laserFree electron laserA free-electron laser, or FEL, is a laser that shares the same optical properties as conventional lasers such as emitting a beam consisting of coherent electromagnetic radiation which can reach high power, but which uses some very different operating principles to form the beam...
(FEL), using a permanent magnet undulatorUndulatorAn undulator is an insertion device from high-energy physics and usually part of a largerinstallation, a synchrotron storage ring. It consists of a periodic structure of dipole magnets . The static magnetic field is alternating along the length of the undulator with a wavelength \lambda_u...
on permanent loan from Jefferson Laboratory. - An ERL transport system that transports electron bunches through the FEL and back to the linac with the correct RF phase to decelerate them and thereby to recover energy from them.
The ALICE accelerator is an Energy Recovery Linac (ERL) that incorporates all the features of the 4th generation light source albeit at smaller scale. An ERL is not restricted by the dynamic properties of storage rings and, therefore, can attain an unprecedented electron beam brightness limited only by the electron gun. Energy recovery allows also a significant increase in an average power of the light sources (without building a dedicated power station nearby!).
The ability to produce ultra-short electron bunches well below 1ps and an availability of several light sources of different “colour” open up numerous possibilities for conducting investigations of fast processes on a femtosecond scale in molecular and solid state physics to name but a few.
Superconducting Radio Frequency
Superconducting Radio Frequency science and technology involves the application of electrical superconductors to radio frequency devices. The ultra-low electrical resistivity of a superconducting material allows an RF resonator to obtain an extremely high quality factor, Q...
accelerating Non-Scaling FFAG ring, known as the EMMA
EMMA (accelerator)
The Electron Machine with Many Applications is a project at Daresbury Laboratory in the UK to build a linear non-scaling FFAG to accelerate electrons from 10 to 20 MeV. A FFAG is a type of accelerator in which the magnetic field in the bending magnets is constant during acceleration...
project. Planning for the EMMA machine is underway and construction began in September 2009. Commissioning of the EMMA machine is due to begin in March 2010.
Principle
A DC photoelectron gun generates short low emittance electron bunches with the length of several ps and accelerates them to a modest 350keV. The nominal bunch charge on ALICE is 80pC. The bunches are produced in trains lasting from ~10ns to 100ms and the train repetition frequency can vary from 1 to 20Hz. Within the train, the bunches are separated by 12.3ns that corresponds to the laser pulse repetition frequency of 81.25MHz.The electron beam is then injected into the superconductive linac (booster), accelerated to the energy of 8.35MeV and transported to the main linac that increases the beam energy to 35MeV. Both superconductive linacs are cooled down to approximately 20 K with liquid helium. The accelerating phase of the main linac is chosen such that a specific energy chirp is introduced along the bunch so that it can be later compressed longitudinally in a magnetic chicane (bunch compressor). The beam reaches the chicane after being turned by 180° in the first triple bend achromat ARC1.
After compression, the beam, consisting now of sub-picosecond bunches, enters the magnetic undulator that constitutes a major part of the mid-IR Free Electron Laser (FEL). This laser generates IR light with the wavelength of ~5mm.
The spent electron beam is returned back to the entrance of the main linac via the second ARC2 at a precise time when the RF phase is exactly opposite to the initial accelerating phase. This condition requires an accurate adjustment of the electron beam path length that is accomplished by moving the ARC1 as a whole. The beam is now decelerated thus giving its energy back to the electromagnetic field inside the linac RF cavities (energy recovery) and emerges from the linac having the original energy of 8.35MeV. This energy recovered beam is diverted to the beam dump ending its short but useful life
Main parameters
| - | Nominal parameters | Currently achieved |
|---|---|---|
| Gun DC voltage | 350kV | 350kV with nominal HV ceramic; currently gun operates at 230kV |
| Nominal bunch charge | 80pC | 80pC (>~200pC can be also delivered) |
| Cathode | NEA GaAs | NEA GaAs |
| Laser Nd:YVO4(2nd harmonic) | 532nm | 532nm |
| Laser spot | 4.1mm FWHM | Variable |
| Laser pulse length | 28ps FWHM | 28ps with laser pulse stacker |
| Quantum efficiency | 1-3% | ~4% (~15% in the lab conditions) |
| Injector energy | 8.35MeV | Currently 7.0MeV |
| Total beam energy | 35MeV | Currently 30 MeV |
| RF frequency | 1.3GHz | 1.3GHZ |
| Bunch repetition frequency | 81.25MHz | 81.25MHz |
| Train length | 0-100ms | Up to 100µs at 40pC |
| Train repetition frequency | 1-20Hz | 1-20Hz |
| Compressed bunch length | <1ps @80pC | To be measured |
| Peak current in compressed bunch | 150A | To be measured |
| Maximum average current | 13 mA | - |
| MAX current within the train | 6.5mA | >6.5mA but at shorter train lengths |