How Does a Linear Accelerator Accelerate Particles in Physics?
A linear accelerator is also named as a linear particle accelerator. In radiation therapy, this linear particle acceleration is used for medicinal purposes because it produces the x-rays and electrons that have high energy. Hence the linear particle accelerator is used for many therapeutic applications. Also, they are useful in particle physics because they can produce the highest kinetic energy that can be achieved directly by the linear accelerator. Furthermore, a linear accelerator is suitable for electrons and protons in particle physics to get high kinetic energy.
The linear accelerator sometimes called linac is a kind of particle accelerator that has the capability to increase the charged subatomic particles or we can say ions where charged particles are subjected to a series of electric potentials that oscillate along with the linear beamline. Well, such a method of charged particle acceleration was first experimented by Leo Szilard. Cancer cells can be cured with medicine in which ionizing radiation damages the DNA of cells.
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Linear Accelerator Construction and Working
A linear accelerator is a machine that can accelerate electrons close to the speed of light with an electromagnetic field. Electrons or protons with more than 18 MeV are bombarding to the target, and higher kinetic energy is produced. In a tungsten target, the particles produce the bremsstrahlung radiation like in the conventional tube of X-ray. Well, the design of the LINAC machine is different from the x-ray tube because of higher energy.
Components of a Linear Accelerator
Here are the steps and essential components to generate high energy photons.
Electron Generation Component: Guide and generate electrons into the accelerating waveguide.
Electron Acceleration Component: Accelerate the electrons nearly to the light speed.
Beam Transport: Transport the electrons to the target.
Ionization Chambers, Collimation and Flattering Filters: Modify the beam before use
Several Accessories For Linear Acceleration Working:
Radiofrequency Generator: Generates electromagnetic waves in the component.
Pulse Modulator: Produces timed energy pulses to the RF generator and electron gun.
Control Panel: operational panel to control the function of the linear accelerator.
Linear Accelerator Working Principle: How Does a Linear Accelerator Work?
In a linear particle accelerator, the drift tube has positive potential while electrons have a negative potential. A bunch of electrons are accelerated to the drift tube because of this potential difference. RF source changes its polarity as soon as the particles enter the first drift tube. Hence, the first drift tube becomes negatively charged, but the second drift tube is positively charged. The inertia of electrons makes them come out from the drift tube. So, electrons are pushed into the first tube, and at the same time, they are attracted to the second tube in the same direction.
Electrons’ velocity turns bigger because of their acceleration. So, this is the reason why drift tubes are longer. Speed of electrons increases as soon as electrons come closer to the target. LINAC is long because of longer drift tubes, and the number of tubes is also higher.
Who Operates this Equipment?
Mostly the radiation oncologists prescribe the treatment dosage and volume to the patients. Furthermore, a dosimetrist and medical physicist will decide the amount and time of dosage, calculating the time for acceleration. Radiation therapy also includes linear acceleration, and therapists may give radiation medication on regular bases to the patients.
Application of Linear Accelerator
Different industries, researches and medicines include the various usage of this highly efficient accelerator for a different purpose.
LINAC Synchrotron Injector: It is the first stage for any high energy accelerator.
Semiconductor Processing: To process various semiconductors.
Boron Neutron Capture Therapy (BNCT): In this therapy, nuclear reactors are used conventionally as a neutron source. A LINAC-based source of the neutron can provide a better-controlled energy spectrum of the neutron. It is a low -cost machine that produces less reactor associated radioactive waste
Isotope Production: Linear particle accelerators are ideal for producing isotopes like PET isotopes.
Linear Accelerator Safety
LINAC machines are used for cancer treatment, and it produces higher radioactive energy. So, this machine may harm patients in many ways, but it is essential to ensure linear accelerator safety for cancer patients.
Radio oncologists will first plan the proper treatment according to the patient’s medical reports. So, before the treatment, the plan is made with the help of a dosimetrist and radiation physicist.
Quality procedures are there that ensures the quality treatment, and before the surgery, the plan is checked thoroughly. Also, the process includes the surety of therapy to deliver in a planned manner. LINAC is designed for controlled radiation, and doctors can set it according to the treatment.
Tracker is a particular machine to check the proper functioning of the machine, and a radiation therapist will check the device before the treatment every morning. The tracker monitors the radiation velocity and intensity to ensure the uniform functioning of beams.
In this process, a radiation physicist also does monthly and weekly checking of the device.
People Who made it Happen
Various physicists and biology experts have contributed to the building of what a linear accelerator is today. It is because of the consistent work of these heroes that, today there is a cure for malignant tumours. Henry Kaplan, Edward Ginzton, Karl Brown and various other notable experts have contributed to the design and working of it. Variety of trials and errors later, the successfully running and evolving machine has changed the lives of many.
It all began when Henry Kaplan thought it was possible to destroy the malignant tumour without actually disturbing or harming the surrounding healthy tissues with an x-ray beam. Giving food for the same thought he began working on it. Soon he felt the need to take the help of physicists for the same. Back then, the linear accelerator was also nicknamed an atom smasher. Edward and Henry spent the first half of the morning discussing the properties of a medical linear accelerator.
Years later, the vision of all those who worked on making this machine happen is carried forward. Kaplan was all in working on it as for him, it was the machine of the future. It was light years ahead of its time, the machine changed the lives of patients and the world of oncology.
History of how the Medical Linear Accelerator was Born
In 1952, two innately talented physicists, Namely Henry Kaplan and Ed Ginzton began working on the concept of a linear accelerator.
In 1956, in the Stanford hospital in San Francisco, the first linear accelerator was installed.
In 1959, The medical linear accelerator was brought to the Palo alto campus, since the Stanford medical school and hospital was moved there.
In 1962, a series of experiments began to see if radiation works best with chemotherapy. Kaplan and Saul Rosenberg worked together to improve the chances of patients' survival.
In 1994, A great invention was made at Stanford. Something called cyberknife was introduced which narrowed down x-ray beams in a precise manner.
In 1997, A further step was taken to advance the use of linear accelerators by combining with intensity modulation radiation therapy. The result was that many thin beams of radiation could be achieved from any desired angle.
In 2004, four-dimensional radiotherapy was implemented.
Facts about the Linear Accelerator
The very first medical use of linear accelerator was done in the year 1953, in hammersmith hospital, on a patient named Gordon Isaacs, he was treated for retinoblastoma.
Stanford linear accelerator is a 2-mile radiation machine that was built in the year 1966 but was later shut down. It is also known as SLAC and it is a positron-electron collider.
Linear accelerators are also called particle accelerators. The particle accelerators are used in a wide variety of fields. Oncology, cosmology, nuclear physics to name a few.
The radiotherapy given by the linear accelerators is far more precise and has advantages over the old traditional method of cobalt therapy.
Apart from radiotherapy, the rays are also used to sterilize certain medical equipment.
During the early use of accelerators, the commonly used ones were called the Cockcroft Walton accelerator and Van de Graaff accelerator. The latter uses the moving fabric belt to carry the charge.
FAQs on Linear Accelerator: Definition, Working Principle & Applications
1. What is a linear accelerator (LINAC)?
A linear accelerator, commonly known as a LINAC, is a type of particle accelerator that accelerates charged particles such as electrons, protons, or ions to very high speeds along a straight path. Unlike circular accelerators, it uses a series of alternating electric fields to progressively boost the energy of the particles as they travel in a straight line through a long evacuated tube.
2. What is the working principle of a linear accelerator?
The working principle of a linear accelerator is based on the use of an oscillating high-frequency alternating electric field. The setup consists of a series of hollow cylindrical electrodes, called drift tubes, arranged in a line. The key steps are:
- A charged particle is injected from an ion source into the first tube.
- An alternating voltage is applied between the drift tubes. The particle is accelerated by the electric field in the gap between the tubes.
- Inside the hollow drift tube, the particle is shielded from the electric field and 'drifts' at a constant velocity.
- During this drift time, the polarity of the electric field is reversed. When the particle emerges from the tube and enters the next gap, it is once again accelerated by the field.
- As the particle gains speed, the drift tubes must get progressively longer to ensure the particle arrives at each gap at the right moment to be accelerated.
3. What are the main applications of a linear accelerator?
Linear accelerators have several important applications across different fields. The most significant uses include:
- Medical Field: They are extensively used in external beam radiotherapy to treat cancer. The high-energy X-rays or electrons produced by the LINAC are precisely targeted to destroy cancerous tumours.
- Industrial Applications: LINACs are used for non-destructive testing of materials and for sterilising medical equipment. They also serve as X-ray sources for scanning cargo containers at ports and borders.
- Scientific Research: In particle physics, they are used for fixed-target experiments and as injectors for larger, more powerful circular accelerators like synchrotrons. They are also used to generate intense X-ray beams for studying materials and biological molecules.
4. What are the key advantages and limitations of a linear accelerator?
Linear accelerators have distinct advantages and limitations.
Advantages:
- They can accelerate particles to very high energies, as the final energy is limited only by the length of the accelerator.
- They do not suffer from synchrotron radiation losses, a major issue for light particles like electrons in circular accelerators.
- The particle beam produced is highly collimated and easy to extract for experiments or treatment.
- They are very large and require a significant amount of physical space, often several kilometres long for high-energy physics.
- The construction and operation are extremely expensive and consume a large amount of electrical power.
- For a given length, a particle only gets one pass of acceleration, unlike in a circular accelerator where particles can be accelerated over many turns.
5. Why do linear accelerators use alternating electric fields instead of a single, constant high voltage?
Using a single, constant high voltage to achieve the immense energies required would be practically impossible. Generating and insulating a static potential of billions of volts would lead to massive electrical breakdown (sparking) and presents insurmountable engineering challenges. The genius of the LINAC design is to use a much lower, oscillating voltage to provide a series of small, synchronised 'pushes'. Each push adds to the particle's kinetic energy, allowing it to reach a very high final energy without ever needing to overcome an impossibly large single potential difference. This method of resonant acceleration is far more efficient and achievable.
6. How does a linear accelerator (LINAC) differ from a circular accelerator like a cyclotron?
The primary difference lies in the particle's trajectory and the method of acceleration.
- Path: In a LINAC, particles travel in a straight line. In a cyclotron, particles travel in an expanding spiral path guided by a strong magnetic field.
- Magnetic Field: A LINAC does not require a large magnetic field for bending the path (only for focusing the beam). A cyclotron fundamentally relies on a constant magnetic field to keep the particles moving in a circular path.
- Acceleration: A LINAC uses a series of drift tubes with an alternating electric field. A cyclotron uses two 'D'-shaped electrodes (Dees) with an alternating electric field in the gap between them.
- Energy Limit: The maximum energy in a LINAC is limited by its physical length. A cyclotron's energy is limited by relativistic effects, where the particle's mass increases at high speeds, causing it to fall out of sync with the accelerating field.
7. In what specific ways is a LINAC used for cancer treatment in modern medicine?
In modern radiotherapy, a medical LINAC generates high-energy beams to destroy cancer cells. The machine accelerates electrons, which are then used in one of two ways:
- The electron beam can be used directly to treat superficial tumours.
- More commonly, the electrons are directed to strike a heavy metal target (like tungsten), which causes them to decelerate rapidly and produce a beam of high-energy X-rays.
