Also, you can type in a page number and press Enter to go directly to that page in the book. Electron beams with energies up to MeV with small normalized emittance of order millimeters to milliradians and nanocoulombs of charge have been generated by plasma wakes in millimeter gas jets.
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Our systems also can be used for photoresist ashing, ink removal, surface activation and wettability improvement. The PC and PC are tabletop plasma cleaning systems using parallel-plate direct plasma. The process chamber enables the user to install multiple sample shelves, and the high degree of flexibility in configuration supports batch processing of a wide degree of products from small electronic components to larger substrates.
Furthermore, the systems can be configured in three different processing modes that enable the user to select the optimum processing environment.
Plasma Surface Modification of Various Materials. SAMCO plasma cleaners are suitable for plasma surface modification. Various materials such as silicon, glass, metals and polymers can be processed for wettability control. Polymethyl methacrylate PMMA samples were processed using a plasma cleaner and characterized with water contact angle.
The samples showed hydrophilic surface after the plasma processing. This surface modification process enhances adhesion of materials, and some customers use this process for bonding of samples in microfluidic device fabrication. Do you need plasma treatment of non-flat samples? Other questions emerge at still higher laser and beam energy densities.
Chirped pulse amplification CPA laser technology has enabled a proliferation of multiterawatt laser systems. When focused, their peak fields exceed several gigavolts per centimeter, and the quiver energy of electrons in these fields exceeds several MeV. These HED beams are creating macroscopic amounts of relativistic matter in the laboratory for the first time.
Not surprisingly, they are producing a bounty of new relativistic phenomena such as relativistic transparency. At this point, the plasma becomes transparent to the laser pulse it would normally reflect.
Other examples of relativistic phenomena accessible with current laser technology include highly nonlinear plasma wakes in which the plasma is driven to complete blowout, ultrastrong plasma lensing of both photons and particles, and intense radiation generation from the terahertz to x-ray frequency range by various mechanisms. Electron beams with energies up to MeV with small normalized emittance of order millimeters to milliradians and nanocoulombs of charge have been generated by plasma wakes in millimeter gas jets.
Although the electron beams in these experiments had large energy spreads, the acceleration gradient they achieved was more than a thousand times the gradient of a conventional linear accelerator. This leads to the question: Can wakefield acceleration yield sufficient energies and beam quality so as to enable high-energy physics on a tabletop?
Can short plasma lenses enhance the final focus of a linear collider? On the horizon are yet higher density beams and lasers. Chirped pulse amplification technology applied to high-energy lasers is making it possible to consider multipetawatt- to exawatt-class lasers in the near future.
The focused field gradients of such lasers will exceed teraelectronvolts per centimeter, and the quiver energies will exceed gigaelectronvolts. As such extreme beams propagate in plasma, they can be expected to create copious electron-positron pairs and possibly heavier pairs.
It may be interesting to consider questions such as: Can beams undergo a stimulated pair scattering instability by coupling parametrically to the pairs they create? Can backscatter amplification or other techniques be used to make even higher energy density pulses, exceeding even chirped pulse amplification limits?
Using ultrahigh-intensity lasers, it may become possible to simulate some of the properties of black holes. This high acceleration could be used to study Unruh radiation, which is similar in many respects to Hawking radiation, induced by gravitational fields. But it is interesting to study at very large accelerations whether, as Unruh has suggested, there is radiation beyond that predicted by Maxwell.
At sufficiently high intensities, even vacuum can be broken down. Although such fields are beyond the horizon, other nonlinear quantum electrodynamics effects could be accessed at more modest fields. For petawatt, kilojoule-class lasers, a nontrivial pair probability density can be created.
It may be possible to scatter off of this grating with a third laser, thereby demonstrating the nonlinear optics of vacuum. Finally, it is noted that an alternate path to the Schwinger field could be an x-ray free-electron laser.
Three applications are described below in some detail, followed by discussion of seven more applications in briefer presentations. The high cost and size associated with conventional rf accelerator technologies has been a prime motivation in advanced accelerator research for more than two decades.
Wakefield accelerators driven by high energy density laser or particle beams promise an entirely new type of technology for building compact high-energy accelerators. Laser pulses propagating in plasmas can generate large-amplitude plasma waves, that is, wakefields, which can be used to trap and accelerate electrons to high energies.
The amplitude of the plasma wave is largest when the laser pulse duration or its modulation is on the order of the plasma period. This laser-plasma interaction forms the basis for the laser wakefield accelerator LWFA. A wealth of new and interesting experimental results on LWFAs has been obtained in recent experiments around the world see Figure 4.
On the theoretical and computational front, detailed analyses of the propagation and stability properties of intense laser pulses in plasma channels have been conducted. Recent advances in algorithms and high-performance computing are enabling fully self-consistent modeling of full-scale wakefield experiments in three dimensions for the first time.
This work provides a strong foundation for next-generation wakefield accelerator research aimed at producing electron beams with gigaelectronvolt energies and high beam quality. To reach multigigaelectronvolt electron energies in an LWFA, it is necessary to propagate an intense laser pulse long distances many Rayleigh ranges in a plasma without disruption.
However, a number of issues associated with long-distance propagation in plasma must be resolved before a viable, practical high-energy accelerator can be developed. These issues include optical guiding, instabilities, electron dephasing, and group velocity dispersion, all of which can limit the acceleration process. The scale length for laser diffraction is given by the Rayleigh range; therefore, the acceleration distance is limited to a few Rayleigh ranges.
Since this is far below that necessary to reach gigaelectronvolt electron energies, optical guiding mechanisms such as relativistic focusing, ponderomotive channeling, and preformed plasma channels are necessary to increase the acceleration distance.
There is, in fact, ample experimental confirmation showing extended guided propagation in plasmas and plasma channels. The combining of such guiding techniques with a. Another approach to achieving longer acceleration distances is being pursued at several particle beam facilities.
These take advantage of the natural tendency of particle beams to propagate longer distances without spreading, compared to lasers. For example, at the SLAC, electron beams have been used to generate wakefields over a meter and to accelerate electrons by as much as MeV.
Lasers incident on solid targets can also be used to accelerate heavier particles— protons and ions. The generation mechanism has been attributed to the electrostatic field set up by the escaping jet of hot electrons from the back of the target. Over the past four decades, the energy of these lasers has increased at a rate comparable to the growth in computer power, culminating in the National Ignition Facility NIF now under construction. The field of laser-plasma interactions is a vital enabling technology for these many applications as well as a remarkable testbed for understanding broadly applicable nonlinear plasma science.
The challenges associated with the interactions of long-pulse high-energy lasers with plasmas is well illustrated by considering the nominal hohlraum target for achieving ignition on the NIF.
As shown in Figure 4. The relative power in these cones is tuned to provide the time-dependent x-ray symmetry required for the implosion. Excellent absorption of the laser beams is desired, and excellent temporal and spatial control of the absorption is required for the requisite implosion symmetry. The interaction physics is extraordinarily rich. The beams can undergo enhanced bending in places where the plasma flow is near sonic, where significant energy transfer among crossing beams can also occur.
These instabilities were controlled in previous. The schematic on the right shows the hohlraum irradiated by NIF beams. Courtesy of Lawrence Livermore National Laboratory. Understanding and controlling their evolution in new regimes and over the centimeter scales and higher energies at NIF pose a significantly greater challenge. Rarely have questions of such a fundamental physics nature been so directly coupled to a programmatic and societal need.
In the past decade, the development of short-pulse, ultrahigh-power lasers has motivated another approach to inertial fusion energy called Fast Ignition. In this case, cold deuterium-tritium DT fuel is first compressed to high density, and fusion burn is then initiated by a rapid heating of a portion of the fuel to high temperature.
Significantly higher gains are possible compared to the conventional approach. Furthermore, the Fast Ignition scheme is less sensitive to hydrodynamic instabilities and mix, since the processes of fuel compression and hot spot creation are separated. The critical issue for Fast Ignition is the efficient generation and transport of a short, ultraintense energy flux to the precompressed fuel, a relatively unexplored topic involving many extremely rich nonlinear physical phenomena and many potential applications.
The following estimates illustrate the challenge: The basic requirement is to heat to about 10 keV a volume of cold fuel with a radius equal to the alpha particle range, which will enable a propagating burn into the remaining fuel. The incident laser energy needs to be roughly an order-of-magnitude larger, depending on the efficiency of energy transfer from the laser to the dense fuel and on the size of the hot spot created.
Just how efficiently such beams can be generated and transported looms as a key fundamental question. Intense laser pulses made with chirped pulse amplification technology provide a key tool for investigating physics in this regime. These enable important features of this ultraintense laser plasma regime to be explored. The features include relativistic self-focusing and filamentation of the laser light, pronounced hole boring into overdense plasma, and a variety of acceleration processes.
Other notable effects include self-generated magnetic fields with an amplitude up to 10 9 G and multi-MeV ion generation. They illustrate several acceleration mechanisms, such as heating due to the oscillating ponderomotive force, conversion of transverse laser fields to longitudinal fields at overdense plasma layers, and electron acceleration at the betatron resonance in relativistic laser channels an inverse free electron laser FEL process.
Many of these effects have now been observed in experiments, but much more work is needed for a quantitative understanding. The transport of ultraintense energetic particle fluxes over distances of hundreds of microns from the laser absorption region to the compressed fuel is another very challenging issue at the forefront of high energy density physics.
For example, if a. Many physical processes then come into play, including strong return current heating, excitation of the Weibel instability, formation and coalescence of current filaments and magnetic channels, as well as various instabilities that can disrupt the beam propagation see Figure 4.
Especially encouraging have been experiments at Osaka University in which cold fuel has been assembled to high density and a significant heating of the fuel by a short, very intense, low-energy J laser pulse has been observed.
An energy transfer efficiency from the short laser pulse to the fuel of approximately 20 percent has been inferred. Contours of magnetic-field structure due to the Weibel instability are shown. Heavy ion drivers are attractive for inertial fusion energy IFE because of their efficiency and because the final focusing onto the target is achieved by magnetic lenses.
The magnetic lenses can be made robust to the effects of the target explosions, which must repeat at rates of order 5 Hz. Such intense beams represent a significant extension beyond current state-of-the-art space-charge dominated beams. The beams behave as nonneutral plasmas, exhibiting collective processes, nonlinear dynamics, and instabilities that must be understood and controlled if heavy ion fusion is to be achieved.
Major issues arise in two parts of the driver system: For example, emittance growth unwanted increase in beam temperature in the driver accelerator can take place through complicated distortions driven by collective processes, imperfect applied fields, image fields from nearby conductors, and interbeam forces.
To assist in the final transport through the chamber, plasma lenses, as employed in other accelerator applications, are being studied experimentally and theoretically for heavy ion fusion.
They offer the promise of stronger focusing with greater chromatic acceptances and reduced demands on beam quality from the driver. However, they introduce beam and background plasma dynamics, including the following: New opportunities for addressing these challenges are afforded by the development of new experimental facilities and computational tools—an example is shown in Figure 4.
Chirped pulse amplification techniques have pushed forward the peak intensity of lasers by orders of magnitude and hence have opened a window on a rich array of new physics topics. It is of interest, then, to consider other mechanisms for amplifying lasers that may potentially exceed even the limits of CPA lasers.
The concept of neutralized drift of intense ion beams through the target chamber is essential for the viability of an economically competitive heavy ion fusion power plant. The physics of neutralized drift has been studied extensively with PIC simulations. To provide quantitative comparisons of theoretical predictions with experiment, the NTX has been developed at Lawrence Berkeley National Laboratory in collaboration with Princeton Plasma Physics Laboratory. The neutralized ion beam drifts for a distance of a meter to converge onto a small focal spot, as witnessed by an image on a glass plate lower right.
The same magnet configuration without plasma yields a large spot at the same location, owing to beam blow-up when the space charge is unneutralized lower left. Hardware for the full neutralization experiment with a radio-frequency plasma source is also complete and will be installed at NTX near the focal point to study volumetric plasma effects to simulate the effects of photoionized plasmas in a fusion chamber and gas interactions.
Courtesy of Lawrence Berkeley National Laboratory. One idea is to store energy in a long pump pulse that is quickly depleted by a short counter-propagating pulse, which can be then focused on target see Figure 4. This counter-propagating wave effect has already been quite successfully employed in Raman amplifiers using neutral gases. But at high power, there appear to be nonlinear effects in plasma that make such methods particularly suitable for high-power pulse compression.
The challenge is to evaluate whether these mechanisms in fact produce compression effects. One issue is whether the short pulse can reach. The first optical system, essentially operating as a flashlamp, delivers energy without providing a strong focus. The second moderate-aperture low-power optical system delivers the short, counter-propagating, focusing pulse that captures, by Raman backscatter in the plasma, the pump fluence, effectively compressing it in time and then focusing it in space.
Also undetermined theoretically is the degree to which amplified pulses can retain focus through practical plasmas. The availability of a compact isotope generator, built around existing or minimally modified target technology, might offer a compact, flexible alternative to cyclotrons. The laser-driven accelerator technology needs to be explored to its full potential in order to determine its global or niche impact in nuclear medicine imaging fields, such as positron emission tomography PET , one of the fastest-growing imaging modalities in the world today.
Experiments are under way to boost activation levels to the tens of millicuries range. Laser-accelerated protons have also been used for isotope production. The generation of extremely intense, short-pulse proton beams by very high intensity laser beams interacting with solid targets has great potential for diagnosing dense plasmas, as illustrated in Figure 4.
Applications for these protons include proton radiography in medicine and weapons programs. To date, the medical application has been generally too expensive for the treatment value added to justify wide deployment of proton beam facilities. This is particularly true in the present climate of medical cost containment. However, a cheaper tabletop proton source, other than a synchrotron or cyclotron, could alter the economics and deliver a new, powerful imaging tool to the physician.
The DOE Stockpile Stewardship program is interested in the use of a large synchrotron for time-resolved tomographic imaging of weapon implosion simulations. As another significant application, multikilojoule, 5- to ps laser beams will enable high-quality radiography using to keV x rays.
This has potential importance for NIF, where the x rays produced can reach acceptable brightness for backlighting studies of the implosion physics of capsules or for equation-of-state studies. The target was heated by a laser; the fine structures shown in the image are due to plasma electric fields that deflect the protons.
Campbell, Imperial College, London; S. Clarke, Rutherford Appleton Laboratory; and A. Mackinnon, Lawrence Livermore National Laboratory. The infrared IR free electron laser at Jefferson National Laboratory has demonstrated simultaneous production of femtosecond x rays from intracavity Thompson scattering of the wiggler IR radiation off the electron beam, regular IR FEL lasing and terahertz THz radiation from the recirculating linac bends, at record fluences in all three parts of the spectrum.
The IR FEL is also beginning to demonstrate the potential value of such radiation for research and development and in the commercial marketplace. There are a number of ways in which high energy density lasers and. The first is to use the laser-accelerated electrons described in the previous sections. These bunches are femtosecond in duration, leading to the possibility of generating ultrashort radiation pulses ranging from the terahertz to the x-ray regime from tabletop devices.
Coherent terahertz radiation can be generated by allowing these femtosecond bunches to radiate using, for example, diffraction or transition radiation. X rays are created when these bunches are allowed to interact back with a part of the laser that generated them. An alternative way to make radiation is within the plasma itself.
Laser-driven plasma wakes have a frequency in the terahertz regime and can be converted into powerful radiators up to gigawatt levels in principle. By applying a perpendicular magnetic field, one can give to the wakes a positive group velocity, enabling them to propagate through and emanate from the plasma as radiation. Coherent light over a broad range of frequencies can also be obtained from an FEL in which the insertion device is a plasma.
When a high-brightness electron beam propagates through a plasma of lower density than the beam, the plasma electrons are blown out, leaving a column of positive ion charge. The ion column produces a focusing force plasma lens on the beam that causes it to radiate.
Thus the plasma acts as a wiggler that is both tunable and strong. The coherent amplification of a signal by this ion channel laser mechanism was demonstrated in the microwave regime in Japan, and spontaneous emission in the x-ray regime was seen recently in the E experiment at SLAC see Figure 4. If this mechanism can be made to lase at higher frequencies, it may provide a simple tunable insertion device for FELs. Electron clouds are one of the most significant performance-limiting factors in circular accelerators and storage rings carrying high energy density positively charged beams, and they are a serious concern for future machines such as the Spallation Neutron Source at Oak Ridge National Laboratory, the Large Hadron Collider at CERN, and heavy ion fusion accelerators.
Although the clouds themselves are very low density, their creation and their collective effect on the beam are a direct consequence of the high energy density of the beams in such accelerators. These electron clouds arise when the circulating beam emits synchrotron radiation or ionizes residual gas, or when stray beam particles hit the walls of the vacuum chamber. Any of these mechanisms generates electrons, which are attracted toward the center of the chamber by the positive potential of the circulating beam see Figure 4.
In addition, the secondary emission process may compound the effect. The long yellow strip is synchrotron radiation from a bending magnet. Reprinted, with permission, from S. The collective fields created in such cases are not unlike highly nonlinear wakes excited in wakefield accelerators. Advanced plasma and beam modeling tools are being applied to this problem; an improved understanding resulting from simulation studies will play an important role in controlling the electron cloud and two-stream instabilities.
The beam not shown occupies a small region at the center of the chamber, of order 1 mm in diameter. Furman, Lawrence Berkeley National Laboratory. Laser wakefield acceleration in high-density plasmas produces longitudinal electric fields comparable to the laser transverse field.
With such fields, particles could be accelerated to relativistic energies in such short distances as to significantly extend their lifetime. Particle-in-cell simulations by A. These protons can be used to produce pions, which have a lifetime at rest of 20 ns and are well synchronized to the fs laser pulse.
This long lifetime would make it possible to accelerate the pions to higher energy, if necessary, with conventional i.