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We report a study of the process of nonlinear Thomson scattering (NTS) of a tightly focused relativistically intense laser pulse by an ensemble of electrons simulating the result of ionisation of an ultrathin nanofoil. The description of all six components of a laser pulse is based on the Stratton – Chu integrals describing radiation focused by an off-axis parabolic mirror into a spot down to the diffraction limit, which is of practical interest for modern experiments with extreme-intensity lasers, including diagnostics of their parameters. The interaction of a laser pulse with electrons is simulated by the test-particle method, and the resulting trajectories are used to calculate the characteristics of secondary electromagnetic radiation. The effect of the laser-pulse focal spot diameter in the range λ – 6λ on the angular distributions of the radiated energy and NTS spectra, as well as of a laser-beam peak intensity of 1021 – 1022 W cm−2 on the spectral width of the secondary radiation is studied in relation to the experimentally implemented focusing scheme using the example of a laser pulse with an initial homogeneous spatial distribution and a duration of ∼25 fs.

A wide variety of plasma geometries and modalities have been utilized for chemical analysis to date, however, there is much left to be understood in terms of the underlying mechanisms. Plasma diagnostics have been used for many years to elucidate these mechanisms, with one of the most powerful techniques being laser scattering approaches. Laser scattering provides information about the energetic species distributions, in terms of kinetic energy and densities, which can provide invaluable insights into the fundamental processes of chemical analysis plasmas with minimal perturbation. Thomson scattering (TS) from free electrons is the most difficult to implement due to the extremely stringent instrumental requirements for discerning the signal from competing scatterers in low-density plasmas, such as those seen in analytical chemistry applications. Nonetheless, relatively few instruments have been developed to satisfy these stringent requirements. In this paper, the design and characterization of a transmission-type triple grating spectrograph (TGS), with high numerical aperture (0.25)/contrast (≤10−6 at 532 ± 0.5 nm)/stray light rejection (∼1.8 × 10−8 at 532 ± 22–32 nm) required for TS, will be presented. In addition, proof-of-principle measurements on glow discharges operated under typical optical emission spectroscopy (OES) conditions demonstrate the high light throughput and low limits-of-detection (∼109 cm−3 at ∼1 eV Te) afforded by the new instrument.

Firstly, the electron density distribution of inductively coupled plasma (ICP) is measured by laser Thomson scattering (TS) method and the features of the ICP under the same experimental conditions are simulated by finite element method (FEM). The simulated results are in good agreement with the experimental results, which verifies the accuracy of the ICP generation simulation model. Secondly, the propagation characteristics of terahertz wave in ICP are measured by terahertz time domain spectroscopy (THz-TDS) and calculated by FEM according to the electron density distribution of ICP simulated in the first step above. The high consistency between the experimental and simulation results of terahertz wave propagation characteristics in ICP further proves the accuracy of terahertz wave transmission model in plasma and the feasibility of joint simulation with ICP generation simulation model.

We present optical Thomson scattering measurements of electron density and temperature in a large-scale (~2 cm) exploding laser plasma produced by irradiating a solid target with a high energy (5-10 J) laser pulse at high repetition rate (1 Hz). The Thomson scattering diagnostic matches this high repetition rate. Unlike previous work performed in single shots at much higher energies, the instrument allows point measurements anywhere inside the plasma by automatically translating the scattering volume using motorized stages as the experiment is repeated at 1 Hz. Measured densities around 4$\times 10^{16}$ cm$^{-3}$ and temperatures around 7 eV result in a scattering parameter near unity, depending on the distance from the target. The measured spectra show the transition from collective scattering close to the target to non-collective scattering at larger distances. Densities obtained by fitting the weakly collective spectra agree to within 10% with an irradiance calibration performed via Raman scattering in nitrogen.

The temporal evolution of the electron temperature T e and density n e has been measured at two positions on the centre-line of an asymmetrically pulsed bi-polar HiPIMS plasma using incoherent laser Thomson scattering (LTS). The magnetron was operated with a tungsten target in argon atmospheres. The results show that in the plasma afterglow when positive voltage pulses are applied (above a threshold of at least 200 V) significant heating of the electrons can occur in which T e can rise to values comparable to the those measured in HiPIMS on-time. The on-set of the rises in T e are significantly delayed relative to the start of the positive pulse, with the delay time decreasing with the magnitude of the positive voltage. The delay is only weakly dependent on the operating pressure. The presence of large positive pulses can also affect the local electron density with n e seen to decay significantly more quickly in the afterglow than for the corresponding unipolar pulsing case, in which no positive pulse is applied. The LTS measurements were complemented by a time-resolved study of the plasma optical emission (neutral argon and tungsten lines). With increasing positive potentials applied in the afterglow the Ar(I) line intensities grow consistent with increasing T e. Interestingly, W(I) line intensities are detected in the afterglow with positive voltages >200 V despite the termination of all target sputtering, suggesting that tungsten is being re-sputtered from the vessel walls. With the aid of emissive probe measurements of the spatial and temporal evolution of plasma potential profile along the centre-line we discuss the phenomena of plasma electron heating and wall sputtering in the positive pulse. This is done in terms of the existence of a non-sustained reverse discharge, in which the vessel walls become an effective cathode.

This contribution describes an approach to realize dichroic mirrors for fifth-harmonic separation with a diameter of 12”. The optics will be used at the National Ignition Facility to build a diagnostic based on Optical Thomson Scattering, which requires a high energy, pulsed laser operating at 211nm wavelength. Since the ultra-violet absorption edge of the most commonly used high refractive coating materials is above 211nm, only a few oxide materials as for example alumina are suitable for this wavelength. The applied material combination Al2O3/SiO2 provides a small refractive index contrast of about 0.2, which requires a coating process with a very high precision and uniformity to realize complex thin film designs. To achieve a physical layer thickness uniformity better than 0.5%, the linear motion concept of the MAXIMA ion beam sputtering machine [1] is combined with an additional substrate rotation. The layer thickness is controlled precisely by optical broad band monitoring in the wavelength range from 220nm to 1050nm. To realize a surface figure of λ/10 at 633nm for a clear aperture of 250mm diameter, the multi-antireflection coating on the backside is utilized for stress compensation. Experimental results regarding the spectral performance, the mechanical stress, the surface roughness and the laser damage resistance will be presented and discussed.

Terahertz (THz) streaking is a novel method to measure the temporal profile of a relativistic electron beam with a few femtosecond (fs) duration. Recently, a THz oscilloscope was proposed for hundred-fs metrology with a significantly increased dynamic range, which used a circular polarized THz pulse instead of a linearly polarized one. In this paper, we propose a THz oscilloscope for temporal characterization of relativistic electron beam with few picosecond (ps) duration, which is crucial for THz free-electron lasers and Thomson scattering X-ray sources, etc.

In this paper, the pixelated phase mask (PPM) method of interferometry is applied to coherence imaging (CI)—a passive, narrowband spectral imaging technique for diagnosing the edge and divertor regions of fusion plasma experiments. Compared to previous CI designs that use a linear phase mask, the PPM method allows for a higher possible spatial resolution. The PPM method is also observed to give a higher instrument contrast (analogous to a more narrow spectrometer instrument function). A single-delay PPM instrument is introduced as well as a multi-delay system that uses a combination of both pixelated and linear phase masks to encode the coherence of the observed radiation at four different interferometer delays simultaneously. The new methods are demonstrated with measurements of electron density ne, via Stark broadening of the Hγ emission line at 434.0 nm, made on the Magnum-PSI linear plasma experiment. A comparison of the Abel-inverted multi-delay CI measurements with Thomson scattering shows agreement across the 3 × 1019 < ne < 1 × 1021 m−3 range. For the single-delay CI results, agreement is found for ne > 1 × 1020 m−3 only. Accurate and independent interpretation of single-delay CI data at lower ne was not possible due to Doppler broadening and continuum emission.

The National Ignition Facility (NIF), the world’s largest and most energetic laser, employs 192 laser beams to achieve inertial confinement fusion by irradiating a mm scale fusion target. The optical Thomson scattering (OTS) laser is being deployed to probe the target and understand the target implosion physics using 3ω and 5ω probe beams. Understanding of the plasma physics will enable improvements of the fusion performance. OTS is a complex system employing many automated alignment loops. Centroid based approach is one of the common approaches for detecting the position of normal Gaussian beams within the OTS for beam alignment. However, due to several optical effects the alignment beam used for one of the pointing loops is shaped like a comet. The pointing beam exhibits a faint tail and a brighter head. Centroiding with a high threshold usually is able to select the brightest spot located within the head. However, there are cases when the brightest region moves around, in some cases the brightest spot appears in the tail, leading to an oscillation in the beam position with the current centroid-based detection scheme. The purpose of this work is to investigate approaches to find a suitable solution to this oscillation and implement a stable beam positioning algorithm.

The radiation character of nonlinear Thomson scattering is investigated in the interaction of Laguerre-Gaussian circularly polarized laser pulses with a single electron in the angular plane. With theoretical analysis and numerical calculation, it is shown that the angular radiation distributions have annular structures with great fourfold or plane symmetry in pulses characterized by comparatively lower laser intensity (a0 < 6), prolonged pulse duration (τ > 50fs)or wide beam waist (b0 > 5μm). In other circumstances, a vortex radiation pattern is found for the first time on the basis of the electron dynamics. Further, by increasing the initial phase of laser pulse, the overall angular radiation has an interesting counter-clockwise rotating trend with a cycle of Δξ0 = 2π. These results would help the understanding of nonlinear Thomson scattering and push forward the research of twisted X/γ-ray generation in optical laboratory.

A new divertor Thomson scattering system has been developed for the MAST-U tokamak. The diagnostic will produce electron density and temperature profiles along the Super-X strike leg. The existing polychromator design has been adapted for low temperature measurements. A new 1061 nm channel with 2 nm bandwidth has been added to enable measurements down below the previous ∼5 eV limit on the core system. The optical filters used in the system have OD6 light rejection alongside a 1064.1 nm laser line filter to reduce stray light in the digitized channels. A new averaging technique has been applied to the scattered signal traces to improve the core Thomson data in the scrape-off layer. The technique reduces the systematic noise level in this region. This leads to a reduction in the error values for electron density and temperature measurements and, in particular, the digitizer noise. The technique has been applied to produce a radial profile for a number of L-mode MAST discharges down to very low densities of ∼1 × 1018 m−3.

A scalable system for real-time analysis of electron temperature and density based on signals from the Thomson scattering diagnostic, initially developed for and installed on the NSTX-U experiment, was recently adapted for the Large Helical Device (LHD) and operated for the first time during plasma discharges. During its initial operation run, it routinely recorded and processed signals for four spatial points at the laser repetition rate of 30 Hz, well within the system's rated capability for 60 Hz. We present examples of data collected from this initial run and describe subsequent adaptations to the analysis code to improve the fidelity of the temperature calculations., 5 pages, 5 figures

Stray laser light is a serious problem that interrupts the measurement of electron temperature and density in Thomson scattering (TS) systems. This paper presents a ray-tracing simulation of stray laser light in HL-2M TS systems. A model including (i) a simplified laser-beam injection system, (ii) the scattered-light collection systems for central-point TS (CPTS) and edge TS (ETS), and (iii) the HL-2M vessel is built using the TracePro and CATIA software packages based on measurements of the bidirectional scattering distribution function at a wavelength of 532 nm. The simulation results show that no stray laser light reaches the injection surface of the collection lens of the CPTS system, and only a few stray laser rays of all the rays reaching the injection surface of the collection lens of the ETS system can be collected when the energy threshold per ray is 1 × 10−16. The stray laser rays that reach the scattered-light collection systems are mainly from the first and second parts of the slides of the beam dump, so decreasing the roughness of those parts could be effective in reducing the level of stray laser light.

A diagnostic system, which has a design goal of high-portability, has been designed at Oak Ridge National Laboratory (ORNL). This project aims at providing measurements of key plasma parameters (ne, Te, ni, Ti) for fusion-relevant devices, utilizing Thomson scattering (TS) and optical emission spectroscopy (OES). The innovative design employs mostly commercial off-the-shelf instrumentation and a traveling team of researchers to conduct measurements at various magnetic-confinement plasma devices. The TS diagnostic uses a Quantel Q-smart 1500 Nd:YAG laser with a 2ω harmonic generator to produce up to 850 mJ of 532 nm laser pulses at 10 Hz. Collection optics placed at the detection port consists of an 11 × 3 optical fiber bundle, where the TS diagnostic uses an 11 × 1 subset array of the fibers, the OES diagnostic uses another 11 fibers, and the remaining fibers are available to the host institution. The detection system is comprised of two separate IsoPlane-320 spectrometers with triple-grating turrets of various line spacing and two PI-MAX 4 intensified CCD detectors, used simultaneously to measure a broad range of ion, impurity, and electron parameters. The self-contained diagnostic package also includes a data processing and storage system. The design and initial implementation of the TS-OES diagnostic system are described. The experiments from the proof-of-principle operation of the portable package on a high density (∼2.5 × 1022 m−3) and low-temperature (∼5 eV) electrothermal arc source at ORNL are also discussed.

As an important component of space environment, the ionospheric plasma is the main background environment for the operation of low-orbit spacecraft. The study of ionospheric plasma environment parameters and the enrichment of plasma environment data are beneficial to improve the reliability of low-orbit spacecraft operation. Langmuir probe is the most popular method for detecting the plasma parameter of ionospheric, however, it has some defects. In this paper, we design a plasma generator based on radio-frequency discharge to imitate the ionospheric plasma environment, and measure plasma parameter based on Thomson scattering by import a Nd: YAG laser oscillate in the plasma generator. The result demonstrates that the intensity of laser Thomson scattering signal is positively correlated with the change of plasma electron density. The electron density in the plasma generator is calculated according to the laser Thomson scattering signal intensity, and the error is less than 10% compared with that measured by the Langmuir probe.

We developed high energy Q-switched 1064 nm and 946 nm Nd:YAG lasers for ITER Divertor Thomson Scattering (DTS). The 1064 nm Nd:YAG laser is designed to be used as the main DTS probing laser and features output energy of 2 J at 3 ns pulse duration. MOPA configuration with phase conjugation mirror provides divergence of 1.3 times the diffraction limit and high stability of the output beam parameters with repetition rate varied from 1 to 50 Hz. The 946 nm Nd:YAG laser designed for calibration by an auxiliary Thomson spectrum at the neighboring wavelength. The 946 nm laser consists of MO based on cavity dumping, high gain regenerative preamplifier and zero diffraction length ring cavity regenerative power amplifier with image-rotation providing 1 J × 50 Hz at 3 ns pulse duration with divergence of 1.5 the diffraction limit. As far as we know this is the highest value of the output energy obtained at 946 nm with nanosecond pulse duration until now. Both lasers use unified pump modules providing high maintainability of the system. The paper describes laser design approaches, state of the art and outlook of further developments.

Laser-induced fluorescence (LIF) on ITER will be used for local measurement of helium density nHe and ion temperature Ti in divertor. The LIF diagnostic is combined with the divertor Thomson scattering (DTS) via common laser injection and signal collection optics. Collisional-radiative model developed for helium ions is used to estimate laser parameters required for robust measurement of laser-induced signals against plasma background radiation. The estimations demonstrate feasibility of measuring nHeII with laser parameters provided by available optical parametric oscillator pumped by Nd:YAG. New approach for measuring Ti is proposed and the expected errors are estimated using numerical simulations.

This paper suggests the use of two optical elements for laser transfer in Thomson scattering diagnostics, which are widely used for other laser applications. YAG lasers amplified by flash lamps (repetition frequency of 50–100 Hz having a few Joules output) can sometimes have adverse effects such as peaked beam profiles and wavefront distortion. We used a beam homogenizer, which is a refractive optical element, to change the beam profile from peaked to non-peaked at a designated position. Using a super-Gaussian output profile when amplifying lasers facilitated longer—by a factor of 1.5 (=300 mm/200 mm) compared with top-hat beam profile—sustained distances, i.e. the distance along the laser path having a non-peaked profile. In terms of beam quality, wavefront distortion broke the beam profile in the far field. We used a deformable mirror to correct and flatten the wavefront of the beam. A YAG laser having a wavefront distortion of 0.46λ peak-to-valley was used to test the application of the deformable mirror, the results of which improved wavefront distortion to a wavelength of 0.1λ peak-to-valley.

A Thomson scattering diagnostic system was developed and successfully measured electron temperature and density of core plasma (R = 0.35 m) in Versatile Experiment Spherical Torus (VEST). However, the current system is able to measure only a single time point in a shot. Therefore, upgrade of the Thomson scattering system has been prepared and is in progress to obtain the time evolution. The upgrade is focused on three parts. First, the laser injection system is improved by introducing a burst mode laser with the energy of 2 J and repetition rate of 1 kHz for 10 ms. Furthermore, the laser injection optics is improved to minimize the optical loss. Second, minimum etendue limit of the collection optics is increased by employing a fiber bundle of three single-core fibers. Finally, a data acquisition system is prepared to record the burst laser signals for high sampling rate. Oscilloscope envelope mode is adopted and tested for measuring ten burst laser signal with 1.25 GS/s. Through the upgrade, the time evolution of electron temperature and density is expected to be measured in a single shot with enhanced signal-to-noise ratio.

This paper describes a data acquisition system for Thomson scattering diagnostics on a gas-dynamic trap (GDT) (the Budker Institute of Nuclear Physics, Novosibirsk, Russia). It allows recording scattered laser radiation pulses of ~10-ns duration with 5-GSPS sampling rate and 14-bit amplitude resolution. The data acquisition system includes eight-channel high-speed recorders and photodetector modules. The photodetector modules are based on avalanche photodiodes and low-noise transimpedance amplifiers. The recording module design uses switched-capacitor array technology.

Accurate dynamic three-dimensional (4D) imaging of the heart of small rodents is required for the preclinical study of cardiac biomechanics and their modification under pathological conditions, but technological challenges are met in laboratory practice due to the very small size and high pulse rate of the heart of mice and rats as compared to humans. In 4D X-ray microtomography (4D μCT), the achievable spatio-temporal resolution is hampered by limitations in conventional X-ray sources and detectors. Here, we propose a proof-of-principle 4D μCT platform, exploiting the unique spatial and temporal features of novel concept, all-optical X-ray sources based on Thomson scattering (TS). The main spatial and spectral properties of the photon source are investigated using a TS simulation code. The entire data acquisition workflow has been also simulated, using a novel 4D numerical phantom of a mouse chest with realistic intra- and inter-cycle motion. The image quality of a typical single 3D time frame has been studied using Monte Carlo simulations, taking into account the effects of the typical structure of the TS X-ray beam. Finally, we discuss the perspectives and shortcomings of the proposed platform.

A Thomson scattering (TS) system has been developed on Versatile Experiment Spherical Torus (VEST) to measure the electron temperature and the density. In VEST, it is quite challenging to measure TS signals because the energy of the utilized pulsed laser and the target electron density are low, 0.85 J and ∼5 × 1018 m−3, respectively. Furthermore, the difficulties caused by filter specifications have to be resolved because of the use of commercial interference filters with broad bandwidth and poor blocking at the laser wavelength. Therefore, we especially optimize the placement order of the filter sets based on the evaluation of the relative errors to overcome the poor spectral resolution. In addition, the amount of the stray light that penetrating filters is reduced by vacuum components such as baffles, louvres, and a viewing dump. With the careful installation and the optimization of the system, we can develop an efficient Thomson scattering system. Recently, TS signals have been successfully measured from the ohmic plasmas, and the electron temperature and the density are determined by analyzing the signals with the Bayesian method.

Petawatt class femtosecond lasers and x-ray free electron lasers (XFEL) open up a new page in research fields related to space and vacuum physics. One of fundamental principles can be explored by these new instruments is the equivalence principle, saying that gravitation and acceleration should be treated equivalently. If it is true this must lead to the appearance of the Unruh effect analogous to Hawking’s black hole radiation. It says that a detector moving with a constant acceleration w sees a boson’s thermal bath with its temperature T w = ℏ w / 2 π k B c . Practical detection of the Unruh effect requires extremely strong acceleration and fast probing sources. Here we demonstrate that x-rays scattering from highly accelerated electrons can be used for such detection. We present two, feasible for the Unruh effect, designs for highly accelerated systems produced in underdense plasma irradiated by high intensity lasers pulses. The first is Thomson scattering of a XFEL pulse from plasma wave excited by an intense laser pulse. Properly chosen observation angles enable us to distinguish the Unruh effect from the normal Doppler shift with a reasonable photon number. The second is a system consisting of electron bunches accelerated by a laser wake-field, as sources and as detectors, which move in a constantly accelerating reference frame (Rindler space) and are probed by x-ray free electron laser pulses. The numbers of photons is shown to be enough to observe reproducible results.

The local measurements of electron density and temperature by Thomson scattering (TS) diagnostics are essential for research of energy confinement, plasma heating, and control at nuclear fusion devices. This paper presents a digital filter polychromator designed for TS spectrum registration. A distinguishing feature of such a digital polychromator is the use of an analog-to-digital converter (ADC) having analog memory with discretization frequency of 5 GHz and 12-bit sampling. The low heat dissipation and compact design of the ADC allow us to integrate the recording and data handling systems in the spectral unit to obtain a standalone device that is totally isolated from other systems and equipment in the voltaic sense. The scattered laser radiation received from the plasma comes to the entrance of the polychromator through a fiber-optic cable, and the processed scattering signals and calculated electron density and temperature are available on a digital interface. The polychromator was tested within the Thomson scattering system at the Globus-M tokamak using two probing lasers: Nd:YAG 1064 nm and Nd:Glass 1055 nm operating with pulse energy up to 2J and FWHM of 4 and 40 ns, respectively. The employed ADCs allowed us to perform superfast signal digitizing in the oscilloscope mode and to demonstrate the possibility of stray signal time separation despite the modest size (~1 m) of the vacuum chamber. The results of measurements performed during the plasma experiment at the Globus-M tokamak are presented, and their comparative analysis with the data obtained at the operating TS system is made.

Tokamak diagnostic window glass is an indispensable optical medium in fusion research. The transmittance of the device affects the optical performance and accuracy of the diagnostic system. Especially, the window glass serves as the entrance of the light source while performing the sealing function for the active diagnosis method represented by Thomson scattering diagnostics. In this work, we studied the influence of the laser irradiation and tokamak discharge on the EAST (Experimental Advanced Superconducting Tokamak) Thomson scattering diagnostic borosilicate glass window. Using X-ray photoelectron spectroscopy (XPS) and Raman scattering, we found that carbon-based impurities in the device aggravated the film damage due to laser irradiation, reducing the performance of the coating of the glass. Besides, the laser and the various rays of tokamak discharge generated many point defects in the glass, increasing the light absorption of the glass. These two factors caused the glass transmittance to drop significantly (from 99.99% to 77.62%). In addition, the long-term laser irradiation primarily reduced the transmittance, while environmental rays had a minor impact on the same. This work provides valuable insights into the selection and effective use of glass in optics-based diagnostics.

Within the frame of electrodynamic and nonlinear Thomson scattering, we utilize MATLAB simulation to study the motion and radiation features of a static electron irradiated by circularly polarized laser pulses. The beam waist of non-tightly focused pulses (NFP) and tightly focused pulses (TFP) are respectively $$30{\lambda }_{0}$$ and $$3{\lambda }_{0}$$ . It is shown that with peak amplitude increasing, the peak radiation azimuth decreases at approximately the same speed regardless of the beam-focusing conditions, whereas the motion intensity has greatly varied rising trends. We also find that the beam-focusing condition only affects the electron’s motion and radiation conditions significantly in intensive laser pulses, where irregular trajectories lead to complex radiated energy distributions in TFP. Furthermore, through investigating the shift of radiation ramifications in circularly polarized laser pulses, we gain novel insight into spatial decoupling process and the dynamic evolving trend of angular radiation.

The Centre for Advanced Laser Applications (CALA) is a new research institute dedicated to bio-medical applications of state-of-the-art lasers, situated at the Garching research campus,. In particular, it is host to the upgraded ATLAS multi-petawatt laser system, which can drive a variety of novel radiation sources, including laser-driven betatron and Thomson X-ray sources. In this presentation, I will first review some of the experimental results obtained by its 100-TW-class predecessor, in particular fast X-ray microtomography of human bone samples [1] and first steps towards a multi-color Thomson X-ray source [2]. In the second part of my talk, I will give an update on the current performance of laser-driven electron acceleration and secondary sources using ATLAS. I will finish by an outlook on promising future concepts, such as betatron radiation from density-tailored plasmas and Thomson scattering with chirped laser pulses. [1] A. Dopp et al., Quick x-ray microtomography using a laser-driven betatron source, Optica, 5, (2018), 199 [2] J. Wenz et al., Dual-energy electron beams from a compact laser-driven accelerator

A 2856-MHz, π-mode, seven-cell standing-wave deflecting cavity was designed and fabricated for bunch length measurement in Tsinghua Thomson scattering X-ray source (TTX) facility. This cavity was installed in the TTX and provided a deflecting voltage of 4.2 MV with an input power of 2.5 MW. Bunch length diagnoses of electron beams with energies up to 39 MeV have been performed. In this article, the RF design of the cavity using HFSS, fabrication, and RF test processes are reviewed. High-power operation with accelerated beams and calibration of the deflecting voltage are also presented.

The world’s largest and most energetic laser facility, the National Ignition Facility (NIF) is dedicated to understanding inertial confinement fusion by irradiating a mm scale fusion target using 192 precisely aligned laser beams. The optical Thompson scattering (OTS) laser is being commissioned to understand the target implosion physics, especially for under-dense plasma conditions. The OTS will enable the diagnosis of the plasma performance leading to better control of the symmetry and efficiency of target implosion. Both 3w and 5w probe beams can be selectively chosen for diagnosing various plasma densities. Just as the NIF laser, the OTS system is aligned using several closed loop controls. CCD images of the laser beams are analyzed using automatic alignment image processing algorithm to provide beam position and motorized mirrors are mobilized to steer those beams to the desired path and location. One such control loop of the OTS uses a pair of far field diffraction pattern generated by a spherical object connected to a shaft. During the control loop alignment movements, the diffraction rings may be partially missing due to obstruction by the aperture. This paper describes the systematic process of algorithm development for detection of the diffraction rings and the necessary modifications as the requirements change. It describes the template design and algorithm for position detection from such images under challenging illumination and obstructive conditions. Among other novelties of this work is the use of a single computational neuron, inspired by a bipolar binary associative memory, employed to evaluate the quality and uncertainty of the location measurement, and avoid false detection.