MW Beam Research Articles

Progress toward a microsecond duration, repetitively pulsed, intense-ion beam for active spectroscopic measurements on ITER

We describe the design of an intense, pulsed, repetitive, neutral beam based on magnetically insulated diode technology for injection into ITER for spectroscopic measurements of thermalizing alpha particle and thermal helium density profiles, ion temperature, plasma rotation, and low Z impurity concentrations throughout the confinement region. The beam is being developed to enhance low signal-to-noise ratios expected with conventional steady-state ion beams because of severe beam attenuation and intense bremsstrahlung emission. A 5 GW (e.g., 100 keV, 50 kA) 1 μs duration beam would increase the charge exchange recombination signal by 103 compared to a conventional 5 MW beam.

The feasibility of high power cyclotrons

The feasibility of cyclotrons to produce high power beams is discussed based on the experience gained with the operation of the upgraded 590 MeV cyclotron facility at PSI in Villigen (Switzerland) at a beam power level up to 0.9 MW. In view of new applications of particle beams in neutron spallation sources, energy amplifier and transmutation technologies a possible design of a 1 GeV cyclotron is presented that would be capable to deliver a 10 MW beam, based on the same contruction principles as used in the PSI 590 MeV Ring cyclotron. Questions concering power conversion efficiency, beam loading and space charge forces are discussed. Space charge effects are not expected to be a major problem in the high energy cyclotron, but they play an important role in the preaccelerator and further studies are needed to propose an optimized configuration.

Circular beam, high power operation of 0.98 [micro sign]m InGaAs/InGaAsP lasers with a tapered waveguide spot-size expander

A 0.98 µm InGaAs/InGaAsP strained quantum well laser with a laterally tapered waveguide spot-size expander is demonstrated to achieve highly reliable and stable lateral mode operation. This laser, which has a 0.8 µm wide ridge-neck at the facet, showed a linear L-I curve up to 340 mW, with circular and narrow beam divergence of 10° × 15°.

Molecular diversity of placental lactogen (PL) in the rat

The purpose of the ITER electron cyclotron resonance heating (ECRH) antennae located in the upper port launcher will be to stabilize the neoclassical tearing modes (NTM) by driving currents locally inside either the q=3/2 or 2 island. The ITER reference design uses a front steering (FS) concept with the moveable mirror close to the plasma. The FS launcher is capable of steering eight 2 MW beams via two sets of steering mirrors [R. Chavan, M. Henderson, R. Bertizzolo, J.-D. Landis, F. Sanchez, H. Shidara, The ECH front steering launcher for the ITER upper port, this conference. [8]].In the adverse invessel operating conditions, reliable operation is required to guarantee the availability of the mirror steering mechanism during the 20-year lifetime of ITER. The dynamic performance and steering accuracy of the mirror system are essential for the localized beam power deposition. In order to increase the steering reliability and accuracy, traditional bearing and push–pull rods are avoided, which tend to introduce backlash or grip. The proposed frictionless and backlash free mechanism design uses elastically compliant structural components to guide and drive the rotating mirror. The actuator system is based on a pressure controlled helium filled bellows array working against a set of preloaded compressive springs. The radiation and temperature sensitive pressure control servovalves are located in the port duct behind the closure plate.Resistance to cyclic fatigue is the critical design requirement for compliant systems. In order to achieve the high reliability, four critical components are identified and described in detail. The bellows, the flexure pivots, the return springs and the spiral cooling tubes are the core elements of the mechanism allowing the controlled rotation of the mirror. Prototypes of the critical components are being tested. Corresponding analytical and cyclic fatigue numerical models of the compliant components are to be validated by fatigue bench tests. The detailed design and the principal tests of the critical components used in the FS mechanism will be presented.

The extrinsic blood coagulation system and an inhibitor in human placenta

The purpose of the ITER electron cyclotron resonance heating (ECRH) antennae located in the upper port launcher will be to stabilize the neoclassical tearing modes (NTM) by driving currents locally inside either the q=3/2 or 2 island. The ITER reference design uses a front steering (FS) concept with the moveable mirror close to the plasma. The FS launcher is capable of steering eight 2 MW beams via two sets of steering mirrors [R. Chavan, M. Henderson, R. Bertizzolo, J.-D. Landis, F. Sanchez, H. Shidara, The ECH front steering launcher for the ITER upper port, this conference. [8]].In the adverse invessel operating conditions, reliable operation is required to guarantee the availability of the mirror steering mechanism during the 20-year lifetime of ITER. The dynamic performance and steering accuracy of the mirror system are essential for the localized beam power deposition. In order to increase the steering reliability and accuracy, traditional bearing and push–pull rods are avoided, which tend to introduce backlash or grip. The proposed frictionless and backlash free mechanism design uses elastically compliant structural components to guide and drive the rotating mirror. The actuator system is based on a pressure controlled helium filled bellows array working against a set of preloaded compressive springs. The radiation and temperature sensitive pressure control servovalves are located in the port duct behind the closure plate.Resistance to cyclic fatigue is the critical design requirement for compliant systems. In order to achieve the high reliability, four critical components are identified and described in detail. The bellows, the flexure pivots, the return springs and the spiral cooling tubes are the core elements of the mechanism allowing the controlled rotation of the mirror. Prototypes of the critical components are being tested. Corresponding analytical and cyclic fatigue numerical models of the compliant components are to be validated by fatigue bench tests. The detailed design and the principal tests of the critical components used in the FS mechanism will be presented.

Measurement of small forces using an optical trap

A simple and sensitive method for detecting small forces applied to an optically trapped microsphere utilizes the transmitted beam of the trapping laser to monitor microsphere deflections within the potential well of the trap. The rms dynamic displacement detection sensitivity measured in the frequency range from 1 Hz to 10 kHz is ∼1 nm in the radial direction and ∼10 nm along the z (optic) axis. Radiation trapping force constants were calibrated against viscous drag on microspheres in the range between the Rayleigh (r<0.2λ) and Mie (r≫λ) size regimes. For a 1-μm-diam polystyrene sphere trapped with a 60 mW beam the rms spontaneous thermal motion limits the force sensitivity to better than 10−12 N and lateral spatial resolution to ∼10 nm in a frequency range from 1 Hz to the viscous rolloff frequency ∼1 kHz. The measured maximum trapping efficiencies are compared with the theoretical predictions of the ray-optics approximation.

Bright squeezed light from a singly resonant frequency doubler.

We present a new technique for the efficient and simple production of amplitude-squeezed light with high coherent excitation, using a frequency doubler, in which only the fundamental wave is resonantly enhanced. Our theory predicts up to nearly 90% squeezing in the second-harmonic wave under ideal conditions. In our first experiment we measured up to 30% squeezing [having taken into account the limited quantum efficiency (63%) of our detection system] in a stable 50 mW beam. Compared to doubly resonant frequency doubling our new approach has considerable technical advantages.

A COMPUTER SIMULATION MODEL FOR ANALYSIS OF RISE IN SKIN TEMPERATURE FOLLOWING IRRADIATION WITH THE GaAlAs DIODE LASER

A popular benchmark for defining a laser therapy systcm is an output power of less than 100 mW, and low reactive-level laser therapy (LLLT) is commonly regarded as ‘safe’ for irradiating skin. However, with very small spot sizes in the order of 200 μm, the power density at tissue of a 100 mW laser therapy system is in the order of 318 W/cm2. If target tissue is painted with black ink or a similar pigment, this power density is quite capable of causing a burn injury. This has obvious implications in the use of such LLLT systems in treating dark-coloured naevi such as naevus cell naevus, or in LLLT on black patients. In order to examine this problem in detail, the authors designed a computer model with a program to calculate and analyze the temperature rise in an irradiated hemispherical block of homogeneous tissue at various powers in the range of 6 mW- 60 mW, and at spot sizes of 200 μm, 400 μm, 1.0 mm and 2.0 mm following 5 seconds irradiation with an 830 nm GaAlAs diode laser, after which the laser was ‘turned off’ The laser was deemed to be applied in the contact pressure mode, thereby compressing superficial blood vessels in the irradiated area so that blood flow cooling could be discounted. At maximum absorption, it was predicted that the 60 mW beam of the GaAlAs diode laser at 830 nm and a 200 μm spot size has the potential for causing thermal injury. The authors would like to stress that this is only a theoretical computer model, with hypothesized constants and a homogeneous target material. However, this model certainly demonstrates the error of applying arbitrary limits as to what constitutes the output power of an LLLT system, and would also appear to limit the application of LLLT at the above parameters on dark-colored naevi or for darker-skinned patients.

THz spectroscopy and source characterization by optoelectronic interferometry

We demonstrate a new type of THz optoelectronic interferometer, by fully characterizing a recently developed THz source to beyond 6 THz, and by measuring the absorption coefficient of high-resistivity GaAs from 1 to 5 THz. The two source THz interferometer is driven with two 4 mW beams of 60 fs dye-laser pulses and produces interferograms with exceptional signal-to-noise ratios.

European Spallation Source workshop

Abstract A meeting of about 70 experts in condensed-matter science took place in late February at Abingdon, UK, to discuss the scientific opportunities and technological challenges of a new 3rd generation spallation source-the so-called European Spallation Source (ESS). This Workshop was, in fact, the third in a series: the first, in September last year at Simonskall near Jiilich, considered the accelerator options; the second in February, in PSI, Villigen, Switzerland, considered the problems of providing targets and monochromators. The meeting openedwithtalksfromS. Martin(Jiilich), G. Bauer (PSI) and J. Carpenter (Argonne) on the accelerator, target, and moderator options, respectively. Although the problems are formidable in all areas, there donot seemtobe any insuperableobstacles for building a system with a 5 MW beam of protons with a short pulse length of ∼1 μ delivered onto two (or more) stationary targets surrounded by a variety of moderators. The heat load on the target could approach 4 MWAitre, similar to that foundin ahigh-flux reactor, but Bauer pronounced that “it can be done.” The neutron productionof suchasourcewould be spectacular, with a peak flux of ∼ 1017 n/sec/cm2 and an average flux close to that of the ILL.

Red and green low-powered He-Ne lasers protect human erythrocytes from hypotonic hemolysis.

The effect of low-powered He-Ne lasers (red beam, 632.8 nm, 10.2 mW, and green beam, 543.5 nm, 0.44 mW) on hypotonic hemolysis in human red cells was investigated. Red cell solutions (0.9% NaCl, pH 7.00) were centrifuged and the sediments were irradiated with the red or the green beam for 0 (control), 1, 3, 5, 7, 10, 15 and 30 minutes. Each of the 40 irradiated samples were transferred into hypotonic solution (0.405% NaCl, pH 7.00). After leaving the samples at room temperature for 10 minutes, optical density of every suspension was measured spectrophotomechanically at a wavelength of 545 nm to determine hemoglobin content. Hemolysis percentages of the control samples in hypotonic solution were 52.2 +/- 10.7% (mean +/- SD, N = 20) in the red group and 55.0 +/- 12.0% (N = 20) in the green group. Relative values of hemolysis in the hypotonic solution after irradiation with the red or the green beam decreased significantly between the 7- and 30-minute irradiation. These results demonstrate that low-powered He-Ne lasers have a protective effect on red cell membranes from hypotonic hemolysis and stabilize the cell membranes.

Charge exchange recombination spectroscopy measurements in the extreme ultraviolet region of central carbon concentrations during high power neutral beam heating in TFTR

The carbon concentration in the central region of TFTR discharges with high power neutral beam heating has been measured by charge exchange recombination spectroscopy (CXRS) of the C5+ n = 3–4 transition in the extreme ultraviolet region. The carbon concentrations were deduced from absolute measurements of the line brightness using a calculation of the beam attenuation and the appropriate cascade corrected line excitation rates. As a result of the high ion temperatures (20–30 keV) in most of the discharges, the contribution of beam halo neutrals to the line brightness was significant and therefore had to be included in the modelling of the data. Carbon concentrations have been measured in discharges with plasma currents Ip in the range 1.0-1.6 MA and beam power in the range 2.6–30 MW, including a number of supershots. The results are in good agreement with carbon concentrations deduced from the visible bremsstrahlung Zeff and with metallic impurity concentrations measured by X-ray pulse height analysis, demonstrating the reliability of the atomic rates used in the beam attenuation and line excitation calculations. Carbon is the dominant impurity species in these discharges; the oxygen concentration measured via CXRS in a high beam power case was 0.0006 of ne, compared to 0.04 for carbon. Trends with plasma current and beam power in the carbon concentration and the inferred deuteron concentration are presented. The carbon concentration is independent of plasma current and decreases from 0.13 at 2.6 MW beam power to 0.04 at 30 MW, while the deuteron concentration increases from 0.25 to 0.75 over the same range of beam power. These changes are primarily the result of beam particle fuelling, as the carbon density did not vary significantly with beam power. The time evolutions of the carbon and deuteron concentrations during two high power beam pulses, one which exhibited a carbon bloom (a sudden influx of carbon due to local heating of the limiter) and one which did not, are compared. In both types of discharge, the carbon concentration decreases early in the beam pulse as a result of beam particle fuelling, and the carbon density rises slowly during the beam pulse until the start of the bloom. The electron density rise during the bloom is primarily due to the increase in the carbon density.

Physics design for the ata tapered wiggler 10.6 μ FEL amplifier experiment

We are presently designing and constructing a high-gain, tapered wiggler 10.6 μ FEL amplifier to operate with the 50 MeV ATA e-beam. The initial experiments will be done with a constant period (λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">w</sub> = 8 cm), 5 m-long linear wiggler. For an input laser power of 800 MW and electron beam brightness of 2.105 A/(rad-cm)2, we hope to achieve a trapped particle fraction ˜0.5 and an energy extraction efficiency of ˜2% with a ˜10% taper in the wiggler magnetic field. This taper corresponds to decelerating the trapped particle approximately two full ponderomotive well (i.e. bucket) heights. In this talk, we will discuss the physics motivations behind our tapered wiggler design and initial experimental diagnostics.

Design Study of Cusptron Amplifier for Accelerators

Research and development of an RF source for next generation electron-positron colliders is proposed based on the newly developed cusptron microwave tubes. The cusptron generates high harmonics of the electron cyclotron frequency by resonant interaction of an axis-encircling electron beam and the modes in a multi-vane conducting wall structure. The strong coupling through the negative mass instability, the relatively low magnetic field requirement, the high current capability, and multi-feed possibility are some of the features of the cusptron that are especially suited for the accelerator applications. The intended parameters for prototype cusptron are P = 100 MW peak power at f = 8.5 GHz using P = 240 MW beam. In order to reach this ultimate goal, first the scaling law of the beam and field parameters for the cusptron is examined, and the RF circuit design in conjunction with these beam parameters are presented. The design parameters for the scaled down experiments, intended as intermediate steps and tests for the scaling laws, are also given.

Ion and electron energy balance calculations for neutral-beam-heated Heliotron-E plasmas

Heliotron E is a high-shear, large-rotational-transform helical system (ℓ = 2) with 19 field periods and an aspect ratio of 11 (R = 2.2 m, a = 0.2 m). Neutral beam injection of up to 1.7 MW beam power into low-Ohmic-current Heliotron E plasmas has produced plasmas with n̄e ≈ 2.1 × 1013 cm−3, Ti(0) ≈ 0.95 keV, Te(0) ≈ 0.70 keV and β(0) ≈ 1.0%, at a helical magnetic field on the magnetic axis of 1.8 T. This paper describes the ion and electron energy balance for these plasmas, paying special attention to the evaluation of the energy transport coefficients during injection. For the two modes of co-injection and co-injection plus perpendicular injection, the experimental ion and electron thermal diffusivities, χi and χe, are examined using numerical ion and electron temperature profile analysis codes which employ, respectively, the neoclassical ion thermal conductivity and the INTOR-scaling electron thermal conductivity as the reference conductivities. From the measured and calculated ion temperature profiles, it is found that ion heating during injection can be reasonably explained in terms of classical beam power deposition (calculated with a Monte-Carlo beam-orbit code) and the usual neoclassical (Hazeltine-Hinton) thermal conduction processes. An attempt to determine the general behaviour of χe has also revealed that the calculated upper limit of χe during injection is of the same order or less than the INTOR-scaling value.

Energy confinement of beam-heated divertor and limiter discharges in Doublet III

Observation of the intensity of the recycling particle flux at the main plasma edge for various limiter and divertor discharges indicates that the gross energy confinement of beam-heated discharges is closely related to the intensity of the edge particle flux. In limiter discharges, the global particle confinement time and the energy confinement time τE show many similarities: 1) linear Ip dependence at Ip < 600 kA, 2) no BT dependence, and 3) deterioration against injection power. Improvement of τE by increasing Ip, for example, is associated with high temperatures at the plasma edge region accompanied by reduced particle recycling. – Divertor discharges with low particle recycling around the main plasma show better energy confinement than limiter discharges at high plasma densities. The improvement of τE is primarily originated in the reduction of heat transport at the main plasma edge region, which is associated with the reduction of recycling particle flux at the main plasma edge. Under certain operation condition, for example, excessive cold-gas puffing, the discharge shows relatively high scrape-off plasma density and strong particle recycling between the main plasma and the limiter. The energy confinement time of these discharges degrades somewhat or reduces completely to that of the limiter discharge. – In low-recycling divertor discharges, the central electron and ion temperature is proportional to the injection power, and the plasma stored energy is proportional to n̄ePabs (scales as INTOR scaling). With ≈ 4 MW beam injection, high-temperature and high-density plasmas were obtained (stored energy up to 280 kJ, Te(0) ≈ Ti(0) ≈ 2.5–3.0 keV at n̄e ≈ (6–7) × 1013 cm−3, τE* ≈ 70 ms).

Experience with a Double-Compensating Beam Calorimeter

In an experiment to measure the D(t,?)n cross section at beam energies of 10 to 120 keV, we have developed a double-compensating beam calorimeter, based on a Swiss Design to measure the particle beam intensity. A Faraday cup is not useful because of considerable charge exchange in the target gas at such low beam energies. We calibrated the calorimeter both with 10- and 3-MeV protons (comparing with a Faraday-cup measurement of the beam flux) and with the heat generated in a precision resistor. Both methods agree and give a calibration accurate to ±0.08% over a range of 10 to 800 mW beam power. Beam powers as low as 5 mW may be used, but with less accuracy. The beam energy must be known in order to calculate the particle intensity. Some difficulties with and peculiarities of the device are discussed.

Degenerate four-wave mixing in InSb at 5K

We report the observation of degenerate four-wave mixing in InSb at 5 K using a cw CO laser operating in the spectral region just below the bandgap energy, where strong self-defocusing and optical bistability have previously been seen. Conversion efficiencies of ≈1% are obtained with <13 mW beam powers, and higher efficiencies are predicted for improved phase-matching.

Demonstration of lens aberrations using a school laser

Describes arrangements for demonstrating spherical aberration, astigmatism and distortion to small groups of students. The use of a He-Ne laser simplifies the arrangements whilst conforming to safety regulations, in that the 1 mW beam is made divergent in all cases, immediately on leaving the source.

Attenuation of giant laser pulses by absorbing filters

Three types of absorbing filters were tested for suitability as reproducible attenuators for a Q-switched ruby laser beam. None of the filters tested were irreversibly damaged when irradiated with pulses having peak powers up to 40 MW (beam cross section ~10(-4) M(2)). However, Tiffen Photar neutral density filters and Corning filters showed reversible photobleaching (optical saturation) at large pulse energies, while Kodak Wratten neutral density filters did not saturate.