CW Mode Of Operation Research Articles

Rf and thermal design studies of a 704.4 MHz, β≈0.2 , continuous-wave rf quadrupole accelerator for frequency jump

The radio-frequency quadrupole (RFQ) linac is often used as the first radio-frequency (rf) structure for both bunching and preaccelerating proton or heavy ion beams directly behind an ion source or a low-energy beam transport section. Typically, RFQ linacs operate at frequencies below 450 MHz and beam velocity ranges from β=0.01–0.08. Taking the MYRRHA project as an example, a 704.4 MHz continuous-wave (cw) RFQ linac has been recently proposed to realize an efficient fourfold frequency jump at β≈0.2. Due to its high frequency, small dimensions, and cw operation mode, careful design studies for the RFQ cavity structure including the water-cooling channels have been further performed, integrating the idea of using additive manufacturing technology for future construction. Systematic rf and thermal simulations and analysis demonstrated the reliability of the 704.4 MHz RFQ linac at cw operation and the frequency tuning ability via water-speed adjustments. This investigation shows that it could be a highly promising solution to perform an efficient frequency jump with a high-frequency RFQ accelerator at β≈0.2 for large-scale hadron linacs, which could potentially shorten the low- and medium-β parts of the whole facility. Published by the American Physical Society 2024

Medium grain niobium SRF cavity production technology for science frontiers and accelerator applications

We present the cost-effective production of superconducting radio frequency (SRF) cavities made of medium grain (MG) niobium (Nb) discs directly sliced from forged and annealed billet. This production method provides clean surface conditions and reliable mechanical characteristics with sub-millimeter average grain size resulting in stable SRF cavity production. We propose to apply this material to particle accelerator in the science and industrial applications. The science applications require high field gradients(≥ 30 MV/m) particularly in pulsed mode. The industrial applications require high Q 0 values with moderate gradients (∼ 20 MV/m) in CW mode operation. This paper describes the MG Nb disc production recently demonstrated and discusses future prospects for application in advanced particle accelerators in the science and industrial applications.

Design of the interaction cavity extending to the nonlinear taper for a 10 kw, W-band gyrotron

ABSTRACT In this paper, the design of an interaction structure for a 10-kW, W-band gyrotron is presented. The beam voltage and beam current are chosen as 30 kV and 1 A, respectively. The mode of interaction was chosen as TE6,2. A parametric design code and a gyro large-signal analysis (LSA) code were developed. The computational steps are discussed in brief. The LSA was done using the in-house developed code and the Gyro-K code. The results of these two codes were found to be in good agreement. The design of the nonlinear taper (NLT) was also carried out. Based on Ohmic loss, the power dissipated in the cavity was estimated. A novel cooling arrangement was proposed with two concentric cylindrical jackets around the cavity. The computational fluid dynamics (CFD) analysis was done using the software FloEFD. Steady-state analysis for the CW mode of operation and the transient analysis for the pulsed mode of operation were carried out for various flow-rates of the coolant.

A 2–20-GHz 10-W High-Efficiency GaN Power Amplifier Using Reactive Matching Technique

In this article, we present the analysis, design, and implementation of a wideband 10-W monolithic microwave integrated circuit power amplifier (PA), fabricated in a low-cost 0.1-μm gallium nitride (GaN) on Si technology. The design is focused on the realization of a low-loss and wideband impedance transformation networks across 2-20 GHz using a reactive matching (RM) technique. The two-stage GaN PA achieves an average output power of 40.1 dBm and a peak output power of 41.6 dBm at 13 GHz, in the CW-mode operation, with a smallsignal gain of S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> > 25.5 dB over the entire bandwidth. The average power-added efficiency (PAE) is 21%, with a peak PAE of 29% at 6 GHz. The PA chip occupies an area of 2.9×2.6 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . To the best of our knowledge, the PA presented in this work demonstrates the highest broadband gain among the reported GaN-based RMPAs with a corresponding output power of about 10 W.

Design and study of a continuous wave RFQ for the BISOL high intensity deuteron driver linac

A high intensity four-vane continue wave (cw) RFQ for the Beijing Isotope Separation On-Line (BISOL) high intensity deuteron driver linac has been designed. This RFQ will accelerate the 25 mA cw deuteron beam the 3.0 MeV with an operating frequency of 162.5 MHz. Three beam dynamics design schemes based on different strategies have been proposed and detailed comparisons, including tolerance study and error analysis, are performed to evaluate them. The final design of RFQ can achieve the requirements with a length of 5.29 m and the transmission of 99.1%. The inter-vane voltage is ramped from 60 kV to 75 kV and the maximum Kilpatrick factor is 1.42, which is very modest and beneficial to cw operation mode. The RFQ electromagnetic design is carried out based on the full-length 3D model, including vane modulation, undercuts, π-mode stabilization rods (PSLs) and tuners. The requirements of correct work frequency and voltage ramp are fulfilled by varying vane width and adjusting undercuts. In addition, the π-mode stabilization rods (PSLs) are inserted and optimized to increase mode separation and enhance voltage stabilization. The rf power loss and effective shunt impendence are 118 kW and 210 kΩ⋅m, respectively. In addition, multi-physics analysis of the cavity, based on the electromagnetic codes CST MWS, HFSS and ANSYS, has been carried out to check the cooling system, the temperature rise and deformation of the cavity, as well as the frequency shift in the cw operation. Finally, the frequency sensitivities to cooling water temperature are studied to obtain water temperature tuning coefficients, which will be used for fine tuning of the RFQ cavity during operation.

ECRIS plasma spectroscopy with a high resolution spectrometer.

Electron Cyclotron Resonance Ion Source (ECRIS) plasmas contain high-energy electrons and highly charged ions implying that only noninvasive methods such as optical emission spectroscopy are reliable in their characterization. A high-resolution spectrometer (10 pm FWHM at 632 nm) enabling the detection of weak emission lines has been developed at University of Jyväskylä, Department of Physics (JYFL) for this purpose. Diagnostics results probing the densities of ions, neutral atoms, and the temperature of the cold electron population in the JYFL 14 GHz ECRIS are described. For example, it has been observed that the cold electron temperature drops from 40 eV to 20 eV when the extraction voltage of the ion source is switched off, accompanied by two orders of magnitude decrease in Ar9+ optical emission intensity, suggesting that diagnostics results of ECRIS plasmas obtained without the extraction voltage are not depicting the plasma conditions of normal ECRIS operation. The relative changes of the plasma optical emission and the ion beam current have been measured in CW and amplitude modulation operation mode of microwave injection. It is concluded that in the CW mode, the ion currents could be limited by diffusion transport and electrostatic confinement of the ions rather than beam formation in the extraction region and subsequent transport. The high resolution of the spectrometer allows determining the ion temperature by measuring the Doppler broadening of the emission lines and subtracting the wavelength dependent instrumental broadening. The measured ion temperatures in the JYFL 14 GHz ECRIS are between 5 and 28 eV, depending on the plasma species and charge state. Gas mixing is shown to be an effective method to decrease the ion temperature of high charge state argon ions from 20 eV in pure argon discharge to 5 eV when mixed with oxygen.

A Stable Wavelength Operation Ho:YAG Laser with Orthogonally Polarized Pump**Supported by the Cooperation Foundation of Changchun Science and Technology Bureau under Grant No 17DY027, the Foundation of Education Department of Jilin Province under Grant No JJKH20181105KJ, and the Foundation of Jilin Province Science and Technology Department under Grant No 20180101033JC.

A stable wavelength operation Ho:YAG laser dual-pumped by two orthogonally polarized Tm:YLF lasers is reported. Under the cw operation mode, a laser output power of 24 W is measured. The corresponding optical-optical conversion efficiency is 44.75% and the slope efficiency is 50.12%. Under the Q-switched operation mode, the output maximum average power is 22.8 W at the re-frequency of 6 kHz. The corresponding optical-optical conversion efficiency and slope efficiency are 42.64% and 48.01%, respectively. The output central wavelength is 2090.73 nm, the linewidth is 0.40 nm, and the beam quality is . Moreover, the shift of the output central wavelength is less than 0.01 nm, and the linewidth shift is also less than 0.01 nm.

RF power tests of rf input coupler for the IFMIF/EVEDA RFQ prototype linac

For the IFMIF/EVEDA accelerator prototype RFQ linac, a 175MHz rf input coupler based on a 6 1/8in. co-axial waveguide is designed and manufactured. The rf coupler has cooling channels into the loop antenna and inner/outer-conductors around the RF window for CW operation mode, and the rf vacuum window module is replaceable by flanged connection. For rf power capability, nominal rf power of 160kW and maximum transmitted rf power of 200kW are required. In order to test the rf power capability, rf power tests using a high-voltage standing waves on a high-Q load circuit are carried out. For manufactured nine rf couplers including one spare, a stable 14s CW operation at the equivalent rf power of 200kW were achieved within 3–5days rf aging. No rf contact defects, no unnecessary low-Q value and no extraordinary outgassing were validated.

Pulsed and CW adjustable 1942 nm single-mode all-fiber Tm-doped fiber laser system for surgical laser soft tissue ablation applications.

A surgical laser soft tissue ablation system based on an adjustable 1942 nm single-mode all-fiber Tm-doped fiber laser operating in pulsed or CW mode with nitrogen assistance is demonstrated. Ex vivo ablation on soft tissue targets such as muscle (chicken breast) and spinal cord (porcine) with intact dura are performed at different ablation conditions to examine the relationship between the system parameters and ablation outcomes. The maximum laser average power is 14.4 W, and its maximum peak power is 133.1 W with 21.3 μJ pulse energy. The maximum CW power density is 2.33 × 106 W/cm2 and the maximum pulsed peak power density is 2.16 × 107 W/cm2. The system parameters examined include the average laser power in CW or pulsed operation mode, gain-switching frequency, total ablation exposure time, and the input gas flow rate. The ablation effects were measured by microscopy and optical coherence tomography (OCT) to evaluate the ablation depth, superficial heat-affected zone diameter (HAZD) and charring diameter (CD). Our results conclude that the system parameters can be tailored to meet different clinical requirements such as ablation for soft tissue cutting or thermal coagulation for future applications of hemostasis.

Beam dynamics design for uranium drift tube linear accelerator

KONUS beam dynamics design of uranium DTL with LORASR code is presented. The 238U34+ beam, whose current is 5.0 emA, is accelerated from injection energy of 0.35 MeV/u to output energy of 1.30 MeV/u by IH-DTL operated at 81.25 MHz in HIAF project at IMP of CAS. It achieves a transmission efficiency of 94.95% with a cavity length of 267.8 cm. The optimization aims are the reduction of emittance growth, beam loss and project costs. Because of the requirements of CW mode operation, the designed average acceleration gradient is about 2.48 MV/m. The maximum axial field is 10.2 MV/m, meanwhile the Kilpatrick breakdown field is 10.56 MV/m at 81.25 MHz.

InAlN/GaN HEMTs based L-band high-power packaged amplifiers

This paper presents power results of L-band packaged hybrid amplifiers using InAlN/GaN/SiC HEMT power dies. The high-power densities achieved both in pulsed and continuous wave (cw) modes confirm the interest of such technology for high-frequency, high-power, and high-temperature operation. We present here record RF power measurements for different versions of amplifiers. Up to 260 W, i.e. 3.6 W/mm, in pulsed (10 µs/10%) conditions, and 105 W, i.e. 2.9 W/mm, in cw conditions were achieved. Such results are made possible thanks to the impressive performances of InAlN/GaN transistors, even when operating at high temperatures. Unit cell transistors deliver output powers of 4.3 W/mm at Vds = 40 V in the cw mode of operation at the frequency of 2 GHz. The transistor process is described here, as well as the amplifiers design and measurements, with a particular focus to the thermal management aspects.

Physics design of an accelerator for an accelerator-driven subcritical system

An accelerator-driven subcritical system (ADS) program was launched in China in 2011, which aims to design and build an ADS demonstration facility with the capability of more than 1000 MW thermal power in multiple phases lasting about 20 years. The driver linac is defined to be 1.5 GeV in energy, 10 mA in current and in cw operation mode. To meet the extremely high reliability and availability, the linac is designed with much installed margin and fault tolerance, including hot-spare injectors and local compensation method for key element failures. The accelerator complex consists of two parallel 10-MeV injectors, a joint medium-energy beam transport line, a main linac, and a high-energy beam transport line. The superconducting acceleration structures are employed except for the radio frequency quadrupole accelerators (RFQs) which are at room temperature. The general design considerations and the beam dynamics design of the driver linac complex are presented here.

CW and quasi-CW laser performance of 10 at.% Yb3+:LuAG ceramic

We have investigated the laser oscillation of 10 at.% Yb3+:LuAG ceramic pumping into the two main absorption peaks in CW and quasi-CW operation modes. Emitting at 1030 and 1046 nm the laser achieves excellent performance, delivering output powers up to 8.8 W. The highest estimated slope efficiencies are 72.6% in CW and 79% in quasi-CW. A tunability range of 57.5 nm is measured.

14 W high-efficiency diode-pumped cw Yb:KGd(WO4)2 laser with low thermo-optic aberrations

A comparative experimental study of thermal lensing effect was performed for diode-pumped Yb3+-doped Y3Al5O12 and Ng-cut KGd(WO4)2 crystals under cw (continuous wavelength) operation mode. For Ng-cut Yb:KGd(WO4)2, thermal lens is positive for rays lying in all meridional planes and at least seven times weaker than that of Yb:Y3Al5O12. This is associated with lower quantum defect under 980-nm pumping (in comparison with 940-nm pumping for Yb:Y3Al5O12) and mutual compensation of negative impact of temperature dependence of the refractive index and positive impact of thermal expansion effect to the thermal lens optical power. Principal meridional planes of thermal lens in Ng-cut Yb:KGd(WO4)2 contain Np and Nm axes of optical indicatrix; corresponding sensitivity factors M=dD/dPabs equal 1.38m−1 and 1.09m−1 (with respect to absorbed pump power). This near-athermal crystal was utilized to produce air-cooled diode-pumped cw laser with output power of 14W, impressive slope efficiency of 76% and excellent beam quality (M2<1.2).

CaF2:Yb laser ceramics

CaF2:Yb fluoride laser ceramics, prepared by hot-forming, exhibit the same optical properties as starting single crystals. Slope efficiency of the Сa0.95Yb0.05F2.05 is equal to 35% in the pulsed mode of laser operation. Decrease of ytterbium concentration in CaF2:Yb samples down to 3mol.% resulted in the essential improvement of Сa0.97Yb0.03F2.03 thermal conductivity from 3.5 to 4.5W/mK, but slightly decreased (down to 30%) slope efficiency of the samples under both pulsed and CW mode of operation. Alternative hot-pressing synthesis of CaF2:Yb fluoride laser ceramics provided materials with superior mechanical properties (microhardness Н=3.2GPa and fracture toughness К1С=0.65МPаm1/2) in comparison with hot-formed and/or single crystal CaF2:Yb specimens. For the first time, lasing has been observed for the novel aforementioned hot-pressed CaF2:Yb ceramics.

Electron cyclotron resonance plasma production by using pulse mode microwaves and dependences of ion beam current and plasma parameters on the pulse condition

We measure the ion beam current and the plasma parameters by using the pulse mode microwave operation in the first stage of a tandem type ECRIS. The time averaged extracted ion beam current in the pulse mode operation is larger than that of the cw mode operation with the same averaged microwave power. The electron density n(e) in the pulse mode is higher and the electron temperature T(e) is lower than those of the cw mode operation. These plasma parameters are considered to cause in the increase of the ion beam current and are suitable to produce molecular or cluster ions.

Quantum dot semiconductor optical amplifiers: optical pumping versus electricalpumping

A comprehensive comparison between the characteristics of conventional electrical pumpingand the new optical pumping (OP) schemes in quantum dot semiconductor opticalamplifiers (QD-SOAs) has been done and has proved that the optical pumping scheme cansignificantly improve the dynamical properties of QD-SOAs. Analytical solutions have beenpresented to justify the optical properties in both pumping methods in CW operationmode. Also, pulse-mode operation has been investigated through numerically solved rateequations. Besides obviating the deficiencies of electrical pumping, optically pumped SOAs(OP-SOAs) can be attractive alternatives for high-speed all-optical signal processing.

Thermal Analysis of InAs/AlSb Short Wavelength Mid-IR Quantum Cascade Lasers

We present the effects of hetero-interfaces and major key parameters on the thermal behaviors and performance of short wavelength mid-IR InAs/AlSb quantum cascade lasers (QCLs). We use a finite element method (FEM) with commercial software, ANSYS, to simulate the heat dissipation in QCLs in cw operation mode with an epilayer-down mounting package. The thermal performance is characterized by the temperature increase ΔT (self-heating effect) between the active region of QCLs and the heatsink. Results show that (1) the self-heating effects of InAs/AlSb QCLs are much less than those in AlInAs/GaInAs QCLs, (2) narrower ridges lead to significantly cooler active regions of InAs/AlSb QCLs due to poor heat transport in the cross-plane direction (across interfaces) and that most of the heat flows out of the active region in the lateral direction, and (3) the cavity length of the laser has little influence on the self-heating effect of the device, but the long cavity reduces mirror loss and threshold current density.

Growth and fabrication of quantum dots superluminescent diodes using the indium-flush technique: A new approach in controlling the bandwidth

Broadband superluminescent diodes incorporating multiple layers of InAs quantum dots (QDs), where the dots height was deliberately varied from one layer to another have been grown and characterized. We used the indium-flush process to accurately control the emission energy of each layer of dots, enabling us to reliability and predictably engineer the bandwidth of the overlapped layers. Photoluminescence spectrum of four combined layers of QDs with full-width at half-maximum of 125 nm at peak wavelength energy of 1.06 μm was obtained. A 3 dB bandwidth emission spectrum of 80 nm and output power of 1 mW was obtained under CW operation mode at room temperature.

Perspectives for the ECLISSE method with third generation ECRIS

The ECLISSE experiment performed at INFN-LNS in 2002 with the superconducting ECR ion source SERSE proved the possibility to couple a laser ion source (LIS) with an electron cyclotron resonance ion source (ECRIS) in order to obtain cw ion beams from refractory metals with characteristics that are not achievable with standard LIS. The oven that is used for the production of vapors inside the ECRIS fails with refractory elements and the sputtering method is not adequate for the production of beams with intensity above a few tens of micro ampere. So the use of a LIS inside the ECRIS plasma chamber may permit to obtain the advantage of a LIS in terms of beam current with the typical features of an ECRIS (high charge states, cw mode operation, relatively low emittance). One of the limiting factors of the previous experiment was the relatively low plasma density of the previous generation ECRIS, working at a frequency between 14 and 18 GHz. Nowadays the availability of third generation ECRIS (operating at 28 GHz or higher, i.e. with a plasma density four times larger) may extend the capabilities of this method, as the denser plasma may catch ions from LIS with energies up to about 1 keV per charge state, much higher than it is possible for sources operating at lower frequency (e.g. about 200 eV per charge state for the SERSE source). The perspectives opened by the availability of MS-ECRIS source operating at 28 GHz will be described along with some details on the proposed experimental programme, to be carried out in 2008 at GSI, Darmstadt.