Effective Shunt Impedance Research Articles

RF electromagnetic design and multi-physics analysis of CW CH-DTL for AB-BNCT

The accelerator-based boron neutron capture therapy (AB-BNCT) facility is being developed worldwide due to its advantages, including easy maintenance, low construction costs, and high safety. To minimize both the length and cost of the accelerator, we propose a combined acceleration structure that utilizes a radiofrequency quadrupole linac (RFQ) in conjunction with a crossbar H-mode drift tube linac (CH-DTL). The CH-DTL rapidly accelerates the beam to the required energy after the RFQ, with output energy adjustable from 2.2 MeV to 3.2 MeV. We have completed the RF electromagnetic design and optimization of the CH-DTL cavity to fulfill beam dynamics requirements while achieving high effective shunt impedance. Additionally, we designed the cooling channels and conducted multi-physics analyses to evaluate the cavity's performance during continuous wave operation.

Development of single mode cavity at 1.5 GHz for the third harmonic RF-system in PETRA IV

The PETRA IV storage ring currently under development at DESY will require a third harmonic 1.5 GHz RF-system to prevent negative effects on both, lifetime and emittance, caused by Touschek effect and Intrabeam scattering. These cavities lengthen the bunches and thereby reduce their charge density. For this 3rd harmonic system, a one-cell single-mode cavity with a simple mechanical and electrical structure is under design that should also reduce Higher Order Modes (HOMs) to a quality factor less than 100. Therefore, the well-known approach of the Choke Mode Cavity was chosen, that use a radial line damper to attenuate the HOMs and a radial choke that traps the acceleration mode. The general behaviour of the choke mode structure was simulated, discussed and optimized for the requirements of a one-cell cavity with high effective shunt impedance, high-quality factor and simple manufacturing.

Additive Manufacturing of Side-Coupled Cavity Linac Structures from Pure Copper: A First Concept

Compared to conventional manufacturing, additive manufacturing (AM) of radio frequency (RF) cavities has the potential to reduce manufacturing costs and complexity and to enable higher performance. This work evaluates whether normal conducting side-coupled linac structures (SCCL), used worldwide for a wide range of applications, can benefit from AM. A unit cell geometry (SC) optimized for 75 MeV protons was developed. Downskins with small downskin angles α were avoided to enable manufacturing by laser powder bed fusion without support structures. SCs with different α were printed and post-processed by Hirtisation (R) (an electrochemical process) to minimize surface roughness. The required accuracy for 3 GHz SCCL (medical linacs) is achieved only for α>45∘. After a material removal of 140 µm due to Hirtisation (R), a quality factor Q0 of 6650 was achieved. This corresponds to 75% of the Q0 simulated by CST®. A 3 GHz SCCL concept consisting of 31 SCs was designed. The effective shunt impedance ZT2 simulated by CST corresponds to 60.13MΩm and is comparable to the ZT2 of SCCL in use. The reduction in ZT2 expected after Hirtisation (R) can be justified in practice by up to 70% lower manufacturing costs. However, future studies will be conducted to further increase Q0.

Construction and measurement of the prototype side-coupled standing-wave tube for electron Linac

Due to Iran's growing need for accelerators in various applications, NSTRI (Nuclear Science and Technology Research Institute) has defined a 6 MeV e-Linac (electron linear accelerator) project for medical and inspection applications. This electron accelerator has a side-coupled standing wave tube that operates in π/2 mode at the frequency of 2998.5 MHz. This paper presents a summary of the construction and cold test stage of the prototype tube for this accelerator. The prototype tube was constructed from aluminum and clamped with bolts.In the cold test stage, low-power RF measurements werecarried out using a side-coupled cavity tuning method and a bead-pull measurement technique. Using a network analyzer, magnetic and electric probes, and a mechanical structure constructed for this tube made the RF tuning possible. After tuning, the resonant frequency, unloaded quality factor, and effective shunt impedance of the aluminum tube were achieved at 2998.57 MHz, 7970, and 83.25 MΩ/m respectively.

Beam-dynamics design of a 2 MeV/u heavy-ion IH-DTL with electromagnetic quadrupole structure

The interdigital H-mode (IH) drift tube linac (DTL) with an electromagnetic quadrupole (EMQ) structure combines an IH-DTL acceleration structure with a quadrupole focusing–defocusing (FD) lattice and can achieve a high acceptance when high shunt impedance is ensured. Between the radio frequency quadrupole (RFQ) and IH-DTL, the IH-EMQ dynamics allows only one quadrupole magnet to match the two structures directly, which is different from KONUS (Kombinierte Null Grad Struktur, combined zero-degree structure) and alternating-phase focusing (APF) dynamics. To match KONUS or APF DTL with the RFQ, at least three quadrupole magnets are required. This paper describes the design process of the IH-EMQ beam dynamics and applies and verifies the method by applying it to design a 2MeV/u heavy-ion IH-DTL with the help of detailed simulation and analysis. With the input energy of 400keV/u, the DTL accelerates particles with a charge-to-mass ratio as low as 1/6.5. The normalized root mean square emittance increases by 7%. The IH-DTL with the IH-EMQ dynamics design offers a normalized transverse acceptance (99% particles) of 3.89(x)/3.56(y)πmm⋅mrad while preserving an effective shunt impedance of 87MΩ/m.

Optimization of the S-band side-coupled cavities for proton acceleration

The proton beam with energy around 100 MeV has seen wide applications in modern scientific research and in various fields. However, proton sources in China fall short for meeting experimental needs owing to the vast size and expensive traditional proton accelerators. The Institute of Nuclear Science and Technology of Sichuan University proposed to build a 3 GHz side-coupled cavity linac (SCL) for re-accelerating a 26 MeV proton beam extracted from a CS-30 cyclotron to 120 MeV. We carried out investigations into several vital factors of S-band SCL for proton acceleration, such as optimization of SCL cavity geometry, end cell tuning, and bridge coupler design. Results demonstrated that the effective shunt impedance per unit length ranged from 22.5 to 59.8 MΩ/m throughout the acceleration process, and the acceleration gradient changed from 11.5 to 15.7 MV/m when the maximum surface electric field was equivalent to Kilpatrick electric field. We obtained equivalent circuit parameters of the biperiodic structures and applied them to the end cell tuning; results of the theoretical analysis agreed well with the 3D simulation. We designed and optimized a bridge coupler based on the previously obtained biperiodic structure parameters, and the field distribution un-uniformness was < 1.5% for a two-tank module. The radio frequency power distribution system of the linac was obtained based on the preliminary beam dynamics design.

Novel deuteron RFQ design with trapezoidal electrodes and double dipole four-vane structure

RFQ-based neutron sources for various applications are being developed and constructed worldwide. To simplify RFQ structure and increase the effective shunt impedance, some novel design strategies have been investigated, including trapezoidal electrode modulations, the double dipole (DD) RFQ structure and use of an internal buncher dynamics strategy. Trapezoidal modulations based on 2TERM profiles are proposed to compensate for the variation of inter-vane capacitance, which helps to simplify rf electromagnetic design and field tuning. The double dipole (DD) four-vane structure increases mode separation without adding other equipment by modifying the RFQ undercut scheme. Furthermore, the entrance gap electric field between endplate and electrodes is designed as a longitudinal buncher, which makes the RFQ bunching section much shorter. By applying these considerations, a novel RFQ has been designed. It operates at 162.5 MHz with a duty factor of 1%, and can accelerate the 10 mA deuteron beam to 1.5 MeV. We have reduced the length of electrodes from 2.2 m to 1.8 m while maintaining transmission efficiency above 98.5%. The rf electromagnetic design has been carried out to fulfill the requirements of the resonant frequency, flat longitudinal field distribution and field tuning.

STUDY ON A HOM TYPE BUNCHER1

Normally, drift tube linacs (DTL) are used following RFQ linacs for beam acceleration in middle and high beam energy region. The acceleration efficiency of DTLs is decreasing with beam energy increasing. Using resonated higher order mode (HOM) of cavity, DTL can achieve higher effective shunt impedance. We proposed a 325 MHz DTL with TE115 mode. In this paper, the dynamics calculation and electromagnetic design of the HOM-DTL will be reported.

Design and low power test of Preparing a prototype HOM linac1

Normally, drift tube linacs (DTLs) are used following RFQ linacs for beam acceleration in middle and high energy region. The acceleration efficiency of DTLs is decreasing with beam energy increasing. Using resonated higher order mode (HOM) of cavity, DTLs can achieve a higher effective shunt impedance. We proposed a 325 MHz DTL with TE115 mode and finished the 1st HOM-DTL assembly. In this paper, the designs and results of low power test of the 1st HOM-DTL will be reported.

Practical design approach for trapezoidal modulation of a radio-frequency quadrupole

Trapezoidal modulation of quadrupole electrodes offers additional benefits to the concept of a radio-frequency quadrupole (RFQ). Because of the significant increase of the effective shunt impedance, RFQs with trapezoidal modulation have a reduced interelectrode voltage or resonator length as compared to conventional RFQs with sinusoidal modulation. This feature is especially valuable for RFQs operating in cw mode, since it reduces the required rf power. We develop a detailed procedure for the design of RFQ electrodes with trapezoidal modulation. With our design procedure and by properly choosing the trapezoidal cell parameters, we can easily control the peak surface fields in the RFQ to the same level as for sinusoidal cell modulation. The procedure is applied to the design of the electrodes for the ReA3 RFQ at Michigan State University.

Development of High Frequency Resonators for Proton Acceleration in the Energy Range from 2.3 Till 5 MeV

High frequency optimization of multigap IH-/CH-resonators requires solving the range of problems, particularly receiving high values of effective shunt impedance and realization of the uniform accelerating field distribution on its axes. H-mode resonators design contains flat vanes (pylons)to reach both of these goals. This article presents the results of electrodynamic modeling of CH- and IH-resonators in case of zero gap between the vanes and resonator end wall. The values of the optimized shunt impedances, Q-factor and field flatness for IH- and CH-designs are shown.

Biperiodic accelerating structure with inner coupling cells offering an increased coupling coefficient

Efforts to increase the coupling coefficient of a biperiodic accelerating structure without deteriorating a high effective shunt impedance and other electrodynamic characteristics are discussed.

Design of a 10 MeV, 352.2 MHz drift tube Linac

A conventional 10 MeV drift tube Linac is designed as a part of the H − front end accelerator system for the future Indian Spallation Neutron Source. The front end Linac consists of a 50 keV H − ion source, low energy beam transport (LEBT), a 3 MeV radio frequency quadrupole (RFQ), and a 10 MeV drift tube Linac (DTL), which will be operated at 1.25% duty factor. Cell geometry of the DTL is optimized to house quadrupole magnets and to get maximum effective shunt impedance. Transmission efficiency and various other output parameters depend on the input design parameters. Beam dynamic studies are done to maximize the transmission efficiency with minimum emittance growth. Errors in the alignment of the quadrupoles inside the drift tubes or the DTL tank alignment with respect to transport line will degrade the beam quality and may reduce the transmission efficiency. Error study is performed to assess the acceptable tolerances on various parameters. This paper describes the 2D and 3D electromagnetic and beam dynamics simulations of the 352.2 MHz, 10 MeV drift tube Linac. Details of the DTL design are reported in this paper.

DTL cavity design and beam dynamics for a TAC linear proton accelerator

A 30 mA drift tube linac (DTL) accelerator has been designed using SUPERFISH code in the energy range of 3–55 MeV in the framework of the Turkish Accelerator Center (TAC) project. Optimization criteria in cavity design are effective shunt impedance (ZTT), transit-time factor and electrical breakdown limit. In geometrical optimization we have aimed to increase the energy gain in each RF gap of the DTL cells by maximizing the effective shunt impedance (ZTT) and the transit-time factor. Beam dynamics studies of the DTL accelerator have been performed using beam dynamics simulation codes of PATH and PARMILA. The results of both codes have been compared. In the beam dynamical studies, the rms values of beam emittance have been taken into account and a low emittance growth in both x and y directions has been attempted.

RF properties of 700 MHz, β = 0.42 elliptical cavity for high current proton acceleration

BARC is developing a technology for the accelerator-driven subcritical system (ADSS) that will be mainly utilized for the transmutation of nuclear waste and enrichment of U233. Design and development of superconducting medium velocity cavity has been taken up as a part of the accelerator-driven subcritical system project. We have studied RF properties of 700 MHz, β = 0.42 single cell elliptical cavity for possible use in high current proton acceleration. The cavity shape optimization studies have been done using SUPERFISH code. A calculation has been done to find out the velocity range over which this cavity can accelerate protons efficiently and to select the number of cells/cavity. The cavity’s peak electric and magnetic fields, power dissipation P c , quality factor Q and effective shunt impedance ZT 2 were calculated for various cavity dimensions using these codes. Based on these analyses a list of design parameters for the inner cell of the cavity has been suggested for possible use in high current proton accelerator.

Multicavity proton cyclotron accelerator

A mechanism for acceleration of protons is described, in which energy gain occurs near cyclotron resonance as protons drift through a sequence of rotating-mode ${\mathrm{TE}}_{111}$ cylindrical cavities in a strong nearly uniform axial magnetic field. Cavity resonance frequencies decrease in sequence from one another with a fixed frequency interval $\ensuremath{\Delta}f$ between cavities, so that synchronism can be maintained between the rf fields and proton bunches injected at intervals of $1/\ensuremath{\Delta}f$. An example is presented in which a 122 mA, 1 MeV proton beam is accelerated to 961 MeV using a cascade of eight cavities in an 8.1 T magnetic field, with the first cavity resonant at 120 MHz and with $\ensuremath{\Delta}f\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}8\mathrm{MHz}$. Average acceleration gradient exceeds 40 MV/m, average effective shunt impedance is $223\mathrm{M}\ensuremath{\Omega}/\mathrm{m}$, but maximum surface field in the cavities does not exceed 7.2 MV/m. These features occur because protons make many orbital turns in each cavity and thus experience acceleration from each cavity field many times. Longitudinal and transverse stability appear to be intrinsic properties of the acceleration mechanism, and an example to illustrate this is presented. This acceleration concept could be developed into a proton accelerator for a high-power neutron spallation source, such as that required for transmutation of nuclear waste or driving a subcritical fission burner, provided a number of significant practical issues can be addressed.

Acceleration test of TIT-IHQ linac for heavy ion irradiation

We have developed an interdigital-H quadrupole (IHQ) linac for industrial applications. This linac was designed to accelerate particles with charge to mass ratio greater than 1/16 from 21.8 up to 145 keV/u. The particles are focused by an electric quadrupole field exited by fingertips on the drift tubes. This IHQ linac was installed at Tokyo Institute of Technology in 1997 and some tests such as low power tuning and vacuum tests were done. Then, proton acceleration tests ware performed in 1998, and the proton beam was successfully accelerated up to the designed energy. As a result of this experiment, the effective shunt impedance was determined to be 210 MΩ/m, the required RF power consumption was 93 W and the beam transmission rate was about 9%. In this paper, the results of the high power acceleration test with H + ion are described.

Heavy-ion postaccelerator at the University of Tsukuba

A linear rf accelerator of the interdigital-H type has been constructed as a heavy-ion postaccelerator for the 12 UD Pelletron tandem accelerator. The high effective shunt impedance of the accelerating cavity resulted in the generation of a total accelerating voltage of 1.77 MV with an rf power of only 8 kW at 100 MHz. By means of this postaccelerator, the energy of 35Cl 15+ ions delivered by the tandem accelerator at 110 MeV increased up to a final energy of 136.5 MeV. A new method of the determination of drift-tube lengths has also been developed. In this method, the gaps between the drift tubes are adjusted by using an empirical formula in order to obtain a uniform distribution of accelerating fields as well as to satisfy the synchronous condition for ions to be accelerated. The present postaccelerator has been successfully used for nuclear spectroscopy as a simple, low-cost and powerful apparatus.

The upgraded Munich linear heavy ion postaccelerator

The linear postaccelerator at the Munich tandem laboratory was extended by a second resonator cavity and a de-/rebuncher, which both have twice the frequency of the first tank. The simple construction principle and the high shunt impedance of the first cavity, an IH structure, can be transferred onto the sections of a long linac by using a special kind of beam dynamics. In addition to the postacceleration of heavy ions, this method also provides an economical acceleration of low energy beams with small q/ A values. The second Munich postaccelerator section has an effective shunt impedance of 167 MΩ/ m for β = 0.1 , its total length is 3 m. The de-/rebuncher (5–7 gaps) shows that also short IH structures are very effective.

Computer simulation of the RF properties and thermal conditions of the disk- and -washer accelerating structure for the CW racetrack microtron

This article reports the results of the computer simulation of parameters of the disk-and-washer accelerating structure for the CW racetrack microtron. Effective shunt impedance of the structure is optimized taking into consideration the parasitic modes. Capture section is simulated and thermal conditions are analyzed.