In order to implement radiotherapy based on a laser accelerator, it is necessary to precisely control the spatial distribution and energy spectrum of the proton beams to meet the requirements of the radiation dose distribution in the three-dimensional biological target. A compact laser plasma accelerator has been built at Peking University, which can reliably generate and transport MeV-energy protons with a specified energy onto the irradiation platform. In this paper, we discuss several technologies for the accurate control of a laser-accelerated proton beam with large divergence angle and broad energy spread, including the determination of the beam source position with micron accuracy, a tuning algorithm for the transport line which we refer to as ``matching-image-point two-dimensional energy analysis'' to realize accurate energy selection, and the control of beam distribution uniformity. In the prototype experiment with low energy protons and 0.5-Hz irradiation rate, a tailored energy deposition is demonstrated, which shows the potential feasibility of future irradiation based on laser-accelerated proton beams.

A compact laser plasma accelerator (CLAPA) that can stably produce and transport proton ions with different energies less than 10 MeV, <1% energy spread, several to tens of pC charge, is demonstrated. The high current proton beam with continuous energy spectrum and a large divergence angle is generated by using a high contrast laser and micron thickness targets, which later is collected, analyzed and refocused by an image-relaying beam line using a combination of quadrupole and bending electromagnets. It eliminates the inherent defects of the laser-driven beams, realizes precise manipulation of the proton beams with reliability, availability, maintainability and inspectability (RAMI), and takes the first step towards applications of this new generation of accelerator. With the development of high-rep rate Petawatt (PW) laser technology, we can now envision a new generation of accelerator for many applications in the near future soon.

A novel approach is proposed to demonstrate the two-photon Breit-Wheeler process by using collimated and wide-bandwidth γ-ray pulses driven by 10-PW lasers. Theoretical calculations suggest that more than 3.2×10^{8} electron-positron pairs with a divergence angle of 7° can be created per shot, and the signal-to-noise ratio is higher than 10^{3}. The positron signal, which is roughly 100 times higher than the detection limit, can be measured by using the existing spectrometers. This approach, which could demonstrate the e^{-}e^{+} pair creation process from two photons, would provide important tests for two-photon physics and other fundamental physical theories.

An all-optical scheme is proposed for studying laser plasma based incoherent photon emission from inverse Compton scattering in the quantum electrodynamic regime. A theoretical model is presented to explain the coupling effects among radiation reaction trapping, the self-generated magnetic field and the spiral attractor in phase space, which guarantees the transfer of energy and angular momentum from electromagnetic fields to particles. Taking advantage of a prospective similar to 10(23) W cm(-2) laser facility, 3D particle-in-cell simulations show a gamma-ray flash with unprecedented multi-petawatt power and brightness of 1.7 x 10(23) photons s(-1) mm(-2) mrad(-2)/0.1% bandwidth (at 1 GeV). These results bode well for new research directions in particle physics and laboratory astrophysics exploring laser plasma interactions.

γ-ray flash generation in near-critical-density target irradiated by four symmetrical colliding laser pulses is numerically investigated. With peak intensities about 10^{23} W/cm^{2}, the laser pulses boost electron energy through direct laser acceleration, while pushing them inward with the ponderomotive force. After backscattering with counterpropagating laser, the accelerated electron is trapped in the electromagnetic standing waves or the ponderomotive potential well created by the coherent overlapping of the laser pulses, and emits γ-ray photons in a multiple-laser-scattering regime, where electrons act as a medium transferring energy from the laser to γ rays in the ponderomotive potential valley.

Gamma-ray explosion from near critical density (NCD) target irradiated by four symmetrical imploding laser pulses is numerically investigated. With peak intensities about $10^{23}$ W/cm$^2$, the laser pulses boost electron energy through direct laser acceleration, while pushing them inward with the ponderomotive force. After backscattering with counter-propagating laser, the accelerated electron will be trapped in the optical lattice or the electromagnetic standing waves (SW) created by the coherent overlapping of the laser pulses, and meanwhile emit gamma-ray photon in Multiple Compton Scattering regime, where electron acts as a medium to transfer energy from laser to gamma-ray. The energy conversion rate from laser pulses to gamma-ray can be as high as around 50%. It may become one of the most efficient gamma-ray sources in laboratory.

The SSC-LINAC project is launched at Institute of Modern Physics in China to develop one new linear accelerator (LINAC) injector for separated sector cyclotron (SSC). It includes a high charge state ion source, a CW RFQ and a DTL section, and is designed to accelerate ions up to 580keV/u. Now the ion source and the RFQ cavity have been installed in the main hall and the beam commissioning has been carried out. Two kinds of ions have been tested, 16O5+ and 40Ar8+. The experiment result of 16O5+ is: the measured beam current is 180μA at entrance of RFQ and 150μA at exit of RFQ. The output energy of 16O5+ is 141.89keV/u. The measured beam current is 210μA at entrance of RFQ and 198μA at exit of RFQ for 40Ar8+. The output energy of 40Ar8+ is 142.78keV/u. The experiment results agree with the design parameters of RFQ very well. This paper presents: the design consideration of beam dynamics, RF and cooling structure design; measurement of the cold model; high power test of RFQ and beam commissioning result.

We show that a high current quasi-monoenergetic electron beam and a peaked brilliant gamma-ray beam can be generated by irradiating an ultra-intense laser pulse on uniform near critical density plasma, with a laser spot radius RL∼(λ/π)2a/n, here λ is the laser wave length, a denotes the normalized laser intensity, and n denotes the normalized plasma density. Due to a relativistic resonant phase locking mechanism, high energy oscillating electrons are trapped to ride on the laser electric field, and an unprecedented ultra-fast ultra-brilliant gamma-ray pulse is emitted from the electrons. Both the high energy electrons and gamma-ray photons are emitted in a small polar angle range. It is similar to a conventional wiggler synchrotron, except that the curvature radius of electron orbits in the laboratory coordinate frame measures in microns rather than in meters.

We demonstrate the instability-free ion acceleration regime by introducing laser control with two parallel circularly polarized laser pulses at an intensity of I = 6.8 × 1021 W/cm2, normally incident on a hydrogen foil. The special structure of the equivalent wave front of those two pulses, which contains Gaussian peaks in both sides and a concavity in the centre (2D), can suppress the transverse instabilities and hole boring effects to constrain a high density ion clump in the centre of the foil, leading to an acceleration over a long distance and gain above 1GeV/u for the ion bunches.

We show that electron betatron resonance acceleration by an ultra-intense ultra-short laser pulse in a near critical density plasma works as a high-brightness gamma-ray source. Compared with laser plasma X-ray sources in under-dense plasma, near critical density plasma provides three benefits for electron radiation: more radiation electrons, larger transverse amplitude, and higher betatron oscillation frequency. Three-dimensional particle-in-cell simulations show that, by using a 7.4J laser pulse, 8.3mJ radiation with critical photon energy 1MeV is emitted. The critical photon energy $E_c$ increases with the incident laser energy %faster than a linear relation. $W_I$ as $E_c \propto W_I^{1.5}$, and the corresponding photon number is proportional to $W_I$. A simple analytical synchrotron-like radiation model is built, which can explain the simulation results.

The high current deuteron RFQ has been developed and widely used in many projects, especially for accelerator based neutron source and its applications. This paper presents the beam dynamics, structure design, RF full power test and beam commissioning of PKUNIFTY (Peking University Neutron Imaging Facility), which consists of a high current compact ECR source, a 201.5 MHz four-rod deuteron RFQ, thick beryllium target, moderator, collimator and neutron radiography system. RF and beam commissioning with duty cycle of 4% show the RFQ inter-vane voltage reaches 70 kV at about 240 kW, the delivered peak current of deuteron beam is about 12 mA at 300 kW with the beam transmission of about 60%. The improvement of transmission is going on. The initial neutron radiography test has been carried out. The results will promote the future development of small accelerator based neutron source.

RF design of a trapezoidal IH-RFQ (T-IH-RFQ) has been completed, combining with the low energy spread beam dynamics to accelerate C from 40 to 500keV at 104MHz. RF properties of the T-IH-RFQ are studied and geometric parameters such as distance between two neighbouring support boards, width of stems and cavity diameter, have been optimized for improving transverse shunt impedance and quality factor, namely, reducing power consumption. Detailed description of the T-IHRFQ and optimized results will be presented in this paper.

The beam dynamics for a 201.25MHz 50mA 2.0MeV Deuteron RFQ accelerator with duty cycle of 10% has been further improved by using equipartitioned method. The RFQ structure, mechanical design, thermal analysis and its cooling method have been investigated. The tuning of RF cavity for the field and other parameters has been simulated. A new developed ECR ion source and its setup have been completed and tested. The LEBT for the injection of RFQ is under the construction, and the HEBT at RFQ exit for the further applications has been designed and to be constructed in the near future. All the development results will be presented in this paper.

The simultaneous acceleration of ${\mathrm{O}}^{+}$ and ${\mathrm{O}}^{\ensuremath{-}}$ beams in a radio frequency quadruple accelerator has been numerically simulated and the results are presented in this paper. The micropulses of ${\mathrm{O}}^{+}$ and ${\mathrm{O}}^{\ensuremath{-}}$ beams have been measured in dual beam acceleration experiments, which verified the numerical simulations and feasibilities of dual beam acceleration.

The dynamics design of radio frequency quadruple (RFQ) Linacs for high intensity beams had been extensively studied by LANL and generalized method had been proposed, however, the beam mismatches are still not paid enough attentions in this dynamics design method. As the beam envelope mismatch is the major source of formation of halo and related emittance growth in high intensity linac, so some extensions based on the generalized method are developed, where the causes of beam mismatch in RFQ are analyzed and a new dynamics method is proposed to minimize the emittance growth and the related beam loss. A dynamics example is given to prove this design method.

The accelerating efficiency of traditional RFQ structure is limited by transverse focusing and the drift tube structure has higher efficiency, so the Seperated Function RFQ (SFRFQ) with diaphragms was proposed in this paper, where the accelerating gaps were formed by diaphragms meanwhile keeping enough electric quadrupole focusing. The reverse fields had been found in the SFRFQ, after the electric field distribution was determined by static solver, then a structure called asymmetrical βλ/4-long diaphragm SFRFQ was developed. Afterwards a RF model had been designed to test the structure technology feasibilities. In order to value the RF efficiencies of RFQ and SFRFQ structures, the shunt impedance had been simulated in MicroWave Studio (MWS). It turned out the RF efficiency will be obviously enhanced after introducing gaps into RFQ strcture. Thus the total length of linac will be largely decreased if the accelerating gaps are introduced earlier, which was proved by the comparison between two dynamics simulations.

The accelerating efficiency of conventional RFQ structure is limited by transverse focusing, and the drift tube structure is more efficient when particle energy is higher. Based on the experience on the 26 MHz heavy-ion Integrated Split Ring RFQ (ISR RFQ) with mini-vane electrodes, RFQ group at Peking University has proposed a novel post-RFQ structure, Separated Function RFQ (SFRFQ) with diaphragms. In such a structure the gaps between diaphragms offer higher accelerating field while keeping sufficient electric quadrupole focusing. However, field distribution calculation shows that decelerating fields exist in the structure with uniformly distributed diaphragms. In order to suppress the decelerating fields, a structure called asymmetrical βλ/4 diaphragm SFRFQ was proposed and designed. After that a RF cold model had been constructed to verify the calculation results and to explore the technological feasibility of the structure. The shunt impedance was calculated with Micro Wave Studio (MWS), which turned out that the RF efficiency is enhanced after introducing gaps into RFQ structure, and the total length of the linac can be shortened considerably, which has been proved with dynamics simulations.

The accelerating efficiency of conventional RFQ structure is limited by transverse focusing, and the drift tube structure is more efficient when particle energy is higher. Based on the experience on the 26 MHz heavy-ion Integrated Split Ring RFQ (ISR RFQ) with mini-vane electrodes, RFQ group at Peking University has proposed a novel post-RFQ structure, Separated Function RFQ (SFRFQ) with diaphragms. In such a structure the gaps between diaphragms offer higher accelerating field while keeping sufficient electric quadrupole focusing. However, field distribution calculation shows that decelerating fields exist in the structure with uniformly distributed diaphragms. In order to suppress the decelerating fields, a structure called asymmetrical βλ/4 diaphragm SFRFQ was proposed and designed. After that a RF cold model had been constructed to verify the calculation results and to explore the technological feasibility of the structure. The shunt impedance was calculated with Micro Wave Studio (MWS), which turned out that the RF efficiency is enhanced after introducing gaps into RFQ structure, and the total length of the linac can be shortened considerably, which has been proved with dynamics simulations.

Two Integral Split Ring (ISR) RFQs with high duty factor of 16.7% have been designed for the application of heavy ion implantation and built in the past several years at Institute of Heavy Ion Physics (IHIP) in Peking University. Two kinds of PIG ion sources with permanent magnets and LEBT were installed and optimized for the injection into these two RFQs. The positive O+ and negative O− ions were extracted and accelerated separately as well as simultaneously. The output macro pulse O− beam current reached 660μA at a transmission efficiency of more than 82%. The N+ beam was also accelerated with similar transmission efficiency, but the output current intensity for positive ions were lower than the negative ions because of the extracted current limitation of ion sources. The improvements, especially for high duty factor and experimental results with the 1MeV ISR RFQ will be presented in this paper.