After many years on the periphery of cancer therapy, the successes of proton and ion beams in tumor therapy are gradually receiving a higher degree of recognition. The considerable construction and acquisition costs are usually invoked to explain the slow market penetration of this favorable treatment modality. Recently, high-intensity lasers have been suggested as a potential, cost-saving alternative to cyclotrons or synchrotrons for oncology. This article will detail the technical requirements necessary for successful implementation of ion beam therapy (IBT)—the general term for proton and heavier-ion therapy. It will summarize the current state of laser acceleration of protons and will outline the very substantial developments still necessary for this technology to be successfully applied to IBT.

The beam heat load and the pressure in the vacuum chamber of the cold bore superconducting undulator installed at ANKA (ANgstrom source KArlsruhe) have been monitored for almost two years. Possible sources of the observed heat load could be synchrotron radiation from upstream magnets, image currents, electron and ion bombardment. In this paper, the various possible contributions to the heat load are discussed and compared with experimental results. The dynamic pressure increases nonlinearly with the average beam current. The current where it assumes a maximum varies both with the bunch intensity and with the initial vacuum pressure. A correlation between the heat load and the dynamic pressure has been observed. This study suggests that electron bombardment could explain the beam heat load and pressure rise observed for a bunch length of 10 mm.

We study the impedance of a tapered transition at small frequencies for an arbitrary shape of the transition cross section. Our approach does not require a symmetry axis in the system (unlike round geometry). We show that the calculation of the impedance reduces to finding a few auxiliary potential functions that satisfy two-dimensional Poisson equations with Dirichlet boundary conditions. In simple cases such solutions can be obtained analytically; for more complicated geometries they can easily be found numerically. We apply our method to axisymmetric geometry and reproduce results known from the literature. We then calculate the impedance of a taper with rectangular cross section in which the vertical dimension of the cross section is a slowly changing function of the longitudinal coordinate. Finally, we find a transverse kick experienced by a beam passing near a conducting wall with a variable distance from the beam to the wall.

A simple method for splitting a high power, continuous wave (cw) proton beam in two or more branches with low losses has been developed in the framework of the EURISOL (European Isotope Separation On-Line Radioactive Ion Beam Facility) design study. The aim of the system is to deliver up to 4 MW of ${\mathrm{H}}^{-}$ beam to the main radioactive ion beam production target, and up to 100 kW of proton beams to three more targets, simultaneously. A three-step method is used, which includes magnetic neutralization of a fraction of the main ${\mathrm{H}}^{-}$ beam, magnetic splitting of ${\mathrm{H}}^{-}$ and ${\mathrm{H}}^0$, and stripping of ${\mathrm{H}}^0$ to ${\mathrm{H}}^{+}$. The method allows slow raising and individual fine adjustment of the beam intensity in each branch.

Measurements were made of the density, species, and velocity of the desorbed gas cloud on intense ${\mathrm{K}}^{+}$ beam bombardment of a stainless steel target. Residual gas analyzer measurements indicate that the gas cloud consists of predominantly ${\mathrm{H}}_2$. Energy analyzer measurements of doubly ionized beam ions show that the ratio of hydrogen gas production to beam density was approximately $3000\mathrm{\text{molecules}}/\mathrm{\text{ion}}$ at normal incidence. Optical measurements of the evolution of the gas cloud during the beam pulse show a distribution with an average expansion velocity of about $0.5\mathrm{mm}/\mu \mathrm{s}$. Comparison is made with a simple model of the gas cloud behavior.

In this paper we show that free-electron laser (FEL) super-radiant (SR) emission can be greatly enhanced by means of energy modulation of the radiating electron bunch. In FELs, super-radiant emission from short electron bunches is strongly reduced as the temporal duration of the bunch is increased. This prevents the realization of SR FELs operating at submillimeter wavelengths. We analyze the performance of a SR FEL source operating in the THz regime, which is driven by an energy-modulated short duration electron bunch. We carried out analytical evaluations and numerical simulations utilizing a space-frequency 3D model. These show that a remarkable improvement in super-radiant emission intensity can be achieved by the use of appropriate linear modulation (chirp) of the beam energy within the bunch. Possible limitations in applying this method are discussed, as well as the spectral purity of the emitted radiation.

A superconducting particle accelerator like the LHC (Large Hadron Collider) at CERN, can only be controlled well if the effects of the magnetic field multipoles on the beam are compensated. The demands on a control system solely based on beam feedback may be too high for the requirements to be reached at the specified bandwidth and accuracy. Therefore, we designed a suitable field description for the LHC (FIDEL) as part of the machine control baseline to act as a feed-forward magnetic field prediction system. FIDEL consists of a physical and empirical parametric field model based on magnetic measurements at warm and in cryogenic conditions. The performance of FIDEL is particularly critical at injection when the field decays, and in the initial part of the acceleration when the field snaps back. These dynamic components are both current and time dependent and are not reproducible from cycle to cycle since they also depend on the magnet powering history. In this paper a qualitative and quantitative description of the dynamic field behavior substantiated by a set of scaling laws is presented.

We present an analytical and numerical study of the equations of motion for bunches coupled by transverse wakefields. We base our study on a recent lattice design for the damping rings in the baseline configuration of the International Linear Collider. Using the macroparticle model, and assuming resistive wall wakefield coupling, we present numerical results on the time evolution of the multibunch modes. Decay modes display growth after initial decay, and mode amplitudes exhibit high-frequency oscillations. These phenomena are not expected if the beta function is assumed to have a constant, averaged value. We show analytically that they can come from coupling between modes caused by variation of the beta function in a real lattice. The effect is shown to be comparable to the effect of a nonuniform fill pattern and significantly larger than that of the higher-order mode wakefield localized in the rf cavities. Turning to the case of constant beta function, we develop a more complete treatment of the equations of motion. We derive general formulas for the bunch trajectories, and show that such formulas can only be valid in the limit of small wakefield coupling.

A Smith-Purcell device can operate as a backward-wave oscillator for intense, narrow-bandwidth, continuous wave radiation at terahertz wavelengths. We determine the requirements on electron beam current and emittance for the system to oscillate based on a three-dimensional extension of our previous two-dimensional analysis. It is found that specially designed electron beams are required with a current that exceeds a certain threshold value and a flat transverse profile that allows the beam to travel very close to the grating surface. Two methods for producing electron beams with the required characteristics are discussed.

An analytical description of volume reflection of charged ultrarelativistic particles in bent single crystals is considered. The relation describing the angle of volume reflection as a function of the transversal energy is obtained. Different angle distributions of the scattered protons in single crystals are found. Results of calculations for 400 GeV protons scattered by the silicon single crystal are presented.

Truly table-top sized radiation sources based on compact laser-plasma accelerators require compact and strong focusing devices and efficient short-period undulators. Complementing our recent theoretical work on the feasibility of a table-top FEL, we here present the design and successful experimental characterizations of a 5 mm period length undulator and miniature quadrupole magnets with field gradients of the order of $500\mathrm{T}/\mathrm{m}$.

A compact rf pulse compressor, fed by a phase-modulated pulse, is described for producing high-power flattop pulses at Ka-band. The compressor consists of a single axisymmetrical cavity operating in a combination of ${\mathrm{TE}}_{0n}$ modes ($n=1$, 2, 3), that have zero electric fields at the walls. This feature enhances the breakdown strength of the system and makes it possible to increase the output power, as compared with a traditional SLED-II pulse compressor. Advantages include use of one channel instead of two, and no requirement for a 3-dB hybrid coupler. This 34 GHz one-channel pulse compressor (OC SLED-II) is designed to multiply peak power produced by the Yale/Omega-P Ka-band magnicon amplifier (30–40 MW, $0.5–1\mu \mathrm{s}$) by $(3–4):1$ and to compress in time by $(5–6):1$. The efficiency of the proposed compressor is similar to that of SLED-II. Results of low-power tests carried out on a 30 GHz prototype of the compressor are discussed.

The superconducting CH structure is a novel multicell cavity for the acceleration of protons and ions in the low and intermediate energy regime. The CH structure is a cross-bar-type cavity; it is the first superconducting low energy multicell cavity operated in an H mode. A superconducting CH-prototype cavity with 19 gaps at $\beta =0.1$ has been built and tested successfully. Maximum surface fields of $25\mathrm{MV}/\mathrm{m}$ and a corresponding effective cavity voltage gain of 3.7 MV have been achieved. In this paper the development and the tests of this new cavity are presented. This includes also tuning and coupling methods as well as a comparison with other low energy cavities.

In this paper the operability of a Smith-Purcell free-electron laser for an arbitrary grating is considered. An arbitrary grating is described in terms of impedance matrix. The consideration is based on the self-consistent set of Maxwell-fluid equations. The dispersion relation is established for the TM mode of electromagnetic waves. The latter is studied considering amplification of the evanescent as well as radiation modes. The small signal gain in various limits is calculated and the dependence of the gain on the electron beam current is analyzed.

By combining the method of images with calculus of complex variables, we provide a simple expression for the electric field of a two-dimensional (2D) static elliptical charge distribution inside a perfectly conducting circular cylinder. The charge distribution need not be concentric with the cylinder.

We report the absolute power measurement of frequency-locked terahertz coherent transition radiation (CTR) from a train of electron bunches produced by a 17.14 GHz accelerator. Frequency measurements were obtained by two independent techniques: a wave meter with a video diode detector, and a double heterodyne system. Good agreement was seen between these two techniques. The emitted radiation was observed to be a comb of frequencies that are harmonics of the 17.14 GHz accelerator frequency. The heterodyne receiver system showed that each of the emitted harmonics has a very narrow bandwidth, about 25 MHz, which corresponds to the transform-limited bandwidth for the bunch train length of 40 ns. The highest observed frequency was 377.08 GHz, the 22nd harmonic of the 17.14 GHz accelerator frequency. The emitted CTR power was measured on an absolute scale to test the theory of CTR. The power was compared with calculations made using an electric field integral equation (EFIE) formulation and excellent agreement was obtained. This agreement serves as a valuable benchmark of the EFIE code, proof of both its validity and usefulness.

Ion back bombardment is believed to be a main cause of degradation of quantum efficiency of photocathodes in fixed-voltage photoguns. Ions produced in collisions of the electron beam with residual gas in the cathode-anode gap are accelerated towards the cathode and bombard the cathode surface, reducing its quantum efficiency. In addition to ions produced in the accelerating gap, there is another source of ions that has been overlooked so far in existing models of ion bombardment: ions produced in a beam transport line beyond the anode and trapped in the electron beam. These ions can drift back to the cathode and increase the rate of ion bombardment. This article shows that the flux of trapped ions can significantly exceed the flux of ions produced directly in the accelerating cathode-anode gap. The paper also describes a simple and effective solution to the problem of trapped ions, a positive potential barrier.

Frequency jumps in an ion linac use to be made in order to provide a large transverse acceptance in the low-energy part and a high accelerating gradient in the high-energy part. This frequency jump may induce a discontinuity in the average longitudinal force per focusing period and shrink the longitudinal acceptance of the linac if this transition is not performed carefully. In this paper, three techniques are developed which produce a “certain” continuity of the channel at the transition between. The continuity type is discussed. It is demonstrated that the longitudinal acceptance can be preserved whatever the frequencies of the cavities in the linac. This point is very important when comparisons between different cavity types are made (spoke and elliptical cavities for, instance). A few examples are shown to illustrate the performances of the three techniques.