Slow Beam Extraction Research Articles

Compensation of the asymmetric phase–space distribution for a slowly extracted beam from a synchrotron

In ion beam cancer therapy, it is generally essential for a scanning-irradiation method and a rotating gantry system to deliver a circular beam profile with a Gaussian distribution. A slow beam extraction method utilized in a synchrotron ring, however, cannot deliver a beam with a Gaussian distribution in the horizontal phase space, because of its extraction mechanism. Furthermore, normally, the size of the horizontal emittance is much smaller than that of the vertical one. Thus, we have proposed a thin scatterer method in order to compensate for the phase–space distribution of a slowly extracted beam, although the emittance is slightly enlarged by scattering. As a result of particle tracking, we verified that the proposed method could change an asymmetric distribution to a Gaussian one in the horizontal phase space and realize a symmetric beam condition for the rotating gantry.

Slow beam-extraction method using a fast Q-magnet assisted by RF-knockout

A new method for slow beam-extraction from a synchrotron ring is proposed, based on controlling a quadrupole field with a fast response (FQ), assisted by a transverse RF-field (RF-knockout). This method works as follows: (1) particles of a circulating beam are diffused by RF-knockout to just inside the boundary of a separatrix produced under a resonant condition, (2) exciting the FQ shrinks the separatrix to a certain size, and the particles outside the separatrix can be extracted, (3) the fast Q-field is turned off, and (4) the above process is repeated until all of the circulating beam is completely extracted. This method can extract prescribed particles at required timings quickly and precisely, because it is controlled with only the fast Q-field. A proof-of-principle experiment was carried out at the Heavy Ion Medical Accelerator in Chiba (HIMAC) synchrotron. As a result, it was verified that the beam was extracted only with exciting the FQ, but not with turning the RF-knockout on.

Optics design of the extraction lines for the MedAustron hadron therapy centre

The MedAustron hadron therapy centre will provide proton and carbon ion beams for tumour treatment. The accelerator complex is based on a synchrotron that will employ slow resonant extraction to provide beams with the time structure required for active scanning. Four medical treatment rooms and two research rooms are foreseen for the centre. The present paper describes the optics design of the extraction lines that link the synchrotron to the different beam application rooms. A modular approach has been adopted to facilitate running-in and operation and to minimise the number of different magnets and power converters to reduce the overall cost. Specific attention was given to the rather special transverse properties of the slow-extracted beam and to the correct matching of the strongly asymmetric beam to the rotational optics of the gantries. Another important aspect for the design was the overall compactness of the centre.

A Pulse Stretcher by Slow Extraction Utilizing the Third-Order Resonance with the RF Knockout Method

A pulse stretcher operation of KSR using slow electron beam extraction by the third-order resonance in combination with an RF knockout method has been accomplished. The extracted beam energy, number of extracted electrons in a single pulse, maximum duration and duty factor are 60 MeV, 1.4×108, 40 s and 90%, respectively. The beam spill can be controlled from 0.2 s to 40 s by adjusting of the power for RF knockout.

A new concept for the control of a slow-extracted beam in a line with rotational optics: Part II

The current trend in hadrontherapy is towards high-precision, conformal scanning of tumours with a `pencil’ beam of light ions or protons, delivered by a synchrotron using slow extraction. The particular shape of the slow-extracted beam segment in phase space and the need to vary the beam size in a lattice with rotating optical elements create a special problem for the design of the extraction transfer line and gantry. The design concept presented in this report is based on telescope modules with integer-π phase advances in both transverse planes. The beam size in the plane of the extraction is controlled by altering the phase advance and hence the rotation of the extracted beam segment in phase space. The vertical beam size is controlled by stepping the vertical betatron amplitude function over a range of values and passing the changed beam size from `hand-to-hand’ through the telescope modules to the various treatment rooms. In the example given, a combined phase shifter and `stepper', at a point close to the synchrotron, controls both of these functions for all treatment rooms in the complex. The modular nature of the design makes it easy to extend the complex.

Slow beam extraction by a transverse RF field with AM and FM

Abstract A beam extraction method using a transverse rf electric field with amplitude and frequency modulation has been studied in order to develop an irradiation method which is synchronized with the breathing of a patient for high-quality charged particle therapy. The dependence of the extracted beam intensity on the voltage, the frequency band width and the center frequency of the transverse rf electric field has been investigated. The extracted beam intensity was slightly increased from that of the ordinary slow extraction method with a third order resonance. The response of the extracted beam intensity to the applied transverse rf electric field was as prompt as within 1 ms. The horizontal emittance of beams extracted by the present method was reduced by about 70% compared with that by the ordinary one due to utilizing a constant separatrix. Amplitude modulation can control the global beam spill structure. The frequency modulation reduced the effect of the current ripple of the main quadrupole magnets.

Effects of rf voltage modulation on particle motion

The effects of rf voltage modulation on synchrotron motion were studied experimentally. The experimental data revealed the resonance islands generated by the rf voltage modulation. With electron cooling, beam particles were observed to damp to the basins of these resonance islands or attractors, which were observed to rotate about the origin of the phase space at a half of the modulation frequency. The measured amplitude of the attractors as a function of the modulation frequency agreed very well with the theoretical prediction. The Poincaré maps in the resonance rotating frame were obtained from the experimental data and compared with tori of the Hamiltonian flow. Based on our theoretical formulation, slow beam extraction using rf voltage modulation and a bent crystal are also studied.

Slow positron beam extraction from high magnetic fields

The high intensity positron beam at PSI will be produced in a high magnetic field region (∼ 1 T). On the other hand, micro-beam formation (through brightness enhancement operations) has to be carried out in field-free space. This requires the extraction of the positron beam into field-free space, an operation which becomes possible when symmetry breaking elements are introduced. In this contribution a method is presented, based on B-field termination through a magnetic shield with an aperture furnished by a magnetically conductive internal structure. The positron beam is first guided to a low field region where the shield is placed and then extracted into field-free space by letting it pass through the aperture. The designed aperture has a diameter of 120 mm, an 80% open area and a thickness of 10 mm. The simulated results of the field distributions show that a factor of nearly two orders of magnitude reduction of the field across the aperture and a spread of B ⊥ in the plane of the aperture opening can be achieved. This reduction factor has been confirmed experimentally. Measurements of transmission efficiency and divergency will be discussed. Two parameters can be varied in order to achieve reasonably small transverse energy of the extracted positrons which makes the following focusing performance highly efficient.

Slow beam extraction at TARN II

A slow beam extraction system using the third order resonance has been constructed at TARN II and beam extraction tests have been performed. By the ordinary scheme where the tune is shifted to the resonance with ramping the excitation strength of the lattice quadrupole magnets, an extraction efficiency of 90% is attained. A new scheme increasing the horizontal emittance of the circulating beam is applied to extract the beam. A very long beam spill of 800 s is obtained by this scheme. A method using a transverse rf field is also studied experimentally, resulting in an extracted beam with smaller emittance.

Time Dependent Structure and Spill Measurements of Proton Beams at the CERN SPS

For fixed target operation the proton beam is extracted at 14 GeV over 5 successive turns of each 2.1µs from the CPS and injected into the SPS. The current from a secondary emission monitor is sampled every 0.1µs by a charge coupled device. The stored signal is afterwards scanned at a lower frequency and provides an accurate profile evolution during injection. For slow proton beam extraction at 450 GeV a new type of detector has been developed. It uses the properties of the transition radiation created by the beam when traversing a thin aluminium foil. Accurate transverse profiles are obtained by such a detector. The disturbances to the beam are an order of magnitude less than with a classical secondary emission monitor.

LAMPF II

We present a plan for two rapid-cycling synchrotrons — a 45 GeV, 40 μA proton synchrotron with a 9 GeV, 200 μA booster. These machines can provide simultaneously 45 GeV slow-extracted beam for the production of kaons, antiprotons, and other secondary particles, and 9 GeV fast-extracted beam for neutrino and pulsed muon physics. The LAMPF II machines are compared with existing and proposed kaon factories. Relative to the Brookhaven AGS as it exists today, LAMPF II will provide 90 tmes as many neutrino events per year and 300 times as many kaons per year. Some design features of the LAMPF II accelerators that are important for reducing beam losses and increasing beam availability are discussed. Because of the large rf power and voltage required, an innovative design of the ferrite-tuned cavities is necessary. A commercially available Mg-Mn ferrite with perpendicular bias has been shown to raise the available ferrite Q by more than a factor of 10 when compared with materials now in use at other accelerators. The 45 GeV LAMPF II synchrotron would produce far more neutrinos, kaons, and antiprotons per unit cost than an upgraded conventional machine. The LAMPF II booster by itself, which can provide 100 μA at 12 GeV, is a very interesting option at moderate cost.

Improved measurements of slow-extracted beam emittance

Beam size measurements have been made for the AGS slow-extracted beam under various conditions. It is shown that profiles measured by the segmented-wire ion chamber technique have several types of distortions, and significant corrections must be made before the resulting profiles are useful for emittance studies. After correction, the vertical profiles are well described by a model with elliptical contours of constant density in phase space and Gaussian density distribution. This model is unsatisfactory for the horizontal phase space, so a parallelogram model, based on calculated properties of the non-linear resonant extraction process, is used. The final results are well described by the models. There are only two free parameters, corresponding to the emittance in each plane.

Slow Extraction from KEK-PS Main Ring

Two different schemes are used for the slow beam extraction from the main ring of KEK-PS. One uses the internal target scattering under the non-resonant condition and the other the half-integer resonance at υx = 7.5. The extraction efficiency is higher for the resonant extraction (99 %) than for the non-resonant scheme (~30 %). The spill feedback system are provided to suppress the intensity modulation of the extracted beam and to obtain the spill duration up to 400 msec. Slow extraction also shares the beam with the internal target in both schemes in order to perform experiments on both floors at the same time.

RF Acceleration in KEK Main Ring

A description of the RF system and measurements of some longitudinal phenomena of the KEK Main Ring are presented. The beam loss at the phase transition has been reduced by the improvement of the radial position detector and by the stabilization of quadrupole oscillations. The debunching for slow beam extraction is done by two successive frequency jumps with simultaneous reduction of the RF voltage.

Search for new particles

We present a description of an experiment carried out at the 30GeV Alternating Gradient Synchrotron of the Brookhaven National Laboratory. The experiment used a high intensity slow extracted proton beam of between 10 10 and 2 × 10 12 protons per pulse and measured the e + e - mass spectrum from the reaction p+Be→e + e - +X. The result of this experiment shows the production of a new type of particle, J, which decays to e + e - with a width consistent with zero. Experimental searches for more new particles will also be presented.

Target Stations and Beam Dumps for the CERN SPS

The design of the absorber blocks for internal and external dumping of the SPS proton beam is discussed. In addition, the external target stations for slow and fast extracted proton beams are described.

The Organization of a JINR Proton Synchrotron Beami Slow Extraction Parameter Monitoring and Contrzol System in the CAMAC Standard on-Line with an US1010 Computer

A general view of the CAMAC proton synchrotron slow extraction (SE) beam parameter monitoring and control system on-line with an US1010 computer is given. CAMAC provides an interface between the computer and transducers, as well as between the remote controlled SE devices, by means of a universal branch driver developed and used at the High Energy Laboratory as a standard interface for large CAMAC installations. The system is used to measure some parameters of the accelerator, which deter mine the operating made of slow extraction, of a slow extraction system and of an ejected beam. The system includes a closed feedback loop for making corrections in order to stabilize the ejected beam and to optimize the operation of the slow extraction system.

Discovery of the new particle J

We present a description of an experiment carried out at the 30 GeV Alternating Gradient Synchrotron of the Brookhaven National Laboratory. The experiment used a high intensity slow extracted proton beam of between 10 10 and 2·10 12 protons per pulse and measured the e +e − mass spectrum from the reaction p + Be→e +e − + X. The results of this experiment shows the production of a new type of particle, J, which decays to e +e − with a width consistent with zero.

One-Third Resonance Extraction from INS AG Electron Synchrotron

Slow beam extraction from the INS-AG electron synchrotron was done by using a one-third resonance of the betatron oscillation. A current strip was used to change the number of the radial betatron oscillation per revolution from 2.25 to 7/3 and to enlarge the amplitude of the oscillation. The extracting beam orbit was analysed using an approximate Hamiltonian which has a separatrix represented by three straight lines and the result was in good agreement with that pursued by a computer. The properties of the extracted beam were as follows; The efficiency was 50% for electrons of 300 MeV up to 1 GeV. The maximum beam intensity was 4×1011 electrons per second. The maximum duty cycle was 3%. Phase volumes for the horizontal and the vertical motions were 10-3 rad cm and 0.75×10-3 rad cm, respectively. The beam transport system and the radiation shielding system are also described.