Numerous applications exist for CW linear accelerators with final energies in the 0.5 to 4.0 MeV proton energy range. Typical proton current at the linac output energy is 20mA. An important subsystem for the accelerator facility is a reliable dc mode proton injector. We present here design and laboratory results for a dc, 25-keV, 30-mA proton injector. The proton source is a 2.45-GHz microwave hydrogen ion source which operates with an 875-G axial magnetic field. Low emittance, high proton fraction (> 85%), beams have been demonstrated from this source. The injector uses a novel dual-solenoid magnet for matching the injector beam into a radio frequency quadrupole (RFQ) linear accelerator. Recently, a dc ion-source development program has given up to 30mA beam current. The dual solenoid is a compact and simple design utilizing tape-wound, edge-cooled coils. The low-energy beam transport design as well as 25-keV beam matching calculations to an RFQ will also be presented.

An injector development program is being pursued at Linac Systems for satisfying linear accelerator input beam requirements. Proton beams with 25-keV beam energy and 30-mA current with variable duty factors are presently being produced. The two main injector ingredients are a microwave plasma source and a singleeinzel lens for matching the proton beam into the Radio Frequency Quadrupole (RFQ) accelerator. By realistic design simulation, the 25-keV rms normalized emittance is predicted to be 0.07 (πmm-mrad) after extraction from the plasma. The proton beam rms normalized emittance is predicted to grow to 0.24 (πmm-mrad) at the RFQ match point for 26 mA proton current. Insertion of a LEBT beam scraper reduces the predicted proton beam current to 15 mA with 0.085 (πmm-mrad) rms normalized emittance. A proton beam with these characteristics is predicted to have good transmission through the 4-bar, 200-MHz RFQ. Recent injector-RFQ measurements are confirming these design predictions, with 18-mA RFQ output current recently measured. 1B

The Rf-Focused Interdigital (RFI) linac structure is under development at Linac Systems. It promises very efficient acceleration of protons, light ions, and heavy ions to tens of MeV in relatively small packages. Recent developments include the discovery of effective geometries for the support of the two-part drift tubes, which provide the rf focusing, and efficient geometries for the end terminations of the interdigital linac tanks. These developments required extensive use of our 3d rf cavity calculational capability. A "cold model" of an RFI linac has been fabricated and tested. The measured and calculated field distributions are in reasonable agreement. The beam dynamics of the structure has been studied with TRACE-3D and a modified version of PARMILA. The structure is capable of remarkably high beam currents (space charge limits). The results of these studies will be presented. The high rf efficiency of the structure promotes the possibility of cw operation. A prime application for the RFI linac structure is the challenging job of providing intense fluxes of epithermal neutrons for the boron neutron capture therapy (BNCT) application. Mechanical designs of the RFI linac structure for that application will be presented. Other applications for the RFI linac structure will be described.

The experience of commissioning a 2.5-MeV, “Proof-of-Principle” prototype of the new RFD linac structure is reported. This structure resembles a drift tube linac (DTL) with radio frequency quadrupole (RFQ) focusing incorporated into each drift tube, hence the name, RF Focused Drift tube (or RFD) Linac. A prototype of this structure, comprising a 25-keV proton ion source, an Einzel-lens-based LEBT, a 0.65-m-long RFQ linac to 0.8 MeV, and a 0.35-m-long RFD linac to 2.5 MeV, has been designed, fabricated, assembled, and commissioned in our laboratory. Comparisons are made between the projected and observed performances of this structure. The effect of this new linac structure on the size, cost and complexity of linac-based systems for practical applications is described. Plans for the use of this new linac structure to satisfy several scientific, industrial and medical applications are outlined

A 2.5-MeV prototype of a ''Compact 12-MeV Proton Linac for PET Isotope Production'' is under construction at Linac Systems. This unit will serve as the ''proof of principle'' for the revolutionary new Rf Focused Drift tube (RFD) linac structure. Both the prototype and the production unit will operate at 600 MHz. The prototype comprises a 25-keV proton ion source, a short LEBT, a 0.65-m-long RFQ linac to 0.8 MeV, and a 0.35-m-long RFD linac to 2.5 MeV. Because of the similarity of the accelerating and focusing properties of the RFQ and RFD linac structures, no matching section is required between them. The two linac structures will be resonantly coupled together and powered by a collection of planar triodes. The prototype is scheduled for completion in the fall of 1997.

The new RF-focused drift-tube (RFD) linac structure resembles a drift tube linac (DTL) structure with RF quadrupole (RFQ) focusing incorporated into each "drift tube". As in the conventional DTL structure, these drift tubes are supported on single stems along the axis of a cylindrical cavity excited in the TM/sub 010/ RF cavity mode. Four electrodes of each drift tube couple energy from the primary cavity mode to produce RF quadrupole focusing fields along the axis of the drift tube. The RF properties of this three-dimensional structure are being studied with the aid of HFSS (3D-RF code), CHARGE-3D (3D-electrostatic code), and SUPERFISH (2D-RF code). The beam dynamics of this structure is being analyzed with the aid of a new PARMILA-like beam dynamics code, PARMIR, and TRACE-3D. The results of these studies and descriptions of our target applications are presented.

The Rf-Focused Drift-tube (RFD) linac structure, under development at Linac Systems, has the high acceleration efficiency of the DTL linac and the strong rf-electric focusing of the RFQ linac. Because of the rf electric focusing, the RFD linac structure operates well at much lower energies than the conventional magnetically focused DTL. Consequently, the transition energy between the RFQ linac, required to capture the unbunched beam from the injector, and the RFD linac can be much lower than for conventional RFQ/DTL combinations. The acceleration efficiency of the RFQ is relatively high, and similar to that of the RFD, at these lower energies. Because of the rf electric focusing in the RFD, the transverse focusing (and beam size) in the RFD is similar to that in the RFQ. Consequently, no complex matching section is required between the two linacs. The consequences of these merits on the cost and complexity of small proton and light-ion linac systems for scientific, medical and industrial applications will be addressed. 1 THE RFD LINAC STRUCTURE The RFD Linac Structure [1-4] resembles a drift tube linac (DTL) with radio frequency quadrupole (RFQ) focusing incorporated into each "drift tube". As in conventional DTLs, these drift tubes are supported on single stems along the axis of cylindrical cavities excited in the TM010 rf cavity mode. The RFD drift tubes comprise two separate electrodes, operating at different electrical potentials as determined by the rf fields in the cavity, each supporting two fingers pointing inwards towards the opposite end of the drift tube forming a fourfinger geometry that produces an rf quadrupole field distribution along the axis. The fundamental periodicity of this structure is equal to the "particle wavelength", βλ. The particles, traveling along the axis, traverse two distinct regions, namely gaps between drift tubes where the acceleration takes place, and regions inside the drift tubes where the rf quadrupole focusing takes place. This structure uses both phases of the rf fields to affect the beam; one for accelerating the beam and the other for focusing the beam. In this case, the "reverse * Work supported by the National Institute of Mental Health (NIMH). phase" does not decelerate the beam because the fields inside the drift tubes are distorted into transverse focusing fields with little longitudinal component. The orientation of the fingers in the focusing regions alternate so as to create an alternating focusing and defocusing action on the beam in each transverse plane. A very important advantage that the RFD structure has over the RFQ structure is acceleration efficiency. A comparison of the rf efficiencies for the RFD and RFQ linac structures is shown in Fig. 1. In the range of 1-to-5 MeV, the RFD structure has approximately 4 times the shunt impedance of the RFQ structure. 2 PRACTICAL LINAC SYSTEMS Most proton and light-ion linac systems start with an RFQ linac section to capture the beam from the ion source and to bunch it for acceleration in more efficient linac structures. As shown in Fig. 1, the rf efficiency of the RFQ linac structure drops rapidly with energy. In proton linac systems, the RFQs have been called upon to accelerate the beam to an energy of 2.0 MeV or so where the magnetically focused DTL can handle it. At this point, however, there is a serious mismatch in the acceleration and focal properties of the two structures, necessitating some provision for “matching” the two. The RFD linac structure provides a graceful way to accelerate the small diameter, tightly bunched beams that come from RFQ linacs to higher energies. Because of the rf electric focusing, the RFD linac structure operates well at much lower energies than the conventional magnetically focused DTL. Consequently, the transition energy between the RFQ linac, required to RF Efficiency at 600 MHz

The Superconducting Super Collider was designed to provide 108 proton‐proton collisions per second in each of four detectors, about 1.7 collisions per bunch crossing. This collision rate requires a luminosity of 1033 cm−2 s−1, a value that can be attained only by strict control of beam emittance in each accelerator in the chain. Emittance control must start with an understanding of the causes of emittance growth as a guide to beam dynamics design. Manufacture, installation, commissioning, and operation of every component of the machine must be accomplished with emittance control as one of the objectives. This paper describes the actions taken to assure tht the linac output emittance is within the design goals of 0.3 π‐mm‐mrad (rms, normalized, transverse) and <0.89×106 π‐eV‐s (rms, longitudinal).

Many different beam dynamics simulation techniques and codes will be used during commissioning of the SSC Linac. As commissioning progresses, these techniques and codes will be developed, improved, tested and integrated into the linac control system. When the initial commissioning is finished, the control system will include a solid basis of simulation capability for normal operational use and periodic tuneup. For instance, some of the procedures that must be supported during both commissioning and normal operation are matching, steering, acceptance scanning, RF tuneup and emittance measurements. These all require simulation capability that should be easily available to the operator in a form that: 1) takes its input directly from linac diagnostics; 2) is immediately useful without sophisticated analysis; and 3) produces whatever output is best suited for the task at hand, be it a graphic on a screen or a control signal to an actuator. We discuss the various approaches that are being pursued to ensure that the necessary beam dynamics simulation capability will be available as needed

This paper provides arguments to choose electrostatic low-energy beam transport (LEBT) over the magnetic LEBT for the SSC linac. We will outline the rules to design the electrostatic LEBTs with examples of SSC LEBTs.

The Superconducting Super Collider Laboratory and the Institute for Nuclear Research are collaboratively developing a Bunch Shape Monitor diagnostics for commission the SSCL linac. The Bunch Shape Monitor is designed to measure the intensity of beam as a function of time over the micro-bunch of the beam. Design resolution for the SSCL monitors is approximately 7 psec. The first monitor will operate at the fundamental frequency of 428 MHz and will be used to measure the output beam of the RFQ Linac. First available results will be presented and compared with predictions. Further development will allow the monitors to fit in a standard SSCL beam box and one will operate at the third harmonic of 428 MHz. Proposals to use the Bunch Shape Monitor to measure the longitudinal phase space distribution of the beam are discussed

A basic set of diagnostics is needed to commission, tune, and monitor the operation of the SSCL linac. This set of diagnostics has been refined in the final stages of design of the linac. Planned diagnostics include current monitors, Faraday cups, beam loss monitors, beam position monitors, wire scanners, absorber-collector phase scan units, slit and collector emittance measurement units, and longitudinal bunch shape monitors. The diagnostics are described and their placement along the linac is given. The use of the diagnostics for tuning the linac is described. The first set of diagnostics will be installed with the RFQ, with additional diagnostics installed with each linac section. >

The RFQ-DTL matching section has four variable field quadrupole magnets in a FODO lattice to match the 2.5-MeV, 27-mA, H/sup -/ beam from the RFQ to the acceptance space of the DTL, as well as to provide beam steering. In addition, there are two rf buncher cavities to provide longitudinal phase space tuning. An ensemble of beam diagnostics including input and output beam current toroids and beam position monitors, a wire scanner for beam profile measurements, a slit and collector device for beam emittance measurements, and a Faraday cup is used to quantify the matching section performance. The finalized design of the major components of the RFQ-DTL matching section is presented as well as the status of its construction.< >

Simulations of the SSC RFQ output beam, run on the RFQ multiparticle code PARMTEQ, are compared with measurements from the SSC linac injector system. Some simulated RFQ input beams are generated from experimental observations of the output beams of the SSC einzel-lens Low Energy Beam Transport (LEBT) that focuses the beam from the ion source into the RFQ; this is the first LEBT to be tested with the RFQ

This paper summarizes error and tolerance studies for the SSC Linac. These studies also include higher-order multipoles. The codes used in these simulations are PARMTEQ, PARMILA, CCLDYN, PARTRACE, and CCLTRACE.<>

Commissioning diagnostics are described in terms of the beam physics requirements of the SSCL linac. Commissioning diagnostics include current monitors, beam position monitors, spectrometer, foil scattering experiment, wire scanners, Faraday cups, and bunch shape monitors. Two DOE integrated contractors, the Superconducting Super Collider Laboratory and Allied Signal, Kansas City Plant, are developing the commissioning diagnostics. The need to measure bright, short linac beam pulses requires special design considerations. High density harps and collectors with up to 50 wires per cm and 128 wires total, and fast, 3.5-MHz amplifiers have been developed. The diagnostics will be first used and tested during beam commissioning of the RFQ

The Superconducting Super Collider ion source/LEBT produces and focuses a 35 keV 30 mA H- beam into the RFQ. The beam emittance (εn-rms, and its other characteristics, are measured using a slit and collector diagnostic system. The resultant data is analyzed by two separate applications. Both the hardware and software involved are discussed. Result examples are presented

The paper presents the details of the physics design of the RFQ-DTL matching section of the SSCL linac. The 2.5 MeV H- beam from the RFQ is matched into the acceptance of the 70 MeV Drift Tube Linac (DTL). For a nominal beam of 27.5 mA with a normalised (r.m.s.) transverse emittance of 0.2 mm.mrad. an emittance growth of about 5% is estimated at the end of the DTL. The behavior of the system with respect to the various type of beams and its sensitivity to fabrication and alignment errors has been analysed. A steering mechanism to align or position the beam anywhere within the acceptance of the DTL is also briefly explained.