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A nonplanar X-band cavity amenable to coating with high-temperature superconducting films by conventional physical vapor deposition processes has been designed, fabricated, and tested. The cavity geometry resembles a symmetric clamshell configuration. It consists of two truncated cones joined at their bases. The specific dimensions of the cavity were calculated using the SUPERFISH computer code. Cavities were constructed using a silver-based alloy, Consil 995. The separate cavity sections were coated with Tl-based high-temperature superconducting material using a two-step deposition and annealing process. The unloaded Q values for this coated clamshell cavity are 66,000 and 105,000 at 77 and 20 K, respectively.

The SCRUNCHER is a superconducting radio-frequency cavity for manipulating the longitudinal phase space of the secondary pion beam from the low energy pion channel at LAMPF. Test results of the cavity performance and initial results from in-beam tests are presented.

Microwave surface resistance measurements were made on large-area (11.4-cm/sup 2/) Tl-Ba-Ca-Cu-O thick films/ss ( approximately 10 mu m) which were magnetron sputtered onto oriented Ag alloy (Consil 995) substrates. Initial films were prepared by depositing a BaF/sub 2/ buffer layer between the superconducting film and the substrate to control the film/substrate interaction; however, films exhibiting the best microwave properties were prepared without a buffer layer. Surface resistance measurements were made by replacing the end wall of an 18-GHz Cu cavity (TE/sub 011/ mode) with the superconducting film. The best surface resistance values obtained on the unbuffered film were 4 and 14 m Omega at 10 K and 77 K, respectively; the corresponding Cu values are 8 m Omega and 21 m Omega . The dependence of surface resistance on surface magnetic field was measured in a similar way except that an Nb cavity was used instead of a Cu one. Films exhibiting the highest degree of c-axis texturing show the weakest dependence of surface resistance on magnetic field and also exhibit the sharpest high-frequency transition into the superconducting state. These results are important for potential cavity applications of these materials.

Thermally stimulated luminescence (TSL) measurements were conducted both on bare substrates and on high-temperature superconducting (HTS) films deposited onto representative substrates, to demonstrate that TSL is applicable to HTS films in detecting the presence of secondary insulating impurities (for example Y 2 O 3 , BaCO 3 , Y 2 BaCuO 5 , BaCuO 2 ). To provide basic information for this particular application we also report TSL glow curves of the frequently used single-crystal substrates Al 2 O 3 , MgO, YSZ, SrTiO 3 , LaAlO 3 , and LaGaO 3 . Analyses of the well-defined glow peaks yield TSL parameters which suggest that the detrapping of an electron or hole from its metastable state and its subsequent recombination produces luminescence that follows a mixed-order kinetic process (1 ⩽ l ⩽ 2). The thermal activation energy required in this process varies between 0.6 and 2.3 eV and the frequency factor ranges from 10 7 to 10 17 s −1 . Although the luminescence mechanisms in these substrates could not be elucidated with the TSL data alone, these results are found to be adequate for ascertaining the presence of insulating impurities in the HTS films by comparing the TSL of the film-on-substrate and the substrate.

It was recognized shortly after the discovery of high-temperature superconductors (HTS) that these materials would exhibit thermally stimulated luminescence (TSL) as a manifestation of their granularity and consequent inclusion of insulating material at grain boundaries. The large optical absorption coefficients of these opaque materials implies that TSL emanates from within ∼1 μm of the surface. Therefore, TSL can be used to assess the quality of HTS by detecting the presence of insulating surface impurities, which are, in general, deleterious to technological performance. For example, surface resistance R s is determined by HTS properties within the London penetration depth, which is the region probed by TSL. The presence of insulating surface impurities contributes to the high-frequency losses as manifested by an enhanced R s and is directly correlated with TSL. Therefore, in addition to radiation dosimetry and archaeological dating, TSL can also be applied to HTS research.

Microwave surface resistance measurements have been made on large-area Ti-Ba-Ca-Cu-O thick films magnetron-sputtered onto oriented Ag alloy substrates by replacing the end wall of an 18 GHz TE/sub 011/ mode Cu cavity with the superconducting film. The best surface resistance values obtained are 4 and 14 m Omega at 10 K and 77 K, respectively; corresponding Cu values are 8 and 21 m Omega . The dependence of the surface resistance on microwave power was measured in a similar way except that a Nb cavity was used instead of a Cu cavity. Typically, the surface resistance of the film begins to rise in 1-10 Oe of microwave field and saturates in 20-60 Oe. A model is presented relating the observed saturation to critical penetration of Josephson junctions. Films exhibiting the highest degree of c-axis texturing show the weakest dependence of surface resistance on power and also exhibit the sharpest transition to the superconducting state as measured at high frequency. >

Microwave surface resistance (R s ) measurements on large-area (11.4 cm2) Tl-based films deposited onto Ag (Consil 995) substrates have been made at a frequency of 18 GHz as a function of temperature. Deposition onto unoriented Ag substrates yields unoriented films characterized byR s values of 8.2 and 33.6 mΩ at 10.6 and 77 K, respectively. In contrast, similar deposition onto oriented Ag substrates yields oriented films with values of 12.6 and 14.6 mΩ at 11.2 and 77 K, respectively; corresponding Cu values are 9 and 21 mΩ. Additionally, it is found that the dependence ofR s on microwave surface magnetic fieldH s is weaker for the oriented films. These results suggest that the effect of orienting thec-axis in Tl films is twofold: (1) the high-frequency superconducting transition is made considerably sharper, resulting in a lowerR s value at 77 K, and (2) the rate of increase inR s with appliedH s is reduced. Both effects have significant ramifications for the potential application of these materials to high-frequency accelerating cavities.

A description of cavities used in the study of the microwave properties of the high-temperature superconductors is followed by a lumped-circuit analysis of the coupling of transmission lines and resonators. The frequency dependence of the reflected and transmitted microwave power and the character of transient cavity response are analyzed. Techniques are discussed for the introduction of samples of the high-temperature superconductors into microwave cavities. Following a discussion of sample surface impedance and sample geometry factor, the connection between surface resistance and cavityQ is examined as well as the connection between cavity frequency shift and surface reactance. Measurement techniques that utilize reflected or transmitted power or transient response are described.

We have measured the surface resistance at 22 GHz, 86 GHz, and 148 GHz of a YBa 2 Cu 3 O 7 film (5000 A) deposited on a LaGaO 3 substrate. X-ray diffraction data show the film to be highly c -axis and a -axis oriented, and the low values of measured surface resistance suggest that the film is of high quality. In the measured spectral range, the temperature-dependent contribution to the surface resistance is, within experimental error, proportional to the square of the frequency, i.e. R s ∝ ω 2 . This result is consistent with various models of loss mechanisms in superconductors.

The Superconducting RF Cavity Development Program at Los Alamos has designed, fabricated, and tested single-cell niobium cavities at 3 GHz and 805 MHz. This work is being done in preparation for procuring and testing a multicell niobium cavity. The multicell cavity is designed to accelerate protons at /spl beta/=0.9; initial tests will be without beam. Programmatic changes have required us to modify our plans to install a 6800 litre helium cryostat and a 12.8 g/s helium pump. We will use an installed cryostat to test the multicell cavity. Also, the cavity will be modified from a seven-cell to a four-cell structure to match the dimensions of the installed cryostat. Previous reports concentrated on 3 GHz results. In this paper, some of the latest results of the 805 MHz cavity tests are presented. Modifications to allow high pulsed power testing on 805 MHz single- and four-cell cavities are proceeding. Glow discharge cleaning of an 805 MHz niobium cavity resulted in a decrease in cavity performance. The cavity was restored to previous performance levels with buffered chemical polishing. Initial results with high-pressure water cleaning show the process is useful in restoring cavity performance. >

The APT high energy beam transport (HEBT) and beam expanders convey the 1700-MeV, 100-mA cw proton beam from the linac to the tritium target/blanket assembly, or a tuning beam stop. The HEBT includes extensive beam diagnostics, collimators, and beam jitter correction, to monitor and control the 170-MW beam prior to expansion. A zero-degree beamline conveys the beam to the beam stop, and an achromatic be and conveys the beam to the tritium production target. Nonlinear beam expanders make use of higher-order multipole magnets and dithering dipoles to expand the beam to a uniform-density, 16-cm wide by 160-cm high rectangular profile on the tritium-production target. The overall optics design are reviewed, and beam simulations are presented.

The increase in the microwave surface resistance Rs of high Tc superconductors at elevated microwave power levels is reported for both oriented and unoriented Tl‐based films as a function of rf magnetic field at 820 MHz and 18 GHz. The application of dc magnetic fields produces qualitatively similar increases in Rs and in the surface reactance Xs. The increase in Rs with dc field is shown to arise from simple decoupling of grains by intergranular magnetic flux. The increase in Rs with microwave power, on the other hand, is a consequence of hysteretic intergranular processes.

The surface resistance Rs of YBa2Cu3O7 (YBCO) thin films (0.6±0.1 μm) deposited onto 2.5‐cm diam (100) LaAlO3 substrates has been measured at 22 GHz using both Cu and Nb cavities. The surface resistance falls precipitously at the superconducting transition (Tc =90 K) from a normal state value of approximately 2 Ω to a 77 K value of 13.7±1 mΩ, which is 1.6 times lower than Cu. At 4 K the surface resistance is 1±0.1 mΩ, as measured in a Nb superconducting cavity, which is an order of magnitude lower than Cu. The critical current density at 77 K is 4.5×104 A/cm2. Pole figure analyses show the ratio of c‐axis to a‐axis‐oriented material in the film is 2.4:1. YBCO films deposited onto either LaGaO3 or LaAlO3 substrates with varying c/a ratios yield surface resistance values at 77 K that are crudely correlated with Rs. Therefore, the principal effect of orienting the material is to improve the sharpness of the high‐frequency superconducting transition, consistent with the notion that the sharpness is associated...

An increase by over three orders of magnitude from 0.58 mΩ to 1.17 Ω was observed at 4.0 K in the 3 GHz microwave surface resistance of ceramic YBa2Cu3O7−δ following exposure to neutrons. The transport resistivity of an unirradiated pellet was linear in temperature down to Tc with a room‐temperature value of 2.13 mΩ cm and a resistivity extrapolated to 4.0 K of 0.53 mΩ cm. Following irradiation, the resistivity rose with decreasing temperature from a room‐temperature value of 1.5 Ω cm to a maximum at around 45 K with little change evident at Tc . These results, in conjunction with eddy current, susceptibility, iodometric titration, and thermally stimulated luminescence measurements on irradiated and unirradiated samples, collectively suggest that the effect of neutron irradiation has been to decrease intergranular coupling without the development of an insulating phase.

Surface resistance measurements on Tl‐Ba‐Ca‐Cu‐O thick films (∼15 μm) magnetron sputtered onto BaF2‐buffered, silver‐based (Consil 995) substrates have been made at a microwave frequency of 22 GHz. The relatively large‐area films (∼5 cm2) are characterized by surface resistance values of 6.9±2 mΩ at 11.3 K and 30.2±1 mΩ at 77 K; the corresponding values for Cu are 10 and 22 mΩ, respectively. These results demonstrate that Tl‐Ba‐Ca‐Cu‐O can be deposited onto large‐area, metallic substrates with characteristic surface resistance values lower than Cu at 4 K. Orientation of the film should improve the surface resistance at 77 K, thereby making the fabrication of microwave cavities that are superior to Cu possible.

For many years now, Los Alamos National Laboratory has been working to develop a conceptual design of a facility for accelerator production of tritium (APT). The APT accelerator will produce high energy protons which will bombard a heavy metal target, resulting in the production of large numbers of spallation neutrons. These neutrons will be captured by a low‐Z target to produce tritium. This paper describes the latest design of a room‐temperature, 1.0 GeV, 100 mA, cw proton accelerator for tritium production. The potential advantages of using superconducting cavities in the high‐energy section of the linac are also discussed and a comparison is made with the baseline room‐temperature accelerator.

We have prepared the thermodynamically stable YBCO‐124 high temperature superconductor in powder form by a chemical precipitation method and have characterized the material by a number of chemical and physical methods, including carbon content, x‐ray diffraction, thermogravimetry, scanning electron microscopy, surface area, thermally stimulated luminescence, and the superconducting transition and magnetization curves. We have also started work on consolidating the powders by hot pressing.

Thick (10-15 µm) Tl-Ba-Ca-Cu-O films have been deposited onto yttria-stabilized zirconia and Ag substrates by d.c. magnetron sputtering techniques. Direct deposition onto 1" diameter yttria-stabilized zirconia yields films with typical 22-GHz surface resistance (Rs) values of 5.2 ± 2 mS2 and 52 ± 2 mK2 at 10 K and 77 K, respectively. For comparison, Rs of Cu at this same frequency is 10 mK2 at 4 K and 22 mg2 at 77 K. Tl-Ba-Ca-Cu-O films have also been deposited onto 1" diameter Ag substrates using Au/Cu, Cu, and BaF2 buffer layers. The lowest Rs values were obtained on films with a BaF2 buffer layer, typical values being 7.8 ± 2 mC2 and 30.6 ± 2 mC/ (measured at 22 GHz) at 10 K and 77 K, respectively. Larger films (1.5" diameter) with similar Rs values were prepared using this same technique, demonstrating that the fabrication process can be scaled to larger surface areas. These films are promising for radiofrequency cavity applications because they are thick (50 -75 times the London penetration depth), have relatively large surface areas, are fabricated on metallic substrates, and have Rs values that are competitive with Cu at 77 K and are lower than Cu at 4 K. Because they are polycrystalline and unoriented, it is anticipated that their Rs values can be lowered by improving the processing technique. High-quality films of YBa2Cu3O7 have been electron-beam deposited onto 1" LaGa03 and 1.5" LaA103 substrates. The 1" sample is characterized by Rs values of 0.2 ± 0.1 mS2 at 4 K and 18.6 ± 2 mΩ at 77 K. The 4-K value is only 2 - 4 times higher than Nb. The 1.5" sample has Rs values (measured at 18 GHz) of 0.93 ± 2 Ω and 71 ± 3 mΩ at 10 K and 77 K, respectively.

Films of Tl‐Ba‐Ca‐Cu were dc magnetron sputtered from a single multielement target. The films were deposited onto substrates of: (1) magnesium oxide, (2) a silver based alloy (Consil 995), (3) a nickel based alloy (Haynes 230), and (4) buffer layers of barium fluoride or copper oxide on Consil. To form superconducting phases, post‐deposition anneals were made on these films using an alumina crucible with an over pressure of thallium and flowing oxygen. After annealing, the film phases were determined using x‐ray diffraction. The film surface resistances (Rs) were measured at 22 GHz in a TE011 cavity.

Thick (8 to 10 µm) Ba-Ca-Cu-O films have been rf magnetron sputtered onto Ag alloy (Consil 995) substrates. The films were given a post-deposition anneal in an over pressure of Ti in order to form the superconducting phases. Annealing protocols were done which result in predominantly the 1212 and 2212 phases. The substrate orientation was varied to determine its effect on film orientation. Material properties of the films were characterized by x-ray diffraction (XRD), ion beam backscattering spectroscopy, energy dispersive x-ray analysis (EDAX), and scanning electron microscopy (SEM). Electrical characterization of the films was done using dynamic impedance (DI) at 10 kHz and rf surface resistance (Rs) at 18 GHz in a TE011 fundamental mode cavity.

Measurements are presented of the transverse properties of the booster synchrotron. The principal transverse limitations to operational performance have been due to restricted aperture and improper multiturn injection. In addition to these features, working point, chromaticities, high-intensity effects, and injection matching are discussed.

Free electron lasers (FELs) require electron beams of high peak brightness. In this presentation, we describe the design of a compact high-brightness electron source for driving short-wavelength FELs. The experiment uses a laser-illuminated Cs 3 Sb photoemitter located in the first rf cavity of an injector linac. The photocathode source and associated hardware are described. The doubled YAG laser (532 nm), which is used to drive the photocathode, produces 75 ps micropulses at 108 MHz repetition rate and peak powers of approximately 300 kW. Diagnostics include a pepper-pot emittance analyzer, a magnetic spectrometer, and a 4 ps resolution streak camera. Present experiments give the following results: micropulse current amplitudes of 100 mA to 400 A, beam emittances ranging from 10 π mm mrad to 40 π mm mrad, an energy spread of ± 3%, and peak current densities of 600 A/cm 2 The design of experiment has now been changed to include a separately phased rf cavity immediately following the first cavity. This modification enables us to study the effects of phasing with the possibility of improving the injector performance. Also, this change will improve the vacuum conditions in the photoelectron source with a consequent improvement in lifetime performance. A brief discussion on the possible applications of this very bright and compact electron source is presented.

A free electron laser oscillator, driven by an RF linac, requires a train of electron bunches delivered to an undulator. The brightness requirement exceeds that from a conventional linac with rf bunchers. The demonstrated high brightness of laser-illuminated photoemitters indicates that the conventional buncher system might be eliminated entirely, thereby avoiding the usual large loss of brightness that occurs in bunchers. A photoemitter with a current density of about 200 A/cm 2 is placed on an end wall of an rf cavity to accelerate a 60 ps bunch of electrons to 1 MeV as rapidly as possible. Preliminary experimental work, simulation calculations, and discussions on emittance measurement techniques and positive ion motion in the rf gun are presented.

The first three months of operation of the NAL linac after first achieving a 200-MeV beam have been encouraging. The design performance has been achieved at beam intensities of about 20 mA both in the transverse emittance and the momentum spread. Attempts have not been made to go to intensities of 100 mA or greater as yet, and it will be interesting to see how the beam quality is affected by intensity. It is expected that when the linac rf phase and amplitude controls are properly working, the beam quality will be less than the design values. In particular, the momentum spread at the present operating currents is sufficiently small so that a debunching cavity currently is not envisioned. The beam measurements made so far confirm the theoretical results obtained with the PARMILA dynamics program. The particle distributions used in the program are those measured at the entrance to the linac. The large number of components in the systems have lead to concern over the reliability of the linac. The performance over the last three months has dispelled some of this concern. As running periods have increased the failure rate has decreased. Only two major problems stand out at this time. The first is the failure of the spring contacts on the filament leads to the power amplifier tubes. Installation care and the elimination of two of the contact rings which were not water-cooled seem to be providing at least a temporary solution.

A free-electron laser (FEL) oscillator, driven by an rf linac, requires a train of electron bunches delivered to an undulator. The electron-beam brightness requirement exceeds that available from a conventional buncher. The demonstrated high peak brightness of laser-illuminated photoemitters indicates that the conventional buncher system might be eliminated entirely without the usual large loss in beam brightness that occurs in bunchers. A photoemitter with a current density of about 200 A/cm2 is located on an end wall of an rf cavity to accelerate a 60-ps bunch of electrons to 1 MeV as rapidly as possible. Preliminary experimental work and simulation calculations are presented.

This paper gives construction details of the dipole and quadrupole magnets, a brief description of the proton injection line, and a short report of the vacuum system design for the existing Fermilab Cooling Ring.

We recently demonstrated that insulating surface impurity phases in high‐temperature superconductors can be detected by thermally stimulated luminescence. Moreover, we suggested that the intensity of luminescence is related to the magnitude of the rf surface resistance. In this work we show that a quantitative correlation exists between these two quantities, and that luminescence can be a very useful technique for estimating rf surface resistance.

We show that thermally stimulated luminescence is an important method for detecting insulating impurity phases that commonly occur in high Tc superconductors. The technique is sensitive to impurity phases at

During adiabatic capture and initial 30 MHz beam bunching in the Fermilab Booster very high frequency structure is observed on the bunches. The structure has the appearance of a bunch shape oscillation instability which appears and disappears in a sporadic manner. A computer simulation of injection dynamics reveals the fact that the observed structure is related to re-appearance of the injected linac bunch structure after relocation within the booster phase space.

It has recently been suggested1 that the present high energy synchrotrons at CERN and Fermilab could be operated as pp storage rings with a center-of-mass energy of some 800 GeV. The Fermilab Energy Doubler/Saver, in addition, would be quite suitable as a high performance storage ring, producing collisions at 2 TeV in the center-of-mass. In order to achieve useful luminosity it is necessary to: 1) collect antiprotons from ˜-80 GeV protons colliding on a stationary target, 2) cool the phase space of the initially diffuse p's, and 3) accumulate the cooled p's over cycles. Several methods have been devised to carry out this repetitive accumulation and cooling. 2,3,4

The intensity of the Fermilab booster accelerator has been limited in part by longitudinal effects. These include longitudinal space charge blowup prior to RF capture, phase space dilution during capture and insufficient voltage to provide bucket area to accelerate the diluted beam. Measurements of beam properties under these conditions, as well as high intensity effects during acceleration, are presented.

At present there are two working injection methods; single-turn using a ferrite kicker magnet and multiturn using a pulsed set of 4 dipoles in one straight section. The operating characteristics of these methods are described. The expected implementation of H injection will involve the incorporation of devices for all three methods in one 6-m long straight section. The H-scheme is described and the expected operating characteristics compared to the present methods.

Surface resistance measurements of films of YBa2Cu3O7 deposited onto single‐crystal substrates of LaGaO3 and SrTiO3 have been made at a frequency of 22 GHz. The measurements were made in either a copper or niobium cavity by replacing the end wall with the superconducting film. Typical surface resistance at 20 K are 1–2 mΩ for films on LaGaO3 and 6–8 mΩ for films on SrTiO3, as measured in the copper cavity. The LaGaO3 values lie within the sensitivity range of the Cu cavity (∼2 mΩ) and can only be considered upper limits. Similar measurements in a Nb superconducting cavity resulted in a surface resistance value of 0.2±0.1 mΩ at 4 K for the best LaGaO3‐based film. This value is more than an order of magnitude lower than Cu, and suggests that LaGaO3‐based films may offer immediate advantages in a number of applications.

The "cooling" of protons by electrons has been studied by the accelerator group at the Institute of Nuclear Physics at Novosibirsk, U.S.S.R.l. They have achieved damping of proton-betatron oscillations by Coulomb interactions with "cold" electrons as described by simple theory. They also observe fast damping when the longitudinal velocities of all the protons and electrons are very nearly the same and the electrons are trapped in a longitudinal magnetic field. This effect results from the extended interaction between the same electrons and protons.

Free‐electron‐laser (FEL) oscillators require a train of high‐brightness bunches. Conventional subharmonic bunchers are currently used with rf linacs to generate pulse trains, but the resulting dilution of the transverse phase space and lower beam brightness are unacceptable for high‐performance FELs. Recent developments suggest that photoemitters of high quantum efficiency combined with rapid acceleration can produce pulse trains of higher brightness than has been achieved before.

Free-electron lasers (FELS) require electron beams of high peak brightness. In this presentation, we describe the design of a compact high-brightness electron source for driving short-wavelength FELs. The experiment uses a laser-illuminated Cs/sub 3/Sb photoemitter located in the first rf cavity of an injector linac. The photocathode source and associated hardware are described. The doubled YAG laser (532 nm), which is used to drive the photocathode, produces 75-ps micropulses at 108-MHz repetition rate and peak powers of approximately 300 kW. Diagnostics include a pepper-pot emittance analyzer, a magnetic spectrometer, and a 4-ps resolution streak camera. Present experiments give the following results: micropulse current amplitude of 100 mA to 400 A, beam emittances ranging from 10 n.mm.mrad to 40 n.mm.mrad, an energy spread of +-3%, and peak current densities of 600 A/cm/sup 2/. A brief discussion on the possible applications of this very bright and compact electron source is presented. 16 refs., 5 figs., 1 tab.

Successful electron cooling of antiproton beams requires a precisely aligned and high quality electron beam. Mean e- momentum and energy are to be held within 0.25 mrad and ? eV respactively. In addition the e- "temperature" about this mean (rest frame velocity spread) should be held to ?? eV. The diagnostics required to align the beam in angle and energy are rather straightforward. The temperature measuring diagnostics (one for T?; one for T?) are more exotic.

Superconducting films of YBa 2 Cu 3 O 7 deposited onto LaGaO 3 substrates were prepared by e-beam and magnetron sputtering techniques. Surface resistance measurements made at 22 GHz, 86 GHz, and 148 GHz show that these films are superior to those deposited by similar techniques onto SrTiO 3 . Typical surface resistance values measured at 22 GHz and 12 K are ∼2 mω with the lowest value being 0.2 mω, which is only 2–4 times higher than Nb. The surface resistance is proportional to the square of the measuring frequency.