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In recent experiments plasma electrons became trapped in a plasma wakefield accelerator (PWFA). The transverse size of these trapped electrons on a downstream diagnostic yields an upper limit measurement of transverse normalized emittance divided by peak current, eN,x/I. The lowest upper limit for eN,x/I measured in the experiment is 1.3⋅10−10 m/A.

Recent experiments at SLAC have shown that high gradient acceleration of electrons is achievable in meter scale plasmas. Results from these experiments show that the wakefield is sensitive to parameters in the electron beam which drives it. In the experiment the bunch lengths were varied systematically at constant charge. The effort to extract a measurement of the decelerating wake from the maximum energy loss of the electron beam is discussed.

This paper reveals a new high-power beam dump concept developed at SLAC. Its principal features are relatively low production costs, simple assembly procedures, compactness, and rather high power absorption capacity. The main power absorption medium is a water-cooled bed of 1 cm diameter aluminum spheres contained in a tube. This "Sphere Beam Dump" is rated at 500 kW and its production costs are compatible with other designs at powers as low as 50 kW. The main features of the dump are discussed with emphasis on heat transfer in the bed of spheres, detection of burnout, and flow and mixing of the coolant. A prototype of such a dump was successfully tested in the electron beam at powers up to 495 kW and at an energy of 18 GeV. The experimental results are discussed and potential applications for other high-power absorbers are indicated. A catalytic hydrogen-oxygen recombiner for removal of radiolytically produced hydrogen from such a dump and other water-cooled power absorbers is described in the second part of the paper. Such topics as operational parameters, instrumentation, safety, and performance are stressed.

In four years of operation at progressively increasing levels of average power new observations on the performance of slits, collimators, and beam dumps of various designs have been accumulated. The inherent longevity of high power beam absorbers based on low-Z or graded-Z design philosophy has been successfully demonstrated. Early operating experience at low power levels in the SLAC beam switchyard has been described previously. The performance of multiple protective interlock circuitry is described and system response patterns are given. Two types of beam line failures are discussed: The air burst resulting from the melting of soft-metal vacuum seals and stainless steel transport pipes at modest power densities; and the water burst resulting from the failure of heat transfer surfaces at high power densities. Problems of beam line restoration in a radiation environment are briefly discussed. Downtime to date attending beam-induced failure of the vacuum envelope has been of the order of 350 hours, averages less than 10 hours per event, and accounts for some 15% of the unscheduled downtime from all sources combined.

This paper deals with recent developments of power absorbing devices such as beam dumps, slits, and collimators. A brief discussion is given of the heat transfer experiments that have been conducted at the Stanford Linear Accelerator Center to establish design heat flux conditions for the various materials to be used for the power absorbing devices. Design concepts of a 2.2 MW, 11 to 25 GeV beam dump, as presently being built at SLAC, are also discussed. Finally, there is a typical analysis which leads to the design of a collimator, with emphasis on beam definition, heat transfer, thermal stress development and material selection.

A precision actuator and shaft encoder combination for remote handling in a high radiation and corrosive environment is described. The package allows accurate positioning of beam transport components in areas where liquid lubrication is not possible. The use of hexagonal lattice metals prevents galling or seizing of the rolling surfaces. The actuator translates rotary motion and torque supplied by a commercial radiation-resistant stepping motor into linear motion and force. Two actuators are in operation with a 7.5 cm output travel. Reproducibility is to ±1 step or 0.0015 cm. The shaft encoder resolves the turns of the motor in 1024 increments with cams and microswitches. The estimated dose rate of 1012 to 1013 ergs/g/yr in the vicinity of a SLAC high-power slit should present no problems. The second part of the paper describes a new quick-disconnect injected indium vacuum seal. Indium is extruded into a gasket groove of a flange through tapped holes by means of bolts. Finally, a blowout fuse employed in the beam stoppers of the SLAC personnel protection system is described. The fuse responds to thermal radiation from the surface of a beam stopper by melting a low-temperature eutectic diaphragm thus letting the vacuum system up to air.

This paper describes an intercepting beam intensity profile and position monitor which was developed at SLAC. It has excellent spacial resolution as well as signal efficiency. The instrument utilizes the electromagnetic cascade shower emission effect. Net charge leakage signals comparable in magnitude to the intercepted beam current are easily obtainable. The latest model of the instrument is described. It consists of an array of closely spaced 0.0025 cm thick tungsten ribbons which are 2 r.1. long in beam direction. Experimental results as well as application of the basic idea to four different instruments are discussed. The instruments are: (1) a spectrum analyzer, (2) a vertical beam position monitor, (3) a ring inflection monitor for the SLAC electron-positron storage ring project, and (4) an accelerator beam phase space measurer.

In vivo studies of 11C isotope distribution in cats given 1-11C-ethanol show accumulation of radioactivity in liver. Redistribution of radiolabel occurs after ethanol loading. Results indicate that some aspects of the matabolism of ethanol in specific tissues can be assessed by gamma-ray scintigraphy.

Cord factor--a mixture of 6,6'-diesters of alpha, alpha-D-trehalose with natural mycolic acids--which is purified from mycobacteria and other microorganisms, is known to have adjuvant activity as well as to enhance nonspecific resistance to infections and tumor development. In this work, trehalose 6,6'-dimycolate (TDM) was found to induce proliferative responses in rat thymus and lymph node cells. With the thymus cells, TDM responses were greater after removal of the adherent cell subpopulation. Consistent with this observation was the finding that addition of phagocytic cells purified from peritoneal or lymph node cell suspensions to nonadherent thymocytes abrogated the response of thymocytes to TDM. With the lymph node cells, the presence or removal of adherent cells had no major consequence on the TDM-induced proliferative response, since similar increases in deoxyribonucleic acid synthesis were observed with unfractionated and nonadherent cells. The difference between the sensitivities of thymus cells and lymph node cells to regulation by adherent cells indicated the existence of more than one type of TDM responder cell in rats. TDM also displayed marked stimulatory activity on thymus and lymph node cells from germ-free rats, ruling out the possibility that TDM might have triggered a specific, secondary, in vitro immune response. Expansion of a selected cell population(s) triggered by TDM may be involved in the manifestation of adjuvant activity and possibly other immunological properties of cord factor.