Plasma electron acceleration driven by a long-wave-infrared laser.

Laser-driven plasma accelerators provide tabletop sources of relativistic electron bunches and femtosecond x-ray pulses, but usually require petawatt-class solid-state-laser pulses of wavelength λL ~ 1 µm. Longer-λL lasers can potentially accelerate higher-quality bunches, since they require less power to drive larger wakes in less dense plasma. Here, we report on a self-injecting plasma accelerator driven by a long-wave-infrared laser: a chirped-pulse-amplified CO2 laser (λL ≈ 10 µm). Through optical scattering experiments, we observed wakes that 4-ps CO2 pulses with < 1/2 terawatt (TW) peak power drove in hydrogen plasma of electron density down to 4 × 1017 cm-3 (1/100 atmospheric density) via a self-modulation (SM) instability. Shorter, more powerful CO2 pulses drove wakes in plasma down to 3 × 1016 cm-3 that captured and accelerated plasma electrons to relativistic energy. Collimated quasi-monoenergetic features in the electron output marked the onset of a transition from SM to bubble-regime acceleration, portending future higher-quality accelerators driven by yet shorter, more powerful pulses.

An inverse free electron laser acceleration-driven Compton scattering X-ray source.

The generation of X-rays and γ-rays based on synchrotron radiation from free electrons, emitted in magnet arrays such as undulators, forms the basis of much of modern X-ray science. This approach has the drawback of requiring very high energy, up to the multi-GeV-scale, electron beams, to obtain the required photon energy. Due to the limit in accelerating gradients in conventional particle accelerators, reaching high energy typically demands use of instruments exceeding 100's of meters in length. Compact, less costly, monochromatic X-ray sources based on very high field acceleration and very short period undulators, however, may enable diverse, paradigm-changing X-ray applications ranging from novel X-ray therapy techniques to active interrogation of sensitive materials, by making them accessible in energy reach, cost and size. Such compactness and enhanced energy reach may be obtained by an all-optical approach, which employs a laser-driven high gradient accelerator based on inverse free electron laser (IFEL), followed by a collision point for inverse Compton scattering (ICS), a scheme where a laser is used to provide undulator fields. We present an experimental proof-of-principle of this approach, where a TW-class CO2 laser pulse is split in two, with half used to accelerate a high quality electron beam up to 84 MeV through the IFEL interaction, and the other half acts as an electromagnetic undulator to generate up to 13 keV X-rays via ICS. These results demonstrate the feasibility of this scheme, which can be joined with other techniques such as laser recirculation to yield very compact photon sources, with both high peak and average brilliance, and with energies extending from the keV to MeV scale. Further, use of the IFEL acceleration with the ICS interaction produces a train of high intensity X-ray pulses, thus enabling a unique tool synchronized with a laser pulse for ultra-fast strobe, pump-probe experimental scenarios.

Experimental Characterization of Electron-Beam-Driven Wakefield Modes in a Dielectric-Woodpile Cartesian Symmetric Structure.

Photonic structures operating in the terahertz (THz) spectral region enable the essential characteristics of confinement, modal control, and electric field shielding for very high gradient accelerators based on wakefields in dielectrics. We report here an experimental investigation of THz wakefield modes in a three-dimensional photonic woodpile structure. Selective control in exciting or suppressing of wakefield modes with a nonzero transverse wave vector is demonstrated by using drive beams of varying transverse ellipticity. Additionally, we show that the wakefield spectrum is insensitive to the offset position of strongly elliptical beams. These results are consistent with analytic theory and three-dimensional simulations and illustrate a key advantage of wakefield systems with Cartesian symmetry: the suppression of transverse wakes by elliptical beams.

Demonstration of Cascaded Modulator-Chicane Microbunching of a Relativistic Electron Beam.

We present results of an experiment showing the first successful demonstration of a cascaded microbunching scheme. Two modulator-chicane prebunchers arranged in series and a high power mid-IR laser seed are used to modulate a 52 MeV electron beam into a train of sharp microbunches phase locked to the external drive laser. This configuration is shown to greatly improve matching of the beam into the small longitudinal phase space acceptance of short-wavelength accelerators. We demonstrate trapping of nearly all (96%) of the electrons in a strongly tapered inverse free-electron laser accelerator, with an order-of-magnitude reduction in injection losses compared to the classical single-buncher scheme. These results represent a critical advance in laser-based longitudinal phase space manipulations and find application in high gradient advanced acceleration as well as in high peak and average power coherent radiation sources.

Generation of Ramped Current Profiles in Relativistic Electron Beams Using Wakefields in Dielectric Structures.

Temporal pulse tailoring of charged-particle beams is essential to optimize efficiency in collinear wakefield acceleration schemes. In this Letter, we demonstrate a novel phase space manipulation method that employs a beam wakefield interaction in a dielectric structure, followed by bunch compression in a permanent magnet chicane, to longitudinally tailor the pulse shape of an electron beam. This compact, passive, approach was used to generate a nearly linearly ramped current profile in a relativistic electron beam experiment carried out at the Brookhaven National Laboratory Accelerator Test Facility. Here, we report on these experimental results including beam and wakefield diagnostics and pulse profile reconstruction techniques.

High Efficiency Energy Extraction from a Relativistic Electron Beam in a Strongly Tapered Undulator.

We present results of an experiment where, using a 200 GW CO_{2} laser seed, a 65 MeV electron beam was decelerated down to 35 MeV in a 54-cm-long strongly tapered helical magnetic undulator, extracting over 30% of the initial electron beam energy to coherent radiation. These results, supported by simulations of the radiation field evolution, demonstrate unparalleled electro-optical conversion efficiencies for a relativistic beam in an undulator field and represent an important step in the development of high peak and average power coherent radiation sources.

Triple assessment is not necessary in most young women referred with breast symptoms.

INTRODUCTION: A palpable lesion in the breast is usually subjected to triple assessment (clinical examination [CE], imaging and core biopsy [CB] or fine needle aspiration [FNA]) to minimise the risk of missing breast cancer. However, breast cancer is rare in young women, and triple assessment (especially CB) is invasive and expensive. Our aim was to see whether CB/FNA could be avoided in young women with benign findings on CE and imaging. METHODS: This study analysed data from a prospectively entered database on female patients aged under 25 years who attended a rapid diagnosis breast clinic over a 68-month period. RESULTS: Among 10,301 patients seen, 955 females (9.3%) were aged <25 years. The most common presenting complaint was a lump, followed by pain and nipple discharge. CE was normal or revealed benign findings in all except 15 patients, in whom it was indeterminate. Ultrasonography was performed in 692 patients (72%) and was normal (n=289) or benign (n=382) in all except 21 patients, in whom it was indeterminate. In six patients, both were indeterminate. A total of 317 patients (35%) had triple assessment: FNA in 106, CB in 239 and both in 9 cases. No cancers were diagnosed. CONCLUSIONS: It would appear safe to omit FNA/CB in patients aged under 25 years when clinical and ultrasonography findings are normal or benign. This approach would have avoided needle biopsies in all but 30 patients (3%) in the study.

High-quality electron beams from a helical inverse free-electron laser accelerator.

Compact, table-top sized accelerators are key to improving access to high-quality beams for use in industry, medicine and academic research. Among laser-based accelerating schemes, the inverse free-electron laser (IFEL) enjoys unique advantages. By using an undulator magnetic field in combination with a laser, GeV m(-1) gradients may be sustained over metre-scale distances using laser intensities several orders of magnitude less than those used in laser wake-field accelerators. Here we show for the first time the capture and high-gradient acceleration of monoenergetic electron beams from a helical IFEL. Using a modest intensity (~10(13) W cm(-2)) laser pulse and strongly tapered 0.5 m long undulator, we demonstrate >100 MV m(-1) accelerating gradient, >50 MeV energy gain and excellent output beam quality. Our results pave the way towards compact, tunable GeV IFEL accelerators for applications such as driving soft X-ray free-electron lasers and producing γ-rays by inverse Compton scattering.

Experimental demonstration of energy-chirp compensation by a tunable dielectric-based structure.

A tunable energy-chirp compensator was used to remove a correlated energy chirp from the 60-MeV beam at the Brookhaven National Laboratory Accelerator Test Facility. The compensator operates through the interaction of the wakefield of the electron bunch with itself and consists of a planar structure comprised of two alumina bars with copper-plated backs separated by an adjustable beam aperture. By changing the gap size, the correlated energy chirp of the electron bunch was completely removed. Calculations show that this device, properly scaled to account for the electron bunch charge and length, can be used to remove residual correlated energy spread at the end of the linacs used for free-electron lasers. The experimental results are shown to be in good agreement with numerical simulations. Application of this technique can significantly simplify linac design and improve free-electron lasers performance.

Planar-dielectric-wakefield accelerator structure using Bragg-reflector boundaries.

We report experimental measurements of narrow-band, single-mode excitation, and drive beam energy modulation, in a dielectric wakefield accelerating structure with planar geometry and Bragg-reflector boundaries. A short, relativistic electron beam (∼1 ps) with moderate charge (∼100 pC) is used to drive the wakefields in the structure. The fundamental mode of the structure is reinforced by constructive interference in the alternating dielectric layers at the boundary, and is characterized by the spectral analysis of the emitted coherent Cherenkov radiation signal. Data analysis shows a narrow-band peak at 210 GHz corresponding to the fundamental mode of the structure. Simulations in both 2D and 3D provide insight into the propagating fields and reproduction of the electron beams dynamics observables and emitted radiation characteristics.

Ultrasound and fine needle aspiration cytology of the axilla in the pre-operative identification of axillary nodal involvement in breast cancer.

AIMS: Pre-operative diagnosis of axillary nodal involvement in breast cancer allows one-stage axillary surgery. We evaluated the efficacy of axillary ultrasound (US) with US guided fine needle aspiration cytology (FNAC) in the diagnosis of axillary nodal involvement. METHODS: Over a 13-month period, we performed US of 369 axillae in patients with screen-detected (n = 278) and symptomatic (n = 91) invasive carcinoma of the breast, at the same time as US of the primary tumour. If abnormal lymph nodes were demonstrated, a single US guided FNAC of the most abnormal node was performed. US and FNAC results were compared with the final histology of the surgically excised lymph nodes. RESULTS: Among the 369 axillae studied, 102 had nodal macrometastases and 38 (37%) were identified by US guided FNAC. The rate was 33% in screen-detected and 44% in symptomatic patients. Sensitivity increased with increasing numbers of positive axillary nodes, and the more abnormal the appearances of the nodes on US. CONCLUSION: US with FNAC of the most abnormal node allows pre-operative detection of a third of node positive axillae in screen-detected and over 40% of those with symptomatic breast cancer, allowing one-stage axillary surgery avoiding the sentinel node biopsy step in these patients.

Malignant pancreatic somatostatinoma in a patient with dermatitis herpetiformis and coeliac disease.

A case of malignant somatostatinoma is reported in a patient with long-standing dermatitis herpetiformis and coeliac disease. The patient had non-specific abdominal pain of several years duration and came to attention because of weight loss despite strict adherence to a gluten-free diet. Plasma somatostatin levels were raised, and laparotomy showed a pancreatic tumour with metastases, which on histology, electron microscopy and immunohistochemistry proved to be a somatostatinoma. After a promising initial response to streptozotocin, she died 30 months later. This is the first reported occurrence of a somatostatinoma in a patient with coeliac disease, adding to the growing list of neoplastic complications in this condition.

HLA antigens in coeliac disease associated with malignancy.

Coeliac patients are at greater risk than the general population of developing malignant neoplasms, particularly lymphomas. The establishment at the Clinical Research Centre of a national collaborative study of coeliac patients with malignancy provided the opportunity to carry out HLA typing for 55 HLA-A, B and C and the 10 recognised DR antigens on a group of coeliac patients with malignancy. Study of a sample of 44 patients with biopsy proven coeliac disease and histologically confirmed malignancy, including 12 with malignant histiocytosis, and 57 coeliac patients without malignancy, failed to show any significant differences in antigen frequencies between patients with and without malignancy. These results indicate that there are no HLA genetic markers associated specifically with the development of malignancy in coeliac disease.

Coeliac disease and malignancy.

Patients with coeliac disease are at greater risk than the general population for the development of malignant neoplasms, particularly lymphomas. Of 259 histologically confirmed malignancies in 235 patients with histologically proven coeliac disease, 133 were malignant lymphomas, the predominant histological type being malignant histiocytosis and the commonest site of this lesion the small intestine. Patients with coeliac disease also have a greatly increased risk for the development of small-intestinal adenocarcinomas. Among 116 invasive non-lymphomatous malignancies there were 19 small-intestinal adenocarcinomas, compared with 0 . 23 expected from national cancer registrations adjusted for sex and age. There were also more oesophageal and pharyngeal squamous carcinomas than expected.

Coeliac disease, splenic function, and malignancy.

Blood films from 41 cases of coeliac disease complicated by malignancy were examined and evidence of hyposplenism found in 12 cases (29%). This is similar to the proportion of adult coeliacs without malignancy who have hypoplenism and it is concluded that impaired splenic function is not associated with the development of malignancy in coeliac disease.

Role of sulphasalazine in the aetiology of folate deficiency in ulcerative colitis.

Only two (2.5%) of 80 outpatients with histologically proven ulcerative colitis had folate deficiency associated with anaemia or macrocytosis. Mean folate absorption, measured using micrograms/kg body weight of a tritium-labelled physiological folate derivative, 5-methyltetrahydroteroylglutamic acid, in six newly diagnosed patients was 76.7% (normal greater than 95%) but fell to 69.4% after three months' treatment with sulphasalazine. Mean difference in individual patients was 7.5% +/- 5.2% (SD) (p less than 0.02). Mean folate absorption in four patients with megaloblastic anaemia or macrocytosis which developed during treatment with sulphasalazine was 66.3%. This rose to 82.4% after the drug was stopped. Mean difference in individual patients was 16.6 +/- 6.6% (SD) (p less than 0.001). All patients who developed anaemia or macrocytosis with sulphasalazine had additional reasons for folate deficiency. These included coeliac disease, severe nutritional deficiencies, and haemolysis. It was concluded that sulphasalazine impairs folate absorption but this only becomes significant if other reasons for folate deficiency are also present.

Control of antivenom treatment in Echis carinatus (Carpet Viper) poisoning.

A study of all the patients treated for Echis carinatus bites in a rural mission hospital in Northern Nigeria in June 1973 showed that not all bleeding during recovery from an Echis bite results directly from the action of the venom; thus not all bleeding requires antivenom for treatment. Evenomation by Echis in West Africa is accompanied by incoagulability of the blood. If coagulability is assessed by a simply performed test, also described, on each occasion bleeding is suspected of being due to Echis venom and if antivenom is given only when incoagulability is demonstrated, expensive antivenom may be used more sparingly and to more benefit.