Development of a long-slot microwave plasma source.

A 20 cm long 10 cm wide microwave plasma source was realized by inserting two 20 cm long 1.5 mm diameter rod antennas into the plasma. Plasma luminous distributions around the antennas were changed by magnetic field arrangement created by permanent magnets attached to the source. The distributions appeared homogeneous in one direction along the antenna when the spacing between the antenna and the source wall was 7.5 mm for the input microwave frequency of 2.45 GHz. Plasma density and temperature at a plane 20 cm downstream from the microwave shield were measured by a Langmuir probe array at 150 W microwave power input. The measured electron density and temperature varied over space from 3.0 × 10(9) cm(-3) to 5.8 × 10(9) cm(-3), and from 1.1 eV to 2.1 eV, respectively.

Dust particle diffusion in ion beam transport region.

Dust particles of µm size produced by a monoplasmatron ion source are observed by a laser light scattering. The scattered light signal from an incident laser at 532 nm wavelength indicates when and where a particle passes through the ion beam transport region. As the result, dusts with the size more than 10 µm are found to be distributed in the center of the ion beam, while dusts with the size less than 10 µm size are distributed along the edge of the ion beam. Floating potential and electron temperature at beam transport region are measured by an electrostatic probe. This observation can be explained by a charge up model of the dust in the plasma boundary region.

Postoperative radiation therapy for extramammary Paget's disease.

BACKGROUND: Extramammary Paget's disease (EMPD) is a rare cutaneous malignancy that is usually treated with surgery. Patients with positive surgical margins require adjuvant therapy, but there have been few reports on the use of radiation therapy. OBJECTIVES: To investigate the effectiveness of postoperative radiation therapy in EMPD. MATERIALS AND METHODS: Twenty-one patients with EMPD involving the genitalia underwent radiation therapy as adjuvant therapy after surgery. Ten patients had inguinal lymph node involvement before radiation therapy, but none had distant metastases. A median total dose of 59·4 Gy (range, 45-64·8 Gy) was delivered to the tumour bed in 30 fractions (range, 23-36 fractions). RESULTS: At a median follow-up period of 38 months, all patients had local control. However, six patients had developed distant metastases 6-43 months after radiation therapy. The distant metastasis-free rates were 66% at 3 years and 55% at 5 years. Inguinal lymph node involvement was a significant risk factor for distant metastases. Four patients died 33-58 months after irradiation; the causes of death were tumour progression in three patients and infectious pneumonia in one. The overall and cause-specific survival rates were both 92% at 3 years, and 62% and 71% at 5 years, respectively. No therapy-related toxicities of grade ≥ 3 were observed. CONCLUSIONS: Postoperative radiation therapy is safe and effective in maintaining local control in patients with EMPD.

Plasma characteristics of single- and dual-electrode ion source systems utilized in low-energy ion extraction.

Discharge characteristics in the upstream as well as in the downstream regions of a 50-eV positive ion beam were measured along the beam axis. Single- and dual-electrode configurations made of 0.1-mm diameter tungsten wires were tested. By varying the upstream discharge parameters, the shape of the sheath edge around the extractors, which can either be "planar" or "cylindrical," can be controlled. The sheath eventually affected the simultaneous extraction of ions and neutralizing electrons. The dual-electrode configuration at the lower discharge current, revealed a homogeneous discharge downstream. At this condition, the edge of the sheath can be inferred to be "planar" which allowed the uniform extraction and propagation of low-energy ions at longer distances. The dual-electrode configuration was capable of transmitting low-energy ions up to 70 mm downstream.

Angular distributions of surface produced H(-) ions for reflection and desorption processes.

A numerical simulation code, Atomic Collision in Amorphous Target, has been run to clarify the effects due to the incident angle of hydrogen flux onto surface collision cascade in the subsurface region of a Cs covered Mo plasma grid. The code has taken into account the threshold energy for negative hydrogen (H(-)) ions to leave the surface. This modification has caused the shift of energy distribution functions of H(-) from that of hydrogen atoms leaving the surface. The results have shown that large incident angle of hydrogen particle tilt the angular distribution of reflection component, while it caused a small effect onto the angular distribution of desorption component. The reflection coefficient has increased, while the desorption yield has decreased for increased angle of incidence measured from the surface normal.

Hydrogen negative ion production in a 14 GHz electron cyclotron resonance compact ion source with a cone-shaped magnetic filter.

The plasma electrode structure of a 14 GHz ECR ion source was modified to enlarge the plasma volume of low electron temperature region. The result shows that the extracted beam current reached about 0.6 mA/cm(2) with about 40 W microwave power. To investigate the correlation between the volume of the low electron temperature region and the H(-) current, a vacuum ultraviolet (VUV) spectrometer had been installed to observe light emission in the VUV wavelength range from the plasma. From the results of the negative ion beam current and that from VUV spectrometry, production rate of vibrationally excited hydrogen molecule seems to be enhanced by increasing the volume of low electron temperature region.

Hollow metal target magnetron sputter type radio frequency ion source.

A 70 mm diameter 70 mm long compact ion source equipped with a hollow sputtering target has been designed and tested. The hollow sputtering target serves as the radio frequency (RF) plasma excitation electrode at 13.56 MHz. A stable beam of Cu(+) has been extracted when Ar was used as the discharge support gas. In the extracted beam, Cu(+) had occupied more than 85% of the total ion current. Further increase in Cu(+) ions in the beam is anticipated by increasing the RF power and Ar pressure.

Radiation therapy for lymph node metastasis from extramammary Paget's disease.

BACKGROUND: Inoperable patients with lymph node metastasis from extramammary Paget's disease (EMPD) have limited curative treatment options. OBJECTIVE: The aim of this study was to review the efficacy and toxicity of radiation therapy for lymph node metastasis from EMPD. METHODS: Eight EMPD patients with pelvic and inguinal lymph node metastasis, representing a total of 43 metastatic lymph nodes, underwent radiation therapy. Of these eight patients, two received radiation therapy as an initial treatment for EMPD and six for recurrence only in the lymph nodes after they had undergone surgery. Total doses of 45-61.2 Gy (median, 59.4 Gy) were delivered to metastatic lymph nodes in 25-34 fractions (median, 33 fractions). RESULTS: Of the 43 metastatic lymph nodes in the eight patients, all but one had no progression at the median follow-up time of 22 months. The 2-year local control rates were 86% in all patients and 98% in all metastatic lymph nodes, respectively. No therapy-related toxicities of grade 3 or greater were observed. CONCLUSION: Radiation therapy is effective and safe, and appears to offer a curative treatment option for lymph node metastasis from EMPD.

Radiation therapy for extramammary Paget's disease: treatment outcomes and prognostic factors.

BACKGROUND: Extramammary Paget's disease (EMPD) is a relatively rare malignancy, and there are few reports related to radiation therapy. In the present study, we investigated the outcome of radiation therapy for EMPD. PATIENTS AND METHODS: Forty-one patients with EMPD in the genitalia underwent radiation therapy with curative intent. Fifteen patients had regional lymph node metastases before radiation therapy, but none had distant metastasis. Total doses of 45-80.2 Gy (median, 60 Gy) were delivered to tumor sites in 23-43 fractions (median, 33 fractions). RESULTS: At a median follow-up period of 41 months, 16 patients had developed recurrences, including 5 with local progression within the radiation field and 12 with lymph node or/and distant metastases outside the radiation field. The local progression-free and disease-free rates were 88% and 55% at 3 years, and 82% and 46% at 5 years, respectively. Nine patients died at 6-73 months after irradiation; the causes of death were tumor progression in five patients, infectious pneumonia in two, renal failure in one and old age in one. The overall and cause-specific survival rates were 93% and 96% at 3 years, and 68% and 84% at 5 years, respectively. Tumor invasion into the dermis and regional lymph node metastasis were significant prognostic factors for both distant metastasis and survival. No therapy-related toxicities of grade ≥3 were observed. CONCLUSIONS: Radiation therapy is safe and effective for patients with EMPD. It appeared to contribute to prolonged survival owing to good tumor control, and to be a promising curative treatment option.

Radiation therapy for primary carcinoma of the eyelid: tumor control and visual function.

BACKGROUND AND PURPOSE: Surgical excision remains the standard and most reliable curative treatment for eyelid carcinoma, but frequently causes functional and cosmetic impairment of the eyelid. We therefore investigated the efficacy and safety of radiation therapy in eyelid carcinoma. PATIENTS AND METHODS: Twenty-three patients with primary carcinoma of the eyelid underwent radiation therapy. Sebaceous carcinoma was histologically confirmed in 16 patients, squamous cell carcinoma in 6, and basal cell carcinoma in 1. A total dose of 50-66.6 Gy (median, 60 Gy) was delivered to tumor sites in 18-37 fractions (median, 30 fractions). RESULTS: All but 3 of the 23 patients had survived at a median follow-up period of 49 months. The overall survival and local progression-free rates were 87% and 93% at 2 years, and 80% and 93% at 5 years, respectively. Although radiation-induced cataracts developed in 3 patients, visual acuity in the other patients was relatively well preserved. There were no other therapy-related toxicities of grade 3 or greater. CONCLUSION: Radiation therapy is safe and effective for patients with primary carcinoma of the eyelid. It appears to contribute to prolonged survival as a result of good tumor control, and it also facilitates functional and cosmetic preservation of the eyelid.

Characteristics of low-energy ion beams extracted from a wire electrode geometry.

Beams of argon ions with energies less than 50 eV were extracted from an ion source through a wire electrode extractor geometry. A retarding potential energy analyzer (RPEA) was constructed in order to characterize the extracted ion beams. The single aperture RPEA was used to determine the ion energy distribution function, the mean ion energy and the ion beam energy spread. The multi-cusp hot cathode ion source was capable of producing a low electron temperature gas discharge to form quiescent plasmas from which ion beam energy as low as 5 eV was realized. At 50 V extraction potential and 0.1 A discharge current, the ion beam current density was around 0.37 mA/cm(2) with an energy spread of 3.6 V or 6.5% of the mean ion energy. The maximum ion beam current density extracted from the source was 0.57 mA/cm(2) for a 50 eV ion beam and 1.78 mA/cm(2) for a 100 eV ion beam.

Extraction of negative hydrogen ions from a compact 14 GHz microwave ion source.

A pair of permanent magnets has formed enough intensity to realize electron cyclotron resonance condition for a 14 GHz microwave in a 2 cm diameter 9 cm long alumina discharge chamber. A three-electrode extraction system assembled in a magnetic shielding has formed a stable beam of negative hydrogen ions (H(-)) in a direction perpendicular to the magnetic field. The measured H(-) current density was about 1 mA∕cm(2) with only 50 W of discharge power, but the beam intensity had shown saturation against further increase in microwave power. The beam current decreased monotonically against increasing pressure.

Hollow target magnetron-sputter-type solid material ion source.

A thin-walled aluminum (Al) hollow electrode has been inserted into an ion source to serve as an electrode for a radio frequency magnetron discharge. The produced plasma stabilized by argon (Ar) gas sputters the Al electrode to form a beam of Al(+) and Ar(+) ions. The total beam current extracted through a 3 mm diameter extraction hole has been 50 µA, with the Al(+) ion beam occupying 30% of the total beam current.

Ion energy distribution functions of low energy beams formed by wire extraction electrodes.

The two-electrode extractor system made of 0.1 mm diameter tungsten wires separated by 0.7 mm has formed an argon ion beam with 50 V extraction potential. Energy spreads of the extracted beams were typically less than 2 eV when the beam current density was low. The beam intensity rapidly decreased as the distance between the extractor and the beam detector increased, indicating space charge limited transport of the beam. Problems associated with the emittance measurements are also discussed.

High frequency operation of a hot filament cathode for a magnetized plasma ion source.

A tungsten filament cathode has been operated with an ac heating current to excite a plasma in a linear magnetic field. Both the discharge current and the ion saturation current in plasma near the extraction hole of the ion source exhibited fluctuations. The discharge current fluctuated with the amplitude less than 2% of the average, and the frequency two times the frequency of the heating current. Fluctuation amplitude of the ion saturation current was about 10% of the average, while the frequency was the same as that of the heating current. The ac operation has prolonged the lifetime of a hot filament cathode by about 50%.

Study on transport of negative ion plasma using dc laser photodetachment method.

Transport of negative ion containing plasma was studied in a hydrogen plasma by injecting a semiconductor laser to make an electron density perturbation by photodetachment of negative ions. Change due to laser irradiation on electron saturation current to a Langmuir probe and that on electron current extracted through an orifice biased at the anode potential were measured phase sensitively by a lock-in-amplifier. The measured transport velocity of the negative ion containing plasma was about 1.4x10(5) cm/s for both cases. The photodetachment signal measured through the orifice had given a larger ratio of negative ion density to electron density. Change in transport of negative ion containing plasma around the Langmuir probe has been also investigated by detecting photodetachment signal onto electron current extracted through an orifice.

Ion beam oscillation due to fluctuation of a hot filament driven magnetized plasma.

Ion beam current extracted from a modified Bernas type ion source occasionally exhibits an oscillation at a frequency of several 100 kHz. Increase in the strength of a linear magnetic field induced to the ion source has either decreased or increased the frequency of this oscillation. The frequency showed an increase in proportion to the ion extraction voltage when the frequency decreased with increasing magnetic field. The change of extraction voltage did not affect the frequency when the frequency increased with the increasing magnetic field. Mechanisms causing these oscillations of an ion beam had been investigated.

Gallium ion extraction from a plasma sputter-type ion source.

A broad mixed ion beam containing positive ions of gallium (Ga) was produced with a plasma sputter-type ion source. Liquid Ga was suspended on a tungsten reservoir to be sputtered and postionized in argon (Ar) plasma excited by a radio frequency (rf) power at 13.56 MHz. Optical emission spectra from the plasma near the Ga sputtering target had indicated that the release of Ga into plasma increased with increasing negative bias to the sputtering target. The ratio of Ga(+) current to Ar(+) current was measured to be about 1% with a quadrupole mass analyzer at 100 V extraction voltage for incident rf power as low as 30 W. Ions in the plasma were extracted through a pair of multiaperture electrodes. The homogeneity of Ga flux was examined by making a Ga deposition pattern on a glass substrate located behind the extractor electrodes.

Compact 2.45 GHz microwave ion/atom source.

Characteristics of a microwave driven 3.4 cm diameter compact ion/atom source equipped with permanent magnets were tested. The source can be mounted to a standard copper gasket flange, and microwave power is supplied through an N-type microwave connector. The ion source plasma was observed through an ion extraction hole with an optical emission spectrometer. Peak height of an optical line spectrum emission corresponding to atomic nitrogen increased in proportion to the microwave input power. Quadrupole mass spectrometer showed that N(+) and N(2)(+) were the dominant species in the extracted ion beam. Nitrogen ion current density of 0.23 mA/cm(2) was obtained with only 10 W discharge power and 6 x 10(-3) Pa source surrounding pressure.

Photodetachment diagnostics of a volume production type negative ion source with a diode-laser.

Time evolution of photodetachment perturbation signal induced by a diode laser was observed in an O(2) plasma. Photodetachment current collected by a Langmuir probe was directly measured and recorded by a digital oscilloscope. After integrating the recorded signal data, the waveform of the photodetachment current showed a time dependence resembling an error function. The waveform had changed its shape in accordance as the position between the probe and the laser beam axis was changed. These characteristics of the photodetachment signal are well explained by a diffusion model. The method has the possibility to yield information on various negative ion containing plasmas, but requires quiescence in the electron saturation current with the fluctuation level less than 10(-4).