[en] Beam properties are often determined by measuring the current induced on intercepting electrodes. To collect the full signal current, it is desirable to bias the electrodes. The system discussed in this note makes use of a current mirror circuit to allow the use of a shared bias supply while dispensing with the need for isolation amplifiers. Low power, high voltage bipolar transistors, matched for best performance, form the mirror. The circuit has a wide dynamic range, which can exceed 10⁴. Though it is unipolar, versions can be made for either positive or negative polarity. Spark protection is provided by including a current limiting circuit. A current mirror system has been constructed and used in a TRIUMF H^- ion source. The device provides eight measurement channels and supplies 400 V at up to 1 mA. (author). 2 refs., 1 tab., 4 figs

[en] The beam is injected into the Proton Storage Ring (PSR) as a train of sub-nanosecond pulses at the linac frequency of 201.25 MHz. This frequency component is sensed by 20 pairs of 200 MHz stripline beam position monitors and multiplexed to an autocorrelation position processor. The analog position information is sampled, digitized and stored under the control of timing circuits. Beam position histograms from sets of monitors are displayed in the control room. Measurements show that the amplitude of the 200 MHz component is constant during the fill indicating that the strength of the most recently injected beam does not drift during the fill. This structure begins to disappear 20 to 20 turns after a particular batch of beam has been injected. The low frequency components, however, persist and might be used to measure the position of the accumulated beam. We report calculations and experimental results for some low frequency processing systems

[en] The large acceptance and the simplicity of H^- extraction makes practical unusual modes of cyclotron operation. RF equipment, initially installed for H^- extraction at TRIUMF, has been used to modulate the beam intensity at the extraction radius. This equipment consists of a 92 MHz, 150 kV cavity (AAC) and an RFD (11.5 MHz, 20 kV). The AAC augments the acceleration provided by the main 23 MHz, RF system; the RFD excites radial betatron oscillations. These devices may be operated at frequencies slightly different from their design multiple; their effect then beats with the main RF. In this mode the AAC, for example, alternately reduces the rate of acceleration, thus increasing the overlap of turns, then enhances it, sweeping the clustered turns onto a probe or foil. Operating the AAC or RFD in this manner gathers the bulk of the charge into peaks a few microseconds wide and spaced between 6 and 50 micros. Changing the frequency offset alters the spacing. The peak to valley ratio was 23:1 and all beam was transmitted to the extraction radius

[en] The TRIUMF cyclotron has 6 probes which travel radially through the beam plane. Signal currents are formed in the probe fingers by the interception or stripping of H^- ions. Two types of heads are used; a vertical head and a differential head. The ac components of the signals are used to measure the energy gain per turn and the machine isochronism while the dc components are used to measure the beam height and the radial beam density. The signals are brought out of the cyclotron vault on balanced twinax cables, about 70 m long, to differential ac and dc amplifiers connected in parallel. This system allows simultaneous measurement of dc and ac signals, optimization of their amplifiers, and avoids multiplexing of the low level current signals. (author)

[en] The beam bunches extracted from the TRIUMF cyclotron are usually about 4 ns long, contain ∼ 4 x 10⁷ protons, and are spaced at 43 ns. A wall current monitor capable of giving the charge distribution within a bunch, on a bunch by bunch basis, has recently been installed together with a sampling system for routine display in the control room. The wall current monitor is enclosed in a vacuum vessel and no ceramic spacer is required. This enhances the response to high frequencies, ferrite rings extend the low frequency response. Bench measurements show a flat response between a few hundred kilohertz and 4.6 GHz. For a permanent display in the control room the oscilloscope will be replaced by a Stanford Research Systems fast sampler module, a scanner module, and an interface module made at TRIUMF. The time to acquire one 10 ns distribution encompassing the beam bunch is 30 ms with a sample width of 100 ps and an average sample spacing of 13 ps. The scan, sample, and retrace signals are buffered carried on 70 m differential lines to the control room. An analog scope in XYZ mode provides a real time display. Signal averaging can be performed by using a digital oscilloscope in YT mode. (author). 6 refs., 2 tabs., 7 figs

[en] The large acceptance and the simplicity of H^- extraction makes practical unusual modes of cyclotron operation. RF equipment, initially installed for H extraction at TRIUMF, has been used to modulate the beam intensity at the extraction radius. This equipment consists of a 92 MHz, 150 kV cavity (AAC) and an RFD (11.5 MHz, 20 kV). The AAC augments the acceleration provided by the main 23 MHz, RF system; the RFD excites radial betatron oscillations. These devices may be operated at frequencies slightly different from their design multiple; their effect then beats with the main RF. In this mode the AAC, for example, alternately reduces the rate of acceleration, thus increasing the overlap of turns, then enhances it, sweeping the clustered turns onto a probe or foil. Operating the AAC or RFD in this manner gathers the bulk of the charge into peaks a few microseconds wide and spaced between 6 and 50 μs. Changing the frequency offset alters the spacing. The peak to valley ratio was 23:1 and all beam was transmitted to the extraction radius. (author)

[en] A microchannel plate (MCP) with a 50 Ω anode has been used to confirm predictions that TRIUMF's phase restricting slits produce beam pulses 0.15 ns wide (1.3⁰ RF). A 194 MeV extracted beam of a few nA passed through a thin, 25 μm, aluminum foil. X-rays from the foil were detected by the MCP mounted 177 mm away. A 110 gaussmeter field between target and channel plate swept all electrons out of the 3 msr acceptance. The MCP was followed immediately by a TRIUMF x 10 hybrid amplifier. The output was taken to standard nucleonics over 36 m of FM-8 cable. The discriminated MCP pulses started a TAC, and the stop was derived from the cyclotron RF. The count rate was approx. =500/nA. The current through the cyclotron slits was equivalent to approx. =5 μA. Several estimates on our narrowest cyclotron tune indicate that the measured 158 ps FWHM is made up from a 140 ps beam contribution and 73 ps from the electronics. The device used to explore the sources of cyclotron instabilities and to provide a low current, cyclotron independent, time pick-up for the experimental program

[en] The beam bunches extracted from the TRIUMF cyclotron are usually about 4 ns long, contain ∼4x10⁷ protons, and are spaced at 43 ns. A wall current monitor capable of giving the charge distribution within a bunch, on a bunch by bunch basis, has recently been installed together with a sampling system for routine display in the control room. The wall current monitor is enclosed in a vacuum vessel and no ceramic spacer is required. This enhances the response to high frequencies; ferrite rings extend the low frequency response. Bench measurements show a flat response between a few hundred kilohertz and 4.6 GHz. For a permanent display in the control room the oscilloscope will be replaced by a Stanford Research Systems fast sampler module, a scanner module, and an interface module made at TRIUMF. The time to acquire one 10 ns distribution encompassing the beam bunch is 30 ms with a sample width of 100 ps and an average sample spacing of 13 ps. The scan, sample, and retrace signals are buffered and carried on 70 m differential lines to the control room. An analog scope in XYZ mode provides a real time display. Signal averaging can be performed by using a digital oscilloscope in YT mode

[en] A basic stripline beam position monitor consists of four strips 90 deg apart inside a circular beam pipe. To avoid signal distortion the strip to wall spacing must be selected to make the strip impedance match that of the end connections. The problem is treated as two dimensional, quasi-TEM and reduces to an electrostatic case. The impedance is first calculated using a finite element relaxation technique to solve the Laplace equation. The energy in the field is then used to obtain the distributed strip capacitance and impedance. This method requires a very fine grid and converges slowly. In the second method the strip is assumed to be thin and is replaced by a set of charge pipes. This method is applicable to the stripline geometry because the cylinder can be replaced by a set of image charge pipes. A modified Green's function is integrated over the charge pipes using a Gauss-Chebyshev quadrature. The result is a set of simultaneous linear equations which can be solved very quickly. A monitor had been constructed and the strip impedance and cross coupling coefficients had been measured. (author). 4 refs., 4 tabs., 7 figs

[en] The TRIUMF cyclotron accelerates H^- ions from 0.3 to 520 MeV. Beam may be lost by dissociation or by collision with mechanical objects in the vacuum tank. To reduce the activation of these components, and to monitor the los, thin foils have been installed to define the vertical aperture for the beam. The foil's projection toward the median plane is greater than that of any other component; they strip H^- ions with a large vertical amplitude to H⁺. Their location (R,θ) is such that the H⁺ ions are energy dispersed along a short region of tank wall. They pass through a thin, 0.8 mm steel, section of wall to enter a thin ion chamber lying between the wall and the surrounding magnet yoke. The chamber is flushed with ArCO₂ gas and the anode-cathode spacing is 6 mm in order to reduce ion recombination. The anode is segmented along the plane of dispersion to yield the region of beam loss. The device is radiation hard, including cabling, and may be removed or installed remotely. It has been calibrated by inducing known amounts of local beam loss and the coefficient scales with stopping power and ion path length as expected