A CW RFQ Accelerator for Deuterons

Abstract

A four-rod RFQ accelerator is being built to accelerate deuterons from 20 keV to 3 MeV. At an operating frequency of 176 MHz the length is 3.8 m and the power consumption 250 kW, the beam current 5 mA. A special feature is the CW-mode operation. The status of the project and properties of the RFQ will be discussed. STATUS OF THE SET-UPTo assemble the RFQ and to put it into operation, mechanical alignment of the electrodes and RF tuning has to be done. First is the mechanical set-up consisting of an exact adjustment of the structure. Mechanical adjusting passes into adjusting of electrical properties.Finally, vacuum, power HF and beam tests will be handled.The actual state of this CW RFQ is the completion of the mechanical adjustment on the one, and some simulations for electrical properties on the other hand. MECHANICAL ADJUSTMENTThe set-up of a structure of 4 m length requires very accurate measurements in a conditioned environment. Already small changes i.e. in temperature can cause big errors. At all, the mechanical adjustment can be classified in three steps: The inner resonant structureThe RF structure, made up of copper, is composed of the base plate, on which the stems are mounted. On the stems, the electrodes are mounted. The electrodes are divided in three parts of about 1.3 m length. Table 1: RFQ property values Alignment to the cavityThe location of the beam, especially at input and output, should be oriented to the outer geometry of the cavity. Therefore, the inner structure, once installed in the cavity, needs to be aligned with respect to the cavity. This was done by the use of an align fixture which was attached to the cavity's head. The align fixture contains an arbour which is centred in the cylindric cavity and can be used as a reference for the beam position. Parts of the inner structure will be aligned to this reference. Exact adjustmentAs an other reference, the top flange of the cavity was used. This works very well, because the whole cavity has only one single lid all over the full length. This gives a very planar and exact reference for measurements in every position along the structure, as shown in figure 1. Adjustment of the electrodes is done in two steps: the vertical and the horizontal setting. For the horizontal, the tolerance of screws is used. The vertical step is more complex. Therefore, so called shims are made, which are Figure 1: Mechanical adjustment and reference face.Injection/output energy 20 / 1500 keV/u Isotope deuterium Frequency 176 MHz electrode voltage 65 kV RFQ length 3.8 m inner diameter 280 mm min. aperture 2.7 mm max. modulation 2.7 power consumption 250 kW vÃrvhprà x,v 160 S mm mrad a / b 0.85 / 0.28 mm mrad -1 number of cells 199 number of stems 40 long.outputemittance e-l 75 S deg. keV/u transmission 0 / 5mA 98 / 96 %

Upgrade of the 4-rod radio frequency quadrupole for SARAF Phase II Linac

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High-power inductive coupler with a high-voltage DC blocker

“…The plan is for the Phase I SARAF injector, which includes the ion source of electron cyclotron resonance [3], low-energy beam transport, and radio-frequency quadrupole (RFQ) [4], to be used in Phase II after a significant upgrade of its control system. The 176-MHz four-rod RFQ of SARAF is the crucial part of the injector that must be able to operate at RF powers of up to 190 kW of continuous wave (CW), and to transport 5 mA CW proton and deuteron beams.…”

Development and beam commissioning of a continuous-wave window-type radio-frequency quadrupole

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