High gradient RF test results of S-band and C-band cavities for medical linear accelerators

Self Cite

A novel high-gradient accelerating structure with low phase velocity, v=c ¼ 0.38, has been designed, manufactured and high-power tested. The structure was designed and built using the methodology and technology developed for CLIC 100 MV=m high-gradient accelerating structures, which have speed of light phase velocity, but adapts them to a structure for nonrelativistic particles. The parameters of the structure were optimized for the compact proton therapy linac project, and specifically to 76 MeV energy protons, but the type of structure opens more generally the possibility of compact low phase velocity linacs. The structure operates in S-band, is backward traveling wave (BTW) with a phase advance of 150 degrees and has an active length of 19 cm. The main objective for designing and testing this structure was to demonstrate that low velocity particles, in particular protons, can be accelerated with high gradients. In addition, the performance of this structure compared to other type of structures provides insights into the factors that limit high gradient operation. The structure was conditioned successfully to high gradient using the same protocol as for CLIC X-band structures. However, after the high power test, data analysis realized that the structure had been installed backwards, that is, the input power had been fed into what is nominally the output end of the structure. This resulted in higher peak fields at the power feed end and a steeply decreasing field profile along the structure, rather than the intended near constant field and gradient profile. A local accelerating gradient of 81 MV=m near the input end was achieved at a pulse length of 1.2 μs and with a breakdown rate (BDR) of 7.2 × 10 −7 1=pulse=m. The reverse configuration was accidental but the operating with this field condition gave very important insights into high-gradient behaviour and a comprehensive analysis has been carried out. A particular attention was paid to the characterization of the distribution of BD positions along the structure and within a cell.

Section: Conditioning Comparison To Clic Prototypesmentioning

confidence: 76%

High-gradient testing of an S -band, normal-conducting low phase velocity accelerating structure

Vnuchenko

Martinez

Benedetti

et al. 2020

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“…The CCL geometry parameters were varied to define the set that maximizes the cavity efficiency (expressed in terms of the effective shunt impedance, ZT 2 ) without exceeding a surface electric field of 120 MV=m, for safety operation below critical breakdown levels. Indeed, experimental results obtained in high gradient experiments conducted by TERA at CERN in collaboration with the CLIC group, show that even higher surface fields (up to 170 MV=m) can be tolerated by wellconditioned cavities [15].…”

Section: B the Rf Design And Beam Dynamics Studiesmentioning

confidence: 99%

Linac booster for high energy proton therapy and imaging

Degiovanni¹,

Amaldi²,

Lomax

et al. 2018

For an optimal exploitation of the benefits of proton therapy the most accurate dose delivery system should be used. The TERA Foundation has extensive experience in the field of high gradient high frequency linacs. This paper describes a particular design of a 3 GHz linac boosting the typical cyclotron beams for proton therapy of 230-250 MeV up to 350 MeV. Such an upgrade of a typical proton therapy facility enables performing proton radiography, as well as extending therapeutic capabilities with high energy proton therapy (HEPT). The recent studies and measurements in high-gradient linac technology demonstrated that average fields in the accelerating structures of up to 25-30 MV=m can be achieved, which results in a total linac length of less than 7 m. To test several characteristics of such a linac as a booster of a cyclotron beam, a design has been made of a linac unit accelerating from 250 MeV to 275 MeV, which could be built and inserted for tests in an existing beam line at the PSI proton therapy facility. The feasibility considerations, along with the design of the linac booster and the issues related to a possible integration in an existing cyclotron beam line are detailed in this study.

“…To make this structure shorter, TERA launched a high gradient research campaign, in collaboration with the CLIC group at CERN, to investigate the high gradient limit of S-Band accelerating structures [11][12][13]. Based on the results of these tests, a high gradient backward traveling wave accelerating structure for β ¼ 0.38 was built and is undergoing testing [14,15].…”

Section: The Tulip All-linac Solutionmentioning

confidence: 99%

“…following a research campaign on S-band and C-band single cavities carried out by TERA Foundation [11,12,21]. An S c limiting value of 1.55 MW=mm 2 is obtained.…”

Section: Ghz High Gradient Btw Structurementioning

confidence: 99%

See 1 more Smart Citation

High gradient linac for proton therapy

Benedetti

Latina

2017

Proposed for the first time almost 30 years ago, the research on radio frequency linacs for hadron therapy experienced a sparkling interest in the past decade. The different projects found a common ground on a relatively high rf operating frequency of 3 GHz, taking advantage of the availability of affordable and reliable commercial klystrons at this frequency. This article presents for the first time the design of a proton therapy linac, called TULIP all-linac, from the source up to 230 MeV. In the first part, we will review the rationale of linacs for hadron therapy. We then divided this paper in two main sections: first, we will discuss the rf design of the different accelerating structures that compose TULIP; second, we will present the beam dynamics design of the different linac sections.