accelerating-news-arc.web.cern.ch - RF

The road to accelerator energy efficiency

Jennifer Toes — Tue, 04 Jul 2017 09:17:20 +0000

The road to accelerator energy efficiency

by Jennifer Toes (CERN)

Construction at CERN of a prototype of a 144:1 power combiner to combine 144 solid-state amplifiers
of 1 kW each (Image: Eric Montesinos)

As accelerators change, grow and advance to continue to make scientific discoveries, so too does their need for energy.

Keeping particle accelerators sustainable, minimising their cost and impact on the public energy grid and environment, is a current goal for many particle physicists and engineers. Work Package 3 (WP3) of the EuCARD-2 project, which ended in April 2017, produced a dedicated report on maximising the energy efficiency of certain accelerator systems and alternate uses for energy wasted in the form of heat.

Radiofrequency (RF) systems, commonly used in accelerators to drive accelerating structures in accelerating particles, are prone to energy wastage and often contribute to the overall energy inefficiency of accelerator facilities. As such, WP3’s Task 3 reviewed concepts and designs for more efficient RF systems, whilst Task 2 investigated avenues for making use of or recovering lost energy by other means.

When considering more efficient RF systems, Task 3 focused on supporting the development of three technologies: 1) multi-beam Inductive Output Tubes (IOTs), 2) an improved bunching mechanism for klystrons, and 3) efficient power combiners for use with solid-state power amplifiers in large accelerators.

Compared to klystrons, IOTs have lower losses of energy between pulses or at low input power. However, klystrons may still be improved with new bunching schemes which would extract the RF power from accelerated electron beams more efficiently. In addition, solid state amplifiers can be realised using a single state power combiner, which combine a large number of transistors for higher RF power.

Whilst minimising the initial energy waste is important, so too is identifying how to recover wasted energy, or how to repurpose potential waste for other uses.

Mike Seidel, WP3 Coordinator and head of Accelerator Operation and Development at the Paul Scherrer Institute (PSI), commented, “Energy efficiency and sustainability is becoming an important consideration for modern accelerator based research infrastructures. During EuCARD-2 we found that even matured technologies, such as klystrons, have significant potential for efficiency improvements. At large facilities wasted energy can be used very beneficially for heating purposes, and as the example of ESS shows, the best concepts can be realised if these are included in the planning of a project from the very beginning.”

The members of WP3 Task 2 surveyed 12 accelerator facilities from seven different European countries on their energy consumption and cost as well as cooling and heat recovery methods. The task aimed to obtain an overall understanding of the energy consumption in accelerator facilities and identify beneficial aspects of various set-ups as well as areas requiring improvement.

Both RF and cryogenic systems (the latter of which uses very low temperature liquids for cooling) contribute large levels of energy wastage in the form of heat. Recovering this heat or harnessing its power for additional applications, such as heating treating wastewater, may help further efficiency efforts.

WP3 has identified the need to develop new technology, improve current systems, and pursue methods to recover or repurpose lost energy to ensure the particle accelerators of tomorrow are as efficient as possible.

EuCARD-2

energy

energy efficiency

heat recovery

radiofrequency

issue 21

Fourth meeting on innovative RF technologies

Jennifer Toes — Mon, 03 Jul 2017 07:42:41 +0000

Fourth meeting on innovative RF technologies
by Peter McIntosh (STFC)

Participants of the EuCARD-2 WP12 gathered at NCBJ in Warsaw, Poland (Image: Peter McIntosh)

As EuCARD-2 came to the end of its four-year duration, the Work Package 12 (WP12) Innovative Radiofrequency (RF) Technologies activity held its fourth and final group meeting at the National Centre for Nuclear Research (NCBJ) in Warsaw, Poland in March 2017.

The group organised previous Annual Meetings at CEA Saclay in France, DESY in Germany, and the STFC Daresbury Laboratory in the United Kingdom. The events aimed to provide specific updates on its areas of activity, which included: Superconducting RF Thin Films, High Gradient Normal Conducting Technologies, Superconducting RF Higher Order Mode Diagnostics, and RF Photocathodes.

The 2017 meeting drew 23 participants from 11 of the 13 collaborating organisations, encompassing representation from the UK, France, Germany, Poland and Sweden. In terms of the diversity balance of the attendees, five (22%) attendees were women and three (13%) were from ethnic minority groups.

It was coordinated by Peter McIntosh (STFC Daresbury Laboratory), who has led the 5M€ WP12 delivery programme since its inception in 2013. The meeting itself was organised by Robert Nietubyć (NCBJ) who provided all of the local logistics.

Professor Krzysztof Kurek addresses participants of the EUCARD-2 WP12 2017 Annual Meeting
(Image: Peter McIntosh)

The event kicked off with an opening address and welcome from the NCBJ Director, Professor Krzysztof Kurek, who placed the capabilities of NCBJ firmly in the context of Innovative RF and accelerator technologies. Peter McIntosh then gave a management overview for the WP12 project as the EuCARD-2 programme comes to an end, before each of the WP12 task leaders presented their respective activity areas.

In the activity focused on SRF Thin films, the first high temperature SRF thin film deposition using Nb3Sn was realised at CERN. In addition, the highest Tc ever reached achieved 17.06K using CVD deposition of NbN by INP Grenoble. A new high precision magnetometry system for larger RF samples was validated at CEA Saclay.

For High Gradient Normal Conducting Technologies, University of Manchester developed an optimised X-band Damped Detuned Structure for the 380 GeV CLIC facility, whilst the first high efficiency ‘Kladistron’ developed by CEA Saclay began fabrication with Thales. Lancaster University also contributed in the development of a new high precision RF distribution system, able to provide ultra-precise timing synchronisation for a pair of CLIC X-band crab cavities.

Regarding the SRF HOM Diagnostics task, the Universities of Rostock and Manchester reported on the optimisation of simulation tools able to model very long linac structures using concatenated analysis and generalised scattering matrix techniques. In addition, the electronics needed to monitor cavity HOM signals have been prototyped and tested on FLASH, and have been implemented on XFEL by DESY.

For the RF Photocathodes activity, STFC has installed a new High Repetition Rate RF gun and cathode exchange system at the CLARA FEL test facility at Daresbury Laboratory. In addition, NCBJ has made optimised lead photocathode surfaces, and their operation was validated by DESY. Furthermore, the performance of magnesium photocathodes was demonstrated at HZDR-Rossendorf.

The local NCBJ organiser also invited the participants to visit the Warsaw Neon Muzeum as well as to tour the NCBJ facilities, including radiotherapy systems developed by NCBJ specialists and provided to commercial organisations.

In the summary of the final WP12 meeting, Peter McIntosh stated that he was tremendously impressed by the depth and breadth of work undertaken over the past four years by the collaborating institutes. The objectives of WP12 to break new ground on RF technologies were certainly ambitious when set-out back in 2013, yet in many areas the teams involved succeeded, laying the groundwork for a long-standing legacy for the international RF and accelerator communities for years to come.

The 2017 EuCARD-2 WP12 Annual Meeting was covered in live time via the ASTeC Twitter account.

The “kladistron project” for high-efficiency klystrons

Alessia Barachetti — Fri, 20 Nov 2015 15:25:09 +0000

The “kladistron project” for high-efficiency klystrons

By Juliette Plouin, Antoine Mollard and Franck Peauger (CEA)

Figure 1: Schematic view of the standard 5 GHz TH2166 klystron (top) and of the 5 GHz kladistron (bottom)

Under the framework of EuCARD-2, the study of high efficiency - high frequency klystrons is in progress in close collaboration between CEA Saclay and Thales Electron Devices. The “Kladistron project” aims to design a high-power 12GHz klystron to be used in CLIC.

The objective of the Innovative RF Technologies activity is to propose affordable and reliable solutions to increase efficiency and thus save high amounts of energy in accelerators. These will be essential for future testing capabilities for the CLIC accelerating structures. To achieve this, a new klystron concept is required. A new electron beam bunching technique has been proposed to increase the beam-to-RF interaction efficiency above the state-of-art limits (> 65%). This method is inspired by the Radio Frequency Quadrupole (RFQ) based injectors which bunch adiabatically a CW (continuous mode) hadron beam with more than 95% transmission. The new proposed device, called kladistron, includes a large number of bunching cavities (typically 15 to 20, which is twice as many as in a conventional klystron) separated by short drift tubes. This enables giving a “soft kick” to the beam in a large number of cavities instead of a “large kick” to the beam in a small number of cavities. The coupling between these cavities and the beam (r/Q) is lower than in a standard klystron. Preliminary calculations at this frequency, made with a 1D code, have given efficiencies around 60 % with 10 cavities and 70 % with 20 cavities.

The first experimental tests will be realized on a 5 GHz demonstrator, constituted of a standard klystron from Thales, the TH2166 (6 cavities, CW mode, 4.9 GHz, 26 kV, 4.3 A, efficiency 50%), in which the intermediate cavities are modified. All the other elements: gun, solenoid, collector, input and output cavities and window, are kept as is and the 4 intermediate cavities are replaced by 14 new cavities with lower r/Q. The overall length is kept the same, to fit in the existing solenoid, and the new cavities are very close to each other. The principle is shown in Figure 1, where the cavities pattern is placed on a schematic klystron for both standard klystron and kladistron. The calculations with Magic (2D Particule In Cell code) give an efficiency equal to 50% (as expected) for the standard klystron, and equal to 60 % for the kladistron. The beam shape given by Magic at the end of the simulation is also shown in Figure 1. One can see that the beam bunching is softer for the kladistron than for the standard klystron

The design of this kladistron demonstrator is nearly ready, and the fabrication and tests are planned in 2016. The aim is to verify that a higher number of low-coupled cavities lead to higher efficiency, all other elements being the same. Once this principle is being validated, it will be possible to reach higher efficiencies with thorough optimization of the electron bunching.

Towards 90% power conversion efficiency of klystrons

Livia Lapadatescu — Fri, 19 Jun 2015 08:04:45 +0000

Towards 90% power conversion efficiency for klystrons

by Igor Syratchev (CERN)

General view of the 6MW, S-band MBK (40 beams) with PPM focusing with expected RF power production efficiency above 75%. Image credit: JSC ‘VDBT’, Moscow, Russia

Computer simulations confirm that RF production efficiency above 90% can be reached in klystrons with a new electrons bunching technique.

The increase in efficiency of RF power generation for future large accelerators such as CLIC, ILC, ESS, FCC and others is considered a high priority issue. It can contribute to a significant reduction of the investment and operational costs of accelerators. The vast majority of existing commercial high power RF klystrons operate in the electronic efficiency range between 40% and 55%. Only a few klystrons available on the market are capable of operating with 65% efficiency or above.

It is commonly considered the high efficiency klystrons require a low perveance. Limited by technically accessible high voltage levels, this can only be obtained by operating with low currents, thus single beam klystrons are incompatible with the need for high power. The concept of multi-beam klystron (MBK) resolved this inconsistency by introducing many single beams which interact with common RF circuits of the klystron, increasing the power with the multiple beams, whilst preserving low perveance per beam. In the standard klystron optimization procedure the target is to minimize the bunch length prior to it entering the output cavity. Independent studies concluded that in this case the 80% efficiency can be achieved and this value remains as a relatively hard limit.

To reach higher efficiency, the intrinsic limits of the bunching processes and deceleration in the output cavity need to be understood at the level of the electron bunch dynamics.

The new method to increase efficiency is based on the concept of a fully saturated bunch formation using the new bunching technique with bunch core oscillations. The first simulations proved that klystron RF power production efficiency close to 90% can be achieved. The new technology demonstration prototypeis now in fabrication in industry, with expected efficiency above 75% (see image above). The testing of this tube is scheduled for November 2015.

Wake field monitoring to improve FEL performance

Livia Lapadatescu — Fri, 19 Jun 2015 07:17:51 +0000

Wake field monitoring to improve FEL performance
by Micha Dehler (PSI), Nicoleta-Ionela Baboi (DESY)

Down stream end of X band structure with wake field monitor pickup. Image credit: PSI

Detecting structure tilts in the spectral density of a WFM signal. Image credit: DESY

Beam degradation due to RF structure misalignments poses a challenge in the operation of ultra high brightness FELs. Wake field monitors offer a direct way to diagnose and correct these effects.

Misalignment between the beam and RF accelerating structures lead to transverse wake field excitation which degrades the beam quality. Wake field monitors (WFMs) are devices which couple these fields and their components, the Higher Order Modes (HOM), and therefore enable their reduction. This is of special interest in modern free electron lasers where the beam quality is of extreme concern.

Two teams from EuCARD2 WP12 are exploring this field, one developing a front end for the WFMs of a 12 GHz RF structure used for the SwissFEL and the other dealing with 1.3 and 3.9 GHz superconducting cavities of the European X-ray Free Electron Laser (E-XFEL).

The RF front end for the 12 GHz structure employs an innovative electro-optical down conversion scheme of the HOM fields, which is attractive in terms of band width, radiation hardness and the capability of transporting signals over kilometers. During first beam tests, by using a spectral analysis method, the system could identify the beam to structure offset and tilt. With the resolution improving to micron range, the device is expected to show even finer details such as structure bends or kinks.

Until recently, the HOM based system at FLASH was only used for beam alignment, but showed drifts over time as a beam position monitor. A way to stabilize the signals has been found based on a frequency domain analysis, such that a resolution of few microns was preserved over several months. A new direct sampling approach for the E-XFEL 1.3 GHz cavities reduces the number of electronic components and therefore their drifts with time. At the same time these are the first electronics to offer the possibility of monitoring the beam phase with respect to the RF pulse, important for optimization of the longitudinal beam properties.

Crab Cavity RF System

Margarita Synanidi — Thu, 20 Nov 2014 11:10:54 +0000

Crab Cavity RF System
by Thomas Hind (CERN) and Rama Calaga (CERN)

Fig 1. 400 MHz Tetrode Amplifier. Image credit: Eric Montesinos (CERN)

As part of the HL-LHC upgrade, a conceptual RF system layout for a local crab crossing scheme has been presented.

Four cavities, grouped into pairs, on each side of the collision point (IP) per beam are required to produce the transverse kick to correct the geometric effects at the collision point. A two-cavity configuration also allows for good sectorization of the cavities, both for spare policy and maintenance.

Each cavity will have an independent powering system for precise control and reliable operation of the cavities. The input power coupler will use a single coaxial disk window to separate the cavity vacuum and the air side. These powering systems are assumed to use two 40kW LEP type Tetrodes modified to 400MHz to deliver the specified 80kW to cope with beam and cavity transients with some additional margin.

Fig 2. Schematic of the crab cavity layout on one side (not to scale) Image credit: Rama Calaga (CERN)

The cavity controls consists of a fast loop to ensure a rapid response time (around 1 microsecond) and a central (slow) control loop, which performs the task of field and phase control in the cavity.

A proof of principle test will be carried out in the SPS as a pre-requisite before an installation in the LHC.

Due to the limited space available in the interaction region, a detailed study is underway to determine the best option to fulfil the RF requirements in a cost effective manner.

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