Systematic studies have been performed on the effect of the surface processing techniques for improving accelerating gradients in superconducting niobium quarter wave resonators (QWR). These include high pressure rinsing (HPR), high temperature heat treatment of cavities and helium pulse processing. Tests done after HPR have not only shown a reduction in field emission in the cavities at high accelerating gradients but also an improvement in the low field quality factor (Q). The effect of the high temperature (650 degrees C) heat treatment of jacketed QWRs (QWR with the outer helium vessel) on the cavity gradients has also been investigated. This was performed for two different QWR designs and a substantial improvement in performance has been observed in both the cases. The increase in gradients is beyond that due to hydrogen degassing alone. Helium pulse processing during 4 K tests has been tried out on several cavities and its effect on the quality factor at both high and low gradients has been observed. This technique has been found to be useful for those resonators which have a high Q at lower fields but are limited due to the field emission at higher gradients. They have exhibited a marked improvement in the high field Q-slope over and above that obtained with conventional pulse processing under high vacuum. A comprehensive overview of all these developments carried out over the past few years has been reported.

Cryogenic network for linear accelerator operations demand a large number of Cryogenic sensors, associated instruments and other control-instrumentation to measure, monitor and control different cryogenic parameters remotely. Here we describe an alternate approach of six types of newly designed integrated intelligent cryogenic instruments called device-servers which has the complete circuitry for various sensor-front-end analog instrumentation and the common digital back-end http-server built together, to make crateless PLC-free model of controls and data acquisition. These identified instruments each sensor-specific viz. LHe server, LN2 Server, Control output server, Pressure server, Vacuum server and Temperature server are completely deployed over LAN for the cryogenic operations of IUAC linac (Inter University Accelerator Centre linear Accelerator), New Delhi. This indigenous design gives certain salient features like global connectivity, low cost due to crateless model, easy signal processing due to integrated design, less cabling and device-interconnectivity etc.

The superconducting linac as a booster of the 15UD Pelletron accelerator was partly commissioned with one linac module housing eight quarter wave bulk niobium cavities along with the superbuncher and rebuncher cryomodules. Subsequently two more linac cryomodules were added to have in total 24 cavities for acceleration. In addition, a new Linde helium refrigerator of capacity 750 W @ 4.2 K was installed in parallel to the earlier CCI refrigerator. The new refrigerator was integrated with the earlier cryogenics network system through a specially designed liquid helium distribution line without any valve box. The cooling philosophy with this new system is modified to have a faster cool down rate in the critical zone (150 - 70 K) to avoid Q disease. The helium gas pressure fluctuation in the cavities is reduced significantly to have stable RF locking. The full linac is being operated and beams with higher energy are being delivered to the users. The present paper will highlight the performance of the new cryogenic system with respect to cool down rate, and helium pressure fluctuation.

The superconducting heavy ion linear accelerator at Inter-University Accelerator Centre Delhi has been in operation since 2007. Initially, the superconducting niobium Quarter Wave Resonators (QWRs) in the linac were phase locked using a combination of electronic and mechanical controls which operated in fast (~10 μsec) and slow (~sec) time scales respectively. In this scheme, fast control was achieved through dynamic phase control whereas slow control of the frequency was done through the niobium tuner bellows installed at the drift tube end of the resonator and flexed using helium gas to change the resonance frequency. In order to improve the dynamics of this control system, an alternate scheme using piezoelectric actuator, instead of helium gas, to flex the same niobium bellows, has been implemented in the QWRs of the second and third accelerating modules of the linac. The piezoelectric actuator is used in closed loop along with the fast dynamic phase control scheme. The feedback loop of the piezoelectric control includes a dual control scheme - an integral control loop to arrest the slow drift, and the positive position feedback (PPF) based control loop to damp the microphonics. This control scheme has been found to arrest slow drifts in the resonator frequency more tightly along with damping of low frequency microphonics (~few tens of Hz) picked up by the resonator from its surrounding environment. This has substantially eased the load from the fast electronic control, resulting in the reduction of the radio frequency (RF) power requirement during operation. In addition, it has improved the stability of phase and amplitude of the QWRs. The details of the new scheme along with results obtained during the online run of the linac for beam acceleration are presented.

The power of Ethernet for control and automation technology is being largely understood by the automation industry in recent times. Ethernet with HTTP (Hypertext Transfer Protocol) is one of the most widely accepted communication standards today. Ethernet is best known for being able to control through internet from anywhere in the globe. The Ethernet interface with built-in on-chip embedded servers ensures global connections for crate-less model of control and data acquisition systems which have several advantages over traditional crate-based control architectures for slow applications. This architecture will completely eliminate the use of any extra PLC (Programmable Logic Controller) or similar control hardware in any automation network as the control functions are firmware coded inside intelligent meters itself. Here, we describe the indigenously built project of a cryogenic control system built for linear accelerator at Inter University Accelerator Centre, known as "CADS," which stands for "Complete Automation of Distribution System." CADS deals with complete hardware, firmware, and software implementation of the automated linac cryogenic distribution system using many Ethernet based embedded cryogenic instruments developed in-house. Each instrument works as an intelligent meter called device-server which has the control functions and control loops built inside the firmware itself. Dedicated meters with built-in servers were designed out of ARM (Acorn RISC (Reduced Instruction Set Computer) Machine) and ATMEL processors and COTS (Commercially Off-the-Shelf) SMD (Surface Mount Devices) components, with analog sensor front-end and a digital back-end web server implementing remote procedure call over HTTP for digital control and readout functions. At present, 24 instruments which run 58 embedded servers inside, each specific to a particular type of sensor-actuator combination for closed loop operations, are now deployed and distributed across control LAN (Local Area Network). A group of six categories of such instruments have been identified for all cryogenic applications required for linac operation which were designed to build this medium-scale cryogenic automation setup. These devices have special features like remote rebooters, daughter boards for PIDs (Proportional Integral Derivative), etc., to operate them remotely in radiation areas and also have emergency switches by which each device can be taken to emergency mode temporarily. Finally, all the data are monitored, logged, controlled, and analyzed online at a central control room which has a user-friendly control interface developed using LabVIEW(®). This paper discusses the overall hardware, firmware, software design, and implementation for the cryogenics setup.

The need of the rf control system of superconducting resonators is to provide amplitude and phase stability. As the superconducting(SC) cavities often have a high Q (>108), the fluctuation of resonant frequency acts as the main disturbance to the stabilization process. The existing phase locking scheme of the quarter wave resonators (QWR) in the first operational module of the superconducting heavy ion linear accelerator consists of electronic and mechanical tuners. The mechanical tuner uses pure helium gas to flex the Niobium tuner bellows for tuning the frequency in slow time scale. The helium gas operated slow tuner turns out to be complicated, somewhat unreliable and expensive for long term operation of the linac. in an alternate scheme to handle the slow time part of the phase control, the tuner bellows is deflected by using a piezoelectric crystal for fine adjustment of the frequency. The piezoelectric actuator is used in closed loop along with dynamic I-Q based electronic tuner inside the crynstat tn phase lock the superconducting cavities. The stiffness and stroke of piezoelectric actuators in cold condition was found to be sufficient to control the maximum frequency variation around the master oscillator.

A superconducting linear accelerator based on niobium quarter wave resonators has recently become operational to boost the energy of the heavy ion beams available from the existing 15 UD ( unit doubled) Pelletron accelerator. The niobium resonators typically performed at an accelerating field of 3-6 MV/m at 6 watts of input power in the test cryostat. When they were tested in the linac cryostat, the accelerating fields were drastically reduced and a number of other problems were also encountered. At present, all the problems have been diagnosed and solved. Many design modifications, e. g., in power coupler, mechanical tuner, helium cooling system, etc. were incorporated to solve the problems. A novel method of vibration damping was also implemented to reduce the effect of microphonics on the resonators. Finally, the accelerated beam through linac was delivered to conduct experiments.

During initial operation of the first linac module, energy gain was found to be much lower due to various problems which are now identified and solved. A novel way of damping mechanical vibration was implemented to reduce RF power. Cooling was improved by installing a hemispherical structure on the resonator. The drive coupler was redesigned to eliminate metal coating. Design of the tuner/transition flange assemblies was modified to avoid cold leak. After incorporation of these modifications, a few on-line beam accelerations through Linac were accomplished. In one of the beam acceleration, pulsed (1.3 ns) Silicon beam of 130 MeV from Pelletron accelerator was further bunched to 250 ps by SC Superbuncher. After acceleration through the linac module and subsequent re-bunching using SC Rebuncher (RB), 158 MeV Silicon beam having pulse width of 400 ps was delivered to conduct experiments.

An on-line test of the LINAC superbuncher at Nuclear Science Centre has been successfully performed. DC O7+ beam of nominal energy 92 MeV was accelerated through the superbuncher resonator, operating at a field of 4.54 MV/m. The total energy gain of the beam was measured to be 4.5 MeV. For the pulsed beam test a phase locked bunched beam of O7+ of nominal energy 92 MeV, FWHM 1.3 ns from the pre-tandem multiharmonic buncher was injected into the superbuncher. By properly adjusting the phase and amplitude of the resonator, the best FWHM of the bunched beam was measured to be 185 ps near the entrance of the first LINAC module. Fully depleted cooled surface barrier detector was used for measuring the time width. In a separate experiment the intrinsic time resolution of the same detector was measured to be 134 ps. Consequently the intrinsic time width of the bunched beam, after correcting for the detector resolution, would be 127 ps. Details of the experiment and results are presented.

This paper reports the construction of a superconducting linear accelerator as a booster to the 15 UD Pelletron accelerator at Nuclear Science Centre, New Delhi. The LINAC will use superconducting niobium quarter wave resonators as the accelerating element. Construction of the linear accelerator has progressed sufficiently. Details of the entire accelerator system including the cryogenics facility, RF electronics development, facilities for fabricating niobium resonators indigenously, and present status of the project are presented.

The Superconducting heavy ion Linac at Inter-University Accelerator Centre (IUAC), New Delhi has been delivering high energy ion beams to users since 2008 [1, 2]. Initially the first accelerating module, housing eight Quarter Wave Resonators (QWRs), became operational together with the Superbuncher having one QWR and the Rebuncher having two QWRs. In subsequent years, the remaining two modules have also been installed and commissioned. The complete Linac was operated recently and several ion beams were delivered for scheduled experiments. The maximum energy gain was 8 MeV per charge state. Operational highlights include, successful operation of four resonators in the third module with Piezo based [3] mechanical tuning, implementation of remote phase locking of all the resonators in the three modules [4], development of a scheme for auto locking of resonators and testing of a capacitive pickup as a beam diagnostic element. Details will be presented vis-à-vis the problems encountered and the future course of action.

The superconducting linac of IUAC consists of five cryostats containing 27 niobium quarter wave resonators. Since last few years, energized ion beams from linac are being delivered routinely for scheduled experiments. In a recently concluded linac operation, all the resonators installed in the five cryostats were used in the acceleration and delivery of the ion beam on the target with an energy gain of 8 MeV/q and a time width of ~ 180 ps. Recently, an improved mechanical damping mechanism has been implemented and piezo actuator based tuning mechanism have replaced the gas based tuner of most of the resonators. Other new developments e.g. automatic phase locking of the resonators and auto beam tuning of the complete linac are being currently pursued.