HiPER laser reference design

ABSTRACT HiPER (Hi gh P ower laser E nergy R esearch) is the first European plan for international cooperation in developing inertial fusion energy. ICF activities are ongoing in a number of nations and the first ignition experiments are underway at the National Ignition Facility (NIF) in the USA. Although HiPER is still in the preparatory phase, it is appropriate for Europe to co mmence planning for future inertial fusion activities that leverage the demonstration of ignition. In this paper we shall detail so me of the key points of the laser design. Some of the main topics of the laser architecture are presented and discussed. Keywords: inertial fusion energy, shock ignition, fast ignition, fusion laser. 1. INTRODUCTION The HiPER project intends to demonstrate the feasibility of inertial fusion schemes suitable to energy production (IFE: inertial fusion energy). As presently envisaged, an IFE reactor will consist of a driver, delivering pulses of a few MJ of energy at rate of 5–20 Hz, inducing compression, ignition and burn of targets containing a few mg of deuterium-tritium mixture. High gain can potentially be achieved by inertial fusion schemes using direct laser compression and advanced ignition schemes, such as fast ignition [1] and shock ignitio n [2]. During the HiPER preparatory-phase, we have studied targets compressed by means of a multi-beam, multi-ns laser pulse of about 250-300 kJ and either fast ignited by an ultra-intense, pulse of about 100 kJ delivered in 15 ps and focused onto a spot of diameter about 30 P m [3], or shock-ignited by a 300-500 ps multi-b eam pulses of similar total energy, but irradia ting a large fraction of the target surface [4]. Compression beams delivering 250 kJ and a peak power of 50-60 TW in a 10 ns shaped pulse at frequency 3Z žthird harmonic of neodymium or ytterbium doped solid-state laser, i.e. wavelength of 0.35 P m — are to be focused as 48 focal spots onto the capsule, providing extremely uniform irradiation. Shock ignition requires a final 300-400 ps long spike at 3Z : 60-100 kJ and 200 TW. On the “laser” side, our objective is to identify the least expensive and most useful driver but not to preclude any alternative laser design that can make the facility more flexible and help achieving fusion. A major challenge for HiPER is to enable rep-rated laser operation around 10 Hz to demonstrate fusion in a burst mode. The availability, operation and performance of large scale/aperture components and component technologies at high average power are an unknown but essential entity. The level of industrial technological maturity with respect to the laser technology needs of HiPER is still someway off, even if in specific areas the industrial potential is evident. Although the laser system is made of a large number of sub-systems, we shall concentrate on some of the main topics of the laser architecture, the final optics assembly and the way it is coupled to the target chamber. A baseline target for HiPER was identified in 2007 [3] and was originally conceived for demonstrating fast ignition and significant energy gain at a minimum total driver energy. The considered concept is a simple moderate-aspect ratio cryogenic fuel shell, with an inserted cone. We have subsequently shown that this target (without the cone) can be shock-ignited by a laser with parameters achievable at the NIF and LMJ facilities [4, 5]. We are devoting a particular effort to